feat: add --bootstrap-peer flag to bypass mDNS for peer discovery

macOS TCC blocks mDNS multicast from SSH sessions, preventing
SSH-spawned exo processes from discovering peers. This adds a
--bootstrap-peer IP:PORT flag that directly dials a known peer,
bypassing mDNS. The flag is additive — mDNS still runs alongside.

Changes across Rust networking, PyO3 bindings, and Python CLI:
- discovery.rs: store bootstrap addresses, dial on startup and retry
- swarm.rs: thread bootstrap_peers through to Behaviour
- networking.rs: accept optional bootstrap_peers in PyO3 constructor
- router.py: pass bootstrap_peers to NetworkingHandle
- main.py: parse --bootstrap-peer CLI arg into multiaddr format

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.mlx_typings/mlx_lm/models/glm_moe_dsa.pyi

@@ -1,46 +0,0 @@
-"""Type stubs for mlx_lm.models.glm_moe_dsa"""
-
-from dataclasses import dataclass
-from typing import Any, Dict, Optional
-
-from .base import BaseModelArgs
-from .deepseek_v32 import Model as DSV32Model
-
-@dataclass
-class ModelArgs(BaseModelArgs):
-    model_type: str
-    vocab_size: int
-    hidden_size: int
-    index_head_dim: int
-    index_n_heads: int
-    index_topk: int
-    intermediate_size: int
-    moe_intermediate_size: int
-    num_hidden_layers: int
-    num_attention_heads: int
-    num_key_value_heads: int
-    n_shared_experts: Optional[int]
-    n_routed_experts: Optional[int]
-    routed_scaling_factor: float
-    kv_lora_rank: int
-    q_lora_rank: int
-    qk_rope_head_dim: int
-    v_head_dim: int
-    qk_nope_head_dim: int
-    topk_method: str
-    scoring_func: str
-    norm_topk_prob: bool
-    n_group: int
-    topk_group: int
-    num_experts_per_tok: int
-    moe_layer_freq: int
-    first_k_dense_replace: int
-    max_position_embeddings: int
-    rms_norm_eps: float
-    rope_parameters: Dict[str, Any]
-    attention_bias: bool
-    rope_scaling: Dict[str, Any] | None
-    rope_theta: float | None
-
-class Model(DSV32Model):
-    def __init__(self, config: ModelArgs) -> None: ...

Cargo.lock

@@ -141,6 +141,12 @@ version = "0.3.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "76a2e8124351fda1ef8aaaa3bbd7ebbcb486bbcd4225aca0aa0d84bb2db8fecb"
 
+[[package]]
+name = "arrayvec"
+version = "0.7.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7c02d123df017efcdfbd739ef81735b36c5ba83ec3c59c80a9d7ecc718f92e50"
+
 [[package]]
 name = "asn1-rs"
 version = "0.7.1"
@@ -298,6 +304,19 @@ version = "1.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "55248b47b0caf0546f7988906588779981c43bb1bc9d0c44087278f80cdb44ba"
 
+[[package]]
+name = "bigdecimal"
+version = "0.4.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "560f42649de9fa436b73517378a147ec21f6c997a546581df4b4b31677828934"
+dependencies = [
+ "autocfg",
+ "libm",
+ "num-bigint",
+ "num-integer",
+ "num-traits",
+]
+
 [[package]]
 name = "bimap"
 version = "0.6.3"
@@ -497,6 +516,15 @@ version = "0.4.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2f421161cb492475f1661ddc9815a745a1c894592070661180fdec3d4872e9c3"
 
+[[package]]
+name = "convert_case"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "633458d4ef8c78b72454de2d54fd6ab2e60f9e02be22f3c6104cdc8a4e0fceb9"
+dependencies = [
+ "unicode-segmentation",
+]
+
 [[package]]
 name = "core-foundation"
 version = "0.9.4"
@@ -718,6 +746,29 @@ dependencies = [
  "powerfmt",
 ]
 
+[[package]]
+name = "derive_more"
+version = "2.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "10b768e943bed7bf2cab53df09f4bc34bfd217cdb57d971e769874c9a6710618"
+dependencies = [
+ "derive_more-impl",
+]
+
+[[package]]
+name = "derive_more-impl"
+version = "2.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6d286bfdaf75e988b4a78e013ecd79c581e06399ab53fbacd2d916c2f904f30b"
+dependencies = [
+ "convert_case",
+ "proc-macro2",
+ "quote",
+ "rustc_version",
+ "syn 2.0.111",
+ "unicode-xid",
+]
+
 [[package]]
 name = "digest"
 version = "0.10.7"
@@ -888,17 +939,22 @@ name = "exo_pyo3_bindings"
 version = "0.0.1"
 dependencies = [
  "delegate",
+ "derive_more",
  "env_logger",
  "extend",
  "futures",
+ "impl-trait-for-tuples",
  "libp2p",
  "log",
  "networking",
+ "once_cell",
  "pin-project",
  "pyo3",
  "pyo3-async-runtimes",
  "pyo3-log",
  "pyo3-stub-gen",
+ "thiserror 2.0.17",
+ "thread_local",
  "tokio",
  "util",
 ]
@@ -1584,6 +1640,17 @@ dependencies = [
  "xmltree",
 ]
 
+[[package]]
+name = "impl-trait-for-tuples"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a0eb5a3343abf848c0984fe4604b2b105da9539376e24fc0a3b0007411ae4fd9"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.111",
+]
+
 [[package]]
 name = "indexmap"
 version = "2.12.1"
@@ -1762,6 +1829,12 @@ version = "0.2.178"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "37c93d8daa9d8a012fd8ab92f088405fb202ea0b6ab73ee2482ae66af4f42091"
 
+[[package]]
+name = "libm"
+version = "0.2.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f9fbbcab51052fe104eb5e5d351cf728d30a5be1fe14d9be8a3b097481fb97de"
+
 [[package]]
 name = "libp2p"
 version = "0.56.0"
@@ -2751,13 +2824,16 @@ name = "networking"
 version = "0.0.1"
 dependencies = [
  "delegate",
+ "derive_more",
  "either",
  "extend",
  "futures",
  "futures-timer",
+ "impl-trait-for-tuples",
  "keccak-const",
  "libp2p",
  "log",
+ "thiserror 2.0.17",
  "tokio",
  "tracing-subscriber",
  "util",
@@ -2842,6 +2918,17 @@ dependencies = [
  "num-traits",
 ]
 
+[[package]]
+name = "num-rational"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f83d14da390562dca69fc84082e73e548e1ad308d24accdedd2720017cb37824"
+dependencies = [
+ "num-bigint",
+ "num-integer",
+ "num-traits",
+]
+
 [[package]]
 name = "num-traits"
 version = "0.2.19"
@@ -3192,14 +3279,28 @@ version = "0.27.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ab53c047fcd1a1d2a8820fe84f05d6be69e9526be40cb03b73f86b6b03e6d87d"
 dependencies = [
+ "bigdecimal",
+ "either",
+ "hashbrown 0.16.1",
+ "indexmap",
  "indoc",
+ "inventory",
  "libc",
+ "lock_api",
  "memoffset",
+ "num-bigint",
+ "num-complex",
+ "num-rational",
+ "num-traits",
  "once_cell",
+ "ordered-float",
+ "parking_lot",
  "portable-atomic",
  "pyo3-build-config",
  "pyo3-ffi",
  "pyo3-macros",
+ "rust_decimal",
+ "smallvec",
  "unindent",
 ]
 
@@ -3640,6 +3741,16 @@ dependencies = [
  "tokio",
 ]
 
+[[package]]
+name = "rust_decimal"
+version = "1.39.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "35affe401787a9bd846712274d97654355d21b2a2c092a3139aabe31e9022282"
+dependencies = [
+ "arrayvec",
+ "num-traits",
+]
+
 [[package]]
 name = "rustc-hash"
 version = "1.1.0"
@@ -4504,12 +4615,24 @@ version = "1.0.22"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9312f7c4f6ff9069b165498234ce8be658059c6728633667c526e27dc2cf1df5"
 
+[[package]]
+name = "unicode-segmentation"
+version = "1.12.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f6ccf251212114b54433ec949fd6a7841275f9ada20dddd2f29e9ceea4501493"
+
 [[package]]
 name = "unicode-width"
 version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b4ac048d71ede7ee76d585517add45da530660ef4390e49b098733c6e897f254"
 
+[[package]]
+name = "unicode-xid"
+version = "0.2.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ebc1c04c71510c7f702b52b7c350734c9ff1295c464a03335b00bb84fc54f853"
+
 [[package]]
 name = "unicode_names2"
 version = "1.3.0"

Cargo.toml

@@ -26,21 +26,49 @@ opt-level = 3
 networking = { path = "rust/networking" }
 util = { path = "rust/util" }
 
+# Proc-macro authoring tools
+syn = "2.0"
+quote = "1.0"
+proc-macro2 = "1.0"
+darling = "0.20"
+
 # Macro dependecies
 extend = "1.2"
 delegate = "0.13"
+impl-trait-for-tuples = "0.2"
+clap = "4.5"
+derive_more = { version = "2.0.1", features = ["display"] }
 pin-project = "1"
 
 # Utility dependencies
+itertools = "0.14"
+thiserror = "2"
+internment = "0.8"
+recursion = "0.5"
+regex = "1.11"
+once_cell = "1.21"
+thread_local = "1.1"
+bon = "3.4"
+generativity = "1.1"
+anyhow = "1.0"
 keccak-const = "0.2"
 
+# Functional generics/lenses frameworks
+frunk_core = "0.4"
+frunk = "0.4"
+frunk_utils = "0.2"
+frunk-enum-core = "0.3"
+
 # Async dependencies
 tokio = "1.46"
 futures = "0.3"
+futures-util = "0.3"
 futures-timer = "3.0"
 
 # Data structures
 either = "1.15"
+ordered-float = "5.0"
+ahash = "0.8"
 
 # Tracing/logging
 log = "0.4"

README.md

@@ -72,23 +72,16 @@ There are two ways to run exo:
 
 ### Run from Source (macOS)
 
-If you have [Nix](https://nixos.org/) installed, you can skip most of the steps below and run exo directly (after accepting the Cachix cache):
-
-```bash
-nix run .#exo
-```
-
 **Prerequisites:**
-- [Xcode](https://developer.apple.com/xcode/) (provides the Metal ToolChain required for MLX compilation)
 - [brew](https://github.com/Homebrew/brew) (for simple package management on macOS)
-
+  
   ```bash
   /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
   ```
 - [uv](https://github.com/astral-sh/uv) (for Python dependency management)
 - [macmon](https://github.com/vladkens/macmon) (for hardware monitoring on Apple Silicon)
 - [node](https://github.com/nodejs/node) (for building the dashboard)
-
+  
   ```bash
   brew install uv macmon node
   ```

app/EXO/EXO/ExoProcessController.swift

@@ -126,37 +126,11 @@ final class ExoProcessController: ObservableObject {
             return
         }
         process.terminationHandler = nil
-        status = .stopped
-
-        guard process.isRunning else {
-            self.process = nil
-            return
+        if process.isRunning {
+            process.terminate()
         }
-
-        let proc = process
         self.process = nil
-
-        Task.detached {
-            proc.interrupt()
-
-            for _ in 0..<50 {
-                if !proc.isRunning { return }
-                try? await Task.sleep(nanoseconds: 100_000_000)
-            }
-
-            if proc.isRunning {
-                proc.terminate()
-            }
-
-            for _ in 0..<30 {
-                if !proc.isRunning { return }
-                try? await Task.sleep(nanoseconds: 100_000_000)
-            }
-
-            if proc.isRunning {
-                kill(proc.processIdentifier, SIGKILL)
-            }
-        }
+        status = .stopped
     }
 
     func restart() {

bench/bench.toml

@@ -1,7 +0,0 @@
-# Canary benchmark manifest
-#
-# Lists the suite files to include. Each file defines benchmarks
-# with shared constraints, topology, and default args.
-include = [
-    "single-m3-ultra.toml",
-]

bench/single-m3-ultra.toml

@@ -1,189 +0,0 @@
-# Single-node M3 Ultra benchmarks
-#
-# Shared constraints applied to ALL benchmarks in this file.
-constraints = [
-    "All(MacOsBuild(=25D125))",
-    "Hosts(=1)",
-    "All(Chip(m3_ultra))",
-    "All(GpuCores(=80))",
-]
-
-[topology]
-type = "none"
-
-# Default args merged into each benchmark's args (benchmark-level args win).
-[defaults]
-pp = [512, 2048, 8192, 16384]
-tg = 128
-
-[[benchmark]]
-model = "mlx-community/Meta-Llama-3.1-70B-Instruct-4bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/gpt-oss-120b-MXFP4-Q8"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/GLM-4.7-Flash-8bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Qwen3-Coder-Next-6bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Qwen3-30B-A3B-8bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Qwen3-0.6B-4bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Qwen3-0.6B-8bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Llama-3.2-1B-Instruct-4bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Llama-3.2-3B-Instruct-4bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Llama-3.2-3B-Instruct-8bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Meta-Llama-3.1-8B-Instruct-4bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Meta-Llama-3.1-8B-Instruct-8bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Meta-Llama-3.1-8B-Instruct-bf16"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/gpt-oss-20b-MXFP4-Q8"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Qwen3-30B-A3B-4bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/GLM-4.7-Flash-4bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/GLM-4.7-Flash-5bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/GLM-4.7-Flash-6bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Llama-3.3-70B-Instruct-4bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Qwen3-Coder-Next-4bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Qwen3-Coder-Next-5bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Qwen3-Coder-Next-8bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Qwen3-Next-80B-A3B-Instruct-4bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Qwen3-Next-80B-A3B-Instruct-8bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Qwen3-Next-80B-A3B-Thinking-4bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Qwen3-Next-80B-A3B-Thinking-8bit"
-extra_constraints = ["All(Memory(>=96GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Llama-3.3-70B-Instruct-8bit"
-extra_constraints = ["All(Memory(>=256GiB))"]
-
-[[benchmark]]
-model = "mlx-community/llama-3.3-70b-instruct-fp16"
-extra_constraints = ["All(Memory(>=256GiB))"]
-
-[[benchmark]]
-model = "mlx-community/GLM-4.5-Air-8bit"
-extra_constraints = ["All(Memory(>=256GiB))"]
-
-[[benchmark]]
-model = "mlx-community/GLM-4.5-Air-bf16"
-extra_constraints = ["All(Memory(>=256GiB))"]
-
-[[benchmark]]
-model = "mlx-community/GLM-4.7-4bit"
-extra_constraints = ["All(Memory(>=256GiB))"]
-
-[[benchmark]]
-model = "mlx-community/MiniMax-M2.1-3bit"
-extra_constraints = ["All(Memory(>=256GiB))"]
-
-[[benchmark]]
-model = "mlx-community/MiniMax-M2.1-8bit"
-extra_constraints = ["All(Memory(>=256GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Qwen3-235B-A22B-Instruct-2507-4bit"
-extra_constraints = ["All(Memory(>=256GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Qwen3-Coder-Next-bf16"
-extra_constraints = ["All(Memory(>=256GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Step-3.5-Flash-4bit"
-extra_constraints = ["All(Memory(>=256GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Step-3.5-Flash-6bit"
-extra_constraints = ["All(Memory(>=256GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Step-3.5-Flash-8Bit"
-extra_constraints = ["All(Memory(>=256GiB))"]
-
-[[benchmark]]
-model = "mlx-community/DeepSeek-V3.1-4bit"
-extra_constraints = ["All(Memory(>=512GiB))"]
-
-[[benchmark]]
-model = "mlx-community/GLM-4.7-6bit"
-extra_constraints = ["All(Memory(>=512GiB))"]
-
-[[benchmark]]
-model = "mlx-community/GLM-4.7-8bit-gs32"
-extra_constraints = ["All(Memory(>=512GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Qwen3-235B-A22B-Instruct-2507-8bit"
-extra_constraints = ["All(Memory(>=512GiB))"]
-
-[[benchmark]]
-model = "mlx-community/Qwen3-Coder-480B-A35B-Instruct-4bit"
-extra_constraints = ["All(Memory(>=512GiB))"]

dashboard/src/lib/components/ChatSidebar.svelte

@@ -185,11 +185,7 @@
 
     let instanceType: string | null = null;
     if (instanceTag === "MlxRingInstance") instanceType = "MLX Ring";
-    else if (
-      instanceTag === "MlxIbvInstance" ||
-      instanceTag === "MlxJacclInstance"
-    )
-      instanceType = "MLX RDMA";
+    else if (instanceTag === "MlxJacclInstance") instanceType = "MLX RDMA";
 
     let sharding: string | null = null;
     const inst = instance as {

dashboard/src/lib/components/ImageParamsPanel.svelte

@@ -59,14 +59,13 @@
   }
 
   const sizeOptions: ImageGenerationParams["size"][] = [
-    "auto",
     "512x512",
     "768x768",
     "1024x1024",
     "1024x768",
     "768x1024",
-    "1024x1536",
-    "1536x1024",
+    "1024x1365",
+    "1365x1024",
   ];
 
   const qualityOptions: ImageGenerationParams["quality"][] = [
@@ -177,90 +176,92 @@
 <div class="border-b border-exo-medium-gray/30 px-3 py-2">
   <!-- Basic params row -->
   <div class="flex items-center gap-3 flex-wrap">
-    <!-- Size -->
-    <div class="flex items-center gap-1.5">
-      <span class="text-xs text-exo-light-gray uppercase tracking-wider"
-        >SIZE:</span
-      >
-      <div class="relative">
-        <button
-          bind:this={sizeButtonRef}
-          type="button"
-          onclick={() => (isSizeDropdownOpen = !isSizeDropdownOpen)}
-          class="bg-exo-medium-gray/50 border border-exo-yellow/30 rounded pl-2 pr-6 py-1 text-xs font-mono text-exo-yellow cursor-pointer transition-all duration-200 hover:border-exo-yellow/50 focus:outline-none focus:border-exo-yellow/70 {isSizeDropdownOpen
-            ? 'border-exo-yellow/70'
-            : ''}"
+    <!-- Size (hidden in edit mode - output size comes from input image) -->
+    {#if !isEditMode}
+      <div class="flex items-center gap-1.5">
+        <span class="text-xs text-exo-light-gray uppercase tracking-wider"
+          >SIZE:</span
         >
-          {params.size.toUpperCase()}
-        </button>
-        <div
-          class="absolute right-1.5 top-1/2 -translate-y-1/2 pointer-events-none transition-transform duration-200 {isSizeDropdownOpen
-            ? 'rotate-180'
-            : ''}"
-        >
-          <svg
-            class="w-3 h-3 text-exo-yellow/60"
-            fill="none"
-            viewBox="0 0 24 24"
-            stroke="currentColor"
+        <div class="relative">
+          <button
+            bind:this={sizeButtonRef}
+            type="button"
+            onclick={() => (isSizeDropdownOpen = !isSizeDropdownOpen)}
+            class="bg-exo-medium-gray/50 border border-exo-yellow/30 rounded pl-2 pr-6 py-1 text-xs font-mono text-exo-yellow cursor-pointer transition-all duration-200 hover:border-exo-yellow/50 focus:outline-none focus:border-exo-yellow/70 {isSizeDropdownOpen
+              ? 'border-exo-yellow/70'
+              : ''}"
           >
-            <path
-              stroke-linecap="round"
-              stroke-linejoin="round"
-              stroke-width="2"
-              d="M19 9l-7 7-7-7"
-            />
-          </svg>
-        </div>
-      </div>
-
-      {#if isSizeDropdownOpen}
-        <!-- Backdrop to close dropdown -->
-        <button
-          type="button"
-          class="fixed inset-0 z-[9998] cursor-default"
-          onclick={() => (isSizeDropdownOpen = false)}
-          aria-label="Close dropdown"
-        ></button>
-
-        <!-- Dropdown Panel - fixed positioning to escape overflow:hidden -->
-        <div
-          class="fixed bg-exo-dark-gray border border-exo-yellow/30 rounded shadow-lg shadow-black/50 z-[9999] max-h-48 overflow-y-auto overflow-x-hidden min-w-max"
-          style="bottom: calc(100vh - {sizeDropdownPosition()
-            .top}px + 4px); left: {sizeDropdownPosition().left}px;"
-        >
-          <div class="py-1">
-            {#each sizeOptions as size}
-              <button
-                type="button"
-                onclick={() => selectSize(size)}
-                class="w-full px-3 py-1.5 text-left text-xs font-mono tracking-wide transition-colors duration-100 flex items-center gap-2 {params.size ===
-                size
-                  ? 'bg-transparent text-exo-yellow'
-                  : 'text-exo-light-gray hover:text-exo-yellow'}"
-              >
-                {#if params.size === size}
-                  <svg
-                    class="w-3 h-3 flex-shrink-0"
-                    fill="currentColor"
-                    viewBox="0 0 20 20"
-                  >
-                    <path
-                      fill-rule="evenodd"
-                      d="M16.707 5.293a1 1 0 010 1.414l-8 8a1 1 0 01-1.414 0l-4-4a1 1 0 011.414-1.414L8 12.586l7.293-7.293a1 1 0 011.414 0z"
-                      clip-rule="evenodd"
-                    />
-                  </svg>
-                {:else}
-                  <span class="w-3"></span>
-                {/if}
-                <span>{size.toUpperCase()}</span>
-              </button>
-            {/each}
+            {params.size}
+          </button>
+          <div
+            class="absolute right-1.5 top-1/2 -translate-y-1/2 pointer-events-none transition-transform duration-200 {isSizeDropdownOpen
+              ? 'rotate-180'
+              : ''}"
+          >
+            <svg
+              class="w-3 h-3 text-exo-yellow/60"
+              fill="none"
+              viewBox="0 0 24 24"
+              stroke="currentColor"
+            >
+              <path
+                stroke-linecap="round"
+                stroke-linejoin="round"
+                stroke-width="2"
+                d="M19 9l-7 7-7-7"
+              />
+            </svg>
           </div>
         </div>
-      {/if}
-    </div>
+
+        {#if isSizeDropdownOpen}
+          <!-- Backdrop to close dropdown -->
+          <button
+            type="button"
+            class="fixed inset-0 z-[9998] cursor-default"
+            onclick={() => (isSizeDropdownOpen = false)}
+            aria-label="Close dropdown"
+          ></button>
+
+          <!-- Dropdown Panel - fixed positioning to escape overflow:hidden -->
+          <div
+            class="fixed bg-exo-dark-gray border border-exo-yellow/30 rounded shadow-lg shadow-black/50 z-[9999] max-h-48 overflow-y-auto min-w-max"
+            style="bottom: calc(100vh - {sizeDropdownPosition()
+              .top}px + 4px); left: {sizeDropdownPosition().left}px;"
+          >
+            <div class="py-1">
+              {#each sizeOptions as size}
+                <button
+                  type="button"
+                  onclick={() => selectSize(size)}
+                  class="w-full px-3 py-1.5 text-left text-xs font-mono tracking-wide transition-colors duration-100 flex items-center gap-2 {params.size ===
+                  size
+                    ? 'bg-transparent text-exo-yellow'
+                    : 'text-exo-light-gray hover:text-exo-yellow'}"
+                >
+                  {#if params.size === size}
+                    <svg
+                      class="w-3 h-3 flex-shrink-0"
+                      fill="currentColor"
+                      viewBox="0 0 20 20"
+                    >
+                      <path
+                        fill-rule="evenodd"
+                        d="M16.707 5.293a1 1 0 010 1.414l-8 8a1 1 0 01-1.414 0l-4-4a1 1 0 011.414-1.414L8 12.586l7.293-7.293a1 1 0 011.414 0z"
+                        clip-rule="evenodd"
+                      />
+                    </svg>
+                  {:else}
+                    <span class="w-3"></span>
+                  {/if}
+                  <span>{size}</span>
+                </button>
+              {/each}
+            </div>
+          </div>
+        {/if}
+      </div>
+    {/if}
 
     <!-- Quality -->
     <div class="flex items-center gap-1.5">
@@ -310,7 +311,7 @@
 
         <!-- Dropdown Panel - fixed positioning to escape overflow:hidden -->
         <div
-          class="fixed bg-exo-dark-gray border border-exo-yellow/30 rounded shadow-lg shadow-black/50 z-[9999] max-h-48 overflow-y-auto overflow-x-hidden min-w-max"
+          class="fixed bg-exo-dark-gray border border-exo-yellow/30 rounded shadow-lg shadow-black/50 z-[9999] max-h-48 overflow-y-auto min-w-max"
           style="bottom: calc(100vh - {qualityDropdownPosition()
             .top}px + 4px); left: {qualityDropdownPosition().left}px;"
         >

dashboard/src/lib/components/ModelCard.svelte

@@ -21,7 +21,7 @@
     } | null;
     nodes?: Record<string, NodeInfo>;
     sharding?: "Pipeline" | "Tensor";
-    runtime?: "MlxRing" | "MlxIbv" | "MlxJaccl";
+    runtime?: "MlxRing" | "MlxJaccl";
     onLaunch?: () => void;
     tags?: string[];
     apiPreview?: PlacementPreview | null;
@@ -348,7 +348,7 @@
   // Debug mode state
   const isDebugMode = $derived(debugMode());
   const topology = $derived(topologyData());
-  const isRdma = $derived(runtime === "MlxIbv" || runtime === "MlxJaccl");
+  const isRdma = $derived(runtime === "MlxJaccl");
 
   // Get interface name for an IP from node data
   function getInterfaceForIp(nodeId: string, ip?: string): string | null {
@@ -575,7 +575,7 @@
       >
         {runtime === "MlxRing"
           ? "MLX Ring"
-          : runtime === "MlxIbv" || runtime === "MlxJaccl"
+          : runtime === "MlxJaccl"
             ? "MLX RDMA"
             : runtime}
       </span>

dashboard/src/lib/stores/app.svelte.ts

@@ -168,7 +168,7 @@ export interface ModelDownloadStatus {
 export interface PlacementPreview {
   model_id: string;
   sharding: "Pipeline" | "Tensor";
-  instance_meta: "MlxRing" | "MlxIbv" | "MlxJaccl";
+  instance_meta: "MlxRing" | "MlxJaccl";
   instance: unknown | null;
   memory_delta_by_node: Record<string, number> | null;
   error: string | null;
@@ -219,7 +219,6 @@ interface RawStateResponse {
     string,
     {
       MlxRingInstance?: Instance;
-      MlxIbvInstance?: Instance;
       MlxJacclInstance?: Instance;
     }
   >;
@@ -250,6 +249,20 @@ interface RawStateResponse {
   >;
   // Thunderbolt bridge cycles (nodes with bridge enabled forming loops)
   thunderboltBridgeCycles?: string[][];
+  // MetaInstances (declarative instance constraints)
+  metaInstances?: Record<string, MetaInstanceData>;
+}
+
+export interface MetaInstanceData {
+  metaInstanceId: string;
+  modelId: string;
+  sharding: string;
+  instanceMeta: string;
+  minNodes: number;
+  nodeIds: string[] | null;
+  placementError: string | null;
+  consecutiveFailures: number;
+  lastFailureError: string | null;
 }
 
 export interface MessageAttachment {
@@ -306,14 +319,13 @@ const IMAGE_PARAMS_STORAGE_KEY = "exo-image-generation-params";
 export interface ImageGenerationParams {
   // Basic params
   size:
-    | "auto"
     | "512x512"
     | "768x768"
     | "1024x1024"
     | "1024x768"
     | "768x1024"
-    | "1024x1536"
-    | "1536x1024";
+    | "1024x1365"
+    | "1365x1024";
   quality: "low" | "medium" | "high";
   outputFormat: "png" | "jpeg";
   numImages: number;
@@ -337,7 +349,7 @@ export interface EditingImage {
 }
 
 const DEFAULT_IMAGE_PARAMS: ImageGenerationParams = {
-  size: "auto",
+  size: "1024x1024",
   quality: "medium",
   outputFormat: "png",
   numImages: 1,
@@ -537,6 +549,7 @@ class AppStore {
   isLoadingPreviews = $state(false);
   previewNodeFilter = $state<Set<string>>(new Set());
   lastUpdate = $state<number | null>(null);
+  metaInstances = $state<Record<string, MetaInstanceData>>({});
   nodeIdentities = $state<Record<string, RawNodeIdentity>>({});
   thunderboltBridgeCycles = $state<string[][]>([]);
   nodeThunderbolt = $state<
@@ -896,11 +909,7 @@ class AppStore {
 
     let instanceType: string | null = null;
     if (instanceTag === "MlxRingInstance") instanceType = "MLX Ring";
-    else if (
-      instanceTag === "MlxIbvInstance" ||
-      instanceTag === "MlxJacclInstance"
-    )
-      instanceType = "MLX RDMA";
+    else if (instanceTag === "MlxJacclInstance") instanceType = "MLX RDMA";
 
     let sharding: string | null = null;
     const inst = instance as {
@@ -1265,6 +1274,8 @@ class AppStore {
       if (data.downloads) {
         this.downloads = data.downloads;
       }
+      // MetaInstances
+      this.metaInstances = data.metaInstances ?? {};
       if (data.nodeDisk) {
         this.nodeDisk = data.nodeDisk;
       }
@@ -3045,6 +3056,7 @@ export const tps = () => appStore.tps;
 export const totalTokens = () => appStore.totalTokens;
 export const topologyData = () => appStore.topologyData;
 export const instances = () => appStore.instances;
+export const metaInstances = () => appStore.metaInstances;
 export const runners = () => appStore.runners;
 export const downloads = () => appStore.downloads;
 export const nodeDisk = () => appStore.nodeDisk;

flake.nix

@@ -115,7 +115,7 @@
           packages = lib.optionalAttrs pkgs.stdenv.hostPlatform.isDarwin (
             let
               uvLock = builtins.fromTOML (builtins.readFile ./uv.lock);
-              mlxPackage = builtins.head (builtins.filter (p: p.name == "mlx" && p.source ? git) uvLock.package);
+              mlxPackage = builtins.head (builtins.filter (p: p.name == "mlx") uvLock.package);
               uvLockMlxVersion = mlxPackage.version;
             in
             {

nix/mlx.nix

@@ -41,16 +41,16 @@ let
 
   mlx = stdenv.mkDerivation rec {
     pname = "mlx";
-    version = let v = "0.30.7.dev20260218+14841977"; in
+    version = let v = "0.30.6"; in
       assert v == uvLockMlxVersion || throw "MLX version mismatch: nix/mlx.nix has ${v} but uv.lock has ${uvLockMlxVersion}. Update both the version and hash in nix/mlx.nix.";
       v;
     pyproject = true;
 
     src = fetchFromGitHub {
-      owner = "rltakashige";
-      repo = "mlx-jaccl-fix-small-recv";
-      rev = "1484197707f35186ad3bd614357c7c47fdf86ebc";
-      hash = "sha256-FupCMoK/SF/ldfKuvMSAKECcOP8c+ANgkQlPZttDsLk=";
+      owner = "ml-explore";
+      repo = "mlx";
+      tag = "v${version}";
+      hash = "sha256-avD5EGhwgmPdXLAyQSqTO6AXk/W3ziH+f6AetjK3Sdo=";
     };
 
     patches = [

pyproject.toml

@@ -6,6 +6,8 @@ readme = "README.md"
 requires-python = ">=3.13"
 dependencies = [
     "aiofiles>=24.1.0",
+    "aiohttp>=3.12.14",
+    "types-aiofiles>=24.1.0.20250708",
     "pydantic>=2.11.7",
     "fastapi>=0.116.1",
     "filelock>=3.18.0",
@@ -15,9 +17,9 @@ dependencies = [
     "loguru>=0.7.3",
     "exo_pyo3_bindings", # rust bindings
     "anyio==4.11.0",
-    "mlx; sys_platform == 'darwin'",
+    "mlx==0.30.6; sys_platform == 'darwin'",
     "mlx[cpu]==0.30.6; sys_platform == 'linux'",
-    "mlx-lm==0.30.7",
+    "mlx-lm==0.30.6",
     "tiktoken>=0.12.0", # required for kimi k2 tokenizer
     "hypercorn>=0.18.0",
     "openai-harmony>=0.0.8",
@@ -62,7 +64,6 @@ members = [
 
 [tool.uv.sources]
 exo_pyo3_bindings = { workspace = true }
-mlx = { git = "https://github.com/rltakashige/mlx-jaccl-fix-small-recv.git", branch = "address-rdma-gpu-locks", marker = "sys_platform == 'darwin'" }
 #mlx-lm = { git = "https://github.com/davidmcc73/mlx-lm", branch = "stable" }
 # Uncomment to use local mlx/mlx-lm development versions:
 # mlx = { path = "/Users/Shared/mlx", editable=true }

python/parts.nix

@@ -58,21 +58,6 @@
         lib.optionalAttrs pkgs.stdenv.hostPlatform.isLinux (
           (lib.mapAttrs (_: ignoreMissing) nvidiaPackages) // {
             mlx = ignoreMissing prev.mlx;
-            mlx-cuda-13 = prev.mlx-cuda-13.overrideAttrs (old: {
-              buildInputs = (old.buildInputs or [ ]) ++ [
-                final.nvidia-cublas
-                final.nvidia-cuda-nvrtc
-                final.nvidia-cudnn-cu13
-                final.nvidia-nccl-cu13
-              ];
-              preFixup = ''
-                addAutoPatchelfSearchPath ${final.nvidia-cublas}
-                addAutoPatchelfSearchPath ${final.nvidia-cuda-nvrtc}
-                addAutoPatchelfSearchPath ${final.nvidia-cudnn-cu13}
-                addAutoPatchelfSearchPath ${final.nvidia-nccl-cu13}
-              '';
-              autoPatchelfIgnoreMissingDeps = [ "libcuda.so.1" ];
-            });
             torch = ignoreMissing prev.torch;
             triton = ignoreMissing prev.triton;
           }
@@ -89,25 +74,14 @@
           linuxOverlay
         ]
       );
-      # mlx-cpu and mlx-cuda-13 both ship mlx/ site-packages files; keep first.
-      # mlx-cpu/mlx-cuda-13 and nvidia-cudnn-cu12/cu13 ship overlapping files.
-      venvCollisionPaths = lib.optionals pkgs.stdenv.hostPlatform.isLinux [
-        "lib/python3.13/site-packages/mlx*"
-        "lib/python3.13/site-packages/nvidia*"
-      ];
-
-      exoVenv = (pythonSet.mkVirtualEnv "exo-env" workspace.deps.default).overrideAttrs {
-        venvIgnoreCollisions = venvCollisionPaths;
-      };
+      exoVenv = pythonSet.mkVirtualEnv "exo-env" workspace.deps.default;
 
       # Virtual environment with dev dependencies for testing
-      testVenv = (pythonSet.mkVirtualEnv "exo-test-env" (
+      testVenv = pythonSet.mkVirtualEnv "exo-test-env" (
         workspace.deps.default // {
           exo = [ "dev" ]; # Include pytest, pytest-asyncio, pytest-env
         }
-      )).overrideAttrs {
-        venvIgnoreCollisions = venvCollisionPaths;
-      };
+      );
 
       mkPythonScript = name: path: pkgs.writeShellApplication {
         inherit name;

resources/inference_model_cards/mlx-community--GLM-5-8bit.toml

@@ -1,12 +0,0 @@
-model_id = "mlx-community/GLM-5-8bit-MXFP8"
-n_layers = 78
-hidden_size = 6144
-supports_tensor = true
-tasks = ["TextGeneration"]
-family = "glm"
-quantization = "8bit"
-base_model = "GLM-5"
-capabilities = ["text", "thinking"]
-
-[storage_size]
-in_bytes = 790517400864

resources/inference_model_cards/mlx-community--GLM-5-MXFP4-Q8.toml

@@ -1,12 +0,0 @@
-model_id = "mlx-community/GLM-5-MXFP4-Q8"
-n_layers = 78
-hidden_size = 6144
-supports_tensor = true
-tasks = ["TextGeneration"]
-family = "glm"
-quantization = "MXFP4-Q8"
-base_model = "GLM-5"
-capabilities = ["text", "thinking"]
-
-[storage_size]
-in_bytes = 405478939008

resources/inference_model_cards/mlx-community--GLM-5-bf16.toml

@@ -1,12 +0,0 @@
-model_id = "mlx-community/GLM-5"
-n_layers = 78
-hidden_size = 6144
-supports_tensor = true
-tasks = ["TextGeneration"]
-family = "glm"
-quantization = "bf16"
-base_model = "GLM-5"
-capabilities = ["text", "thinking"]
-
-[storage_size]
-in_bytes = 1487822475264

rust/exo_pyo3_bindings/Cargo.toml

@@ -25,17 +25,17 @@ workspace = true
 networking = { workspace = true }
 
 # interop
-pyo3 = { version = "0.27.2", features = [
-    # "abi3-py313", # tells pyo3 (and maturin) to build using the stable ABI with minimum Python version 3.13
+pyo3 = { version = "0.27.1", features = [
+    # "abi3-py311", # tells pyo3 (and maturin) to build using the stable ABI with minimum Python version 3.11
     "nightly", # enables better-supported GIL integration
     "experimental-async", # async support in #[pyfunction] & #[pymethods]
     #"experimental-inspect", # inspection of generated binary => easier to automate type-hint generation
     #"py-clone", # adding Clone-ing of `Py<T>` without GIL (may cause panics - remove if panics happen)
-    # "multiple-pymethods", # allows multiple #[pymethods] sections per class
+    "multiple-pymethods", # allows multiple #[pymethods] sections per class
 
     # integrations with other libraries
-    # "arc_lock", "bigdecimal", "either", "hashbrown", "indexmap", "num-bigint", "num-complex", "num-rational",
-    # "ordered-float", "rust_decimal", "smallvec",
+    "arc_lock", "bigdecimal", "either", "hashbrown", "indexmap", "num-bigint", "num-complex", "num-rational",
+    "ordered-float", "rust_decimal", "smallvec",
     # "anyhow", "chrono", "chrono-local", "chrono-tz", "eyre", "jiff-02", "lock_api", "parking-lot", "time",  "serde",
 ] }
 pyo3-stub-gen = { version = "0.17.2" }
@@ -45,6 +45,8 @@ pyo3-log = "0.13.2"
 # macro dependencies
 extend = { workspace = true }
 delegate = { workspace = true }
+impl-trait-for-tuples = { workspace = true }
+derive_more = { workspace = true }
 pin-project = { workspace = true }
 
 # async runtime
@@ -52,11 +54,24 @@ tokio = { workspace = true, features = ["full", "tracing"] }
 futures = { workspace = true }
 
 # utility dependencies
+once_cell = "1.21.3"
+thread_local = "1.1.9"
 util = { workspace = true }
+thiserror = { workspace = true }
+#internment = { workspace = true }
+#recursion = { workspace = true }
+#generativity = { workspace = true }
+#itertools = { workspace = true }
+
 
 # Tracing
+#tracing = "0.1"
+#tracing-subscriber = "0.3"
+#console-subscriber = "0.1.5"
+#tracing-log = "0.2.0"
 log = { workspace = true }
 env_logger = "0.11"
 
+
 # Networking
 libp2p = { workspace = true, features = ["full"] }

rust/exo_pyo3_bindings/exo_pyo3_bindings.pyi

@@ -130,7 +130,7 @@ class Multiaddr:
 
 @typing.final
 class NetworkingHandle:
-    def __new__(cls, identity: Keypair) -> NetworkingHandle: ...
+    def __new__(cls, identity: Keypair, bootstrap_peers: builtins.list[builtins.str] = ...) -> NetworkingHandle: ...
     async def connection_update_recv(self) -> ConnectionUpdate:
         r"""
         Receives the next `ConnectionUpdate` from networking.

rust/exo_pyo3_bindings/src/allow_threading.rs

@@ -6,7 +6,7 @@ use pyo3::marker::Ungil;
 use pyo3::prelude::*;
 use std::{
     future::Future,
-    pin::Pin,
+    pin::{Pin, pin},
     task::{Context, Poll},
 };
 
@@ -33,6 +33,8 @@ where
 
     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
         let waker = cx.waker();
-        Python::attach(|py| py.detach(|| self.project().0.poll(&mut Context::from_waker(waker))))
+        Python::with_gil(|py| {
+            py.allow_threads(|| self.project().0.poll(&mut Context::from_waker(waker)))
+        })
     }
 }

rust/exo_pyo3_bindings/src/examples/mod.rs

@@ -0,0 +1,240 @@
+//! This module exists to hold examples of some pyo3 patterns that may be too complex to
+//! re-create from scratch, but too inhomogenous to create an abstraction/wrapper around.
+//!
+//! Pattern examples include:
+//!  - Async task handles: with GC-integrated cleanup
+//!  - Sync/async callbacks from python: with propper eventloop handling
+//!
+//! Mutability pattern: https://pyo3.rs/v0.26.0/async-await.html#send--static-constraint
+//!  - Store mutable fields in tokio's `Mutex<T>`
+//!  - For async code: take `&self` and `.lock().await`
+//!  - For sync code: take `&mut self` and `.get_mut()`
+
+use crate::ext::{PyResultExt as _, ResultExt as _, TokioRuntimeExt as _};
+use futures::FutureExt as _;
+use futures::future::BoxFuture;
+use pyo3::exceptions::PyRuntimeError;
+use pyo3::prelude::{PyModule, PyModuleMethods as _};
+use pyo3::{
+    Bound, Py, PyAny, PyErr, PyResult, PyTraverseError, PyVisit, Python, pyclass, pymethods,
+};
+use std::time::Duration;
+use tokio::sync::mpsc;
+use tokio::sync::mpsc::error::TryRecvError;
+
+fn needs_tokio_runtime() {
+    tokio::runtime::Handle::current();
+}
+
+type SyncCallback = Box<dyn Fn() + Send + Sync>;
+type AsyncCallback = Box<dyn Fn() -> BoxFuture<'static, ()> + Send + Sync>;
+
+enum AsyncTaskMessage {
+    SyncCallback(SyncCallback),
+    AsyncCallback(AsyncCallback),
+}
+
+async fn async_task(
+    sender: mpsc::UnboundedSender<()>,
+    mut receiver: mpsc::UnboundedReceiver<AsyncTaskMessage>,
+) {
+    log::info!("RUST: async task started");
+
+    // task state
+    let mut interval = tokio::time::interval(Duration::from_secs(1));
+
+    let mut sync_cbs: Vec<SyncCallback> = vec![];
+    let mut async_cbs: Vec<AsyncCallback> = vec![];
+
+    loop {
+        tokio::select! {
+            // handle incoming messages from task-handle
+            message = receiver.recv() => {
+                // handle closed channel by exiting
+                let Some(message) = message else {
+                    log::info!("RUST: channel closed");
+                    break;
+                };
+
+                // dispatch incoming event
+                match message {
+                    AsyncTaskMessage::SyncCallback(cb) => {
+                        sync_cbs.push(cb);
+                    }
+                    AsyncTaskMessage::AsyncCallback(cb) => {
+                        async_cbs.push(cb);
+                    }
+                }
+            }
+
+            // handle all other events
+            _ = interval.tick() => {
+                log::info!("RUST: async task tick");
+
+                // call back all sync callbacks
+                for cb in &sync_cbs {
+                    cb();
+                }
+
+                // call back all async callbacks
+                for cb in &async_cbs {
+                    cb().await;
+                }
+
+                // send event on unbounded channel
+                sender.send(()).expect("handle receiver cannot be closed/dropped");
+            }
+        }
+    }
+
+    log::info!("RUST: async task stopped");
+}
+
+// #[gen_stub_pyclass]
+#[pyclass(name = "AsyncTaskHandle")]
+#[derive(Debug)]
+struct PyAsyncTaskHandle {
+    sender: Option<mpsc::UnboundedSender<AsyncTaskMessage>>,
+    receiver: mpsc::UnboundedReceiver<()>,
+}
+
+#[allow(clippy::expect_used)]
+impl PyAsyncTaskHandle {
+    const fn sender(&self) -> &mpsc::UnboundedSender<AsyncTaskMessage> {
+        self.sender
+            .as_ref()
+            .expect("The sender should only be None after de-initialization.")
+    }
+
+    const fn sender_mut(&mut self) -> &mpsc::UnboundedSender<AsyncTaskMessage> {
+        self.sender
+            .as_mut()
+            .expect("The sender should only be None after de-initialization.")
+    }
+
+    const fn new(
+        sender: mpsc::UnboundedSender<AsyncTaskMessage>,
+        receiver: mpsc::UnboundedReceiver<()>,
+    ) -> Self {
+        Self {
+            sender: Some(sender),
+            receiver,
+        }
+    }
+}
+
+// #[gen_stub_pymethods]
+#[pymethods]
+impl PyAsyncTaskHandle {
+    #[new]
+    fn py_new(py: Python<'_>) -> PyResult<Self> {
+        use pyo3_async_runtimes::tokio::get_runtime;
+
+        // create communication channel TOWARDS our task
+        let (h_sender, t_receiver) = mpsc::unbounded_channel::<AsyncTaskMessage>();
+
+        // create communication channel FROM our task
+        let (t_sender, h_receiver) = mpsc::unbounded_channel::<()>();
+
+        // perform necessary setup within tokio context - or it crashes
+        let () = get_runtime().block_on(async { needs_tokio_runtime() });
+
+        // spawn tokio task with this thread's task-locals - without this, async callbacks on the new threads will not work!!
+        _ = get_runtime().spawn_with_scope(py, async move {
+            async_task(t_sender, t_receiver).await;
+        });
+        Ok(Self::new(h_sender, h_receiver))
+    }
+
+    /// NOTE: exceptions in callbacks are silently ignored until end of execution
+    fn add_sync_callback(
+        &self,
+        // #[gen_stub(override_type(
+        //     type_repr="collections.abc.Callable[[], None]",
+        //     imports=("collections.abc")
+        // ))]
+        callback: Py<PyAny>,
+    ) -> PyResult<()> {
+        // blocking call to async method -> can do non-blocking if needed
+        self.sender()
+            .send(AsyncTaskMessage::SyncCallback(Box::new(move || {
+                _ = Python::with_gil(|py| callback.call0(py).write_unraisable_with(py));
+            })))
+            .pyerr()?;
+        Ok(())
+    }
+
+    /// NOTE: exceptions in callbacks are silently ignored until end of execution
+    fn add_async_callback(
+        &self,
+        // #[gen_stub(override_type(
+        //     type_repr="collections.abc.Callable[[], collections.abc.Awaitable[None]]",
+        //     imports=("collections.abc")
+        // ))]
+        callback: Py<PyAny>,
+    ) -> PyResult<()> {
+        // blocking call to async method -> can do non-blocking if needed
+        self.sender()
+            .send(AsyncTaskMessage::AsyncCallback(Box::new(move || {
+                let c = Python::with_gil(|py| callback.clone_ref(py));
+                async move {
+                    if let Some(f) = Python::with_gil(|py| {
+                        let coroutine = c.call0(py).write_unraisable_with(py)?;
+                        pyo3_async_runtimes::tokio::into_future(coroutine.into_bound(py))
+                            .write_unraisable_with(py)
+                    }) {
+                        _ = f.await.write_unraisable();
+                    }
+                }
+                .boxed()
+            })))
+            .pyerr()?;
+        Ok(())
+    }
+
+    async fn receive_unit(&mut self) -> PyResult<()> {
+        self.receiver
+            .recv()
+            .await
+            .ok_or(PyErr::new::<PyRuntimeError, _>(
+                "cannot receive unit on closed channel",
+            ))
+    }
+
+    fn drain_units(&mut self) -> PyResult<i32> {
+        let mut cnt = 0;
+        loop {
+            match self.receiver.try_recv() {
+                Err(TryRecvError::Disconnected) => {
+                    return Err(PyErr::new::<PyRuntimeError, _>(
+                        "cannot receive unit on closed channel",
+                    ));
+                }
+                Err(TryRecvError::Empty) => return Ok(cnt),
+                Ok(()) => {
+                    cnt += 1;
+                    continue;
+                }
+            }
+        }
+    }
+
+    // #[gen_stub(skip)]
+    const fn __traverse__(&self, _visit: PyVisit<'_>) -> Result<(), PyTraverseError> {
+        Ok(()) // This is needed purely so `__clear__` can work
+    }
+
+    // #[gen_stub(skip)]
+    fn __clear__(&mut self) {
+        // TODO: may or may not need to await a "kill-signal" oneshot channel message,
+        //       to ensure that the networking task is done BEFORE exiting the clear function...
+        //       but this may require GIL?? and it may not be safe to call GIL here??
+        self.sender = None; // Using Option<T> as a trick to force `sender` channel to be dropped
+    }
+}
+
+pub fn examples_submodule(m: &Bound<'_, PyModule>) -> PyResult<()> {
+    m.add_class::<PyAsyncTaskHandle>()?;
+
+    Ok(())
+}

rust/exo_pyo3_bindings/src/lib.rs

@@ -17,6 +17,7 @@
 
 extern crate core;
 mod allow_threading;
+mod examples;
 pub(crate) mod networking;
 pub(crate) mod pylibp2p;
 
@@ -24,6 +25,7 @@ use crate::networking::networking_submodule;
 use crate::pylibp2p::ident::ident_submodule;
 use crate::pylibp2p::multiaddr::multiaddr_submodule;
 use pyo3::prelude::PyModule;
+use pyo3::prelude::*;
 use pyo3::{Bound, PyResult, pyclass, pymodule};
 use pyo3_stub_gen::define_stub_info_gatherer;
 
@@ -34,10 +36,14 @@ pub(crate) mod r#const {
 
 /// Namespace for all the type/trait aliases used by this crate.
 pub(crate) mod alias {
+    use std::error::Error;
     use std::marker::Tuple;
 
     pub trait SendFn<Args: Tuple + Send + 'static, Output> =
         Fn<Args, Output = Output> + Send + 'static;
+
+    pub type AnyError = Box<dyn Error + Send + Sync + 'static>;
+    pub type AnyResult<T> = Result<T, AnyError>;
 }
 
 /// Namespace for crate-wide extension traits/methods
@@ -45,6 +51,7 @@ pub(crate) mod ext {
     use crate::allow_threading::AllowThreads;
     use extend::ext;
     use pyo3::exceptions::{PyConnectionError, PyRuntimeError};
+    use pyo3::marker::Ungil;
     use pyo3::types::PyBytes;
     use pyo3::{Py, PyErr, PyResult, Python};
     use tokio::runtime::Runtime;
@@ -55,7 +62,7 @@ pub(crate) mod ext {
     #[ext(pub, name = ByteArrayExt)]
     impl [u8] {
         fn pybytes(&self) -> Py<PyBytes> {
-            Python::attach(|py| PyBytes::new(py, self).unbind())
+            Python::with_gil(|py| PyBytes::new(py, self).unbind())
         }
     }
 
@@ -91,7 +98,7 @@ pub(crate) mod ext {
     #[ext(pub, name = PyResultExt)]
     impl<T> PyResult<T> {
         fn write_unraisable(self) -> Option<T> {
-            Python::attach(|py| self.write_unraisable_with(py))
+            Python::with_gil(|py| self.write_unraisable_with(py))
         }
 
         fn write_unraisable_with(self, py: Python<'_>) -> Option<T> {
@@ -168,6 +175,24 @@ pub(crate) mod ext {
     }
 }
 
+pub(crate) mod private {
+    use std::marker::Sized;
+
+    /// Sealed traits support
+    pub trait Sealed {}
+    impl<T: ?Sized> Sealed for T {}
+}
+
+/// A wrapper around [`Py`] that implements [`Clone`] using [`Python::with_gil`].
+#[repr(transparent)]
+pub(crate) struct ClonePy<T>(pub Py<T>);
+
+impl<T> Clone for ClonePy<T> {
+    fn clone(&self) -> Self {
+        Python::with_gil(|py| Self(self.0.clone_ref(py)))
+    }
+}
+
 /// A Python module implemented in Rust. The name of this function must match
 /// the `lib.name` setting in the `Cargo.toml`, else Python will not be able to
 /// import the module.

rust/exo_pyo3_bindings/src/networking.rs

@@ -11,9 +11,9 @@ use crate::ext::{ResultExt as _, TokioMpscReceiverExt as _, TokioMpscSenderExt a
 use crate::pyclass;
 use crate::pylibp2p::ident::{PyKeypair, PyPeerId};
 use libp2p::futures::StreamExt as _;
-use libp2p::gossipsub;
 use libp2p::gossipsub::{IdentTopic, Message, MessageId, PublishError};
 use libp2p::swarm::SwarmEvent;
+use libp2p::{gossipsub, mdns};
 use networking::discovery;
 use networking::swarm::create_swarm;
 use pyo3::prelude::{PyModule, PyModuleMethods as _};
@@ -25,7 +25,7 @@ use tokio::sync::{Mutex, mpsc, oneshot};
 
 mod exception {
     use pyo3::types::PyTuple;
-    use pyo3::{exceptions::PyException, prelude::*};
+    use pyo3::{PyErrArguments, exceptions::PyException, prelude::*};
     use pyo3_stub_gen::derive::*;
 
     #[gen_stub_pyclass]
@@ -155,6 +155,7 @@ async fn networking_task(
 ) {
     use SwarmEvent::*;
     use ToTask::*;
+    use mdns::Event::*;
     use networking::swarm::BehaviourEvent::*;
 
     log::info!("RUST: networking task started");
@@ -341,8 +342,10 @@ impl PyNetworkingHandle {
     // ---- Lifecycle management methods ----
 
     #[new]
-    fn py_new(identity: Bound<'_, PyKeypair>) -> PyResult<Self> {
+    #[pyo3(signature = (identity, bootstrap_peers=vec![]))]
+    fn py_new(identity: Bound<'_, PyKeypair>, bootstrap_peers: Vec<String>) -> PyResult<Self> {
         use pyo3_async_runtimes::tokio::get_runtime;
+        use std::str::FromStr;
 
         // create communication channels
         let (to_task_tx, to_task_rx) = mpsc::channel(MPSC_CHANNEL_SIZE);
@@ -352,9 +355,20 @@ impl PyNetworkingHandle {
         // get identity
         let identity = identity.borrow().0.clone();
 
+        // parse bootstrap peer multiaddrs
+        let parsed_peers: Vec<libp2p::Multiaddr> = bootstrap_peers
+            .into_iter()
+            .map(|s| libp2p::Multiaddr::from_str(&s))
+            .collect::<Result<_, _>>()
+            .pyerr()?;
+
+        if !parsed_peers.is_empty() {
+            log::info!("RUST: bootstrap peers: {:?}", parsed_peers);
+        }
+
         // create networking swarm (within tokio context!! or it crashes)
         let swarm = get_runtime()
-            .block_on(async { create_swarm(identity) })
+            .block_on(async { create_swarm(identity, parsed_peers) })
             .pyerr()?;
 
         // spawn tokio task running the networking logic
@@ -484,7 +498,7 @@ impl PyNetworkingHandle {
         let (tx, rx) = oneshot::channel();
 
         // send off request to subscribe
-        let data = Python::attach(|py| Vec::from(data.as_bytes(py)));
+        let data = Python::with_gil(|py| Vec::from(data.as_bytes(py)));
         self.to_task_tx()
             .send_py(ToTask::GossipsubPublish {
                 topic,

rust/networking/Cargo.toml

@@ -19,6 +19,8 @@ either = { workspace = true }
 # macro dependencies
 extend = { workspace = true }
 delegate = { workspace = true }
+impl-trait-for-tuples = { workspace = true }
+derive_more = { workspace = true }
 
 # async
 tokio = { workspace = true, features = ["full"] }
@@ -27,6 +29,11 @@ futures-timer = { workspace = true }
 
 # utility dependencies
 util = { workspace = true }
+thiserror = { workspace = true }
+#internment = { workspace = true }
+#recursion = { workspace = true }
+#generativity = { workspace = true }
+#itertools = { workspace = true }
 tracing-subscriber = { version = "0.3.19", features = ["default", "env-filter"] }
 keccak-const = { workspace = true }
 
@@ -34,4 +41,4 @@ keccak-const = { workspace = true }
 log = { workspace = true }
 
 # networking
-libp2p = { workspace = true, features = ["full"] }
+libp2p = { workspace = true, features = ["full"] }

rust/networking/examples/chatroom_manual.rs

@@ -24,8 +24,8 @@ use libp2p::{
     swarm::{NetworkBehaviour, SwarmEvent},
     tcp, yamux,
 };
-use std::error::Error;
 use std::time::Duration;
+use std::{error::Error, hash::Hash};
 use tokio::{io, io::AsyncBufReadExt, select};
 use tracing_subscriber::EnvFilter;
 

rust/networking/src/discovery.rs

@@ -1,4 +1,5 @@
 use crate::ext::MultiaddrExt;
+use crate::keep_alive;
 use delegate::delegate;
 use either::Either;
 use futures::FutureExt;
@@ -105,6 +106,9 @@ pub struct Behaviour {
     managed: managed::Behaviour,
     mdns_discovered: HashMap<PeerId, BTreeSet<Multiaddr>>,
 
+    /// Addresses provided via --bootstrap-peer, re-dialed on the retry loop.
+    bootstrap_addrs: Vec<Multiaddr>,
+
     retry_delay: Delay, // retry interval
 
     // pending events to emmit => waker-backed Deque to control polling
@@ -112,13 +116,21 @@ pub struct Behaviour {
 }
 
 impl Behaviour {
-    pub fn new(keypair: &identity::Keypair) -> io::Result<Self> {
-        Ok(Self {
+    pub fn new(keypair: &identity::Keypair, bootstrap_peers: Vec<Multiaddr>) -> io::Result<Self> {
+        let mut behaviour = Self {
             managed: managed::Behaviour::new(keypair)?,
             mdns_discovered: HashMap::new(),
+            bootstrap_addrs: bootstrap_peers,
             retry_delay: Delay::new(RETRY_CONNECT_INTERVAL),
             pending_events: WakerDeque::new(),
-        })
+        };
+
+        // Immediately dial all bootstrap peers
+        for addr in &behaviour.bootstrap_addrs.clone() {
+            behaviour.dial_addr(addr.clone());
+        }
+
+        Ok(behaviour)
     }
 
     fn dial(&mut self, peer_id: PeerId, addr: Multiaddr) {
@@ -127,6 +139,14 @@ impl Behaviour {
         })
     }
 
+    /// Dial by address only — PeerId is resolved via Noise handshake on connect.
+    /// Used for bootstrap peers where only IP:port is known.
+    fn dial_addr(&mut self, addr: Multiaddr) {
+        self.pending_events.push_back(ToSwarm::Dial {
+            opts: DialOpts::unknown_peer_id().address(addr).build(),
+        })
+    }
+
     fn close_connection(&mut self, peer_id: PeerId, connection: ConnectionId) {
         // push front to make this IMMEDIATE
         self.pending_events.push_front(ToSwarm::CloseConnection {
@@ -361,13 +381,16 @@ impl NetworkBehaviour for Behaviour {
             Poll::Pending => {}
         }
 
-        // retry connecting to all mDNS peers periodically (fails safely if already connected)
+        // retry connecting to all mDNS + bootstrap peers periodically (fails safely if already connected)
         if self.retry_delay.poll_unpin(cx).is_ready() {
             for (p, mas) in self.mdns_discovered.clone() {
                 for ma in mas {
                     self.dial(p, ma)
                 }
             }
+            for addr in self.bootstrap_addrs.clone() {
+                self.dial_addr(addr)
+            }
             self.retry_delay.reset(RETRY_CONNECT_INTERVAL) // reset timeout
         }
 

rust/networking/src/keep_alive.rs

@@ -0,0 +1,44 @@
+use delegate::delegate;
+use libp2p::swarm::handler::ConnectionEvent;
+use libp2p::swarm::{ConnectionHandlerEvent, SubstreamProtocol, dummy, handler};
+use std::task::{Context, Poll};
+
+/// An implementation of [`ConnectionHandler`] that doesn't handle any protocols, but it keeps
+/// the connection alive.
+#[derive(Clone)]
+#[repr(transparent)]
+pub struct ConnectionHandler(dummy::ConnectionHandler);
+
+impl ConnectionHandler {
+    pub fn new() -> Self {
+        ConnectionHandler(dummy::ConnectionHandler)
+    }
+}
+
+impl handler::ConnectionHandler for ConnectionHandler {
+    // delegate types and implementation mostly to dummy handler
+    type FromBehaviour = <dummy::ConnectionHandler as handler::ConnectionHandler>::FromBehaviour;
+    type ToBehaviour = <dummy::ConnectionHandler as handler::ConnectionHandler>::ToBehaviour;
+    type InboundProtocol =
+        <dummy::ConnectionHandler as handler::ConnectionHandler>::InboundProtocol;
+    type OutboundProtocol =
+        <dummy::ConnectionHandler as handler::ConnectionHandler>::OutboundProtocol;
+    type InboundOpenInfo =
+        <dummy::ConnectionHandler as handler::ConnectionHandler>::InboundOpenInfo;
+    type OutboundOpenInfo =
+        <dummy::ConnectionHandler as handler::ConnectionHandler>::OutboundOpenInfo;
+
+    delegate! {
+        to self.0 {
+            fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo>;
+            fn poll(&mut self, cx: &mut Context<'_>) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, Self::OutboundOpenInfo, Self::ToBehaviour>>;
+            fn on_behaviour_event(&mut self, event: Self::FromBehaviour);
+            fn on_connection_event(&mut self, event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol, Self::InboundOpenInfo, Self::OutboundOpenInfo>);
+        }
+    }
+
+    // specifically override this to force connection to stay alive
+    fn connection_keep_alive(&self) -> bool {
+        true
+    }
+}

rust/networking/src/lib.rs

@@ -3,7 +3,19 @@
 //! this is here as a placeholder documentation
 //!
 //!
+
+// enable Rust-unstable features for convenience
+#![feature(trait_alias)]
+// #![feature(stmt_expr_attributes)]
+// #![feature(unboxed_closures)]
+// #![feature(assert_matches)]
+// #![feature(async_fn_in_dyn_trait)]
+// #![feature(async_for_loop)]
+// #![feature(auto_traits)]
+// #![feature(negative_impls)]
+
 pub mod discovery;
+pub mod keep_alive;
 pub mod swarm;
 
 /// Namespace for all the type/trait aliases used by this crate.
@@ -42,3 +54,11 @@ pub(crate) mod ext {
         }
     }
 }
+
+pub(crate) mod private {
+    #![allow(dead_code)]
+
+    /// Sealed traits support
+    pub trait Sealed {}
+    impl<T: ?Sized> Sealed for T {}
+}

rust/networking/src/swarm.rs

@@ -1,7 +1,7 @@
 use crate::alias;
 use crate::swarm::transport::tcp_transport;
 pub use behaviour::{Behaviour, BehaviourEvent};
-use libp2p::{SwarmBuilder, identity};
+use libp2p::{Multiaddr, SwarmBuilder, identity};
 
 pub type Swarm = libp2p::Swarm<Behaviour>;
 
@@ -16,11 +16,14 @@ pub const NETWORK_VERSION: &[u8] = b"v0.0.1";
 pub const OVERRIDE_VERSION_ENV_VAR: &str = "EXO_LIBP2P_NAMESPACE";
 
 /// Create and configure a swarm which listens to all ports on OS
-pub fn create_swarm(keypair: identity::Keypair) -> alias::AnyResult<Swarm> {
+pub fn create_swarm(
+    keypair: identity::Keypair,
+    bootstrap_peers: Vec<Multiaddr>,
+) -> alias::AnyResult<Swarm> {
     let mut swarm = SwarmBuilder::with_existing_identity(keypair)
         .with_tokio()
         .with_other_transport(tcp_transport)?
-        .with_behaviour(Behaviour::new)?
+        .with_behaviour(|kp| Behaviour::new(kp, bootstrap_peers))?
         .build();
 
     // Listen on all interfaces and whatever port the OS assigns
@@ -105,7 +108,7 @@ mod transport {
 mod behaviour {
     use crate::{alias, discovery};
     use libp2p::swarm::NetworkBehaviour;
-    use libp2p::{gossipsub, identity};
+    use libp2p::{Multiaddr, gossipsub, identity};
 
     /// Behavior of the Swarm which composes all desired behaviors:
     /// Right now its just [`discovery::Behaviour`] and [`gossipsub::Behaviour`].
@@ -116,9 +119,12 @@ mod behaviour {
     }
 
     impl Behaviour {
-        pub fn new(keypair: &identity::Keypair) -> alias::AnyResult<Self> {
+        pub fn new(
+            keypair: &identity::Keypair,
+            bootstrap_peers: Vec<Multiaddr>,
+        ) -> alias::AnyResult<Self> {
             Ok(Self {
-                discovery: discovery::Behaviour::new(keypair)?,
+                discovery: discovery::Behaviour::new(keypair, bootstrap_peers)?,
                 gossipsub: gossipsub_behaviour(keypair),
             })
         }

src/exo/download/coordinator.py

@@ -14,7 +14,6 @@ from exo.download.download_utils import (
     map_repo_download_progress_to_download_progress_data,
 )
 from exo.download.shard_downloader import ShardDownloader
-from exo.shared.constants import EXO_MODELS_DIR
 from exo.shared.models.model_cards import ModelId
 from exo.shared.types.commands import (
     CancelDownload,
@@ -47,7 +46,6 @@ class DownloadCoordinator:
     download_command_receiver: Receiver[ForwarderDownloadCommand]
     local_event_sender: Sender[ForwarderEvent]
     event_index_counter: Iterator[int]
-    offline: bool = False
 
     # Local state
     download_status: dict[ModelId, DownloadProgress] = field(default_factory=dict)
@@ -63,13 +61,8 @@ class DownloadCoordinator:
 
     def __post_init__(self) -> None:
         self.event_sender, self.event_receiver = channel[Event]()
-        if self.offline:
-            self.shard_downloader.set_internet_connection(False)
         self.shard_downloader.on_progress(self._download_progress_callback)
 
-    def _model_dir(self, model_id: ModelId) -> str:
-        return str(EXO_MODELS_DIR / model_id.normalize())
-
     async def _download_progress_callback(
         self, callback_shard: ShardMetadata, progress: RepoDownloadProgress
     ) -> None:
@@ -81,7 +74,6 @@ class DownloadCoordinator:
                 shard_metadata=callback_shard,
                 node_id=self.node_id,
                 total_bytes=progress.total_bytes,
-                model_directory=self._model_dir(model_id),
             )
             self.download_status[model_id] = completed
             await self.event_sender.send(
@@ -101,7 +93,6 @@ class DownloadCoordinator:
                 download_progress=map_repo_download_progress_to_download_progress_data(
                     progress
                 ),
-                model_directory=self._model_dir(model_id),
             )
             self.download_status[model_id] = ongoing
             await self.event_sender.send(
@@ -110,17 +101,13 @@ class DownloadCoordinator:
             self._last_progress_time[model_id] = current_time()
 
     async def run(self) -> None:
-        logger.info(
-            f"Starting DownloadCoordinator{' (offline mode)' if self.offline else ''}"
-        )
-        if not self.offline:
-            self._test_internet_connection()
+        logger.info("Starting DownloadCoordinator")
+        self._test_internet_connection()
         async with self._tg as tg:
             tg.start_soon(self._command_processor)
             tg.start_soon(self._forward_events)
             tg.start_soon(self._emit_existing_download_progress)
-            if not self.offline:
-                tg.start_soon(self._check_internet_connection)
+            tg.start_soon(self._check_internet_connection)
 
     def _test_internet_connection(self) -> None:
         try:
@@ -183,11 +170,7 @@ class DownloadCoordinator:
                 return
 
         # Emit pending status
-        progress = DownloadPending(
-            shard_metadata=shard,
-            node_id=self.node_id,
-            model_directory=self._model_dir(model_id),
-        )
+        progress = DownloadPending(shard_metadata=shard, node_id=self.node_id)
         self.download_status[model_id] = progress
         await self.event_sender.send(NodeDownloadProgress(download_progress=progress))
 
@@ -201,7 +184,6 @@ class DownloadCoordinator:
                 shard_metadata=shard,
                 node_id=self.node_id,
                 total_bytes=initial_progress.total_bytes,
-                model_directory=self._model_dir(model_id),
             )
             self.download_status[model_id] = completed
             await self.event_sender.send(
@@ -209,20 +191,6 @@ class DownloadCoordinator:
             )
             return
 
-        if self.offline:
-            logger.warning(
-                f"Offline mode: model {model_id} is not fully available locally, cannot download"
-            )
-            failed = DownloadFailed(
-                shard_metadata=shard,
-                node_id=self.node_id,
-                error_message=f"Model files not found locally in offline mode: {model_id}",
-                model_directory=self._model_dir(model_id),
-            )
-            self.download_status[model_id] = failed
-            await self.event_sender.send(NodeDownloadProgress(download_progress=failed))
-            return
-
         # Start actual download
         self._start_download_task(shard, initial_progress)
 
@@ -238,7 +206,6 @@ class DownloadCoordinator:
             download_progress=map_repo_download_progress_to_download_progress_data(
                 initial_progress
             ),
-            model_directory=self._model_dir(model_id),
         )
         self.download_status[model_id] = status
         self.event_sender.send_nowait(NodeDownloadProgress(download_progress=status))
@@ -252,7 +219,6 @@ class DownloadCoordinator:
                     shard_metadata=shard,
                     node_id=self.node_id,
                     error_message=str(e),
-                    model_directory=self._model_dir(model_id),
                 )
                 self.download_status[model_id] = failed
                 await self.event_sender.send(
@@ -287,7 +253,6 @@ class DownloadCoordinator:
             pending = DownloadPending(
                 shard_metadata=current_status.shard_metadata,
                 node_id=self.node_id,
-                model_directory=self._model_dir(model_id),
             )
             await self.event_sender.send(
                 NodeDownloadProgress(download_progress=pending)
@@ -330,18 +295,21 @@ class DownloadCoordinator:
                             node_id=self.node_id,
                             shard_metadata=progress.shard,
                             total_bytes=progress.total_bytes,
-                            model_directory=self._model_dir(
-                                progress.shard.model_card.model_id
-                            ),
                         )
                     elif progress.status in ["in_progress", "not_started"]:
-                        if progress.downloaded_bytes_this_session.in_bytes == 0:
-                            status = DownloadPending(
+                        if (
+                            progress.downloaded_bytes.in_bytes
+                            >= progress.total_bytes.in_bytes
+                            > 0
+                        ):
+                            status = DownloadCompleted(
                                 node_id=self.node_id,
                                 shard_metadata=progress.shard,
-                                model_directory=self._model_dir(
-                                    progress.shard.model_card.model_id
-                                ),
+                                total_bytes=progress.total_bytes,
+                            )
+                        elif progress.downloaded_bytes_this_session.in_bytes == 0:
+                            status = DownloadPending(
+                                node_id=self.node_id, shard_metadata=progress.shard
                             )
                         else:
                             status = DownloadOngoing(
@@ -350,9 +318,6 @@ class DownloadCoordinator:
                                 download_progress=map_repo_download_progress_to_download_progress_data(
                                     progress
                                 ),
-                                model_directory=self._model_dir(
-                                    progress.shard.model_card.model_id
-                                ),
                             )
                     else:
                         continue

src/exo/download/download_utils.py

@@ -8,13 +8,13 @@ import traceback
 from collections.abc import Awaitable
 from datetime import timedelta
 from pathlib import Path
-from typing import Callable, Literal, cast
+from typing import Callable, Literal
 from urllib.parse import urljoin
 
 import aiofiles
 import aiofiles.os as aios
+import aiohttp
 import certifi
-import httpx
 from huggingface_hub import (
     snapshot_download,  # pyright: ignore[reportUnknownVariableType]
 )
@@ -330,17 +330,17 @@ async def _fetch_file_list(
     headers = await get_download_headers()
     async with (
         create_http_session(timeout_profile="short") as session,
+        session.get(url, headers=headers) as response,
     ):
-        response = await session.get(url, headers=headers)
-        if response.status_code in [401, 403]:
-            msg = await _build_auth_error_message(response.status_code, model_id)
+        if response.status in [401, 403]:
+            msg = await _build_auth_error_message(response.status, model_id)
             raise HuggingFaceAuthenticationError(msg)
-        elif response.status_code == 429:
+        elif response.status == 429:
             raise HuggingFaceRateLimitError(
                 f"Couldn't download {model_id} because of HuggingFace rate limit."
             )
-        elif response.status_code == 200:
-            data_json = response.text
+        elif response.status == 200:
+            data_json = await response.text()
             data = TypeAdapter(list[FileListEntry]).validate_json(data_json)
             files: list[FileListEntry] = []
             for item in data:
@@ -353,7 +353,7 @@ async def _fetch_file_list(
                     files.extend(subfiles)
             return files
         else:
-            raise Exception(f"Failed to fetch file list: {response.status_code}")
+            raise Exception(f"Failed to fetch file list: {response.status}")
 
 
 async def get_download_headers() -> dict[str, str]:
@@ -361,29 +361,34 @@ async def get_download_headers() -> dict[str, str]:
 
 
 def create_http_session(
+    auto_decompress: bool = False,
     timeout_profile: Literal["short", "long"] = "long",
-) -> httpx.AsyncClient:
+) -> aiohttp.ClientSession:
     if timeout_profile == "short":
         total_timeout = 30
         connect_timeout = 10
-        read_timeout = 30
+        sock_read_timeout = 30
+        sock_connect_timeout = 10
     else:
         total_timeout = 1800
         connect_timeout = 60
-        read_timeout = 60
+        sock_read_timeout = 60
+        sock_connect_timeout = 60
 
     ssl_context = ssl.create_default_context(
         cafile=os.getenv("SSL_CERT_FILE") or certifi.where()
     )
+    connector = aiohttp.TCPConnector(ssl=ssl_context)
 
-    # default here is to load env vars
-    return httpx.AsyncClient(
-        verify=ssl_context,
-        timeout=httpx.Timeout(
+    return aiohttp.ClientSession(
+        auto_decompress=auto_decompress,
+        connector=connector,
+        proxy=os.getenv("HTTPS_PROXY") or os.getenv("HTTP_PROXY") or None,
+        timeout=aiohttp.ClientTimeout(
+            total=total_timeout,
             connect=connect_timeout,
-            read=read_timeout,
-            write=total_timeout,
-            pool=total_timeout,
+            sock_read=sock_read_timeout,
+            sock_connect=sock_connect_timeout,
         ),
     )
 
@@ -410,28 +415,26 @@ async def file_meta(
     headers = await get_download_headers()
     async with (
         create_http_session(timeout_profile="short") as session,
-        session.stream("HEAD", url, headers=headers) as r,
+        session.head(url, headers=headers) as r,
     ):
-        if r.status_code == 307:
+        if r.status == 307:
             # On redirect, only trust Hugging Face's x-linked-* headers.
-            x_linked_size = cast(str | None, r.headers.get("x-linked-size"))
-            x_linked_etag = cast(str | None, r.headers.get("x-linked-etag"))
+            x_linked_size = r.headers.get("x-linked-size")
+            x_linked_etag = r.headers.get("x-linked-etag")
             if x_linked_size and x_linked_etag:
                 content_length = int(x_linked_size)
                 etag = trim_etag(x_linked_etag)
                 return content_length, etag
             # Otherwise, follow the redirect to get authoritative size/hash
-            redirected_location = cast(str | None, r.headers.get("location"))
+            redirected_location = r.headers.get("location")
             return await file_meta(model_id, revision, path, redirected_location)
-        if r.status_code in [401, 403]:
-            msg = await _build_auth_error_message(r.status_code, model_id)
+        if r.status in [401, 403]:
+            msg = await _build_auth_error_message(r.status, model_id)
             raise HuggingFaceAuthenticationError(msg)
-        content_length = cast(
-            str | None,
-            r.headers.get("x-linked-size") or r.headers.get("content-length"),
+        content_length = int(
+            r.headers.get("x-linked-size") or r.headers.get("content-length") or 0
         )
-        content_length = 0 if content_length is None else int(content_length)
-        etag = cast(str | None, r.headers.get("x-linked-etag") or r.headers.get("etag"))
+        etag = r.headers.get("x-linked-etag") or r.headers.get("etag")
         assert content_length > 0, f"No content length for {url}"
         assert etag is not None, f"No remote hash for {url}"
         etag = trim_etag(etag)
@@ -445,13 +448,12 @@ async def download_file_with_retry(
     target_dir: Path,
     on_progress: Callable[[int, int, bool], None] = lambda _, __, ___: None,
     on_connection_lost: Callable[[], None] = lambda: None,
-    skip_internet: bool = False,
 ) -> Path:
     n_attempts = 3
     for attempt in range(n_attempts):
         try:
             return await _download_file(
-                model_id, revision, path, target_dir, on_progress, skip_internet
+                model_id, revision, path, target_dir, on_progress
             )
         except HuggingFaceAuthenticationError:
             raise
@@ -485,14 +487,10 @@ async def _download_file(
     path: str,
     target_dir: Path,
     on_progress: Callable[[int, int, bool], None] = lambda _, __, ___: None,
-    skip_internet: bool = False,
 ) -> Path:
     target_path = target_dir / path
 
     if await aios.path.exists(target_path):
-        if skip_internet:
-            return target_path
-
         local_size = (await aios.stat(target_path)).st_size
 
         # Try to verify against remote, but allow offline operation
@@ -512,11 +510,6 @@ async def _download_file(
             )
             return target_path
 
-    if skip_internet:
-        raise FileNotFoundError(
-            f"File {path} not found locally and cannot download in offline mode"
-        )
-
     await aios.makedirs((target_dir / path).parent, exist_ok=True)
     length, etag = await file_meta(model_id, revision, path)
     remote_hash = etag[:-5] if etag.endswith("-gzip") else etag
@@ -534,20 +527,20 @@ async def _download_file(
         n_read = resume_byte_pos or 0
         async with (
             create_http_session(timeout_profile="long") as session,
-            session.stream("GET", url, headers=headers, follow_redirects=True) as r,
+            session.get(url, headers=headers) as r,
         ):
-            if r.status_code == 404:
+            if r.status == 404:
                 raise FileNotFoundError(f"File not found: {url}")
-            if r.status_code in [401, 403]:
-                msg = await _build_auth_error_message(r.status_code, model_id)
+            if r.status in [401, 403]:
+                msg = await _build_auth_error_message(r.status, model_id)
                 raise HuggingFaceAuthenticationError(msg)
-            assert r.status_code in [200, 206], (
-                f"Failed to download {path} from {url}: {r.status_code}"
+            assert r.status in [200, 206], (
+                f"Failed to download {path} from {url}: {r.status}"
             )
             async with aiofiles.open(
                 partial_path, "ab" if resume_byte_pos else "wb"
             ) as f:
-                async for chunk in r.aiter_bytes(8 * 1024 * 1024):
+                while chunk := await r.content.read(8 * 1024 * 1024):
                     n_read = n_read + (await f.write(chunk))
                     on_progress(n_read, length, False)
 
@@ -821,7 +814,6 @@ async def download_shard(
                     file, curr_bytes, total_bytes, is_renamed
                 ),
                 on_connection_lost=on_connection_lost,
-                skip_internet=skip_internet,
             )
 
     if not skip_download:

src/exo/download/impl_shard_downloader.py

@@ -189,7 +189,6 @@ class ResumableShardDownloader(ShardDownloader):
             try:
                 yield await task
             except Exception as e:
-                task.cancel()
                 logger.warning(f"Error downloading shard: {type(e).__name__}")
 
     async def get_shard_download_status_for_shard(

src/exo/download/tests/test_offline_mode.py

@@ -1,230 +0,0 @@
-"""Tests for offline/air-gapped mode."""
-
-from collections.abc import AsyncIterator
-from pathlib import Path
-from unittest.mock import AsyncMock, patch
-
-import aiofiles
-import aiofiles.os as aios
-import pytest
-
-from exo.download.download_utils import (
-    _download_file,  # pyright: ignore[reportPrivateUsage]
-    download_file_with_retry,
-    fetch_file_list_with_cache,
-)
-from exo.shared.types.common import ModelId
-from exo.shared.types.worker.downloads import FileListEntry
-
-
-@pytest.fixture
-def model_id() -> ModelId:
-    return ModelId("test-org/test-model")
-
-
-@pytest.fixture
-async def temp_models_dir(tmp_path: Path) -> AsyncIterator[Path]:
-    models_dir = tmp_path / "models"
-    await aios.makedirs(models_dir, exist_ok=True)
-    with patch("exo.download.download_utils.EXO_MODELS_DIR", models_dir):
-        yield models_dir
-
-
-class TestDownloadFileOffline:
-    """Tests for _download_file with skip_internet=True."""
-
-    async def test_returns_local_file_without_http_verification(
-        self, model_id: ModelId, tmp_path: Path
-    ) -> None:
-        """When skip_internet=True and file exists locally, return it immediately
-        without making any HTTP calls (no file_meta verification)."""
-        target_dir = tmp_path / "downloads"
-        await aios.makedirs(target_dir, exist_ok=True)
-
-        local_file = target_dir / "model.safetensors"
-        async with aiofiles.open(local_file, "wb") as f:
-            await f.write(b"model weights data")
-
-        with patch(
-            "exo.download.download_utils.file_meta",
-            new_callable=AsyncMock,
-        ) as mock_file_meta:
-            result = await _download_file(
-                model_id,
-                "main",
-                "model.safetensors",
-                target_dir,
-                skip_internet=True,
-            )
-
-            assert result == local_file
-            mock_file_meta.assert_not_called()
-
-    async def test_raises_file_not_found_for_missing_file(
-        self, model_id: ModelId, tmp_path: Path
-    ) -> None:
-        """When skip_internet=True and file does NOT exist locally,
-        raise FileNotFoundError instead of attempting download."""
-        target_dir = tmp_path / "downloads"
-        await aios.makedirs(target_dir, exist_ok=True)
-
-        with pytest.raises(FileNotFoundError, match="offline mode"):
-            await _download_file(
-                model_id,
-                "main",
-                "missing_model.safetensors",
-                target_dir,
-                skip_internet=True,
-            )
-
-    async def test_returns_local_file_in_subdirectory(
-        self, model_id: ModelId, tmp_path: Path
-    ) -> None:
-        """When skip_internet=True and file exists in a subdirectory,
-        return it without HTTP calls."""
-        target_dir = tmp_path / "downloads"
-        subdir = target_dir / "transformer"
-        await aios.makedirs(subdir, exist_ok=True)
-
-        local_file = subdir / "diffusion_pytorch_model.safetensors"
-        async with aiofiles.open(local_file, "wb") as f:
-            await f.write(b"weights")
-
-        with patch(
-            "exo.download.download_utils.file_meta",
-            new_callable=AsyncMock,
-        ) as mock_file_meta:
-            result = await _download_file(
-                model_id,
-                "main",
-                "transformer/diffusion_pytorch_model.safetensors",
-                target_dir,
-                skip_internet=True,
-            )
-
-            assert result == local_file
-            mock_file_meta.assert_not_called()
-
-
-class TestDownloadFileWithRetryOffline:
-    """Tests for download_file_with_retry with skip_internet=True."""
-
-    async def test_propagates_skip_internet_to_download_file(
-        self, model_id: ModelId, tmp_path: Path
-    ) -> None:
-        """Verify skip_internet is passed through to _download_file."""
-        target_dir = tmp_path / "downloads"
-        await aios.makedirs(target_dir, exist_ok=True)
-
-        local_file = target_dir / "config.json"
-        async with aiofiles.open(local_file, "wb") as f:
-            await f.write(b'{"model_type": "qwen2"}')
-
-        with patch(
-            "exo.download.download_utils.file_meta",
-            new_callable=AsyncMock,
-        ) as mock_file_meta:
-            result = await download_file_with_retry(
-                model_id,
-                "main",
-                "config.json",
-                target_dir,
-                skip_internet=True,
-            )
-
-            assert result == local_file
-            mock_file_meta.assert_not_called()
-
-    async def test_file_not_found_does_not_retry(
-        self, model_id: ModelId, tmp_path: Path
-    ) -> None:
-        """FileNotFoundError from offline mode should not trigger retries."""
-        target_dir = tmp_path / "downloads"
-        await aios.makedirs(target_dir, exist_ok=True)
-
-        with pytest.raises(FileNotFoundError):
-            await download_file_with_retry(
-                model_id,
-                "main",
-                "nonexistent.safetensors",
-                target_dir,
-                skip_internet=True,
-            )
-
-
-class TestFetchFileListOffline:
-    """Tests for fetch_file_list_with_cache with skip_internet=True."""
-
-    async def test_uses_cached_file_list(
-        self, model_id: ModelId, temp_models_dir: Path
-    ) -> None:
-        """When skip_internet=True and cache file exists, use it without network."""
-        from pydantic import TypeAdapter
-
-        cache_dir = temp_models_dir / "caches" / model_id.normalize()
-        await aios.makedirs(cache_dir, exist_ok=True)
-
-        cached_list = [
-            FileListEntry(type="file", path="model.safetensors", size=1000),
-            FileListEntry(type="file", path="config.json", size=200),
-        ]
-        cache_file = cache_dir / f"{model_id.normalize()}--main--file_list.json"
-        async with aiofiles.open(cache_file, "w") as f:
-            await f.write(
-                TypeAdapter(list[FileListEntry]).dump_json(cached_list).decode()
-            )
-
-        with patch(
-            "exo.download.download_utils.fetch_file_list_with_retry",
-            new_callable=AsyncMock,
-        ) as mock_fetch:
-            result = await fetch_file_list_with_cache(
-                model_id, "main", skip_internet=True
-            )
-
-            assert result == cached_list
-            mock_fetch.assert_not_called()
-
-    async def test_falls_back_to_local_directory_scan(
-        self, model_id: ModelId, temp_models_dir: Path
-    ) -> None:
-        """When skip_internet=True and no cache but local files exist,
-        build file list from local directory."""
-        import json
-
-        model_dir = temp_models_dir / model_id.normalize()
-        await aios.makedirs(model_dir, exist_ok=True)
-
-        async with aiofiles.open(model_dir / "config.json", "w") as f:
-            await f.write('{"model_type": "qwen2"}')
-
-        index_data = {
-            "metadata": {},
-            "weight_map": {"model.layers.0.weight": "model.safetensors"},
-        }
-        async with aiofiles.open(model_dir / "model.safetensors.index.json", "w") as f:
-            await f.write(json.dumps(index_data))
-
-        async with aiofiles.open(model_dir / "model.safetensors", "wb") as f:
-            await f.write(b"x" * 500)
-
-        with patch(
-            "exo.download.download_utils.fetch_file_list_with_retry",
-            new_callable=AsyncMock,
-        ) as mock_fetch:
-            result = await fetch_file_list_with_cache(
-                model_id, "main", skip_internet=True
-            )
-
-            mock_fetch.assert_not_called()
-            paths = {entry.path for entry in result}
-            assert "config.json" in paths
-            assert "model.safetensors" in paths
-
-    async def test_raises_when_no_cache_and_no_local_files(
-        self, model_id: ModelId, temp_models_dir: Path
-    ) -> None:
-        """When skip_internet=True and neither cache nor local files exist,
-        raise FileNotFoundError."""
-        with pytest.raises(FileNotFoundError, match="No internet"):
-            await fetch_file_list_with_cache(model_id, "main", skip_internet=True)

src/exo/main.py

@@ -39,7 +39,6 @@ class Node:
 
     node_id: NodeId
     event_index_counter: Iterator[int]
-    offline: bool
     _tg: TaskGroup = field(init=False, default_factory=anyio.create_task_group)
 
     @classmethod
@@ -47,7 +46,12 @@ class Node:
         keypair = get_node_id_keypair()
         node_id = NodeId(keypair.to_peer_id().to_base58())
         session_id = SessionId(master_node_id=node_id, election_clock=0)
-        router = Router.create(keypair)
+        bootstrap_peers: list[str] = []
+        if args.bootstrap_peer:
+            ip, port = args.bootstrap_peer.rsplit(":", 1)
+            bootstrap_peers.append(f"/ip4/{ip}/tcp/{port}")
+            logger.info(f"Bootstrap peer: {args.bootstrap_peer}")
+        router = Router.create(keypair, bootstrap_peers=bootstrap_peers)
         await router.register_topic(topics.GLOBAL_EVENTS)
         await router.register_topic(topics.LOCAL_EVENTS)
         await router.register_topic(topics.COMMANDS)
@@ -69,7 +73,6 @@ class Node:
                 download_command_receiver=router.receiver(topics.DOWNLOAD_COMMANDS),
                 local_event_sender=router.sender(topics.LOCAL_EVENTS),
                 event_index_counter=event_index_counter,
-                offline=args.offline,
             )
         else:
             download_coordinator = None
@@ -134,13 +137,10 @@ class Node:
             api,
             node_id,
             event_index_counter,
-            args.offline,
         )
 
     async def run(self):
         async with self._tg as tg:
-            signal.signal(signal.SIGINT, lambda _, __: self.shutdown())
-            signal.signal(signal.SIGTERM, lambda _, __: self.shutdown())
             tg.start_soon(self.router.run)
             tg.start_soon(self.election.run)
             if self.download_coordinator:
@@ -152,6 +152,8 @@ class Node:
             if self.api:
                 tg.start_soon(self.api.run)
             tg.start_soon(self._elect_loop)
+            signal.signal(signal.SIGINT, lambda _, __: self.shutdown())
+            signal.signal(signal.SIGTERM, lambda _, __: self.shutdown())
 
     def shutdown(self):
         # if this is our second call to shutdown, just sys.exit
@@ -225,7 +227,6 @@ class Node:
                             ),
                             local_event_sender=self.router.sender(topics.LOCAL_EVENTS),
                             event_index_counter=self.event_index_counter,
-                            offline=self.offline,
                         )
                         self._tg.start_soon(self.download_coordinator.run)
                     if self.worker:
@@ -258,15 +259,12 @@ def main():
     target = min(max(soft, 65535), hard)
     resource.setrlimit(resource.RLIMIT_NOFILE, (target, hard))
 
-    mp.set_start_method("spawn")
+    mp.set_start_method("spawn", force=True)
     # TODO: Refactor the current verbosity system
     logger_setup(EXO_LOG, args.verbosity)
     logger.info("Starting EXO")
     logger.info(f"EXO_LIBP2P_NAMESPACE: {os.getenv('EXO_LIBP2P_NAMESPACE')}")
 
-    if args.offline:
-        logger.info("Running in OFFLINE mode — no internet checks, local models only")
-
     # Set FAST_SYNCH override env var for runner subprocesses
     if args.fast_synch is True:
         os.environ["EXO_FAST_SYNCH"] = "on"
@@ -289,8 +287,8 @@ class Args(CamelCaseModel):
     tb_only: bool = False
     no_worker: bool = False
     no_downloads: bool = False
-    offline: bool = False
     fast_synch: bool | None = None  # None = auto, True = force on, False = force off
+    bootstrap_peer: str | None = None
 
     @classmethod
     def parse(cls) -> Self:
@@ -337,11 +335,6 @@ class Args(CamelCaseModel):
             action="store_true",
             help="Disable the download coordinator (node won't download models)",
         )
-        parser.add_argument(
-            "--offline",
-            action="store_true",
-            help="Run in offline/air-gapped mode: skip internet checks, use only pre-staged local models",
-        )
         fast_synch_group = parser.add_mutually_exclusive_group()
         fast_synch_group.add_argument(
             "--fast-synch",
@@ -356,6 +349,13 @@ class Args(CamelCaseModel):
             dest="fast_synch",
             help="Force MLX FAST_SYNCH off",
         )
+        parser.add_argument(
+            "--bootstrap-peer",
+            type=str,
+            dest="bootstrap_peer",
+            default=None,
+            help="IP:PORT of an existing node to connect to (bypasses mDNS)",
+        )
 
         args = parser.parse_args()
         return cls(**vars(args))  # pyright: ignore[reportAny] - We are intentionally validating here, we can't do it statically

src/exo/master/adapters/responses.py

@@ -144,8 +144,8 @@ async def collect_responses_response(
             for tool in chunk.tool_calls:
                 function_call_items.append(
                     ResponseFunctionCallItem(
-                        id=tool.id,
-                        call_id=tool.id,
+                        id=f"fc_{tool.id}",
+                        call_id=f"call_{tool.id}",
                         name=tool.name,
                         arguments=tool.arguments,
                     )

src/exo/master/api.py

@@ -71,8 +71,11 @@ from exo.shared.types.api import (
     ChatCompletionResponse,
     CreateInstanceParams,
     CreateInstanceResponse,
+    CreateMetaInstanceParams,
+    CreateMetaInstanceResponse,
     DeleteDownloadResponse,
     DeleteInstanceResponse,
+    DeleteMetaInstanceResponse,
     ErrorInfo,
     ErrorResponse,
     FinishReason,
@@ -85,7 +88,6 @@ from exo.shared.types.api import (
     ImageGenerationTaskParams,
     ImageListItem,
     ImageListResponse,
-    ImageSize,
     ModelList,
     ModelListModel,
     PlaceInstanceParams,
@@ -101,7 +103,6 @@ from exo.shared.types.api import (
     TraceRankStats,
     TraceResponse,
     TraceStatsResponse,
-    normalize_image_size,
 )
 from exo.shared.types.chunks import (
     ErrorChunk,
@@ -117,8 +118,10 @@ from exo.shared.types.claude_api import (
 from exo.shared.types.commands import (
     Command,
     CreateInstance,
+    CreateMetaInstance,
     DeleteDownload,
     DeleteInstance,
+    DeleteMetaInstance,
     DownloadCommand,
     ForwarderCommand,
     ForwarderDownloadCommand,
@@ -131,7 +134,7 @@ from exo.shared.types.commands import (
     TaskFinished,
     TextGeneration,
 )
-from exo.shared.types.common import CommandId, Id, NodeId, SessionId
+from exo.shared.types.common import CommandId, Id, MetaInstanceId, NodeId, SessionId
 from exo.shared.types.events import (
     ChunkGenerated,
     Event,
@@ -140,6 +143,7 @@ from exo.shared.types.events import (
     TracesMerged,
 )
 from exo.shared.types.memory import Memory
+from exo.shared.types.meta_instance import MetaInstance
 from exo.shared.types.openai_responses import (
     ResponsesRequest,
     ResponsesResponse,
@@ -278,6 +282,9 @@ class API:
         self.app.get("/instance/previews")(self.get_placement_previews)
         self.app.get("/instance/{instance_id}")(self.get_instance)
         self.app.delete("/instance/{instance_id}")(self.delete_instance)
+        self.app.get("/meta_instances")(self.list_meta_instances)
+        self.app.post("/meta_instance")(self.create_meta_instance)
+        self.app.delete("/meta_instance/{meta_instance_id}")(self.delete_meta_instance)
         self.app.get("/models")(self.get_models)
         self.app.get("/v1/models")(self.get_models)
         self.app.post("/models/add")(self.add_custom_model)
@@ -307,12 +314,27 @@ class API:
         self.app.get("/v1/traces/{task_id}/raw")(self.get_trace_raw)
 
     async def place_instance(self, payload: PlaceInstanceParams):
+        model_card = await ModelCard.load(payload.model_id)
         command = PlaceInstance(
-            model_card=await ModelCard.load(payload.model_id),
+            model_card=model_card,
             sharding=payload.sharding,
             instance_meta=payload.instance_meta,
             min_nodes=payload.min_nodes,
         )
+
+        # Validate placement before sending — fail fast with a clear error
+        # instead of silently dropping the command in the master.
+        try:
+            get_instance_placements(
+                command,
+                topology=self.state.topology,
+                current_instances=self.state.instances,
+                node_memory=self.state.node_memory,
+                node_network=self.state.node_network,
+            )
+        except ValueError as exc:
+            raise HTTPException(status_code=400, detail=str(exc)) from exc
+
         await self._send(command)
 
         return CreateInstanceResponse(
@@ -524,6 +546,44 @@ class API:
             instance_id=instance_id,
         )
 
+    def list_meta_instances(self) -> dict[MetaInstanceId, MetaInstance]:
+        return dict(self.state.meta_instances)
+
+    async def create_meta_instance(
+        self, payload: CreateMetaInstanceParams
+    ) -> CreateMetaInstanceResponse:
+        meta_instance = MetaInstance(
+            model_id=payload.model_id,
+            sharding=payload.sharding,
+            instance_meta=payload.instance_meta,
+            min_nodes=payload.min_nodes,
+            node_ids=payload.node_ids,
+        )
+        command = CreateMetaInstance(meta_instance=meta_instance)
+        await self._send(command)
+        return CreateMetaInstanceResponse(
+            message="Command received.",
+            command_id=command.command_id,
+            meta_instance_id=meta_instance.meta_instance_id,
+        )
+
+    async def delete_meta_instance(
+        self, meta_instance_id: MetaInstanceId
+    ) -> DeleteMetaInstanceResponse:
+        meta = self.state.meta_instances.get(meta_instance_id)
+        if not meta:
+            raise HTTPException(status_code=404, detail="MetaInstance not found")
+
+        # Command processor handles cascade-deleting backing instances
+        command = DeleteMetaInstance(meta_instance_id=meta_instance_id)
+        await self._send(command)
+
+        return DeleteMetaInstanceResponse(
+            message="Command received.",
+            command_id=command.command_id,
+            meta_instance_id=meta_instance_id,
+        )
+
     async def _token_chunk_stream(
         self, command_id: CommandId
     ) -> AsyncGenerator[ErrorChunk | ToolCallChunk | TokenChunk, None]:
@@ -753,11 +813,9 @@ class API:
         When stream=True and partial_images > 0, returns a StreamingResponse
         with SSE-formatted events for partial and final images.
         """
+        payload.model = await self._validate_image_model(ModelId(payload.model))
         payload = payload.model_copy(
-            update={
-                "model": await self._validate_image_model(ModelId(payload.model)),
-                "advanced_params": _ensure_seed(payload.advanced_params),
-            }
+            update={"advanced_params": _ensure_seed(payload.advanced_params)}
         )
 
         command = ImageGeneration(
@@ -1013,13 +1071,12 @@ class API:
     async def bench_image_generations(
         self, request: Request, payload: BenchImageGenerationTaskParams
     ) -> BenchImageGenerationResponse:
+        payload.model = await self._validate_image_model(ModelId(payload.model))
+
+        payload.stream = False
+        payload.partial_images = 0
         payload = payload.model_copy(
-            update={
-                "model": await self._validate_image_model(ModelId(payload.model)),
-                "stream": False,
-                "partial_images": 0,
-                "advanced_params": _ensure_seed(payload.advanced_params),
-            }
+            update={"advanced_params": _ensure_seed(payload.advanced_params)}
         )
 
         command = ImageGeneration(
@@ -1040,7 +1097,7 @@ class API:
         prompt: str,
         model: ModelId,
         n: int,
-        size: ImageSize,
+        size: str,
         response_format: Literal["url", "b64_json"],
         input_fidelity: Literal["low", "high"],
         stream: bool,
@@ -1110,7 +1167,7 @@ class API:
         prompt: str = Form(...),
         model: str = Form(...),
         n: int = Form(1),
-        size: str | None = Form(None),
+        size: str = Form("1024x1024"),
         response_format: Literal["url", "b64_json"] = Form("b64_json"),
         input_fidelity: Literal["low", "high"] = Form("low"),
         stream: str = Form("false"),
@@ -1136,7 +1193,7 @@ class API:
             prompt=prompt,
             model=ModelId(model),
             n=n,
-            size=normalize_image_size(size),
+            size=size,
             response_format=response_format,
             input_fidelity=input_fidelity,
             stream=stream_bool,
@@ -1172,7 +1229,7 @@ class API:
         prompt: str = Form(...),
         model: str = Form(...),
         n: int = Form(1),
-        size: str | None = Form(None),
+        size: str = Form("1024x1024"),
         response_format: Literal["url", "b64_json"] = Form("b64_json"),
         input_fidelity: Literal["low", "high"] = Form("low"),
         quality: Literal["high", "medium", "low"] = Form("medium"),
@@ -1192,7 +1249,7 @@ class API:
             prompt=prompt,
             model=ModelId(model),
             n=n,
-            size=normalize_image_size(size),
+            size=size,
             response_format=response_format,
             input_fidelity=input_fidelity,
             stream=False,

src/exo/master/main.py

@@ -1,4 +1,5 @@
-from datetime import datetime, timedelta, timezone
+from collections.abc import Sequence
+from datetime import datetime, timezone
 
 import anyio
 from anyio.abc import TaskGroup
@@ -12,11 +13,22 @@ from exo.master.placement import (
     get_transition_events,
     place_instance,
 )
+from exo.master.process_managers import ProcessManager
+from exo.master.process_managers.instance_health import InstanceHealthReconciler
+from exo.master.process_managers.meta_instance import MetaInstanceReconciler
+from exo.master.process_managers.node_timeout import NodeTimeoutReconciler
+from exo.master.reconcile import (
+    find_unsatisfied_meta_instances,
+    try_place_for_meta_instance,
+)
 from exo.shared.apply import apply
 from exo.shared.constants import EXO_EVENT_LOG_DIR, EXO_TRACING_ENABLED
+from exo.shared.models.model_cards import ModelCard
 from exo.shared.types.commands import (
     CreateInstance,
+    CreateMetaInstance,
     DeleteInstance,
+    DeleteMetaInstance,
     ForwarderCommand,
     ForwarderDownloadCommand,
     ImageEdits,
@@ -36,8 +48,12 @@ from exo.shared.types.events import (
     IndexedEvent,
     InputChunkReceived,
     InstanceDeleted,
+    JacclSideChannelData,
+    JacclSideChannelGathered,
+    MetaInstanceCreated,
+    MetaInstanceDeleted,
+    MetaInstancePlacementFailed,
     NodeGatheredInfo,
-    NodeTimedOut,
     TaskCreated,
     TaskDeleted,
     TaskStatusUpdated,
@@ -60,7 +76,8 @@ from exo.shared.types.tasks import (
     TextGeneration as TextGenerationTask,
 )
 from exo.shared.types.worker.instances import InstanceId
-from exo.utils.channels import Receiver, Sender, channel
+from exo.shared.types.worker.runners import RunnerId
+from exo.utils.channels import Receiver, Sender
 from exo.utils.event_buffer import MultiSourceBuffer
 
 
@@ -84,16 +101,16 @@ class Master:
         self.local_event_receiver = local_event_receiver
         self.global_event_sender = global_event_sender
         self.download_command_sender = download_command_sender
-        send, recv = channel[Event]()
-        self.event_sender: Sender[Event] = send
-        self._loopback_event_receiver: Receiver[Event] = recv
-        self._loopback_event_sender: Sender[ForwarderEvent] = (
-            local_event_receiver.clone_sender()
-        )
         self._multi_buffer = MultiSourceBuffer[NodeId, Event]()
         self._event_log = DiskEventLog(EXO_EVENT_LOG_DIR / "master")
         self._pending_traces: dict[TaskId, dict[int, list[TraceEventData]]] = {}
         self._expected_ranks: dict[TaskId, set[int]] = {}
+        self._jaccl_pending: dict[InstanceId, dict[int, dict[RunnerId, bytes]]] = {}
+        self._process_managers: Sequence[ProcessManager] = [
+            InstanceHealthReconciler(),
+            NodeTimeoutReconciler(),
+            MetaInstanceReconciler(),
+        ]
 
     async def run(self):
         logger.info("Starting Master")
@@ -102,15 +119,12 @@ class Master:
             async with self._tg as tg:
                 tg.start_soon(self._event_processor)
                 tg.start_soon(self._command_processor)
-                tg.start_soon(self._loopback_processor)
-                tg.start_soon(self._plan)
+                tg.start_soon(self._reconcile)
         finally:
             self._event_log.close()
             self.global_event_sender.close()
             self.local_event_receiver.close()
             self.command_receiver.close()
-            self._loopback_event_sender.close()
-            self._loopback_event_receiver.close()
 
     async def shutdown(self):
         logger.info("Stopping Master")
@@ -292,6 +306,85 @@ class Master:
                                     )
                                 )
                             generated_events.extend(transition_events)
+                        case CreateMetaInstance():
+                            logger.info(
+                                f"Creating MetaInstance for {command.meta_instance.model_id}"
+                                f" (min_nodes={command.meta_instance.min_nodes},"
+                                f" sharding={command.meta_instance.sharding})"
+                            )
+                            # Apply immediately so self.state is fresh across
+                            # the await below and the reconciler won't race.
+                            await self._apply_and_broadcast(
+                                MetaInstanceCreated(meta_instance=command.meta_instance)
+                            )
+                            # Immediate placement attempt for responsiveness
+                            model_card = await ModelCard.load(
+                                command.meta_instance.model_id
+                            )
+                            # Re-check: reconciler may have satisfied it during the await
+                            meta_id = command.meta_instance.meta_instance_id
+                            still_unsatisfied = any(
+                                m.meta_instance_id == meta_id
+                                for m in find_unsatisfied_meta_instances(
+                                    self.state.meta_instances,
+                                    self.state.instances,
+                                    self.state.topology,
+                                )
+                            )
+                            if still_unsatisfied:
+                                result = try_place_for_meta_instance(
+                                    command.meta_instance,
+                                    model_card,
+                                    self.state.topology,
+                                    self.state.instances,
+                                    self.state.node_memory,
+                                    self.state.node_network,
+                                )
+                                generated_events.extend(result.events)
+                                if result.error is not None:
+                                    generated_events.append(
+                                        MetaInstancePlacementFailed(
+                                            meta_instance_id=meta_id,
+                                            reason=result.error,
+                                        )
+                                    )
+                        case DeleteMetaInstance():
+                            backing_count = sum(
+                                1
+                                for inst in self.state.instances.values()
+                                if inst.meta_instance_id == command.meta_instance_id
+                            )
+                            logger.info(
+                                f"Deleting MetaInstance {command.meta_instance_id}"
+                                f" (cascade-deleting {backing_count} backing instance(s))"
+                            )
+                            generated_events.append(
+                                MetaInstanceDeleted(
+                                    meta_instance_id=command.meta_instance_id
+                                )
+                            )
+                            # Cascade-delete backing instances atomically,
+                            # cancelling any active tasks first.
+                            for iid, inst in self.state.instances.items():
+                                if inst.meta_instance_id == command.meta_instance_id:
+                                    for task in self.state.tasks.values():
+                                        if (
+                                            task.instance_id == iid
+                                            and task.task_status
+                                            in (
+                                                TaskStatus.Pending,
+                                                TaskStatus.Running,
+                                            )
+                                        ):
+                                            generated_events.append(
+                                                TaskStatusUpdated(
+                                                    task_status=TaskStatus.Cancelled,
+                                                    task_id=task.task_id,
+                                                )
+                                            )
+                                    generated_events.append(
+                                        InstanceDeleted(instance_id=iid)
+                                    )
                         case PlaceInstance():
                             placement = place_instance(
                                 command,
@@ -354,31 +447,32 @@ class Master:
                             ):
                                 await self._send_event(IndexedEvent(idx=i, event=event))
                     for event in generated_events:
-                        await self.event_sender.send(event)
+                        await self._apply_and_broadcast(event)
                 except ValueError as e:
                     logger.opt(exception=e).warning("Error in command processor")
 
-    # These plan loops are the cracks showing in our event sourcing architecture - more things could be commands
-    async def _plan(self) -> None:
+    async def _apply_and_broadcast(self, event: Event) -> None:
+        """Apply event to state, persist to disk, and broadcast to workers.
+
+        State is updated synchronously (before any await), so callers can
+        rely on ``self.state`` reflecting this event immediately after the
+        call.  Python's cooperative scheduling guarantees no interleaving
+        between the state read and write.
+        """
+        logger.debug(f"Master indexing event: {str(event)[:100]}")
+        indexed = IndexedEvent(event=event, idx=len(self._event_log))
+        self.state = apply(self.state, indexed)
+        event._master_time_stamp = datetime.now(tz=timezone.utc)  # pyright: ignore[reportPrivateUsage]
+        self._event_log.append(event)
+        await self._send_event(indexed)
+
+    async def _reconcile(self) -> None:
         while True:
-            # kill broken instances
-            connected_node_ids = set(self.state.topology.list_nodes())
-            for instance_id, instance in self.state.instances.items():
-                for node_id in instance.shard_assignments.node_to_runner:
-                    if node_id not in connected_node_ids:
-                        await self.event_sender.send(
-                            InstanceDeleted(instance_id=instance_id)
-                        )
-                        break
-
-            # time out dead nodes
-            for node_id, time in self.state.last_seen.items():
-                now = datetime.now(tz=timezone.utc)
-                if now - time > timedelta(seconds=30):
-                    logger.info(f"Manually removing node {node_id} due to inactivity")
-                    await self.event_sender.send(NodeTimedOut(node_id=node_id))
-
-            await anyio.sleep(10)
+            for pm in self._process_managers:
+                events = await pm.reconcile(self.state)
+                for event in events:
+                    await self._apply_and_broadcast(event)
+            await anyio.sleep(1)
 
     async def _event_processor(self) -> None:
         with self.local_event_receiver as local_events:
@@ -396,32 +490,15 @@ class Master:
                         await self._handle_traces_collected(event)
                         continue
 
-                    logger.debug(f"Master indexing event: {str(event)[:100]}")
-                    indexed = IndexedEvent(event=event, idx=len(self._event_log))
-                    self.state = apply(self.state, indexed)
+                    if isinstance(event, JacclSideChannelData):
+                        await self._apply_and_broadcast(event)
+                        await self._handle_jaccl_side_channel(event)
+                        continue
 
-                    event._master_time_stamp = datetime.now(tz=timezone.utc)  # pyright: ignore[reportPrivateUsage]
                     if isinstance(event, NodeGatheredInfo):
                         event.when = str(datetime.now(tz=timezone.utc))
 
-                    self._event_log.append(event)
-                    await self._send_event(indexed)
-
-    async def _loopback_processor(self) -> None:
-        # this would ideally not be necessary.
-        # this is WAY less hacky than how I was working around this before
-        local_index = 0
-        with self._loopback_event_receiver as events:
-            async for event in events:
-                await self._loopback_event_sender.send(
-                    ForwarderEvent(
-                        origin=NodeId(f"master_{self.node_id}"),
-                        origin_idx=local_index,
-                        session=self.session_id,
-                        event=event,
-                    )
-                )
-                local_index += 1
+                    await self._apply_and_broadcast(event)
 
     # This function is re-entrant, take care!
     async def _send_event(self, event: IndexedEvent):
@@ -453,10 +530,49 @@ class Master:
         for trace_data in self._pending_traces[task_id].values():
             all_trace_data.extend(trace_data)
 
-        await self.event_sender.send(
+        await self._apply_and_broadcast(
             TracesMerged(task_id=task_id, traces=all_trace_data)
         )
 
         del self._pending_traces[task_id]
         if task_id in self._expected_ranks:
             del self._expected_ranks[task_id]
+
+    async def _handle_jaccl_side_channel(self, event: JacclSideChannelData) -> None:
+        """Accumulate SideChannel contributions; when all runners for an instance
+        have submitted for the same sequence, emit JacclSideChannelGathered."""
+        iid = event.instance_id
+        seq = event.sequence
+
+        if iid not in self._jaccl_pending:
+            self._jaccl_pending[iid] = {}
+        if seq not in self._jaccl_pending[iid]:
+            self._jaccl_pending[iid][seq] = {}
+        self._jaccl_pending[iid][seq][event.runner_id] = event.data
+
+        instance = self.state.instances.get(iid)
+        if instance is None:
+            logger.warning(f"JacclSideChannelData for unknown instance {iid}")
+            return
+
+        expected_runners = set(instance.shard_assignments.runner_to_shard.keys())
+        submitted = set(self._jaccl_pending[iid][seq].keys())
+
+        logger.info(
+            f"JACCL side channel: instance={iid} seq={seq} "
+            f"submitted={len(submitted)}/{len(expected_runners)}"
+        )
+
+        if submitted >= expected_runners:
+            gathered = dict(self._jaccl_pending[iid][seq])
+            del self._jaccl_pending[iid][seq]
+            if not self._jaccl_pending[iid]:
+                del self._jaccl_pending[iid]
+
+            await self._apply_and_broadcast(
+                JacclSideChannelGathered(
+                    instance_id=iid,
+                    sequence=seq,
+                    gathered_data=gathered,
+                )
+            )

src/exo/master/placement.py

@@ -6,11 +6,11 @@ from typing import Sequence
 from exo.master.placement_utils import (
     Cycle,
     filter_cycles_by_memory,
+    get_largest_cycles,
     get_mlx_jaccl_coordinators,
     get_mlx_jaccl_devices_matrix,
     get_mlx_ring_hosts_by_node,
     get_shard_assignments,
-    get_smallest_cycles,
 )
 from exo.shared.models.model_cards import ModelId
 from exo.shared.topology import Topology
@@ -106,23 +106,27 @@ def place_instance(
             "Pipeline parallelism is not supported for DeepSeek V3.1 (8-bit)"
         )
 
-    smallest_cycles = get_smallest_cycles(cycles_with_sufficient_memory)
+    largest_cycles = get_largest_cycles(cycles_with_sufficient_memory)
 
-    smallest_rdma_cycles = [
-        cycle for cycle in smallest_cycles if topology.is_rdma_cycle(cycle)
+    largest_rdma_cycles = [
+        cycle for cycle in largest_cycles if topology.is_rdma_cycle(cycle)
     ]
 
-    if command.instance_meta == InstanceMeta.MlxJaccl and smallest_rdma_cycles != []:
-        smallest_cycles = smallest_rdma_cycles
+    if command.instance_meta == InstanceMeta.MlxJaccl:
+        if not largest_rdma_cycles:
+            raise ValueError(
+                "Requested RDMA (MlxJaccl) but no RDMA-connected cycles available"
+            )
+        largest_cycles = largest_rdma_cycles
 
     cycles_with_leaf_nodes: list[Cycle] = [
         cycle
-        for cycle in smallest_cycles
+        for cycle in largest_cycles
         if any(topology.node_is_leaf(node_id) for node_id in cycle)
     ]
 
     selected_cycle = max(
-        cycles_with_leaf_nodes if cycles_with_leaf_nodes != [] else smallest_cycles,
+        cycles_with_leaf_nodes if cycles_with_leaf_nodes != [] else largest_cycles,
         key=lambda cycle: sum(
             (node_memory[node_id].ram_available for node_id in cycle),
             start=Memory(),

src/exo/master/placement_utils.py

@@ -37,11 +37,11 @@ def filter_cycles_by_memory(
     return filtered_cycles
 
 
-def get_smallest_cycles(
+def get_largest_cycles(
     cycles: list[Cycle],
 ) -> list[Cycle]:
-    min_nodes = min(len(cycle) for cycle in cycles)
-    return [cycle for cycle in cycles if len(cycle) == min_nodes]
+    max_nodes = max(len(cycle) for cycle in cycles)
+    return [cycle for cycle in cycles if len(cycle) == max_nodes]
 
 
 def allocate_layers_proportionally(

src/exo/master/process_managers/__init__.py

@@ -0,0 +1,12 @@
+from collections.abc import Sequence
+from typing import Protocol, runtime_checkable
+
+from exo.shared.types.events import Event
+from exo.shared.types.state import State
+
+
+@runtime_checkable
+class ProcessManager(Protocol):
+    """A reconciliation step that examines state and returns corrective events."""
+
+    async def reconcile(self, state: State) -> Sequence[Event]: ...

src/exo/master/process_managers/instance_health.py

@@ -0,0 +1,62 @@
+from collections.abc import Sequence
+from typing import final
+
+from loguru import logger
+
+from exo.master.reconcile import instance_connections_healthy, instance_runners_failed
+from exo.shared.types.events import Event, InstanceDeleted, InstanceRetrying
+from exo.shared.types.state import State
+
+MAX_INSTANCE_RETRIES = 3
+
+
+@final
+class InstanceHealthReconciler:
+    """Delete instances whose network connections are broken or whose runners have all failed."""
+
+    async def reconcile(self, state: State) -> Sequence[Event]:
+        events: list[Event] = []
+        for instance_id, instance in state.instances.items():
+            if not instance_connections_healthy(instance, state.topology):
+                events.append(
+                    InstanceDeleted(
+                        instance_id=instance_id,
+                        failure_error="Network connection lost",
+                    )
+                )
+                continue
+
+            is_failed, error_message = instance_runners_failed(
+                instance, state.runners, state.node_identities
+            )
+            if is_failed:
+                # Retry within the same instance if backed by a MetaInstance
+                mid = instance.meta_instance_id
+                mi = state.meta_instances.get(mid) if mid else None
+                if mid and mi and mi.consecutive_failures < MAX_INSTANCE_RETRIES:
+                    logger.info(
+                        f"Instance {instance_id} failed (attempt"
+                        f" {mi.consecutive_failures + 1}/{MAX_INSTANCE_RETRIES}),"
+                        f" retrying: {error_message}"
+                    )
+                    events.append(
+                        InstanceRetrying(
+                            instance_id=instance_id,
+                            meta_instance_id=mid,
+                            failure_error=error_message or "Runner failed",
+                        )
+                    )
+                else:
+                    if mid and mi:
+                        logger.warning(
+                            f"Instance {instance_id} exceeded retry limit"
+                            f" ({MAX_INSTANCE_RETRIES}), deleting:"
+                            f" {error_message}"
+                        )
+                    events.append(
+                        InstanceDeleted(
+                            instance_id=instance_id,
+                            failure_error=error_message,
+                        )
+                    )
+        return events

src/exo/master/process_managers/meta_instance.py

@@ -0,0 +1,91 @@
+from collections.abc import Sequence
+from typing import final
+
+import anyio
+from loguru import logger
+
+from exo.master.reconcile import (
+    find_unsatisfied_meta_instances,
+    try_place_for_meta_instance,
+)
+from exo.shared.models.model_cards import ModelCard
+from exo.shared.types.events import Event, InstanceCreated, MetaInstancePlacementFailed
+from exo.shared.types.state import State
+from exo.shared.types.worker.instances import Instance, InstanceId
+
+MODEL_CARD_LOAD_TIMEOUT_SECONDS = 10
+
+
+@final
+class MetaInstanceReconciler:
+    """Place instances for unsatisfied MetaInstances."""
+
+    async def reconcile(self, state: State) -> Sequence[Event]:
+        all_events: list[Event] = []
+        # Local copy for intermediate tracking — so placement of B
+        # sees A's instance and doesn't double-place on same resources.
+        current_instances: dict[InstanceId, Instance] = dict(state.instances)
+
+        unsatisfied = find_unsatisfied_meta_instances(
+            state.meta_instances,
+            current_instances,
+            state.topology,
+        )
+        for meta_instance in unsatisfied:
+            try:
+                with anyio.fail_after(MODEL_CARD_LOAD_TIMEOUT_SECONDS):
+                    model_card = await ModelCard.load(meta_instance.model_id)
+            except TimeoutError:
+                logger.warning(
+                    f"ModelCard.load timed out for {meta_instance.model_id}, skipping this cycle"
+                )
+                continue
+            except Exception as exc:
+                logger.warning(
+                    f"ModelCard.load failed for {meta_instance.model_id}: {exc}"
+                )
+                error = f"Failed to load model card: {exc}"
+                if meta_instance.placement_error != error:
+                    all_events.append(
+                        MetaInstancePlacementFailed(
+                            meta_instance_id=meta_instance.meta_instance_id,
+                            reason=error,
+                        )
+                    )
+                continue
+
+            result = try_place_for_meta_instance(
+                meta_instance,
+                model_card,
+                state.topology,
+                current_instances,
+                state.node_memory,
+                state.node_network,
+            )
+            # Update local instance map so next placement sees this one
+            for event in result.events:
+                if isinstance(event, InstanceCreated):
+                    logger.info(
+                        f"MetaInstance reconciler placed instance"
+                        f" {event.instance.instance_id} for"
+                        f" {meta_instance.model_id}"
+                    )
+                    current_instances[event.instance.instance_id] = event.instance
+            all_events.extend(result.events)
+
+            # Emit placement failure if error differs from what's already in state
+            if (
+                result.error is not None
+                and meta_instance.placement_error != result.error
+            ):
+                logger.warning(
+                    f"MetaInstance placement failed for"
+                    f" {meta_instance.model_id}: {result.error}"
+                )
+                all_events.append(
+                    MetaInstancePlacementFailed(
+                        meta_instance_id=meta_instance.meta_instance_id,
+                        reason=result.error,
+                    )
+                )
+        return all_events

src/exo/master/process_managers/node_timeout.py

@@ -0,0 +1,27 @@
+from collections.abc import Sequence
+from datetime import datetime, timedelta, timezone
+from typing import final
+
+from loguru import logger
+
+from exo.shared.types.events import Event, NodeTimedOut
+from exo.shared.types.state import State
+
+_DEFAULT_TIMEOUT = timedelta(seconds=30)
+
+
+@final
+class NodeTimeoutReconciler:
+    """Time out nodes that haven't been seen recently."""
+
+    def __init__(self, timeout: timedelta = _DEFAULT_TIMEOUT) -> None:
+        self.timeout = timeout
+
+    async def reconcile(self, state: State) -> Sequence[Event]:
+        now = datetime.now(tz=timezone.utc)
+        events: list[Event] = []
+        for node_id, last_seen in state.last_seen.items():
+            if now - last_seen > self.timeout:
+                logger.info(f"Removing node {node_id} due to inactivity")
+                events.append(NodeTimedOut(node_id=node_id))
+        return events

src/exo/master/reconcile.py

@@ -0,0 +1,240 @@
+from collections.abc import Mapping, Sequence
+from typing import NamedTuple
+
+from loguru import logger
+
+from exo.master.placement import get_transition_events, place_instance
+from exo.shared.models.model_cards import ModelCard
+from exo.shared.topology import Topology
+from exo.shared.types.commands import PlaceInstance
+from exo.shared.types.common import MetaInstanceId, NodeId
+from exo.shared.types.events import Event
+from exo.shared.types.meta_instance import MetaInstance
+from exo.shared.types.profiling import MemoryUsage, NodeIdentity, NodeNetworkInfo
+from exo.shared.types.topology import RDMAConnection, SocketConnection
+from exo.shared.types.worker.instances import (
+    BaseInstance,
+    Instance,
+    InstanceId,
+    MlxJacclInstance,
+    MlxRingInstance,
+)
+from exo.shared.types.worker.runners import (
+    RunnerFailed,
+    RunnerId,
+    RunnerShutdown,
+    RunnerStatus,
+)
+
+
+class PlacementResult(NamedTuple):
+    """Result of a placement attempt: events to apply and optional error reason."""
+
+    events: Sequence[Event]
+    error: str | None
+
+
+def _get_ring_order(instance: BaseInstance) -> list[NodeId]:
+    """Reconstruct ring order from shard device_rank."""
+    node_ranks: list[tuple[NodeId, int]] = []
+    for node_id, runner_id in instance.shard_assignments.node_to_runner.items():
+        shard = instance.shard_assignments.runner_to_shard[runner_id]
+        node_ranks.append((node_id, shard.device_rank))
+    node_ranks.sort(key=lambda x: x[1])
+    return [node_id for node_id, _ in node_ranks]
+
+
+def _ring_connections_healthy(instance: MlxRingInstance, topology: Topology) -> bool:
+    """Check that the specific IPs used by a ring instance still exist in the topology."""
+    ring = _get_ring_order(instance)
+    n = len(ring)
+    for node in ring:
+        hosts = instance.hosts_by_node[node]
+        for idx in range(n):
+            host = hosts[idx]
+            if host.ip in ("0.0.0.0", "198.51.100.1"):
+                continue  # self or placeholder
+            # Real connection: node → ring[idx]. Check specific IP.
+            connections = topology.get_all_connections_between(node, ring[idx])
+            if not any(
+                isinstance(c, SocketConnection)
+                and c.sink_multiaddr.ip_address == host.ip
+                for c in connections
+            ):
+                return False
+    return True
+
+
+def _jaccl_connections_healthy(instance: MlxJacclInstance, topology: Topology) -> bool:
+    """Check that the specific RDMA interfaces used by a JACCL instance still exist."""
+    ring = _get_ring_order(instance)
+    n = len(ring)
+    for i in range(n):
+        for j in range(n):
+            iface = instance.jaccl_devices[i][j]
+            if iface is None:
+                continue
+            connections = topology.get_all_connections_between(ring[i], ring[j])
+            if not any(
+                isinstance(c, RDMAConnection) and c.source_rdma_iface == iface
+                for c in connections
+            ):
+                return False
+    return True
+
+
+def instance_connections_healthy(instance: Instance, topology: Topology) -> bool:
+    """Check that an instance's nodes and specific connections are still in the topology."""
+    instance_nodes = set(instance.shard_assignments.node_to_runner.keys())
+    if not all(topology.contains_node(n) for n in instance_nodes):
+        return False
+    if len(instance_nodes) <= 1:
+        return True
+    match instance:
+        case MlxRingInstance():
+            return _ring_connections_healthy(instance, topology)
+        case MlxJacclInstance():
+            return _jaccl_connections_healthy(instance, topology)
+
+
+def instance_runners_failed(
+    instance: Instance,
+    runners: Mapping[RunnerId, RunnerStatus],
+    node_identities: Mapping[NodeId, NodeIdentity],
+) -> tuple[bool, str | None]:
+    """Check if an instance's runners have all reached terminal failure states.
+
+    Returns ``(True, error_message)`` when ALL runners are terminal
+    (``RunnerFailed`` or ``RunnerShutdown``) and at least one is ``RunnerFailed``.
+
+    Returns ``(False, None)`` when runners are still active, haven't reported
+    yet, or all gracefully shut down (no ``RunnerFailed``).
+    """
+    instance_runner_ids = set(instance.shard_assignments.node_to_runner.values())
+
+    if not instance_runner_ids:
+        return False, None
+
+    # Build reverse mapping: runner_id -> node_id
+    runner_to_node: dict[RunnerId, NodeId] = {
+        runner_id: node_id
+        for node_id, runner_id in instance.shard_assignments.node_to_runner.items()
+    }
+
+    has_any_failed = False
+    error_messages: list[str] = []
+
+    for runner_id in instance_runner_ids:
+        status = runners.get(runner_id)
+        if status is None:
+            # Runner hasn't reported yet — instance is still starting
+            return False, None
+        if isinstance(status, RunnerFailed):
+            has_any_failed = True
+            if status.error_message:
+                node_id = runner_to_node.get(runner_id)
+                name = (
+                    node_identities[node_id].friendly_name
+                    if node_id and node_id in node_identities
+                    else node_id or "unknown"
+                )
+                error_messages.append(f"{name}: {status.error_message}")
+        elif isinstance(status, RunnerShutdown):
+            pass  # Terminal but not a failure indicator on its own
+        else:
+            # Runner is still active (connecting, loading, running, etc.)
+            return False, None
+
+    if has_any_failed:
+        return True, "; ".join(error_messages) if error_messages else "Runner failed"
+
+    # All runners are Shutdown but none Failed — graceful shutdown, not a failure
+    return False, None
+
+
+def instance_satisfies_meta_instance(
+    meta_instance: MetaInstance,
+    instance: Instance,
+) -> bool:
+    """Check if a single instance satisfies a meta-instance's constraints.
+
+    This is a pure constraint check (model, min_nodes, node_ids).
+    Use ``instance_connections_healthy`` separately for topology health.
+    """
+    if instance.shard_assignments.model_id != meta_instance.model_id:
+        return False
+
+    instance_nodes = set(instance.shard_assignments.node_to_runner.keys())
+
+    if len(instance_nodes) < meta_instance.min_nodes:
+        return False
+
+    return meta_instance.node_ids is None or set(meta_instance.node_ids).issubset(
+        instance_nodes
+    )
+
+
+def find_unsatisfied_meta_instances(
+    meta_instances: Mapping[MetaInstanceId, MetaInstance],
+    instances: Mapping[InstanceId, Instance],
+    topology: Topology,
+) -> Sequence[MetaInstance]:
+    """Return meta-instances that have no healthy backing instance."""
+    unsatisfied: list[MetaInstance] = []
+    for meta_id, meta_instance in meta_instances.items():
+        has_healthy_backing = any(
+            instance.meta_instance_id == meta_id
+            and instance_connections_healthy(instance, topology)
+            for instance in instances.values()
+        )
+        if not has_healthy_backing:
+            unsatisfied.append(meta_instance)
+    return unsatisfied
+
+
+def try_place_for_meta_instance(
+    meta_instance: MetaInstance,
+    model_card: ModelCard,
+    topology: Topology,
+    current_instances: Mapping[InstanceId, Instance],
+    node_memory: Mapping[NodeId, MemoryUsage],
+    node_network: Mapping[NodeId, NodeNetworkInfo],
+) -> PlacementResult:
+    """Try to place an instance satisfying the meta-instance constraints.
+
+    Returns a :class:`PlacementResult` with events on success, or an error
+    reason on failure.
+    """
+    command = PlaceInstance(
+        model_card=model_card,
+        sharding=meta_instance.sharding,
+        instance_meta=meta_instance.instance_meta,
+        min_nodes=meta_instance.min_nodes,
+    )
+    try:
+        target_instances = place_instance(
+            command,
+            topology,
+            current_instances,
+            node_memory,
+            node_network,
+            required_nodes=(
+                set(meta_instance.node_ids) if meta_instance.node_ids else None
+            ),
+        )
+        # Tag the new instance with meta_instance_id
+        new_instance_ids = set(target_instances.keys()) - set(current_instances.keys())
+        if new_instance_ids:
+            new_id = next(iter(new_instance_ids))
+            target_instances[new_id] = target_instances[new_id].model_copy(
+                update={"meta_instance_id": meta_instance.meta_instance_id}
+            )
+        return PlacementResult(
+            events=list(get_transition_events(current_instances, target_instances, {})),
+            error=None,
+        )
+    except ValueError as e:
+        logger.debug(
+            f"MetaInstance placement not possible for {meta_instance.model_id}: {e}"
+        )
+        return PlacementResult(events=[], error=str(e))

src/exo/master/tests/test_meta_instance_edge_cases.py

@@ -0,0 +1,778 @@
+"""Edge-case and regression tests for MetaInstance lifecycle, concurrent operations, and error handling."""
+
+import pytest
+
+from exo.master.process_managers.instance_health import (
+    MAX_INSTANCE_RETRIES,
+    InstanceHealthReconciler,
+)
+from exo.master.process_managers.meta_instance import MetaInstanceReconciler
+from exo.master.reconcile import (
+    find_unsatisfied_meta_instances,
+    instance_connections_healthy,
+    instance_runners_failed,
+    instance_satisfies_meta_instance,
+)
+from exo.shared.apply import apply
+from exo.shared.models.model_cards import ModelCard, ModelId, ModelTask
+from exo.shared.topology import Topology
+from exo.shared.types.common import Host, MetaInstanceId, NodeId
+from exo.shared.types.events import (
+    IndexedEvent,
+    InstanceCreated,
+    InstanceDeleted,
+    InstanceRetrying,
+    MetaInstanceCreated,
+    MetaInstanceDeleted,
+    MetaInstancePlacementFailed,
+    TaskStatusUpdated,
+)
+from exo.shared.types.memory import Memory
+from exo.shared.types.meta_instance import MetaInstance
+from exo.shared.types.multiaddr import Multiaddr
+from exo.shared.types.profiling import NodeIdentity
+from exo.shared.types.state import State
+from exo.shared.types.tasks import LoadModel, TaskId, TaskStatus
+from exo.shared.types.topology import Connection, SocketConnection
+from exo.shared.types.worker.instances import (
+    InstanceId,
+    MlxRingInstance,
+)
+from exo.shared.types.worker.runners import (
+    RunnerFailed,
+    RunnerId,
+    RunnerReady,
+    ShardAssignments,
+)
+from exo.shared.types.worker.shards import PipelineShardMetadata
+
+# --- Helpers (copied from test_reconcile.py for independence) ---
+
+
+def _model_card(model_id: str = "test-org/test-model") -> ModelCard:
+    return ModelCard(
+        model_id=ModelId(model_id),
+        storage_size=Memory.from_kb(1000),
+        n_layers=10,
+        hidden_size=30,
+        supports_tensor=True,
+        tasks=[ModelTask.TextGeneration],
+    )
+
+
+def _topology(*node_ids: str, connect: bool = True) -> Topology:
+    t = Topology()
+    nodes = [NodeId(n) for n in node_ids]
+    for n in nodes:
+        t.add_node(n)
+    if connect and len(nodes) > 1:
+        for i in range(len(nodes)):
+            j = (i + 1) % len(nodes)
+            t.add_connection(
+                Connection(
+                    source=nodes[i],
+                    sink=nodes[j],
+                    edge=SocketConnection(
+                        sink_multiaddr=Multiaddr(
+                            address=f"/ip4/10.0.0.{j + 1}/tcp/50000"
+                        )
+                    ),
+                )
+            )
+            t.add_connection(
+                Connection(
+                    source=nodes[j],
+                    sink=nodes[i],
+                    edge=SocketConnection(
+                        sink_multiaddr=Multiaddr(
+                            address=f"/ip4/10.0.0.{i + 1}/tcp/50000"
+                        )
+                    ),
+                )
+            )
+    return t
+
+
+def _meta_instance(
+    model_id: str = "test-org/test-model",
+    *,
+    min_nodes: int = 1,
+    node_ids: list[NodeId] | None = None,
+    meta_instance_id: MetaInstanceId | None = None,
+    consecutive_failures: int = 0,
+    last_failure_error: str | None = None,
+    placement_error: str | None = None,
+) -> MetaInstance:
+    return MetaInstance(
+        meta_instance_id=meta_instance_id or MetaInstanceId(),
+        model_id=ModelId(model_id),
+        min_nodes=min_nodes,
+        node_ids=node_ids,
+        consecutive_failures=consecutive_failures,
+        last_failure_error=last_failure_error,
+        placement_error=placement_error,
+    )
+
+
+def _instance(
+    model_id: str = "test-org/test-model",
+    node_ids: list[str] | None = None,
+    instance_id: InstanceId | None = None,
+    meta_instance_id: MetaInstanceId | None = None,
+) -> tuple[InstanceId, MlxRingInstance]:
+    iid = instance_id or InstanceId()
+    nodes = node_ids or ["node-a"]
+    n = len(nodes)
+    mc = _model_card(model_id)
+    ephemeral_port = 50000
+    node_to_runner = {NodeId(nd): RunnerId() for nd in nodes}
+    runner_to_shard = {
+        runner_id: PipelineShardMetadata(
+            model_card=mc,
+            device_rank=i,
+            world_size=n,
+            start_layer=0,
+            end_layer=mc.n_layers,
+            n_layers=mc.n_layers,
+        )
+        for i, runner_id in enumerate(node_to_runner.values())
+    }
+    hosts_by_node: dict[NodeId, list[Host]] = {}
+    for r, node_str in enumerate(nodes):
+        hosts: list[Host] = []
+        for idx in range(n):
+            if idx == r:
+                hosts.append(Host(ip="0.0.0.0", port=ephemeral_port))
+            elif n > 1 and idx in ((r - 1) % n, (r + 1) % n):
+                hosts.append(Host(ip=f"10.0.0.{idx + 1}", port=ephemeral_port))
+            else:
+                hosts.append(Host(ip="198.51.100.1", port=0))
+        hosts_by_node[NodeId(node_str)] = hosts
+    return iid, MlxRingInstance(
+        instance_id=iid,
+        shard_assignments=ShardAssignments(
+            model_id=ModelId(model_id),
+            runner_to_shard=runner_to_shard,
+            node_to_runner=node_to_runner,
+        ),
+        hosts_by_node=hosts_by_node,
+        ephemeral_port=ephemeral_port,
+        meta_instance_id=meta_instance_id,
+    )
+
+
+# =============================================================================
+# 1. MetaInstance lifecycle edge cases
+# =============================================================================
+
+
+def test_meta_instance_model_is_frozen():
+    """MetaInstance should be immutable (frozen model)."""
+    meta = _meta_instance()
+    try:
+        meta.model_id = ModelId("something-else")
+        raise AssertionError("Should have raised")
+    except Exception:
+        pass  # Expected — frozen model
+
+
+def test_meta_instance_created_then_deleted_roundtrip():
+    """Create and delete a MetaInstance through apply — state should be clean."""
+    state = State()
+    meta = _meta_instance()
+    state = apply(
+        state, IndexedEvent(idx=0, event=MetaInstanceCreated(meta_instance=meta))
+    )
+    assert meta.meta_instance_id in state.meta_instances
+    state = apply(
+        state,
+        IndexedEvent(
+            idx=1, event=MetaInstanceDeleted(meta_instance_id=meta.meta_instance_id)
+        ),
+    )
+    assert meta.meta_instance_id not in state.meta_instances
+    assert len(state.meta_instances) == 0
+
+
+def test_delete_nonexistent_meta_instance_is_safe():
+    """Deleting a MetaInstance that doesn't exist should not crash."""
+    state = State()
+    event = MetaInstanceDeleted(meta_instance_id=MetaInstanceId("nonexistent"))
+    new_state = apply(state, IndexedEvent(idx=0, event=event))
+    assert len(new_state.meta_instances) == 0
+
+
+def test_placement_failed_for_nonexistent_meta_instance_is_safe():
+    """MetaInstancePlacementFailed for unknown ID should not crash."""
+    state = State()
+    event = MetaInstancePlacementFailed(
+        meta_instance_id=MetaInstanceId("nonexistent"),
+        reason="test",
+    )
+    new_state = apply(state, IndexedEvent(idx=0, event=event))
+    assert len(new_state.meta_instances) == 0
+
+
+def test_multiple_meta_instances_for_same_model():
+    """Multiple MetaInstances for the same model are tracked independently."""
+    state = State()
+    meta_a = _meta_instance("test-org/model-x")
+    meta_b = _meta_instance("test-org/model-x")
+    state = apply(
+        state, IndexedEvent(idx=0, event=MetaInstanceCreated(meta_instance=meta_a))
+    )
+    state = apply(
+        state, IndexedEvent(idx=1, event=MetaInstanceCreated(meta_instance=meta_b))
+    )
+    assert len(state.meta_instances) == 2
+    assert meta_a.meta_instance_id in state.meta_instances
+    assert meta_b.meta_instance_id in state.meta_instances
+
+
+# =============================================================================
+# 2. Retry logic edge cases
+# =============================================================================
+
+
+def test_retry_counter_resets_on_successful_instance_creation():
+    """When a new instance is created for a meta-instance, failures should reset."""
+    meta = _meta_instance(consecutive_failures=2, last_failure_error="old")
+    _, inst = _instance(node_ids=["node-a"], meta_instance_id=meta.meta_instance_id)
+    state = State(meta_instances={meta.meta_instance_id: meta})
+    state = apply(state, IndexedEvent(idx=0, event=InstanceCreated(instance=inst)))
+    mi = state.meta_instances[meta.meta_instance_id]
+    assert mi.consecutive_failures == 0
+    # last_failure_error is preserved (for UI display)
+    assert mi.last_failure_error == "old"
+
+
+async def test_retry_count_increments_through_full_cycle():
+    """Walk through MAX_INSTANCE_RETRIES worth of retries, then verify delete."""
+    meta = _meta_instance()
+    iid, inst = _instance(node_ids=["node-a"], meta_instance_id=meta.meta_instance_id)
+    topology = _topology("node-a")
+    state = State(
+        meta_instances={meta.meta_instance_id: meta},
+        instances={iid: inst},
+        topology=topology,
+    )
+
+    runner_ids = list(inst.shard_assignments.node_to_runner.values())
+    for idx, i in enumerate(range(MAX_INSTANCE_RETRIES)):
+        # Simulate runners failing
+        state_with_runners = state.model_copy(
+            update={"runners": {runner_ids[0]: RunnerFailed(error_message=f"fail-{i}")}}
+        )
+        reconciler = InstanceHealthReconciler()
+        events = await reconciler.reconcile(state_with_runners)
+        assert len(events) == 1
+        assert isinstance(events[0], InstanceRetrying), f"iteration {i}"
+        state = apply(state, IndexedEvent(idx=idx, event=events[0]))
+
+    # After MAX_INSTANCE_RETRIES retries, failure counter should be at max
+    mi = state.meta_instances[meta.meta_instance_id]
+    assert mi.consecutive_failures == MAX_INSTANCE_RETRIES
+
+    # Next failure should result in deletion
+    state_with_runners = state.model_copy(
+        update={"runners": {runner_ids[0]: RunnerFailed(error_message="final")}}
+    )
+    reconciler = InstanceHealthReconciler()
+    events = await reconciler.reconcile(state_with_runners)
+    assert len(events) == 1
+    assert isinstance(events[0], InstanceDeleted)
+
+
+async def test_health_reconciler_respects_exact_limit():
+    """At exactly MAX_INSTANCE_RETRIES, reconciler should delete, not retry."""
+    meta = _meta_instance(consecutive_failures=MAX_INSTANCE_RETRIES)
+    iid, inst = _instance(node_ids=["node-a"], meta_instance_id=meta.meta_instance_id)
+    runner_ids = list(inst.shard_assignments.node_to_runner.values())
+    state = State(
+        meta_instances={meta.meta_instance_id: meta},
+        instances={iid: inst},
+        runners={runner_ids[0]: RunnerFailed(error_message="OOM")},
+        topology=_topology("node-a"),
+    )
+    reconciler = InstanceHealthReconciler()
+    events = await reconciler.reconcile(state)
+    assert len(events) == 1
+    assert isinstance(events[0], InstanceDeleted)
+
+
+async def test_health_reconciler_at_limit_minus_one_retries():
+    """At MAX_INSTANCE_RETRIES - 1, reconciler should still retry."""
+    meta = _meta_instance(consecutive_failures=MAX_INSTANCE_RETRIES - 1)
+    iid, inst = _instance(node_ids=["node-a"], meta_instance_id=meta.meta_instance_id)
+    runner_ids = list(inst.shard_assignments.node_to_runner.values())
+    state = State(
+        meta_instances={meta.meta_instance_id: meta},
+        instances={iid: inst},
+        runners={runner_ids[0]: RunnerFailed(error_message="OOM")},
+        topology=_topology("node-a"),
+    )
+    reconciler = InstanceHealthReconciler()
+    events = await reconciler.reconcile(state)
+    assert len(events) == 1
+    assert isinstance(events[0], InstanceRetrying)
+
+
+# =============================================================================
+# 3. Error handling edge cases
+# =============================================================================
+
+
+def test_runners_failed_with_empty_error_message():
+    """RunnerFailed with empty error_message should still report as failed."""
+    _, inst = _instance(node_ids=["node-a"])
+    runners = {
+        rid: RunnerFailed(error_message="")
+        for rid in inst.shard_assignments.node_to_runner.values()
+    }
+    is_failed, error = instance_runners_failed(inst, runners, {})
+    assert is_failed is True
+    # Empty error message means we get the fallback
+    assert error == "Runner failed"
+
+
+def test_runners_failed_with_none_error_message():
+    """RunnerFailed with None error_message should still report as failed."""
+    _, inst = _instance(node_ids=["node-a"])
+    runners = {
+        rid: RunnerFailed(error_message=None)
+        for rid in inst.shard_assignments.node_to_runner.values()
+    }
+    is_failed, error = instance_runners_failed(inst, runners, {})
+    assert is_failed is True
+    assert error == "Runner failed"
+
+
+def test_runners_failed_collects_all_error_messages():
+    """With multiple failed runners, all error messages should be collected."""
+    _, inst = _instance(node_ids=["node-a", "node-b", "node-c"])
+    runner_ids = list(inst.shard_assignments.node_to_runner.values())
+    runners = {
+        runner_ids[0]: RunnerFailed(error_message="OOM on GPU 0"),
+        runner_ids[1]: RunnerFailed(error_message="OOM on GPU 1"),
+        runner_ids[2]: RunnerFailed(error_message="OOM on GPU 2"),
+    }
+    is_failed, error = instance_runners_failed(inst, runners, {})
+    assert is_failed is True
+    assert error is not None
+    assert "OOM on GPU 0" in error
+    assert "OOM on GPU 1" in error
+    assert "OOM on GPU 2" in error
+
+
+def test_runners_failed_includes_friendly_name():
+    """Error messages should include node friendly names when available."""
+    _, inst = _instance(node_ids=["node-a"])
+    node_id = NodeId("node-a")
+    runner_ids = list(inst.shard_assignments.node_to_runner.values())
+    runners = {runner_ids[0]: RunnerFailed(error_message="OOM")}
+    identities = {node_id: NodeIdentity(friendly_name="My Mac Studio")}
+    is_failed, error = instance_runners_failed(inst, runners, identities)
+    assert is_failed is True
+    assert error is not None
+    assert "My Mac Studio" in error
+
+
+def test_instance_retrying_for_missing_instance_is_safe():
+    """InstanceRetrying for an instance not in state should not crash.
+
+    NOTE: When the instance is missing, the handler returns early WITHOUT
+    incrementing the MetaInstance failure counter. This means stale retry
+    events for already-deleted instances are silently dropped. This is
+    acceptable since the InstanceDeleted handler already increments failures.
+    """
+    meta = _meta_instance()
+    state = State(meta_instances={meta.meta_instance_id: meta})
+    event = InstanceRetrying(
+        instance_id=InstanceId("nonexistent"),
+        meta_instance_id=meta.meta_instance_id,
+        failure_error="crash",
+    )
+    new_state = apply(state, IndexedEvent(idx=0, event=event))
+    # Does not crash, but failure count is NOT incremented (early return)
+    mi = new_state.meta_instances[meta.meta_instance_id]
+    assert mi.consecutive_failures == 0
+
+
+# =============================================================================
+# 4. Backward compatibility
+# =============================================================================
+
+
+def test_instance_without_meta_instance_id_works():
+    """Instances created without meta_instance_id should still function normally."""
+    _, inst = _instance(node_ids=["node-a"])
+    assert inst.meta_instance_id is None
+    topology = _topology("node-a")
+    assert instance_connections_healthy(inst, topology) is True
+
+
+def test_instance_deleted_without_meta_does_not_affect_meta_instances():
+    """Deleting an instance without meta_instance_id should not affect meta_instances."""
+    meta = _meta_instance()
+    iid, inst = _instance(node_ids=["node-a"])  # no meta_instance_id
+    state = State(
+        meta_instances={meta.meta_instance_id: meta},
+        instances={iid: inst},
+    )
+    event = InstanceDeleted(instance_id=iid, failure_error="crash")
+    new_state = apply(state, IndexedEvent(idx=0, event=event))
+    mi = new_state.meta_instances[meta.meta_instance_id]
+    assert mi.consecutive_failures == 0  # unchanged
+
+
+def test_satisfies_ignores_meta_instance_id_binding():
+    """instance_satisfies_meta_instance checks constraints only, not binding."""
+    meta = _meta_instance()
+    _, inst = _instance(node_ids=["node-a"])  # no meta_instance_id set
+    # Should match on constraints (model, min_nodes) regardless of binding
+    assert instance_satisfies_meta_instance(meta, inst) is True
+
+
+def test_find_unsatisfied_uses_binding_not_constraints():
+    """find_unsatisfied checks meta_instance_id binding, not just constraint matching."""
+    meta = _meta_instance()
+    # Instance matches constraints but is NOT bound to this meta_instance
+    iid, inst = _instance(node_ids=["node-a"])
+    topology = _topology("node-a")
+    result = find_unsatisfied_meta_instances(
+        {meta.meta_instance_id: meta}, {iid: inst}, topology
+    )
+    # Should be unsatisfied because instance.meta_instance_id != meta.meta_instance_id
+    assert list(result) == [meta]
+
+
+# =============================================================================
+# 5. Concurrent / multi-instance scenarios
+# =============================================================================
+
+
+async def test_health_reconciler_handles_multiple_failing_instances():
+    """Multiple instances failing simultaneously should each get their own event."""
+    meta_a = _meta_instance()
+    meta_b = _meta_instance()
+    iid_a, inst_a = _instance(
+        node_ids=["node-a"], meta_instance_id=meta_a.meta_instance_id
+    )
+    iid_b, inst_b = _instance(
+        node_ids=["node-b"], meta_instance_id=meta_b.meta_instance_id
+    )
+    runner_ids_a = list(inst_a.shard_assignments.node_to_runner.values())
+    runner_ids_b = list(inst_b.shard_assignments.node_to_runner.values())
+    state = State(
+        meta_instances={
+            meta_a.meta_instance_id: meta_a,
+            meta_b.meta_instance_id: meta_b,
+        },
+        instances={iid_a: inst_a, iid_b: inst_b},
+        runners={
+            runner_ids_a[0]: RunnerFailed(error_message="OOM"),
+            runner_ids_b[0]: RunnerFailed(error_message="OOM"),
+        },
+        topology=_topology("node-a", "node-b"),
+    )
+    reconciler = InstanceHealthReconciler()
+    events = await reconciler.reconcile(state)
+    assert len(events) == 2
+    # Both should be InstanceRetrying since failures < MAX
+    assert all(isinstance(e, InstanceRetrying) for e in events)
+    instance_ids = {e.instance_id for e in events}  # type: ignore[union-attr]
+    assert instance_ids == {iid_a, iid_b}
+
+
+async def test_health_reconciler_mixed_healthy_and_failing():
+    """Only failing instances should produce events; healthy ones should not."""
+    meta_healthy = _meta_instance()
+    meta_failing = _meta_instance()
+    iid_h, inst_h = _instance(
+        node_ids=["node-a"], meta_instance_id=meta_healthy.meta_instance_id
+    )
+    iid_f, inst_f = _instance(
+        node_ids=["node-b"], meta_instance_id=meta_failing.meta_instance_id
+    )
+    runner_ids_h = list(inst_h.shard_assignments.node_to_runner.values())
+    runner_ids_f = list(inst_f.shard_assignments.node_to_runner.values())
+    state = State(
+        meta_instances={
+            meta_healthy.meta_instance_id: meta_healthy,
+            meta_failing.meta_instance_id: meta_failing,
+        },
+        instances={iid_h: inst_h, iid_f: inst_f},
+        runners={
+            runner_ids_h[0]: RunnerReady(),
+            runner_ids_f[0]: RunnerFailed(error_message="crash"),
+        },
+        topology=_topology("node-a", "node-b"),
+    )
+    reconciler = InstanceHealthReconciler()
+    events = await reconciler.reconcile(state)
+    assert len(events) == 1
+    assert isinstance(events[0], InstanceRetrying)
+    assert events[0].instance_id == iid_f
+
+
+async def test_meta_instance_reconciler_empty_state():
+    """MetaInstanceReconciler with no meta_instances should produce no events."""
+    state = State()
+    reconciler = MetaInstanceReconciler()
+    events = await reconciler.reconcile(state)
+    assert len(events) == 0
+
+
+# =============================================================================
+# 6. Placement error tracking
+# =============================================================================
+
+
+def test_placement_failed_sets_error():
+    """MetaInstancePlacementFailed should set placement_error on the MetaInstance."""
+    meta = _meta_instance()
+    state = State(meta_instances={meta.meta_instance_id: meta})
+    event = MetaInstancePlacementFailed(
+        meta_instance_id=meta.meta_instance_id,
+        reason="Not enough memory",
+    )
+    new_state = apply(state, IndexedEvent(idx=0, event=event))
+    mi = new_state.meta_instances[meta.meta_instance_id]
+    assert mi.placement_error == "Not enough memory"
+
+
+def test_instance_created_clears_placement_error():
+    """InstanceCreated should clear placement_error on the MetaInstance."""
+    meta = _meta_instance(placement_error="Not enough memory")
+    _, inst = _instance(node_ids=["node-a"], meta_instance_id=meta.meta_instance_id)
+    state = State(meta_instances={meta.meta_instance_id: meta})
+    state = apply(state, IndexedEvent(idx=0, event=InstanceCreated(instance=inst)))
+    mi = state.meta_instances[meta.meta_instance_id]
+    assert mi.placement_error is None
+
+
+def test_placement_error_does_not_increment_failures():
+    """Placement failures should only set placement_error, not increment consecutive_failures."""
+    meta = _meta_instance()
+    state = State(meta_instances={meta.meta_instance_id: meta})
+    event = MetaInstancePlacementFailed(
+        meta_instance_id=meta.meta_instance_id,
+        reason="No resources",
+    )
+    new_state = apply(state, IndexedEvent(idx=0, event=event))
+    mi = new_state.meta_instances[meta.meta_instance_id]
+    assert mi.consecutive_failures == 0
+    assert mi.placement_error == "No resources"
+
+
+# =============================================================================
+# 7. State serialization roundtrip
+# =============================================================================
+
+
+def test_state_with_meta_instances_serializes():
+    """State with meta_instances should serialize and deserialize correctly."""
+    meta = _meta_instance(consecutive_failures=2, last_failure_error="test")
+    iid, inst = _instance(node_ids=["node-a"], meta_instance_id=meta.meta_instance_id)
+    state = State(
+        meta_instances={meta.meta_instance_id: meta},
+        instances={iid: inst},
+    )
+    json_str = state.model_dump_json()
+    restored = State.model_validate_json(json_str)
+    assert meta.meta_instance_id in restored.meta_instances
+    mi = restored.meta_instances[meta.meta_instance_id]
+    assert mi.model_id == meta.model_id
+    assert mi.consecutive_failures == 2
+    assert mi.last_failure_error == "test"
+    assert iid in restored.instances
+    assert restored.instances[iid].meta_instance_id == meta.meta_instance_id
+
+
+# =============================================================================
+# 8. MetaInstanceReconciler error handling
+# =============================================================================
+
+
+async def test_meta_instance_reconciler_model_load_error_emits_placement_failed(
+    monkeypatch: "pytest.MonkeyPatch",
+):
+    """When ModelCard.load raises, reconciler emits MetaInstancePlacementFailed."""
+    import exo.master.process_managers.meta_instance as mi_mod
+
+    meta = _meta_instance()
+    topo = _topology("node-a")
+    state = State(
+        meta_instances={meta.meta_instance_id: meta},
+        topology=topo,
+    )
+
+    async def _failing_load(_model_id: ModelId) -> ModelCard:
+        raise RuntimeError("Network error")
+
+    monkeypatch.setattr(
+        mi_mod, "ModelCard", type("MC", (), {"load": staticmethod(_failing_load)})
+    )
+
+    reconciler = MetaInstanceReconciler()
+    events = await reconciler.reconcile(state)
+
+    placement_failed = [e for e in events if isinstance(e, MetaInstancePlacementFailed)]
+    assert len(placement_failed) == 1
+    assert "Failed to load model card" in placement_failed[0].reason
+    assert meta.meta_instance_id == placement_failed[0].meta_instance_id
+
+
+async def test_meta_instance_reconciler_model_load_error_skips_dedup(
+    monkeypatch: "pytest.MonkeyPatch",
+):
+    """When ModelCard.load error matches existing placement_error, no duplicate event."""
+    import exo.master.process_managers.meta_instance as mi_mod
+
+    meta = _meta_instance(placement_error="Failed to load model card: Network error")
+    topo = _topology("node-a")
+    state = State(
+        meta_instances={meta.meta_instance_id: meta},
+        topology=topo,
+    )
+
+    async def _failing_load(_model_id: ModelId) -> ModelCard:
+        raise RuntimeError("Network error")
+
+    monkeypatch.setattr(
+        mi_mod, "ModelCard", type("MC", (), {"load": staticmethod(_failing_load)})
+    )
+
+    reconciler = MetaInstanceReconciler()
+    events = await reconciler.reconcile(state)
+
+    # Error matches existing placement_error, so no duplicate event emitted
+    assert len(events) == 0
+
+
+async def test_meta_instance_reconciler_continues_after_error(
+    monkeypatch: "pytest.MonkeyPatch",
+):
+    """Reconciler should continue to next meta-instance after one fails to load."""
+    import exo.master.process_managers.meta_instance as mi_mod
+
+    meta_a = _meta_instance(model_id="org/model-a")
+    meta_b = _meta_instance(model_id="org/model-b")
+    topo = _topology("node-a")
+    state = State(
+        meta_instances={
+            meta_a.meta_instance_id: meta_a,
+            meta_b.meta_instance_id: meta_b,
+        },
+        topology=topo,
+    )
+
+    call_count = 0
+
+    async def _load_second_fails(model_id: ModelId) -> ModelCard:
+        nonlocal call_count
+        call_count += 1
+        raise RuntimeError(f"Cannot load {model_id}")
+
+    monkeypatch.setattr(
+        mi_mod, "ModelCard", type("MC", (), {"load": staticmethod(_load_second_fails)})
+    )
+
+    reconciler = MetaInstanceReconciler()
+    events = await reconciler.reconcile(state)
+
+    # Both meta-instances should have been attempted (not short-circuited)
+    assert call_count == 2
+    # Both should have placement failed events
+    placement_failed = [e for e in events if isinstance(e, MetaInstancePlacementFailed)]
+    assert len(placement_failed) == 2
+
+
+# =============================================================================
+# 8. Cascade delete with task cancellation
+# =============================================================================
+
+
+def test_cascade_delete_cancels_active_tasks():
+    """Deleting a MetaInstance should cancel tasks on backing instances.
+
+    Regression test: previously, cascade-deleting backing instances via
+    DeleteMetaInstance did not emit TaskStatusUpdated(Cancelled) for active
+    tasks, leaving orphaned task references in state.
+    """
+    meta = _meta_instance()
+    iid, inst = _instance(node_ids=["node-a"], meta_instance_id=meta.meta_instance_id)
+    task_id = TaskId()
+    task = LoadModel(task_id=task_id, instance_id=iid, task_status=TaskStatus.Running)
+
+    # Build state with meta-instance, backing instance, and active task
+    state = State(
+        meta_instances={meta.meta_instance_id: meta},
+        instances={iid: inst},
+        tasks={task_id: task},
+        topology=_topology("node-a"),
+    )
+
+    # Simulate the cascade-delete event sequence produced by main.py:
+    # 1. MetaInstanceDeleted
+    # 2. TaskStatusUpdated(Cancelled) for active tasks
+    # 3. InstanceDeleted
+    idx = 0
+    state = apply(
+        state,
+        IndexedEvent(
+            idx=idx,
+            event=MetaInstanceDeleted(meta_instance_id=meta.meta_instance_id),
+        ),
+    )
+    idx += 1
+    state = apply(
+        state,
+        IndexedEvent(
+            idx=idx,
+            event=TaskStatusUpdated(task_id=task_id, task_status=TaskStatus.Cancelled),
+        ),
+    )
+    idx += 1
+    state = apply(
+        state,
+        IndexedEvent(idx=idx, event=InstanceDeleted(instance_id=iid)),
+    )
+
+    # Verify everything is cleaned up
+    assert len(state.meta_instances) == 0
+    assert len(state.instances) == 0
+    assert state.tasks[task_id].task_status == TaskStatus.Cancelled
+
+
+def test_cascade_delete_skips_completed_tasks():
+    """Cascade delete should only cancel Pending/Running tasks, not completed ones."""
+    meta = _meta_instance()
+    iid, inst = _instance(node_ids=["node-a"], meta_instance_id=meta.meta_instance_id)
+
+    running_task_id = TaskId()
+    completed_task_id = TaskId()
+    running_task = LoadModel(
+        task_id=running_task_id, instance_id=iid, task_status=TaskStatus.Running
+    )
+    completed_task = LoadModel(
+        task_id=completed_task_id, instance_id=iid, task_status=TaskStatus.Complete
+    )
+
+    state = State(
+        meta_instances={meta.meta_instance_id: meta},
+        instances={iid: inst},
+        tasks={running_task_id: running_task, completed_task_id: completed_task},
+        topology=_topology("node-a"),
+    )
+
+    # Only the running task should be cancelled — we verify the logic pattern
+    # by checking which tasks are Pending or Running
+    active_tasks = [
+        t
+        for t in state.tasks.values()
+        if t.instance_id == iid
+        and t.task_status in (TaskStatus.Pending, TaskStatus.Running)
+    ]
+    assert len(active_tasks) == 1
+    assert active_tasks[0].task_id == running_task_id

src/exo/master/tests/test_placement_utils.py

@@ -3,10 +3,10 @@ import pytest
 from exo.master.placement_utils import (
     allocate_layers_proportionally,
     filter_cycles_by_memory,
+    get_largest_cycles,
     get_mlx_jaccl_coordinators,
     get_shard_assignments,
     get_shard_assignments_for_pipeline_parallel,
-    get_smallest_cycles,
 )
 from exo.master.tests.conftest import (
     create_node_memory,
@@ -143,7 +143,7 @@ def test_filter_multiple_cycles_by_memory():
     }
 
 
-def test_get_smallest_cycles():
+def test_get_largest_cycles():
     # arrange
     node_a_id = NodeId()
     node_b_id = NodeId()
@@ -175,12 +175,12 @@ def test_get_smallest_cycles():
     cycles = [c for c in topology.get_cycles() if len(c) != 1]  # ignore singletons
 
     # act
-    smallest_cycles = get_smallest_cycles(cycles)
+    largest_cycles = get_largest_cycles(cycles)
 
     # assert
-    assert len(smallest_cycles) == 1
-    assert len(smallest_cycles[0]) == 2
-    assert set(n for n in smallest_cycles[0]) == {node_a_id, node_b_id}
+    assert len(largest_cycles) == 1
+    assert len(largest_cycles[0]) == 3
+    assert set(n for n in largest_cycles[0]) == {node_a_id, node_b_id, node_c_id}
 
 
 @pytest.mark.parametrize(

src/exo/master/tests/test_reconcile.py

@@ -0,0 +1,742 @@
+from exo.master.process_managers.instance_health import InstanceHealthReconciler
+from exo.master.reconcile import (
+    find_unsatisfied_meta_instances,
+    instance_connections_healthy,
+    instance_runners_failed,
+    instance_satisfies_meta_instance,
+)
+from exo.shared.apply import apply
+from exo.shared.models.model_cards import ModelCard, ModelId, ModelTask
+from exo.shared.topology import Topology
+from exo.shared.types.common import Host, MetaInstanceId, NodeId
+from exo.shared.types.events import (
+    IndexedEvent,
+    InstanceCreated,
+    InstanceDeleted,
+    InstanceRetrying,
+    MetaInstanceCreated,
+    MetaInstanceDeleted,
+)
+from exo.shared.types.memory import Memory
+from exo.shared.types.meta_instance import MetaInstance
+from exo.shared.types.multiaddr import Multiaddr
+from exo.shared.types.state import State
+from exo.shared.types.topology import Connection, SocketConnection
+from exo.shared.types.worker.instances import (
+    InstanceId,
+    MlxRingInstance,
+)
+from exo.shared.types.worker.runners import (
+    RunnerFailed,
+    RunnerId,
+    RunnerLoading,
+    RunnerReady,
+    RunnerShutdown,
+    ShardAssignments,
+)
+from exo.shared.types.worker.shards import PipelineShardMetadata
+
+
+def _model_card(model_id: str = "test-org/test-model") -> ModelCard:
+    return ModelCard(
+        model_id=ModelId(model_id),
+        storage_size=Memory.from_kb(1000),
+        n_layers=10,
+        hidden_size=30,
+        supports_tensor=True,
+        tasks=[ModelTask.TextGeneration],
+    )
+
+
+def _topology(*node_ids: str, connect: bool = True) -> Topology:
+    """Build a topology with nodes connected in a bidirectional ring with unique IPs.
+
+    Node at index ``i`` gets IP ``10.0.0.{i+1}``. Edges go in both directions
+    between consecutive nodes (including wrap-around).
+    """
+    t = Topology()
+    nodes = [NodeId(n) for n in node_ids]
+    for n in nodes:
+        t.add_node(n)
+    if connect and len(nodes) > 1:
+        for i in range(len(nodes)):
+            j = (i + 1) % len(nodes)
+            t.add_connection(
+                Connection(
+                    source=nodes[i],
+                    sink=nodes[j],
+                    edge=SocketConnection(
+                        sink_multiaddr=Multiaddr(
+                            address=f"/ip4/10.0.0.{j + 1}/tcp/50000"
+                        )
+                    ),
+                )
+            )
+            t.add_connection(
+                Connection(
+                    source=nodes[j],
+                    sink=nodes[i],
+                    edge=SocketConnection(
+                        sink_multiaddr=Multiaddr(
+                            address=f"/ip4/10.0.0.{i + 1}/tcp/50000"
+                        )
+                    ),
+                )
+            )
+    return t
+
+
+def _meta_instance(
+    model_id: str = "test-org/test-model",
+    *,
+    min_nodes: int = 1,
+    node_ids: list[NodeId] | None = None,
+    meta_instance_id: MetaInstanceId | None = None,
+) -> MetaInstance:
+    return MetaInstance(
+        meta_instance_id=meta_instance_id or MetaInstanceId(),
+        model_id=ModelId(model_id),
+        min_nodes=min_nodes,
+        node_ids=node_ids,
+    )
+
+
+def _instance(
+    model_id: str = "test-org/test-model",
+    node_ids: list[str] | None = None,
+    instance_id: InstanceId | None = None,
+    meta_instance_id: MetaInstanceId | None = None,
+) -> tuple[InstanceId, MlxRingInstance]:
+    """Create a test instance with hosts_by_node matching ``_topology()`` IPs."""
+    iid = instance_id or InstanceId()
+    nodes = node_ids or ["node-a"]
+    n = len(nodes)
+    mc = _model_card(model_id)
+    ephemeral_port = 50000
+    node_to_runner = {NodeId(nd): RunnerId() for nd in nodes}
+    runner_to_shard = {
+        runner_id: PipelineShardMetadata(
+            model_card=mc,
+            device_rank=i,
+            world_size=n,
+            start_layer=0,
+            end_layer=mc.n_layers,
+            n_layers=mc.n_layers,
+        )
+        for i, runner_id in enumerate(node_to_runner.values())
+    }
+    # Build hosts_by_node with IPs matching _topology() convention:
+    # node at index idx has IP 10.0.0.{idx+1}
+    hosts_by_node: dict[NodeId, list[Host]] = {}
+    for r, node_str in enumerate(nodes):
+        hosts: list[Host] = []
+        for idx in range(n):
+            if idx == r:
+                hosts.append(Host(ip="0.0.0.0", port=ephemeral_port))
+            elif n > 1 and idx in ((r - 1) % n, (r + 1) % n):
+                hosts.append(Host(ip=f"10.0.0.{idx + 1}", port=ephemeral_port))
+            else:
+                hosts.append(Host(ip="198.51.100.1", port=0))
+        hosts_by_node[NodeId(node_str)] = hosts
+    return iid, MlxRingInstance(
+        instance_id=iid,
+        shard_assignments=ShardAssignments(
+            model_id=ModelId(model_id),
+            runner_to_shard=runner_to_shard,
+            node_to_runner=node_to_runner,
+        ),
+        hosts_by_node=hosts_by_node,
+        ephemeral_port=ephemeral_port,
+        meta_instance_id=meta_instance_id,
+    )
+
+
+# --- instance_satisfies_meta_instance (pure constraint matching) ---
+
+
+def test_satisfies_matching_model():
+    meta = _meta_instance()
+    _, inst = _instance(node_ids=["node-a"])
+    assert instance_satisfies_meta_instance(meta, inst) is True
+
+
+def test_not_satisfies_wrong_model():
+    meta = _meta_instance("test-org/model-a")
+    _, inst = _instance("test-org/model-b")
+    assert instance_satisfies_meta_instance(meta, inst) is False
+
+
+def test_not_satisfies_missing_required_node():
+    meta = _meta_instance(node_ids=[NodeId("node-c")])
+    _, inst = _instance(node_ids=["node-a", "node-b"])
+    assert instance_satisfies_meta_instance(meta, inst) is False
+
+
+def test_not_satisfies_fewer_than_min_nodes():
+    meta = _meta_instance(min_nodes=3)
+    _, inst = _instance(node_ids=["node-a", "node-b"])
+    assert instance_satisfies_meta_instance(meta, inst) is False
+
+
+def test_satisfies_with_node_ids_specified():
+    meta = _meta_instance(node_ids=[NodeId("node-a"), NodeId("node-b")], min_nodes=2)
+    _, inst = _instance(node_ids=["node-a", "node-b", "node-c"])
+    assert instance_satisfies_meta_instance(meta, inst) is True
+
+
+# --- instance_connections_healthy ---
+
+
+def test_healthy_single_node_present():
+    _, inst = _instance(node_ids=["node-a"])
+    topology = _topology("node-a")
+    assert instance_connections_healthy(inst, topology) is True
+
+
+def test_unhealthy_single_node_missing():
+    _, inst = _instance(node_ids=["node-a"])
+    topology = Topology()  # empty
+    assert instance_connections_healthy(inst, topology) is False
+
+
+def test_healthy_two_node_ring():
+    _, inst = _instance(node_ids=["node-a", "node-b"])
+    topology = _topology("node-a", "node-b")
+    assert instance_connections_healthy(inst, topology) is True
+
+
+def test_unhealthy_two_node_edge_removed():
+    """Nodes present but edge removed — ring broken."""
+    _, inst = _instance(node_ids=["node-a", "node-b"])
+    topology = _topology("node-a", "node-b", connect=False)
+    assert instance_connections_healthy(inst, topology) is False
+
+
+def test_unhealthy_two_node_ip_changed():
+    """Edge exists but with a different IP than instance was configured with."""
+    _, inst = _instance(node_ids=["node-a", "node-b"])
+    # Build topology with different IPs than _instance() expects
+    topology = Topology()
+    topology.add_node(NodeId("node-a"))
+    topology.add_node(NodeId("node-b"))
+    topology.add_connection(
+        Connection(
+            source=NodeId("node-a"),
+            sink=NodeId("node-b"),
+            edge=SocketConnection(
+                sink_multiaddr=Multiaddr(address="/ip4/192.168.99.99/tcp/50000")
+            ),
+        )
+    )
+    topology.add_connection(
+        Connection(
+            source=NodeId("node-b"),
+            sink=NodeId("node-a"),
+            edge=SocketConnection(
+                sink_multiaddr=Multiaddr(address="/ip4/192.168.99.98/tcp/50000")
+            ),
+        )
+    )
+    assert instance_connections_healthy(inst, topology) is False
+
+
+def test_healthy_three_node_ring():
+    _, inst = _instance(node_ids=["node-a", "node-b", "node-c"])
+    topology = _topology("node-a", "node-b", "node-c")
+    assert instance_connections_healthy(inst, topology) is True
+
+
+def test_unhealthy_three_node_one_edge_removed():
+    """Remove one edge from a three-node ring — instance unhealthy."""
+    _, inst = _instance(node_ids=["node-a", "node-b", "node-c"])
+    # Build topology with one direction of one edge missing
+    topology = Topology()
+    nodes = [NodeId("node-a"), NodeId("node-b"), NodeId("node-c")]
+    for n in nodes:
+        topology.add_node(n)
+    # Add all edges except node-a → node-b
+    topology.add_connection(
+        Connection(
+            source=nodes[1],
+            sink=nodes[0],
+            edge=SocketConnection(
+                sink_multiaddr=Multiaddr(address="/ip4/10.0.0.1/tcp/50000")
+            ),
+        )
+    )
+    topology.add_connection(
+        Connection(
+            source=nodes[1],
+            sink=nodes[2],
+            edge=SocketConnection(
+                sink_multiaddr=Multiaddr(address="/ip4/10.0.0.3/tcp/50000")
+            ),
+        )
+    )
+    topology.add_connection(
+        Connection(
+            source=nodes[2],
+            sink=nodes[1],
+            edge=SocketConnection(
+                sink_multiaddr=Multiaddr(address="/ip4/10.0.0.2/tcp/50000")
+            ),
+        )
+    )
+    topology.add_connection(
+        Connection(
+            source=nodes[2],
+            sink=nodes[0],
+            edge=SocketConnection(
+                sink_multiaddr=Multiaddr(address="/ip4/10.0.0.1/tcp/50000")
+            ),
+        )
+    )
+    topology.add_connection(
+        Connection(
+            source=nodes[0],
+            sink=nodes[2],
+            edge=SocketConnection(
+                sink_multiaddr=Multiaddr(address="/ip4/10.0.0.3/tcp/50000")
+            ),
+        )
+    )
+    # Missing: node-a → node-b (ip 10.0.0.2)
+    assert instance_connections_healthy(inst, topology) is False
+
+
+def test_unhealthy_node_missing_from_topology():
+    """Instance has a node that's not in the topology at all."""
+    _, inst = _instance(node_ids=["node-a", "node-b"])
+    topology = _topology("node-a")  # node-b not present
+    assert instance_connections_healthy(inst, topology) is False
+
+
+def test_healthy_extra_nodes_in_topology():
+    """Extra nodes in topology don't affect instance health."""
+    _, inst = _instance(node_ids=["node-a", "node-b"])
+    topology = _topology("node-a", "node-b", "node-c")
+    assert instance_connections_healthy(inst, topology) is True
+
+
+# --- find_unsatisfied_meta_instances ---
+
+
+def test_unsatisfied_no_meta_instances():
+    result = find_unsatisfied_meta_instances({}, {}, Topology())
+    assert list(result) == []
+
+
+def test_unsatisfied_one_satisfied():
+    meta = _meta_instance()
+    id_a, inst_a = _instance(meta_instance_id=meta.meta_instance_id)
+    topology = _topology("node-a")
+    result = find_unsatisfied_meta_instances(
+        {meta.meta_instance_id: meta},
+        {id_a: inst_a},
+        topology,
+    )
+    assert list(result) == []
+
+
+def test_unsatisfied_one_not_satisfied():
+    meta = _meta_instance("test-org/model-x")
+    id_a, inst_a = _instance("test-org/model-y")
+    topology = _topology("node-a")
+    result = find_unsatisfied_meta_instances(
+        {meta.meta_instance_id: meta}, {id_a: inst_a}, topology
+    )
+    assert list(result) == [meta]
+
+
+def test_unsatisfied_mix():
+    meta_satisfied = _meta_instance("test-org/model-a")
+    meta_unsatisfied = _meta_instance("test-org/model-b")
+    id_a, inst_a = _instance(
+        "test-org/model-a", meta_instance_id=meta_satisfied.meta_instance_id
+    )
+    topology = _topology("node-a")
+    result = find_unsatisfied_meta_instances(
+        {
+            meta_satisfied.meta_instance_id: meta_satisfied,
+            meta_unsatisfied.meta_instance_id: meta_unsatisfied,
+        },
+        {id_a: inst_a},
+        topology,
+    )
+    assert list(result) == [meta_unsatisfied]
+
+
+def test_unsatisfied_node_disconnect():
+    meta = _meta_instance()
+    id_a, inst_a = _instance(
+        node_ids=["node-a", "node-b"], meta_instance_id=meta.meta_instance_id
+    )
+    topology = _topology("node-a")  # node-b disconnected
+    result = find_unsatisfied_meta_instances(
+        {meta.meta_instance_id: meta},
+        {id_a: inst_a},
+        topology,
+    )
+    assert list(result) == [meta]
+
+
+def test_unsatisfied_edge_break():
+    """Instance exists but its connections broke — meta-instance becomes unsatisfied."""
+    meta = _meta_instance()
+    id_a, inst_a = _instance(
+        node_ids=["node-a", "node-b"], meta_instance_id=meta.meta_instance_id
+    )
+    topology = _topology("node-a", "node-b", connect=False)  # nodes present, no edges
+    result = find_unsatisfied_meta_instances(
+        {meta.meta_instance_id: meta},
+        {id_a: inst_a},
+        topology,
+    )
+    assert list(result) == [meta]
+
+
+def test_unsatisfied_idempotent():
+    meta = _meta_instance("test-org/model-x")
+    topology = _topology("node-a")
+    meta_instances = {meta.meta_instance_id: meta}
+    instances: dict[InstanceId, MlxRingInstance] = {}
+    result_1 = list(
+        find_unsatisfied_meta_instances(meta_instances, instances, topology)
+    )
+    result_2 = list(
+        find_unsatisfied_meta_instances(meta_instances, instances, topology)
+    )
+    assert result_1 == result_2
+
+
+def test_unsatisfied_exclusive_binding():
+    """Two MetaInstances for the same model: one is bound via meta_instance_id, the other is unsatisfied."""
+    meta_a = _meta_instance("test-org/model-x")
+    meta_b = _meta_instance("test-org/model-x")
+    id_inst, inst = _instance(
+        "test-org/model-x", meta_instance_id=meta_a.meta_instance_id
+    )
+    topology = _topology("node-a")
+    result = find_unsatisfied_meta_instances(
+        {
+            meta_a.meta_instance_id: meta_a,
+            meta_b.meta_instance_id: meta_b,
+        },
+        {id_inst: inst},
+        topology,
+    )
+    assert list(result) == [meta_b]
+
+
+# --- apply handlers ---
+
+
+def test_apply_meta_instance_created():
+    state = State()
+    meta = _meta_instance()
+    event = MetaInstanceCreated(meta_instance=meta)
+    new_state = apply(state, IndexedEvent(idx=0, event=event))
+    assert meta.meta_instance_id in new_state.meta_instances
+    assert new_state.meta_instances[meta.meta_instance_id] == meta
+
+
+def test_apply_meta_instance_deleted():
+    meta = _meta_instance()
+    state = State(meta_instances={meta.meta_instance_id: meta})
+    event = MetaInstanceDeleted(meta_instance_id=meta.meta_instance_id)
+    new_state = apply(state, IndexedEvent(idx=0, event=event))
+    assert meta.meta_instance_id not in new_state.meta_instances
+
+
+def test_apply_meta_instance_deleted_clears_failure_info():
+    meta = _meta_instance().model_copy(
+        update={"consecutive_failures": 2, "last_failure_error": "OOM"}
+    )
+    state = State(meta_instances={meta.meta_instance_id: meta})
+    event = MetaInstanceDeleted(meta_instance_id=meta.meta_instance_id)
+    new_state = apply(state, IndexedEvent(idx=0, event=event))
+    assert meta.meta_instance_id not in new_state.meta_instances
+
+
+# --- instance_runners_failed ---
+
+
+def test_runners_failed_all_failed():
+    """All runners in RunnerFailed -> instance is failed."""
+    _, inst = _instance(node_ids=["node-a", "node-b"])
+    runners = {
+        rid: RunnerFailed(error_message="OOM")
+        for rid in inst.shard_assignments.node_to_runner.values()
+    }
+    is_failed, error = instance_runners_failed(inst, runners, {})
+    assert is_failed is True
+    assert error is not None
+    assert "OOM" in error
+
+
+def test_runners_failed_mixed_failed_shutdown():
+    """One Failed + one Shutdown = failed."""
+    _, inst = _instance(node_ids=["node-a", "node-b"])
+    runner_ids = list(inst.shard_assignments.node_to_runner.values())
+    runners = {
+        runner_ids[0]: RunnerFailed(error_message="crash"),
+        runner_ids[1]: RunnerShutdown(),
+    }
+    is_failed, error = instance_runners_failed(inst, runners, {})
+    assert is_failed is True
+    assert error is not None
+    assert "crash" in error
+
+
+def test_runners_not_failed_all_shutdown():
+    """All Shutdown (graceful) = not a failure."""
+    _, inst = _instance(node_ids=["node-a"])
+    runners = {
+        rid: RunnerShutdown() for rid in inst.shard_assignments.node_to_runner.values()
+    }
+    is_failed, _ = instance_runners_failed(inst, runners, {})
+    assert is_failed is False
+
+
+def test_runners_not_failed_still_active():
+    """Some runners still active = not failed yet."""
+    _, inst = _instance(node_ids=["node-a", "node-b"])
+    runner_ids = list(inst.shard_assignments.node_to_runner.values())
+    runners = {
+        runner_ids[0]: RunnerFailed(error_message="OOM"),
+        runner_ids[1]: RunnerLoading(),
+    }
+    is_failed, _ = instance_runners_failed(inst, runners, {})
+    assert is_failed is False
+
+
+def test_runners_not_failed_no_status():
+    """Runner not yet reported = not failed."""
+    _, inst = _instance(node_ids=["node-a"])
+    is_failed, _ = instance_runners_failed(inst, {}, {})
+    assert is_failed is False
+
+
+def test_runners_not_failed_healthy():
+    """Runners in Ready state = not failed."""
+    _, inst = _instance(node_ids=["node-a"])
+    runners = {
+        rid: RunnerReady() for rid in inst.shard_assignments.node_to_runner.values()
+    }
+    is_failed, _ = instance_runners_failed(inst, runners, {})
+    assert is_failed is False
+
+
+# --- failure tracking in apply_instance_deleted ---
+
+
+def test_apply_instance_deleted_tracks_failure():
+    """InstanceDeleted with failure_error increments meta instance failure count."""
+    meta = _meta_instance()
+    iid, inst = _instance(node_ids=["node-a"], meta_instance_id=meta.meta_instance_id)
+    state = State(
+        meta_instances={meta.meta_instance_id: meta},
+        instances={iid: inst},
+    )
+    event = InstanceDeleted(instance_id=iid, failure_error="Runner OOM")
+    new_state = apply(state, IndexedEvent(idx=0, event=event))
+    mi = new_state.meta_instances[meta.meta_instance_id]
+    assert mi.consecutive_failures == 1
+    assert mi.last_failure_error == "Runner OOM"
+
+
+def test_apply_instance_deleted_increments_failure():
+    """Subsequent failures increment the counter."""
+    meta = _meta_instance().model_copy(
+        update={"consecutive_failures": 2, "last_failure_error": "previous error"}
+    )
+    iid, inst = _instance(node_ids=["node-a"], meta_instance_id=meta.meta_instance_id)
+    state = State(
+        meta_instances={meta.meta_instance_id: meta},
+        instances={iid: inst},
+    )
+    event = InstanceDeleted(instance_id=iid, failure_error="new error")
+    new_state = apply(state, IndexedEvent(idx=0, event=event))
+    mi = new_state.meta_instances[meta.meta_instance_id]
+    assert mi.consecutive_failures == 3
+    assert mi.last_failure_error == "new error"
+
+
+def test_apply_instance_deleted_no_failure_no_tracking():
+    """InstanceDeleted without failure_error does not track."""
+    meta = _meta_instance()
+    iid, inst = _instance(node_ids=["node-a"], meta_instance_id=meta.meta_instance_id)
+    state = State(
+        meta_instances={meta.meta_instance_id: meta},
+        instances={iid: inst},
+    )
+    event = InstanceDeleted(instance_id=iid)
+    new_state = apply(state, IndexedEvent(idx=0, event=event))
+    mi = new_state.meta_instances[meta.meta_instance_id]
+    assert mi.consecutive_failures == 0
+
+
+def test_apply_instance_deleted_orphan_no_tracking():
+    """InstanceDeleted for orphan instance (no meta_instance_id) does not track."""
+    iid, inst = _instance(node_ids=["node-a"])
+    state = State(instances={iid: inst})
+    event = InstanceDeleted(instance_id=iid, failure_error="crash")
+    new_state = apply(state, IndexedEvent(idx=0, event=event))
+    assert len(new_state.meta_instances) == 0
+
+
+# --- InstanceRetrying ---
+
+
+def test_apply_instance_retrying_removes_runners():
+    """InstanceRetrying removes the instance's runners from state but keeps the instance."""
+    meta = _meta_instance()
+    iid, inst = _instance(
+        node_ids=["node-a", "node-b"], meta_instance_id=meta.meta_instance_id
+    )
+    runner_ids = list(inst.shard_assignments.node_to_runner.values())
+    runners = {
+        runner_ids[0]: RunnerFailed(error_message="OOM"),
+        runner_ids[1]: RunnerShutdown(),
+    }
+    state = State(
+        meta_instances={meta.meta_instance_id: meta},
+        instances={iid: inst},
+        runners=runners,
+    )
+    event = InstanceRetrying(
+        instance_id=iid,
+        meta_instance_id=meta.meta_instance_id,
+        failure_error="OOM",
+    )
+    new_state = apply(state, IndexedEvent(idx=0, event=event))
+    # Instance still exists
+    assert iid in new_state.instances
+    # Runners removed
+    assert runner_ids[0] not in new_state.runners
+    assert runner_ids[1] not in new_state.runners
+
+
+def test_apply_instance_retrying_increments_failure():
+    """InstanceRetrying increments consecutive_failures on the MetaInstance."""
+    meta = _meta_instance()
+    iid, inst = _instance(node_ids=["node-a"], meta_instance_id=meta.meta_instance_id)
+    state = State(
+        meta_instances={meta.meta_instance_id: meta},
+        instances={iid: inst},
+    )
+    event = InstanceRetrying(
+        instance_id=iid,
+        meta_instance_id=meta.meta_instance_id,
+        failure_error="crash",
+    )
+    new_state = apply(state, IndexedEvent(idx=0, event=event))
+    mi = new_state.meta_instances[meta.meta_instance_id]
+    assert mi.consecutive_failures == 1
+    assert mi.last_failure_error == "crash"
+
+
+def test_apply_instance_retrying_skips_missing_runners():
+    """InstanceRetrying doesn't assert if runners haven't reported yet."""
+    meta = _meta_instance()
+    iid, inst = _instance(node_ids=["node-a"], meta_instance_id=meta.meta_instance_id)
+    # No runners in state at all
+    state = State(
+        meta_instances={meta.meta_instance_id: meta},
+        instances={iid: inst},
+    )
+    event = InstanceRetrying(
+        instance_id=iid,
+        meta_instance_id=meta.meta_instance_id,
+        failure_error="crash",
+    )
+    # Should not raise
+    new_state = apply(state, IndexedEvent(idx=0, event=event))
+    assert iid in new_state.instances
+
+
+def test_apply_instance_created_resets_failure_counter():
+    """InstanceCreated resets consecutive_failures but preserves last_failure_error."""
+    meta = _meta_instance().model_copy(
+        update={"consecutive_failures": 3, "last_failure_error": "old error"}
+    )
+    _, inst = _instance(node_ids=["node-a"], meta_instance_id=meta.meta_instance_id)
+    state = State(meta_instances={meta.meta_instance_id: meta})
+    event = InstanceCreated(instance=inst)
+    new_state = apply(state, IndexedEvent(idx=0, event=event))
+    mi = new_state.meta_instances[meta.meta_instance_id]
+    assert mi.consecutive_failures == 0
+    assert mi.last_failure_error == "old error"
+    assert mi.placement_error is None
+
+
+# --- InstanceHealthReconciler retry-vs-delete ---
+
+
+async def test_health_reconciler_retries_when_under_limit():
+    """InstanceHealthReconciler emits InstanceRetrying when consecutive_failures < 3."""
+    meta = _meta_instance()
+    iid, inst = _instance(node_ids=["node-a"], meta_instance_id=meta.meta_instance_id)
+    runner_ids = list(inst.shard_assignments.node_to_runner.values())
+    state = State(
+        meta_instances={meta.meta_instance_id: meta},
+        instances={iid: inst},
+        runners={runner_ids[0]: RunnerFailed(error_message="OOM")},
+        topology=_topology("node-a"),
+    )
+    reconciler = InstanceHealthReconciler()
+    events = await reconciler.reconcile(state)
+    assert len(events) == 1
+    assert isinstance(events[0], InstanceRetrying)
+    assert events[0].instance_id == iid
+    assert events[0].meta_instance_id == meta.meta_instance_id
+
+
+async def test_health_reconciler_deletes_when_limit_reached():
+    """InstanceHealthReconciler emits InstanceDeleted when consecutive_failures >= 3."""
+    meta = _meta_instance().model_copy(update={"consecutive_failures": 3})
+    iid, inst = _instance(node_ids=["node-a"], meta_instance_id=meta.meta_instance_id)
+    runner_ids = list(inst.shard_assignments.node_to_runner.values())
+    state = State(
+        meta_instances={meta.meta_instance_id: meta},
+        instances={iid: inst},
+        runners={runner_ids[0]: RunnerFailed(error_message="OOM")},
+        topology=_topology("node-a"),
+    )
+    reconciler = InstanceHealthReconciler()
+    events = await reconciler.reconcile(state)
+    assert len(events) == 1
+    assert isinstance(events[0], InstanceDeleted)
+
+
+async def test_health_reconciler_deletes_without_meta_instance():
+    """Instances without a MetaInstance are deleted immediately on runner failure."""
+    iid, inst = _instance(node_ids=["node-a"])
+    runner_ids = list(inst.shard_assignments.node_to_runner.values())
+    state = State(
+        instances={iid: inst},
+        runners={runner_ids[0]: RunnerFailed(error_message="crash")},
+        topology=_topology("node-a"),
+    )
+    reconciler = InstanceHealthReconciler()
+    events = await reconciler.reconcile(state)
+    assert len(events) == 1
+    assert isinstance(events[0], InstanceDeleted)
+
+
+async def test_health_reconciler_network_failure_always_deletes():
+    """Network failure always triggers InstanceDeleted regardless of retry count."""
+    meta = _meta_instance()
+    iid, inst = _instance(
+        node_ids=["node-a", "node-b"], meta_instance_id=meta.meta_instance_id
+    )
+    state = State(
+        meta_instances={meta.meta_instance_id: meta},
+        instances={iid: inst},
+        topology=_topology("node-a"),  # node-b missing
+    )
+    reconciler = InstanceHealthReconciler()
+    events = await reconciler.reconcile(state)
+    assert len(events) == 1
+    assert isinstance(events[0], InstanceDeleted)
+    assert events[0].failure_error == "Network connection lost"

src/exo/routing/router.py

@@ -101,8 +101,12 @@ class TopicRouter[T: CamelCaseModel]:
 
 class Router:
     @classmethod
-    def create(cls, identity: Keypair) -> "Router":
-        return cls(handle=NetworkingHandle(identity))
+    def create(
+        cls,
+        identity: Keypair,
+        bootstrap_peers: list[str] | None = None,
+    ) -> "Router":
+        return cls(handle=NetworkingHandle(identity, bootstrap_peers or []))
 
     def __init__(self, handle: NetworkingHandle):
         self.topic_routers: dict[str, TopicRouter[CamelCaseModel]] = {}

src/exo/shared/apply.py

@@ -4,7 +4,7 @@ from datetime import datetime
 
 from loguru import logger
 
-from exo.shared.types.common import NodeId
+from exo.shared.types.common import MetaInstanceId, NodeId
 from exo.shared.types.events import (
     ChunkGenerated,
     Event,
@@ -12,6 +12,12 @@ from exo.shared.types.events import (
     InputChunkReceived,
     InstanceCreated,
     InstanceDeleted,
+    InstanceRetrying,
+    JacclSideChannelData,
+    JacclSideChannelGathered,
+    MetaInstanceCreated,
+    MetaInstanceDeleted,
+    MetaInstancePlacementFailed,
     NodeDownloadProgress,
     NodeGatheredInfo,
     NodeTimedOut,
@@ -28,6 +34,7 @@ from exo.shared.types.events import (
     TracesCollected,
     TracesMerged,
 )
+from exo.shared.types.meta_instance import MetaInstance
 from exo.shared.types.profiling import (
     NodeIdentity,
     NodeNetworkInfo,
@@ -66,12 +73,22 @@ def event_apply(event: Event, state: State) -> State:
             | InputChunkReceived()
             | TracesCollected()
             | TracesMerged()
+            | JacclSideChannelData()
+            | JacclSideChannelGathered()
         ):  # Pass-through events that don't modify state
             return state
         case InstanceCreated():
             return apply_instance_created(event, state)
         case InstanceDeleted():
             return apply_instance_deleted(event, state)
+        case InstanceRetrying():
+            return apply_instance_retrying(event, state)
+        case MetaInstanceCreated():
+            return apply_meta_instance_created(event, state)
+        case MetaInstanceDeleted():
+            return apply_meta_instance_deleted(event, state)
+        case MetaInstancePlacementFailed():
+            return apply_meta_instance_placement_failed(event, state)
         case NodeTimedOut():
             return apply_node_timed_out(event, state)
         case NodeDownloadProgress():
@@ -174,20 +191,123 @@ def apply_task_failed(event: TaskFailed, state: State) -> State:
     return state.model_copy(update={"tasks": new_tasks})
 
 
+def _update_meta_instance(
+    state: State, mid: MetaInstanceId, **fields: object
+) -> Mapping[MetaInstanceId, MetaInstance]:
+    mi = state.meta_instances[mid]
+    return {**state.meta_instances, mid: mi.model_copy(update=fields)}
+
+
 def apply_instance_created(event: InstanceCreated, state: State) -> State:
     instance = event.instance
     new_instances: Mapping[InstanceId, Instance] = {
         **state.instances,
         instance.instance_id: instance,
     }
-    return state.model_copy(update={"instances": new_instances})
+    update: dict[str, object] = {"instances": new_instances}
+    # Reset failure tracking when a new instance is created for a meta-instance
+    if instance.meta_instance_id and instance.meta_instance_id in state.meta_instances:
+        mi = state.meta_instances[instance.meta_instance_id]
+        if mi.placement_error is not None or mi.consecutive_failures > 0:
+            update["meta_instances"] = _update_meta_instance(
+                state,
+                instance.meta_instance_id,
+                placement_error=None,
+                consecutive_failures=0,
+            )
+    return state.model_copy(update=update)
 
 
 def apply_instance_deleted(event: InstanceDeleted, state: State) -> State:
+    deleted_instance = state.instances.get(event.instance_id)
     new_instances: Mapping[InstanceId, Instance] = {
         iid: inst for iid, inst in state.instances.items() if iid != event.instance_id
     }
-    return state.model_copy(update={"instances": new_instances})
+    update: dict[str, object] = {"instances": new_instances}
+
+    # Track failure on the MetaInstance itself
+    if (
+        event.failure_error
+        and deleted_instance
+        and deleted_instance.meta_instance_id
+        and deleted_instance.meta_instance_id in state.meta_instances
+    ):
+        mid = deleted_instance.meta_instance_id
+        mi = state.meta_instances[mid]
+        update["meta_instances"] = {
+            **state.meta_instances,
+            mid: mi.model_copy(
+                update={
+                    "consecutive_failures": mi.consecutive_failures + 1,
+                    "last_failure_error": event.failure_error,
+                }
+            ),
+        }
+
+    return state.model_copy(update=update)
+
+
+def apply_instance_retrying(event: InstanceRetrying, state: State) -> State:
+    """Runners failed but retry limit not reached — remove runners, keep instance."""
+    instance = state.instances.get(event.instance_id)
+    if instance is None:
+        # Instance was already deleted (e.g. cascade from DeleteMetaInstance).
+        # The InstanceDeleted handler already incremented consecutive_failures
+        # on the MetaInstance, so skipping here avoids double-counting.
+        return state
+
+    # Remove all runners belonging to this instance from state
+    runner_ids_to_remove = set(instance.shard_assignments.node_to_runner.values())
+    new_runners: Mapping[RunnerId, RunnerStatus] = {
+        rid: rs for rid, rs in state.runners.items() if rid not in runner_ids_to_remove
+    }
+
+    update: dict[str, object] = {"runners": new_runners}
+
+    # Increment failure count on the MetaInstance
+    if event.meta_instance_id in state.meta_instances:
+        update["meta_instances"] = _update_meta_instance(
+            state,
+            event.meta_instance_id,
+            consecutive_failures=state.meta_instances[
+                event.meta_instance_id
+            ].consecutive_failures
+            + 1,
+            last_failure_error=event.failure_error,
+        )
+
+    return state.model_copy(update=update)
+
+
+def apply_meta_instance_created(event: MetaInstanceCreated, state: State) -> State:
+    new_meta: Mapping[MetaInstanceId, MetaInstance] = {
+        **state.meta_instances,
+        event.meta_instance.meta_instance_id: event.meta_instance,
+    }
+    return state.model_copy(update={"meta_instances": new_meta})
+
+
+def apply_meta_instance_deleted(event: MetaInstanceDeleted, state: State) -> State:
+    new_meta: Mapping[MetaInstanceId, MetaInstance] = {
+        mid: mi
+        for mid, mi in state.meta_instances.items()
+        if mid != event.meta_instance_id
+    }
+    return state.model_copy(update={"meta_instances": new_meta})
+
+
+def apply_meta_instance_placement_failed(
+    event: MetaInstancePlacementFailed, state: State
+) -> State:
+    if event.meta_instance_id not in state.meta_instances:
+        return state
+    return state.model_copy(
+        update={
+            "meta_instances": _update_meta_instance(
+                state, event.meta_instance_id, placement_error=event.reason
+            )
+        }
+    )
 
 
 def apply_runner_status_updated(event: RunnerStatusUpdated, state: State) -> State:
@@ -218,6 +338,11 @@ def apply_node_timed_out(event: NodeTimedOut, state: State) -> State:
         key: value for key, value in state.downloads.items() if key != event.node_id
     }
     # Clean up all granular node mappings
+    node_identities = {
+        key: value
+        for key, value in state.node_identities.items()
+        if key != event.node_id
+    }
     node_memory = {
         key: value for key, value in state.node_memory.items() if key != event.node_id
     }
@@ -258,6 +383,7 @@ def apply_node_timed_out(event: NodeTimedOut, state: State) -> State:
             "downloads": downloads,
             "topology": topology,
             "last_seen": last_seen,
+            "node_identities": node_identities,
             "node_memory": node_memory,
             "node_disk": node_disk,
             "node_system": node_system,

src/exo/shared/models/model_cards.py

@@ -44,8 +44,7 @@ async def _refresh_card_cache():
         async for toml_file in path.rglob("*.toml"):
             try:
                 card = await ModelCard.load_from_path(toml_file)
-                if card.model_id not in _card_cache:
-                    _card_cache[card.model_id] = card
+                _card_cache[card.model_id] = card
             except (ValidationError, TOMLKitError):
                 pass
 
@@ -183,7 +182,6 @@ class ConfigData(BaseModel):
     def supports_tensor(self) -> bool:
         return self.architectures in [
             ["Glm4MoeLiteForCausalLM"],
-            ["GlmMoeDsaForCausalLM"],
             ["DeepseekV32ForCausalLM"],
             ["DeepseekV3ForCausalLM"],
             ["Qwen3NextForCausalLM"],

src/exo/shared/types/api.py

@@ -1,12 +1,12 @@
 import time
 from collections.abc import Generator
-from typing import Annotated, Any, Literal, get_args
+from typing import Annotated, Any, Literal
 from uuid import uuid4
 
-from pydantic import BaseModel, Field, field_validator
+from pydantic import BaseModel, Field
 
 from exo.shared.models.model_cards import ModelCard, ModelId
-from exo.shared.types.common import CommandId, NodeId
+from exo.shared.types.common import CommandId, MetaInstanceId, NodeId
 from exo.shared.types.memory import Memory
 from exo.shared.types.worker.instances import Instance, InstanceId, InstanceMeta
 from exo.shared.types.worker.shards import Sharding, ShardMetadata
@@ -262,25 +262,24 @@ class DeleteInstanceResponse(BaseModel):
     instance_id: InstanceId
 
 
-ImageSize = Literal[
-    "auto",
-    "512x512",
-    "768x768",
-    "1024x768",
-    "768x1024",
-    "1024x1024",
-    "1024x1536",
-    "1536x1024",
-]
+class CreateMetaInstanceParams(BaseModel):
+    model_id: ModelId
+    sharding: Sharding = Sharding.Pipeline
+    instance_meta: InstanceMeta = InstanceMeta.MlxRing
+    min_nodes: int = 1
+    node_ids: list[NodeId] | None = None
 
 
-def normalize_image_size(v: object) -> ImageSize:
-    """Shared validator for ImageSize fields: maps None → "auto" and rejects invalid values."""
-    if v is None:
-        return "auto"
-    if v not in get_args(ImageSize):
-        raise ValueError(f"Invalid size: {v!r}. Must be one of {get_args(ImageSize)}")
-    return v  # pyright: ignore[reportReturnType]
+class CreateMetaInstanceResponse(BaseModel):
+    message: str
+    command_id: CommandId
+    meta_instance_id: MetaInstanceId
+
+
+class DeleteMetaInstanceResponse(BaseModel):
+    message: str
+    command_id: CommandId
+    meta_instance_id: MetaInstanceId
 
 
 class AdvancedImageParams(BaseModel):
@@ -302,7 +301,7 @@ class ImageGenerationTaskParams(BaseModel):
     partial_images: int | None = 0
     quality: Literal["high", "medium", "low"] | None = "medium"
     response_format: Literal["url", "b64_json"] | None = "b64_json"
-    size: ImageSize = "auto"
+    size: str | None = "1024x1024"
     stream: bool | None = False
     style: str | None = "vivid"
     user: str | None = None
@@ -310,11 +309,6 @@ class ImageGenerationTaskParams(BaseModel):
     # Internal flag for benchmark mode - set by API, preserved through serialization
     bench: bool = False
 
-    @field_validator("size", mode="before")
-    @classmethod
-    def normalize_size(cls, v: object) -> ImageSize:
-        return normalize_image_size(v)
-
 
 class BenchImageGenerationTaskParams(ImageGenerationTaskParams):
     bench: bool = True
@@ -331,18 +325,13 @@ class ImageEditsTaskParams(BaseModel):
     quality: Literal["high", "medium", "low"] | None = "medium"
     output_format: Literal["png", "jpeg", "webp"] = "png"
     response_format: Literal["url", "b64_json"] | None = "b64_json"
-    size: ImageSize = "auto"
+    size: str | None = "1024x1024"
     image_strength: float | None = 0.7
     stream: bool = False
     partial_images: int | None = 0
     advanced_params: AdvancedImageParams | None = None
     bench: bool = False
 
-    @field_validator("size", mode="before")
-    @classmethod
-    def normalize_size(cls, v: object) -> ImageSize:
-        return normalize_image_size(v)
-
     def __repr_args__(self) -> Generator[tuple[str, Any], None, None]:
         for name, value in super().__repr_args__():  # pyright: ignore[reportAny]
             if name == "image_data":

src/exo/shared/types/commands.py

@@ -6,7 +6,8 @@ from exo.shared.types.api import (
     ImageGenerationTaskParams,
 )
 from exo.shared.types.chunks import InputImageChunk
-from exo.shared.types.common import CommandId, NodeId
+from exo.shared.types.common import CommandId, MetaInstanceId, NodeId
+from exo.shared.types.meta_instance import MetaInstance
 from exo.shared.types.text_generation import TextGenerationTaskParams
 from exo.shared.types.worker.instances import Instance, InstanceId, InstanceMeta
 from exo.shared.types.worker.shards import Sharding, ShardMetadata
@@ -48,6 +49,14 @@ class DeleteInstance(BaseCommand):
     instance_id: InstanceId
 
 
+class CreateMetaInstance(BaseCommand):
+    meta_instance: MetaInstance
+
+
+class DeleteMetaInstance(BaseCommand):
+    meta_instance_id: MetaInstanceId
+
+
 class TaskCancelled(BaseCommand):
     cancelled_command_id: CommandId
 
@@ -93,6 +102,8 @@ Command = (
     | PlaceInstance
     | CreateInstance
     | DeleteInstance
+    | CreateMetaInstance
+    | DeleteMetaInstance
     | TaskCancelled
     | TaskFinished
     | SendInputChunk

src/exo/shared/types/common.py

@@ -42,6 +42,10 @@ class CommandId(Id):
     pass
 
 
+class MetaInstanceId(Id):
+    """Identifier for a MetaInstance."""
+
+
 class Host(CamelCaseModel):
     ip: str
     port: int

src/exo/shared/types/events.py

@@ -1,11 +1,14 @@
+import base64
+from collections.abc import Mapping
 from datetime import datetime
-from typing import final
+from typing import Annotated, final
 
-from pydantic import Field
+from pydantic import BeforeValidator, Field, PlainSerializer
 
 from exo.shared.topology import Connection
 from exo.shared.types.chunks import GenerationChunk, InputImageChunk
-from exo.shared.types.common import CommandId, Id, NodeId, SessionId
+from exo.shared.types.common import CommandId, Id, MetaInstanceId, NodeId, SessionId
+from exo.shared.types.meta_instance import MetaInstance
 from exo.shared.types.tasks import Task, TaskId, TaskStatus
 from exo.shared.types.worker.downloads import DownloadProgress
 from exo.shared.types.worker.instances import Instance, InstanceId
@@ -14,6 +17,28 @@ from exo.utils.info_gatherer.info_gatherer import GatheredInfo
 from exo.utils.pydantic_ext import CamelCaseModel, FrozenModel, TaggedModel
 
 
+def _decode_base64_bytes(v: bytes | str) -> bytes:
+    if isinstance(v, bytes):
+        return v
+    return base64.b64decode(v)
+
+
+def _encode_base64_bytes(v: bytes) -> str:
+    return base64.b64encode(v).decode("ascii")
+
+
+Base64Bytes = Annotated[
+    bytes,
+    BeforeValidator(_decode_base64_bytes),
+    PlainSerializer(_encode_base64_bytes, return_type=str),
+]
+"""bytes that serialize to/from base64 strings in JSON.
+
+Needed because TaggedModel's wrap validator converts JSON→Python validation
+context, which breaks strict-mode bytes deserialization from JSON strings.
+"""
+
+
 class EventId(Id):
     """
     Newtype around `ID`
@@ -66,6 +91,30 @@ class InstanceCreated(BaseEvent):
 
 class InstanceDeleted(BaseEvent):
     instance_id: InstanceId
+    failure_error: str | None = None
+
+
+class MetaInstanceCreated(BaseEvent):
+    meta_instance: MetaInstance
+
+
+class MetaInstanceDeleted(BaseEvent):
+    meta_instance_id: MetaInstanceId
+
+
+@final
+class MetaInstancePlacementFailed(BaseEvent):
+    meta_instance_id: MetaInstanceId
+    reason: str
+
+
+@final
+class InstanceRetrying(BaseEvent):
+    """Runners failed but retry count is below the limit — restart runners, keep instance."""
+
+    instance_id: InstanceId
+    meta_instance_id: MetaInstanceId
+    failure_error: str
 
 
 class RunnerStatusUpdated(BaseEvent):
@@ -132,6 +181,25 @@ class TracesMerged(BaseEvent):
     traces: list[TraceEventData]
 
 
+@final
+class JacclSideChannelData(BaseEvent):
+    """A runner's local contribution to a JACCL SideChannel all_gather round."""
+
+    instance_id: InstanceId
+    runner_id: RunnerId
+    sequence: int
+    data: Base64Bytes
+
+
+@final
+class JacclSideChannelGathered(BaseEvent):
+    """Gathered result of a JACCL SideChannel all_gather round."""
+
+    instance_id: InstanceId
+    sequence: int
+    gathered_data: Mapping[RunnerId, Base64Bytes]
+
+
 Event = (
     TestEvent
     | TaskCreated
@@ -141,6 +209,10 @@ Event = (
     | TaskAcknowledged
     | InstanceCreated
     | InstanceDeleted
+    | InstanceRetrying
+    | MetaInstanceCreated
+    | MetaInstanceDeleted
+    | MetaInstancePlacementFailed
     | RunnerStatusUpdated
     | RunnerDeleted
     | NodeTimedOut
@@ -152,6 +224,8 @@ Event = (
     | TopologyEdgeDeleted
     | TracesCollected
     | TracesMerged
+    | JacclSideChannelData
+    | JacclSideChannelGathered
 )
 
 

src/exo/shared/types/meta_instance.py

@@ -0,0 +1,25 @@
+from typing import final
+
+from pydantic import Field
+
+from exo.shared.models.model_cards import ModelId
+from exo.shared.types.common import MetaInstanceId, NodeId
+from exo.shared.types.worker.instances import InstanceMeta
+from exo.shared.types.worker.shards import Sharding
+from exo.utils.pydantic_ext import FrozenModel
+
+
+@final
+class MetaInstance(FrozenModel):
+    """Declarative constraint: ensure an instance matching these parameters always exists."""
+
+    meta_instance_id: MetaInstanceId = Field(default_factory=MetaInstanceId)
+    model_id: ModelId
+    sharding: Sharding = Sharding.Pipeline
+    instance_meta: InstanceMeta = InstanceMeta.MlxRing
+    min_nodes: int = 1
+    node_ids: list[NodeId] | None = None
+    # Failure tracking
+    placement_error: str | None = None
+    consecutive_failures: int = 0
+    last_failure_error: str | None = None

src/exo/shared/types/state.py

@@ -6,7 +6,8 @@ from pydantic import ConfigDict, Field, field_serializer, field_validator
 from pydantic.alias_generators import to_camel
 
 from exo.shared.topology import Topology, TopologySnapshot
-from exo.shared.types.common import NodeId
+from exo.shared.types.common import MetaInstanceId, NodeId
+from exo.shared.types.meta_instance import MetaInstance
 from exo.shared.types.profiling import (
     DiskUsage,
     MemoryUsage,
@@ -41,6 +42,7 @@ class State(CamelCaseModel):
         arbitrary_types_allowed=True,
     )
     instances: Mapping[InstanceId, Instance] = {}
+    meta_instances: Mapping[MetaInstanceId, MetaInstance] = {}
     runners: Mapping[RunnerId, RunnerStatus] = {}
     downloads: Mapping[NodeId, Sequence[DownloadProgress]] = {}
     tasks: Mapping[TaskId, Task] = {}

src/exo/shared/types/worker/downloads.py

@@ -26,7 +26,6 @@ class DownloadProgressData(CamelCaseModel):
 class BaseDownloadProgress(TaggedModel):
     node_id: NodeId
     shard_metadata: ShardMetadata
-    model_directory: str = ""
 
 
 class DownloadPending(BaseDownloadProgress):

src/exo/shared/types/worker/instances.py

@@ -2,7 +2,7 @@ from enum import Enum
 
 from pydantic import model_validator
 
-from exo.shared.types.common import Host, Id, NodeId
+from exo.shared.types.common import Host, Id, MetaInstanceId, NodeId
 from exo.shared.types.worker.runners import RunnerId, ShardAssignments, ShardMetadata
 from exo.utils.pydantic_ext import CamelCaseModel, TaggedModel
 
@@ -19,6 +19,7 @@ class InstanceMeta(str, Enum):
 class BaseInstance(TaggedModel):
     instance_id: InstanceId
     shard_assignments: ShardAssignments
+    meta_instance_id: MetaInstanceId | None = None
 
     def shard(self, runner_id: RunnerId) -> ShardMetadata | None:
         return self.shard_assignments.runner_to_shard.get(runner_id, None)

src/exo/utils/banner.py

@@ -1,7 +1,5 @@
-import sys
-
-
 def print_startup_banner(port: int) -> None:
+    """Print a prominent startup banner with API endpoint information."""
     dashboard_url = f"http://localhost:{port}"
     banner = f"""
 ╔═══════════════════════════════════════════════════════════════════════╗
@@ -29,4 +27,4 @@ def print_startup_banner(port: int) -> None:
 
 """
 
-    print(banner, file=sys.stderr)
+    print(banner)

src/exo/utils/keyed_backoff.py

@@ -1,8 +1,10 @@
 import time
-from collections.abc import Hashable
+from typing import Generic, TypeVar
+
+K = TypeVar("K")
 
 
-class KeyedBackoff[K: Hashable]:
+class KeyedBackoff(Generic[K]):
     """Tracks exponential backoff state per key."""
 
     def __init__(self, base: float = 0.5, cap: float = 10.0):

src/exo/worker/engines/image/generate.py

@@ -14,7 +14,6 @@ from exo.shared.types.api import (
     ImageEditsTaskParams,
     ImageGenerationStats,
     ImageGenerationTaskParams,
-    ImageSize,
 )
 from exo.shared.types.memory import Memory
 from exo.shared.types.worker.runner_response import (
@@ -24,9 +23,9 @@ from exo.shared.types.worker.runner_response import (
 from exo.worker.engines.image.distributed_model import DistributedImageModel
 
 
-def parse_size(size_str: ImageSize) -> tuple[int, int]:
+def parse_size(size_str: str | None) -> tuple[int, int]:
     """Parse size parameter like '1024x1024' to (width, height) tuple."""
-    if size_str == "auto":
+    if not size_str:
         return (1024, 1024)
 
     try:
@@ -110,9 +109,6 @@ def generate_image(
             # Decode base64 image data and save to temp file
             image_path = Path(tmpdir) / "input.png"
             image_path.write_bytes(base64.b64decode(task.image_data))
-            if task.size == "auto":
-                with Image.open(image_path) as img:
-                    width, height = img.size
 
         for image_num in range(num_images):
             # Increment seed for each image to ensure unique results

src/exo/worker/engines/mlx/auto_parallel.py

@@ -163,14 +163,11 @@ class PipelineLastLayer(CustomMlxLayer):
                 output, (self.r + 1) % self.s, group=self.group
             )
             if cache is not None:
-                # CacheList (used by MLA models like DeepSeekV32, GLM MoE DSA)
-                # doesn't have .keys directly; access via first sub-cache.
-                _cache = cache[0] if hasattr(cache, "caches") else cache  # type: ignore
-                _cache.keys = mx.depends(_cache.keys, output)  # type: ignore
+                cache.keys = mx.depends(cache.keys, output)  # type: ignore[reportUnknownMemberType]
             if self.is_prefill:
                 mx.eval(output)
                 if cache is not None:
-                    mx.eval(_cache.keys)  # type: ignore
+                    mx.eval(cache.keys)  # type: ignore
 
         if not self.is_prefill:
             output = mx.distributed.all_gather(output, group=self.group)[
@@ -310,9 +307,7 @@ def patch_pipeline_model[T](model: T, group: mx.distributed.Group) -> T:
 
         # Add dependency to last cache entry to ensure distributed ops are evaluated
         if cache is not None:
-            last = cache[-1]  # type: ignore
-            dep_cache = last[0] if hasattr(last, "caches") else last  # type: ignore
-            dep_cache.keys = mx.depends(dep_cache.keys, logits)  # type: ignore
+            cache[-1].state = mx.depends(cache[-1].state, logits)  # type: ignore
 
         return logits
 
@@ -338,9 +333,7 @@ def patch_tensor_model[T](model: T) -> T:
 
         # Add dependency to last cache entry to ensure distributed ops are evaluated
         if cache is not None and len(cache) > 0:  # pyright: ignore[reportAny]
-            last = cache[-1]  # pyright: ignore[reportAny]
-            dep_cache = last[0] if hasattr(last, "caches") else last  # pyright: ignore[reportAny]
-            dep_cache.keys = mx.depends(dep_cache.keys, logits)  # pyright: ignore[reportAny,reportUnknownMemberType]
+            cache[-1].state = mx.depends(cache[-1].state, logits)  # pyright: ignore[reportAny,reportUnknownMemberType]
 
         return logits
 
@@ -554,12 +547,10 @@ class DeepSeekShardingStrategy(TensorParallelShardingStrategy):
         on_timeout: TimeoutCallback | None,
     ) -> nn.Module:
         model = cast(DeepseekV3Model, model)
-
         for layer in model.layers:
             eval_with_timeout(
                 layer.parameters(), timeout_seconds / len(model.layers), on_timeout
             )
-
             # Shard the self attention
             if layer.self_attn.q_lora_rank is None:
                 layer.self_attn.q_proj = self.all_to_sharded_linear(
@@ -590,18 +581,12 @@ class DeepSeekShardingStrategy(TensorParallelShardingStrategy):
                 layer.mlp.down_proj = self.sharded_to_all_linear(layer.mlp.down_proj)
                 layer.mlp.up_proj = self.all_to_sharded_linear(layer.mlp.up_proj)
 
-            # Shard the MoE.
+            # Shard the MoE. Shard in place since the MoE should be responsible
+            # for aggregating the results.
             else:
-                if getattr(layer.mlp, "shared_experts", None) is not None:
-                    self.all_to_sharded_linear_in_place(
-                        layer.mlp.shared_experts.gate_proj
-                    )
-                    self.sharded_to_all_linear_in_place(
-                        layer.mlp.shared_experts.down_proj
-                    )
-                    self.all_to_sharded_linear_in_place(
-                        layer.mlp.shared_experts.up_proj
-                    )
+                self.all_to_sharded_linear_in_place(layer.mlp.shared_experts.gate_proj)
+                self.sharded_to_all_linear_in_place(layer.mlp.shared_experts.down_proj)
+                self.all_to_sharded_linear_in_place(layer.mlp.shared_experts.up_proj)
                 self.all_to_sharded_linear_in_place(layer.mlp.switch_mlp.gate_proj)
                 self.sharded_to_all_linear_in_place(layer.mlp.switch_mlp.down_proj)
                 self.all_to_sharded_linear_in_place(layer.mlp.switch_mlp.up_proj)
@@ -794,7 +779,8 @@ class MiniMaxShardingStrategy(TensorParallelShardingStrategy):
 
             layer.self_attn = WrappedMiniMaxAttention(layer.self_attn, self.group)  # pyright: ignore[reportAttributeAccessIssue,reportArgumentType]
 
-            # Shard the MoE.
+            # Shard the MoE. Shard in place since the MoE should be responsible
+            # for aggregating the results.
             self.all_to_sharded_linear_in_place(
                 layer.block_sparse_moe.switch_mlp.gate_proj
             )
@@ -907,7 +893,8 @@ class QwenShardingStrategy(TensorParallelShardingStrategy):
                     layer.self_attn.num_attention_heads //= self.N
                     layer.self_attn.num_key_value_heads //= self.N
 
-            # Shard the MoE.
+            # Shard the MoE. Shard in place since the MoE should be responsible
+            # for aggregating the results.
             if isinstance(layer.mlp, (Qwen3MoeSparseMoeBlock, Qwen3NextSparseMoeBlock)):
                 self.all_to_sharded_linear_in_place(layer.mlp.switch_mlp.gate_proj)
                 self.sharded_to_all_linear_in_place(layer.mlp.switch_mlp.down_proj)

src/exo/worker/engines/mlx/generator/generate.py

@@ -57,7 +57,6 @@ def prefill(
     sampler: Callable[[mx.array], mx.array],
     prompt_tokens: mx.array,
     cache: KVCacheType,
-    group: mx.distributed.Group | None = None,
 ) -> tuple[float, int, list[CacheSnapshot]]:
     """Prefill the KV cache with prompt tokens.
 
@@ -87,9 +86,6 @@ def prefill(
 
     set_pipeline_prefill(model, is_prefill=True)
 
-    mx_barrier(group)
-    logger.info("Starting prefill")
-
     # Use max_tokens=1 because max_tokens=0 does not work.
     # We just throw away the generated token - we only care about filling the cache
     for _ in stream_generate(
@@ -309,9 +305,16 @@ def mlx_generate(
     )
     max_stop_len = max((len(s) for s in stop_sequences), default=0)
 
+    mx_barrier(group)
+    logger.info("Ready to prefill")
+
     # Prefill cache with all tokens except the last one
     prefill_tps, prefill_tokens, ssm_snapshots_list = prefill(
-        model, tokenizer, sampler, prompt_tokens[:-1], caches, group
+        model,
+        tokenizer,
+        sampler,
+        prompt_tokens[:-1],
+        caches,
     )
     cache_snapshots: list[CacheSnapshot] | None = ssm_snapshots_list or None
 
@@ -328,7 +331,6 @@ def mlx_generate(
     think_start = tokenizer.think_start
     think_end = tokenizer.think_end
 
-    logger.info("Starting decode")
     mx_barrier(group)
 
     for completion_tokens, out in enumerate(

src/exo/worker/engines/mlx/utils_mlx.py

@@ -285,12 +285,10 @@ def get_eos_token_ids_for_model(model_id: ModelId) -> list[int] | None:
     model_id_lower = model_id.lower()
     if "kimi-k2" in model_id_lower:
         return [163586]
-    elif "glm-5" in model_id_lower or "glm-4.7" in model_id_lower:
-        # For GLM-5 and GLM-4.7
+    elif "glm-4.7-flash" in model_id_lower:
         # 154820: <|endoftext|>, 154827: <|user|>, 154829: <|observation|>
         return [154820, 154827, 154829]
     elif "glm" in model_id_lower:
-        # For GLM-4.5 and older
         return [151336, 151329, 151338]
     return None
 
@@ -355,13 +353,7 @@ def load_tokenizer_for_model_id(
             return list(hf_tokenizer.model.encode(text, allowed_special="all"))  # pyright: ignore[reportUnknownMemberType,reportUnknownArgumentType]
 
         hf_tokenizer.encode = _patched_encode
-        return TokenizerWrapper(
-            hf_tokenizer,
-            eos_token_ids=eos_token_ids,
-            tool_call_start="<|tool_calls_section_begin|>",
-            tool_call_end="<|tool_calls_section_end|>",
-            tool_parser=_parse_kimi_tool_calls,
-        )
+        return TokenizerWrapper(hf_tokenizer, eos_token_ids=eos_token_ids)
 
     tokenizer = load_tokenizer(
         model_path,
@@ -593,41 +585,3 @@ def mx_barrier(group: Group | None):
             mx.array(1.0), group=group, stream=mx.default_stream(mx.Device(mx.cpu))
         )
     )
-
-
-def _parse_kimi_tool_calls(text: str):
-    import regex as re
-
-    # kimi has a fixed function naming scheme, with a json formatted arg
-    #   functions.multiply:0<|tool_call_argument_begin|>{"a": 2, "b": 3}
-    _func_name_regex = re.compile(
-        r"^\s*((?:functions\.)?(.+?):\d+)\s*<\|tool_call_argument_begin\|>", re.DOTALL
-    )
-    _func_arg_regex = re.compile(r"<\|tool_call_argument_begin\|>\s*(.*)\s*", re.DOTALL)
-    _tool_call_split_regex = re.compile(
-        r"<\|tool_call_begin\|>(.*?)<\|tool_call_end\|>", re.DOTALL
-    )
-
-    def _parse_single_tool(text: str) -> dict[str, Any]:
-        func_name_match = _func_name_regex.search(text)
-        if func_name_match is None:
-            raise ValueError("No tool call found.")
-        tool_call_id = func_name_match.group(1)  # e.g. "functions.get_weather:0"
-        func_name = func_name_match.group(2)  # e.g. "get_weather"
-
-        func_args_match = _func_arg_regex.search(text)
-        if func_args_match is None:
-            raise ValueError("No tool call arguments found.")
-        func_args = func_args_match.group(1)
-        try:
-            arg_dct = json.loads(func_args)  # pyright: ignore[reportAny]
-        except Exception:
-            arg_dct = None
-
-        return dict(id=tool_call_id, name=func_name, arguments=arg_dct)
-
-    tool_matches = _tool_call_split_regex.findall(text)
-    if tool_matches:
-        return [_parse_single_tool(match) for match in tool_matches]  # pyright: ignore[reportAny]
-    else:
-        return [_parse_single_tool(text)]

src/exo/worker/main.py

@@ -24,6 +24,7 @@ from exo.shared.types.events import (
     ForwarderEvent,
     IndexedEvent,
     InputChunkReceived,
+    JacclSideChannelGathered,
     NodeGatheredInfo,
     TaskCreated,
     TaskStatusUpdated,
@@ -159,6 +160,15 @@ class Worker:
                 for idx, event in indexed_events:
                     self.state = apply(self.state, IndexedEvent(idx=idx, event=event))
 
+                    # Dispatch JACCL gathered events to the relevant RunnerSupervisor
+                    if isinstance(event, JacclSideChannelGathered):
+                        for runner in self.runners.values():
+                            if (
+                                runner.bound_instance.instance.instance_id
+                                == event.instance_id
+                            ):
+                                runner.notify_gathered(event)
+
                     # Buffer input image chunks for image editing
                     if isinstance(event, InputChunkReceived):
                         cmd_id = event.command_id

src/exo/worker/plan.py

@@ -35,6 +35,7 @@ from exo.shared.types.worker.runners import (
     RunnerLoading,
     RunnerReady,
     RunnerRunning,
+    RunnerShutdown,
     RunnerStatus,
     RunnerWarmingUp,
 )
@@ -56,7 +57,7 @@ def plan(
     return (
         _cancel_tasks(runners, tasks)
         or _kill_runner(runners, all_runners, instances)
-        or _create_runner(node_id, runners, instances)
+        or _create_runner(node_id, runners, instances, all_runners)
         or _model_needs_download(node_id, runners, global_download_status)
         or _init_distributed_backend(runners, all_runners)
         or _load_model(runners, all_runners, global_download_status)
@@ -75,6 +76,12 @@ def _kill_runner(
         if (instance_id := runner.bound_instance.instance.instance_id) not in instances:
             return Shutdown(instance_id=instance_id, runner_id=runner_id)
 
+        # Master removed our runner from state (retry signal) and process is dead
+        if runner_id not in all_runners and isinstance(
+            runner.status, (RunnerFailed, RunnerShutdown)
+        ):
+            return Shutdown(instance_id=instance_id, runner_id=runner_id)
+
         for (
             global_runner_id
         ) in runner.bound_instance.instance.shard_assignments.node_to_runner.values():
@@ -92,6 +99,7 @@ def _create_runner(
     node_id: NodeId,
     runners: Mapping[RunnerId, RunnerSupervisor],
     instances: Mapping[InstanceId, Instance],
+    all_runners: Mapping[RunnerId, RunnerStatus],
 ) -> CreateRunner | None:
     for instance in instances.values():
         runner_id = instance.shard_assignments.node_to_runner.get(node_id, None)
@@ -101,6 +109,16 @@ def _create_runner(
         if runner_id in runners:
             continue
 
+        # Don't create while any peer runner is in a terminal state — wait for
+        # the master to emit InstanceRetrying which removes them from state.
+        has_terminal_peer = any(
+            isinstance(all_runners.get(peer_rid), (RunnerFailed, RunnerShutdown))
+            for peer_rid in instance.shard_assignments.node_to_runner.values()
+            if peer_rid != runner_id
+        )
+        if has_terminal_peer:
+            continue
+
         shard = instance.shard(runner_id)
         assert shard is not None
 

src/exo/worker/runner/bootstrap.py

@@ -17,6 +17,7 @@ def entrypoint(
     task_receiver: MpReceiver[Task],
     cancel_receiver: MpReceiver[TaskId],
     _logger: "loguru.Logger",
+    pipe_fifo_paths: tuple[str, str] | None = None,
 ) -> None:
     fast_synch_override = os.environ.get("EXO_FAST_SYNCH")
     if fast_synch_override == "on" or (
@@ -30,6 +31,16 @@ def entrypoint(
     else:
         os.environ["MLX_METAL_FAST_SYNCH"] = "0"
 
+    # Open JACCL FIFOs by path and set env vars for C++ SideChannel.
+    # Named pipes (FIFOs) work across multiprocessing spawn (macOS default).
+    if pipe_fifo_paths is not None:
+        fifo_c2p, fifo_p2c = pipe_fifo_paths
+        # C++ reads gathered data from p2c (PIPE_IN), writes local data to c2p (PIPE_OUT)
+        pipe_in_fd = os.open(fifo_p2c, os.O_RDONLY)
+        pipe_out_fd = os.open(fifo_c2p, os.O_WRONLY)
+        os.environ["MLX_JACCL_PIPE_IN"] = str(pipe_in_fd)
+        os.environ["MLX_JACCL_PIPE_OUT"] = str(pipe_out_fd)
+
     global logger
     logger = _logger
 

src/exo/worker/runner/runner.py

@@ -1,10 +1,11 @@
 import base64
+import json
 import math
 import resource
 import time
 from collections.abc import Generator
 from functools import cache
-from typing import Literal
+from typing import Any, Callable, Literal
 
 import mlx.core as mx
 from mlx_lm.models.gpt_oss import Model as GptOssModel
@@ -15,6 +16,7 @@ from openai_harmony import (  # pyright: ignore[reportMissingTypeStubs]
     StreamableParser,
     load_harmony_encoding,
 )
+from pydantic import ValidationError
 
 from exo.shared.constants import EXO_MAX_CHUNK_SIZE, EXO_TRACING_ENABLED
 from exo.shared.models.model_cards import ModelId, ModelTask
@@ -91,8 +93,6 @@ from exo.worker.engines.mlx.utils_mlx import (
 )
 from exo.worker.runner.bootstrap import logger
 
-from .tool_parsers import ToolParser, make_mlx_parser
-
 
 def _is_primary_output_node(shard_metadata: ShardMetadata) -> bool:
     """Check if this node is the primary output node for image generation.
@@ -138,7 +138,6 @@ def main(
     inference_model: Model | None = None
     image_model: DistributedImageModel | None = None
     tokenizer = None
-    tool_parser: ToolParser | None = None
     group = None
     kv_prefix_cache: KVPrefixCache | None = None
     check_for_cancel_every: int | None = None
@@ -204,17 +203,8 @@ def main(
                             bound_instance, group, on_timeout=on_model_load_timeout
                         )
                         logger.info(
-                            f"model has_tool_calling={tokenizer.has_tool_calling} using tokens {tokenizer.tool_call_start}, {tokenizer.tool_call_end}"
+                            f"model has_tool_calling={tokenizer.has_tool_calling}"
                         )
-                        if tokenizer.has_tool_calling:
-                            assert tokenizer.tool_call_start
-                            assert tokenizer.tool_call_end
-                            assert tokenizer.tool_parser  # pyright: ignore[reportAny]
-                            tool_parser = make_mlx_parser(
-                                tokenizer.tool_call_start,
-                                tokenizer.tool_call_end,
-                                tokenizer.tool_parser,  # pyright: ignore[reportAny]
-                            )
                         kv_prefix_cache = KVPrefixCache(group)
 
                     elif (
@@ -320,11 +310,31 @@ def main(
                                 mlx_generator, tokenizer
                             )
 
+                        # Kimi-K2 has tool call sections - we don't care about them
+                        if "kimi" in shard_metadata.model_card.model_id.lower():
+                            mlx_generator = filter_kimi_tokens(mlx_generator)
+                            patch_kimi_tokenizer(tokenizer)
+
+                        # GLM models need patched parser (upstream has bug with None regex match)
+                        elif "glm" in shard_metadata.model_card.model_id.lower():
+                            patch_glm_tokenizer(tokenizer)
+
                         # GPT-OSS specific parsing to match other model formats.
-                        if isinstance(inference_model, GptOssModel):
+                        elif isinstance(inference_model, GptOssModel):
                             mlx_generator = parse_gpt_oss(mlx_generator)
-                        elif tool_parser:
-                            mlx_generator = parse_tool_calls(mlx_generator, tool_parser)
+
+                        if tokenizer.has_tool_calling and not isinstance(
+                            inference_model, GptOssModel
+                        ):
+                            assert tokenizer.tool_call_start
+                            assert tokenizer.tool_call_end
+                            assert tokenizer.tool_parser  # pyright: ignore[reportAny]
+                            mlx_generator = parse_tool_calls(
+                                mlx_generator,
+                                tokenizer.tool_call_start,
+                                tokenizer.tool_call_end,
+                                tokenizer.tool_parser,  # pyright: ignore[reportAny]
+                            )
 
                         completion_tokens = 0
                         tokens_since_last_cancel_check = 0
@@ -577,8 +587,21 @@ def get_gpt_oss_encoding():
     return encoding
 
 
+def filter_kimi_tokens(
+    responses: Generator[GenerationResponse | ToolCallResponse],
+) -> Generator[GenerationResponse]:
+    for resp in responses:
+        assert isinstance(resp, GenerationResponse)
+        if (
+            resp.text == "<|tool_calls_section_begin|>"
+            or resp.text == "<|tool_calls_section_end|>"
+        ):
+            continue
+        yield resp
+
+
 def parse_gpt_oss(
-    responses: Generator[GenerationResponse],
+    responses: Generator[GenerationResponse | ToolCallResponse],
 ) -> Generator[GenerationResponse | ToolCallResponse]:
     encoding = get_gpt_oss_encoding()
     stream = StreamableParser(encoding, role=Role.ASSISTANT)
@@ -635,9 +658,9 @@ def parse_gpt_oss(
 
 
 def parse_thinking_models(
-    responses: Generator[GenerationResponse],
+    responses: Generator[GenerationResponse | ToolCallResponse],
     tokenizer: TokenizerWrapper,
-) -> Generator[GenerationResponse]:
+) -> Generator[GenerationResponse | ToolCallResponse]:
     """
     For models that inject thinking tags in the prompt (like GLM-4.7),
     prepend the thinking tag to the output stream so the frontend
@@ -758,55 +781,221 @@ def _process_image_response(
 
 
 def parse_tool_calls(
-    responses: Generator[GenerationResponse], tool_parser: ToolParser
+    responses: Generator[GenerationResponse | ToolCallResponse],
+    tool_call_start: str,
+    tool_call_end: str,
+    tool_parser: Callable[[str], dict[str, Any] | list[dict[str, Any]]],
 ) -> Generator[GenerationResponse | ToolCallResponse]:
     in_tool_call = False
     tool_call_text_parts: list[str] = []
     for response in responses:
-        if response.text.startswith(tool_parser.start_parsing):
+        assert isinstance(response, GenerationResponse)
+        # assumption: the tool call start is one token
+        if response.text == tool_call_start:
             in_tool_call = True
-
-        if in_tool_call:
-            tool_call_text_parts.append(response.text)
-            if response.text.endswith(tool_parser.end_parsing):
-                # parse the actual tool calls from the tool call text
-                parsed = tool_parser.parse_tool_calls(
-                    "".join(tool_call_text_parts).strip()
-                )
+            continue
+        # assumption: the tool call end is one token
+        if in_tool_call and response.text == tool_call_end:
+            try:
+                # tool_parser returns an arbitrarily nested python dictionary
+                # we actually don't want the python dictionary, we just want to
+                # parse the top level { function: ..., arguments: ... } structure
+                # as we're just gonna hand it back to the api anyway
+                parsed = tool_parser("".join(tool_call_text_parts).strip())
                 logger.info(f"parsed {tool_call_text_parts=} into {parsed=}")
-                if parsed is not None:
-                    yield ToolCallResponse(
-                        tool_calls=parsed, usage=response.usage, stats=response.stats
-                    )
+                if isinstance(parsed, list):
+                    tools = [_validate_single_tool(tool) for tool in parsed]
                 else:
-                    logger.warning(
-                        f"tool call parsing failed for text {''.join(tool_call_text_parts)}"
-                    )
-                    response.text = "".join(tool_call_text_parts)
-                    yield response
-
-                in_tool_call = False
-                tool_call_text_parts = []
-                continue
-
-            if response.finish_reason is not None:
-                logger.info(
-                    "tool call parsing interrupted, yield partial tool call as text"
+                    tools = [_validate_single_tool(parsed)]
+                yield ToolCallResponse(
+                    tool_calls=tools, usage=response.usage, stats=response.stats
                 )
-                response = response.model_copy(
-                    update={
-                        "text": "".join(tool_call_text_parts),
-                        "token": 0,
-                    }
+
+            except (
+                json.JSONDecodeError,
+                ValidationError,
+                ValueError,
+                AttributeError,
+            ) as e:
+                # ValueError: our parsers raise this for malformed tool calls
+                # AttributeError: upstream parsers (e.g. glm47) may raise this when regex doesn't match
+                logger.opt(exception=e).warning("tool call parsing failed")
+                # assumption: talking about tool calls, not making a tool call
+                response.text = (
+                    tool_call_start + "".join(tool_call_text_parts) + tool_call_end
                 )
                 yield response
 
+            in_tool_call = False
+            tool_call_text_parts = []
             continue
 
+        if in_tool_call:
+            tool_call_text_parts.append(response.text)
+            if response.finish_reason is not None:
+                logger.info(
+                    "toll call parsing interrupted, yield partial tool call as text"
+                )
+                yield GenerationResponse(
+                    text=tool_call_start + "".join(tool_call_text_parts),
+                    token=0,
+                    finish_reason=response.finish_reason,
+                    usage=response.usage,
+                    stats=response.stats,
+                )
+            continue
         # fallthrough
         yield response
 
 
+def patch_kimi_tokenizer(tokenizer: TokenizerWrapper):
+    """
+    Version of to-be-upstreamed kimi-k2 tool parser
+    """
+    import ast
+    import json
+    from typing import Any
+
+    import regex as re
+
+    # kimi has a fixed function naming scheme, with a json formatted arg
+    #   functions.multiply:0 <|tool_call_argument_begin|> {"a": 2, "b": 3}
+    #   Also needs to handle tools like call_0<|tool_call_argument_begin|>{"filePath": "..."}
+    _func_name_regex = re.compile(
+        r"^\s*(.+)[:](\d+)\s*<\|tool_call_argument_begin\|>", re.DOTALL
+    )
+    _func_arg_regex = re.compile(r"<\|tool_call_argument_begin\|>\s*(.*)\s*", re.DOTALL)
+
+    # kimi has a tool_calls_section - we're leaving this up to the caller to handle
+    tool_call_start = "<|tool_call_begin|>"
+    tool_call_end = "<|tool_call_end|>"
+
+    def _deserialize(value: str) -> Any:  # pyright: ignore[reportAny]
+        try:
+            return json.loads(value)  # pyright: ignore[reportAny]
+        except Exception:
+            pass
+
+        try:
+            return ast.literal_eval(value)  # pyright: ignore[reportAny]
+        except Exception:
+            pass
+        return value
+
+    def parse_tool_call(text: str, tools: Any | None = None):
+        func_name_match = _func_name_regex.search(text)
+        if func_name_match is None:
+            raise ValueError(f"Could not parse function name from tool call: {text!r}")
+        original_func_name = func_name_match.group(1)
+        tool_id = func_name_match.group(2)
+        # strip off the `functions.` prefix, if it exists.
+        func_name = original_func_name[original_func_name.find(".") + 1 :]
+
+        func_args_match = _func_arg_regex.search(text)
+        if func_args_match is None:
+            raise ValueError(f"Could not parse function args from tool call: {text!r}")
+        func_args = func_args_match.group(1)
+        # the args should be valid json - no need to check against our tools to deserialize
+        arg_dct = _deserialize(func_args)  # pyright: ignore[reportAny]
+
+        return dict(
+            id=f"{original_func_name}:{tool_id}",
+            name=func_name,
+            arguments=arg_dct,  # pyright: ignore[reportAny]
+        )
+
+    tokenizer._tool_call_start = tool_call_start
+    tokenizer._tool_call_end = tool_call_end
+    tokenizer._tool_parser = parse_tool_call
+
+
+def patch_glm_tokenizer(tokenizer: TokenizerWrapper):
+    """
+    Fixed version of mlx_lm's glm47 tool parser that handles regex match failures.
+    """
+    import ast
+    import json
+    from typing import Any
+
+    import regex as re
+
+    _func_name_regex = re.compile(r"^(.*?)<arg_key>", re.DOTALL)
+    _func_arg_regex = re.compile(
+        r"<arg_key>(.*?)</arg_key>(?:\n|\s)*<arg_value>(.*?)(?:</arg_value>|(?=<arg_key>)|$)",
+        re.DOTALL,
+    )
+
+    tool_call_start = "<tool_call>"
+    tool_call_end = "</tool_call>"
+
+    def _is_string_type(
+        tool_name: str,
+        arg_name: str,
+        tools: list[Any] | None,
+    ) -> bool:
+        if tools is None:
+            return False
+        for tool in tools:  # pyright: ignore[reportAny]
+            func = tool["function"]  # pyright: ignore[reportAny]
+            if func["name"] == tool_name:
+                params = func["parameters"]  # pyright: ignore[reportAny]
+                if params is None:
+                    return False
+                props = params.get("properties", {})  # pyright: ignore[reportAny]
+                arg_props = props.get(arg_name, {})  # pyright: ignore[reportAny]
+                arg_type = arg_props.get("type", None)  # pyright: ignore[reportAny]
+                return arg_type == "string"  # pyright: ignore[reportAny]
+        return False
+
+    def _deserialize(value: str) -> Any:  # pyright: ignore[reportAny]
+        try:
+            return json.loads(value)  # pyright: ignore[reportAny]
+        except Exception:
+            pass
+        try:
+            return ast.literal_eval(value)  # pyright: ignore[reportAny]
+        except Exception:
+            pass
+        return value
+
+    def parse_tool_call(text: str, tools: list[Any] | None = None):
+        func_name_match = _func_name_regex.search(text)
+        if func_name_match is None:
+            raise ValueError(f"Could not parse function name from tool call: {text!r}")
+        func_name = func_name_match.group(1)
+
+        pairs = _func_arg_regex.findall(text)
+        arg_dct: dict[str, Any] = {}
+        for key, value in pairs:  # pyright: ignore[reportAny]
+            arg_key = key.strip()  # pyright: ignore[reportAny]
+            arg_val = value.strip()  # pyright: ignore[reportAny]
+            if not _is_string_type(func_name, arg_key, tools):  # pyright: ignore[reportAny]
+                arg_val = _deserialize(arg_val)  # pyright: ignore[reportAny]
+            arg_dct[arg_key] = arg_val
+        return dict(name=func_name, arguments=arg_dct)
+
+    tokenizer._tool_call_start = tool_call_start
+    tokenizer._tool_call_end = tool_call_end
+    tokenizer._tool_parser = parse_tool_call
+
+
+def _validate_single_tool(obj: dict[str, Any]) -> ToolCallItem:
+    if (
+        ((name := obj.get("name")) is not None)
+        and ((args := obj.get("arguments")) is not None)
+        and isinstance(name, str)
+    ):
+        raw_id: object = obj.get("id")
+        extra = {"id": str(raw_id)} if raw_id is not None else {}
+        return ToolCallItem(
+            **extra,
+            name=name,
+            arguments=json.dumps(args),
+        )
+    else:
+        raise ValidationError
+
+
 EXO_RUNNER_MUST_FAIL = "EXO RUNNER MUST FAIL"
 EXO_RUNNER_MUST_OOM = "EXO RUNNER MUST OOM"
 EXO_RUNNER_MUST_TIMEOUT = "EXO RUNNER MUST TIMEOUT"

src/exo/worker/runner/runner_supervisor.py

@@ -1,6 +1,10 @@
 import contextlib
+import os
 import signal
+import struct
+import tempfile
 from dataclasses import dataclass, field
+from functools import partial
 from multiprocessing import Process
 from typing import Self
 
@@ -14,12 +18,14 @@ from loguru import logger
 
 from exo.shared.types.events import (
     Event,
+    JacclSideChannelData,
+    JacclSideChannelGathered,
     RunnerStatusUpdated,
     TaskAcknowledged,
     TaskStatusUpdated,
 )
 from exo.shared.types.tasks import Task, TaskId, TaskStatus
-from exo.shared.types.worker.instances import BoundInstance
+from exo.shared.types.worker.instances import BoundInstance, MlxJacclInstance
 from exo.shared.types.worker.runners import (
     RunnerConnecting,
     RunnerFailed,
@@ -34,6 +40,26 @@ from exo.shared.types.worker.shards import ShardMetadata
 from exo.utils.channels import MpReceiver, MpSender, Sender, mp_channel
 from exo.worker.runner.bootstrap import entrypoint
 
+
+def _pipe_read_exact(fd: int, n: int) -> bytes | None:
+    """Read exactly n bytes from a file descriptor. Returns None on EOF."""
+    data = b""
+    while len(data) < n:
+        chunk = os.read(fd, n - len(data))
+        if not chunk:
+            return None
+        data += chunk
+    return data
+
+
+def _pipe_write_all(fd: int, data: bytes) -> None:
+    """Write all bytes to a file descriptor."""
+    view = memoryview(data)
+    while view:
+        written = os.write(fd, view)
+        view = view[written:]
+
+
 PREFILL_TIMEOUT_SECONDS = 60
 DECODE_TIMEOUT_SECONDS = 5
 
@@ -48,10 +74,19 @@ class RunnerSupervisor:
     _task_sender: MpSender[Task]
     _event_sender: Sender[Event]
     _cancel_sender: MpSender[TaskId]
+    _pipe_read_fd: int | None = None  # Python reads runner's pipe output
+    _pipe_write_fd: int | None = None  # Python writes gathered data to runner
+    _child_pipe_fds: tuple[int, int] | None = None  # fds to close after fork
+    _fifo_dir: str | None = None  # Temp dir for FIFO files (for cleanup)
+    _fifo_c2p: str | None = None  # FIFO path: C++ writes → Python reads
+    _fifo_p2c: str | None = None  # FIFO path: Python writes → C++ reads
     status: RunnerStatus = field(default_factory=RunnerIdle, init=False)
     pending: dict[TaskId, anyio.Event] = field(default_factory=dict, init=False)
     completed: set[TaskId] = field(default_factory=set, init=False)
     cancelled: set[TaskId] = field(default_factory=set, init=False)
+    _gathered_waiters: dict[
+        int, tuple[anyio.Event, JacclSideChannelGathered | None]
+    ] = field(default_factory=dict, init=False)
 
     @classmethod
     def create(
@@ -65,6 +100,23 @@ class RunnerSupervisor:
         task_sender, task_recv = mp_channel[Task]()
         cancel_sender, cancel_recv = mp_channel[TaskId]()
 
+        # For MlxJaccl instances, create named pipes (FIFOs) for SideChannel relay.
+        # Named pipes work across multiprocessing.Process spawn (macOS default).
+        # FIFO c2p: C++ writes local data → Python reads it
+        # FIFO p2c: Python writes gathered data → C++ reads it
+        fifo_dir: str | None = None
+        fifo_c2p: str | None = None
+        fifo_p2c: str | None = None
+        pipe_fifo_paths: tuple[str, str] | None = None
+
+        if isinstance(bound_instance.instance, MlxJacclInstance):
+            fifo_dir = tempfile.mkdtemp(prefix="exo_jaccl_")
+            fifo_c2p = os.path.join(fifo_dir, "c2p")  # C++ → Python
+            fifo_p2c = os.path.join(fifo_dir, "p2c")  # Python → C++
+            os.mkfifo(fifo_c2p)
+            os.mkfifo(fifo_p2c)
+            pipe_fifo_paths = (fifo_c2p, fifo_p2c)
+
         runner_process = Process(
             target=entrypoint,
             args=(
@@ -73,6 +125,7 @@ class RunnerSupervisor:
                 task_recv,
                 cancel_recv,
                 logger,
+                pipe_fifo_paths,
             ),
             daemon=True,
         )
@@ -88,13 +141,45 @@ class RunnerSupervisor:
             _task_sender=task_sender,
             _cancel_sender=cancel_sender,
             _event_sender=event_sender,
+            _fifo_dir=fifo_dir,
+            _fifo_c2p=fifo_c2p,
+            _fifo_p2c=fifo_p2c,
         )
 
         return self
 
     async def run(self):
         self.runner_process.start()
-        await self._forward_events()
+
+        if self._fifo_c2p is not None and self._fifo_p2c is not None:
+            # Open FIFOs from parent side. These block until child opens the other end,
+            # so we run them in threads concurrently to avoid deadlock.
+            fifo_c2p = self._fifo_c2p
+            fifo_p2c = self._fifo_p2c
+
+            async def open_read() -> None:
+                self._pipe_read_fd = await to_thread.run_sync(
+                    partial(os.open, fifo_c2p, os.O_RDONLY)
+                )
+
+            async def open_write() -> None:
+                self._pipe_write_fd = await to_thread.run_sync(
+                    partial(os.open, fifo_p2c, os.O_WRONLY)
+                )
+
+            async with anyio.create_task_group() as open_tg:
+                open_tg.start_soon(open_read)
+                open_tg.start_soon(open_write)
+
+            logger.info(
+                f"JACCL pipe relay: FIFOs opened (read_fd={self._pipe_read_fd}, write_fd={self._pipe_write_fd})"
+            )
+
+            async with anyio.create_task_group() as tg:
+                tg.start_soon(self._pipe_relay)
+                tg.start_soon(self._forward_events)
+        else:
+            await self._forward_events()
 
     def shutdown(self):
         logger.info("Runner supervisor shutting down")
@@ -103,6 +188,7 @@ class RunnerSupervisor:
         self._event_sender.close()
         self._cancel_sender.send(TaskId("CANCEL_CURRENT_TASK"))
         self._cancel_sender.close()
+        self._close_pipe_fds()
         self.runner_process.join(1)
         if not self.runner_process.is_alive():
             logger.info("Runner process succesfully terminated")
@@ -181,6 +267,110 @@ class RunnerSupervisor:
                 for tid in self.pending:
                     self.pending[tid].set()
 
+    def _close_pipe_fds(self) -> None:
+        if self._pipe_read_fd is not None:
+            with contextlib.suppress(OSError):
+                os.close(self._pipe_read_fd)
+            self._pipe_read_fd = None
+        if self._pipe_write_fd is not None:
+            with contextlib.suppress(OSError):
+                os.close(self._pipe_write_fd)
+            self._pipe_write_fd = None
+        if self._child_pipe_fds is not None:
+            for fd in self._child_pipe_fds:
+                with contextlib.suppress(OSError):
+                    os.close(fd)
+            self._child_pipe_fds = None
+        # Clean up FIFO files
+        if self._fifo_c2p is not None:
+            with contextlib.suppress(OSError):
+                os.unlink(self._fifo_c2p)
+            self._fifo_c2p = None
+        if self._fifo_p2c is not None:
+            with contextlib.suppress(OSError):
+                os.unlink(self._fifo_p2c)
+            self._fifo_p2c = None
+        if self._fifo_dir is not None:
+            with contextlib.suppress(OSError):
+                os.rmdir(self._fifo_dir)
+            self._fifo_dir = None
+
+    async def _pipe_relay(self) -> None:
+        """Relay JACCL SideChannel all_gather rounds between runner pipes and exo events."""
+        assert self._pipe_read_fd is not None
+        assert self._pipe_write_fd is not None
+        read_fd = self._pipe_read_fd
+        write_fd = self._pipe_write_fd
+        sequence = 0
+
+        try:
+            while True:
+                # 1. Read local data from runner: [uint32 size][size bytes]
+                header = await to_thread.run_sync(partial(_pipe_read_exact, read_fd, 4))
+                if header is None:
+                    logger.info("JACCL pipe relay: runner closed pipe (EOF)")
+                    break
+                data_size: int = struct.unpack("<I", header)[0]  # pyright: ignore[reportAny]
+                local_data = await to_thread.run_sync(
+                    partial(_pipe_read_exact, read_fd, data_size)
+                )
+                if local_data is None:
+                    logger.warning("JACCL pipe relay: EOF reading data payload")
+                    break
+
+                logger.info(
+                    f"JACCL pipe relay: read {data_size} bytes from runner, seq={sequence}"
+                )
+
+                # 2. Emit JacclSideChannelData event
+                waiter = anyio.Event()
+                self._gathered_waiters[sequence] = (waiter, None)
+                await self._event_sender.send(
+                    JacclSideChannelData(
+                        instance_id=self.bound_instance.instance.instance_id,
+                        runner_id=self.bound_instance.bound_runner_id,
+                        sequence=sequence,
+                        data=local_data,
+                    )
+                )
+
+                # 3. Wait for gathered result
+                await waiter.wait()
+                _, gathered_event = self._gathered_waiters.pop(sequence)
+                assert gathered_event is not None
+
+                # 4. Order gathered data by runner rank and concatenate
+                instance = self.bound_instance.instance
+                assert isinstance(instance, MlxJacclInstance)
+                runner_order = list(instance.shard_assignments.runner_to_shard.keys())
+                ordered_data = b"".join(
+                    gathered_event.gathered_data[rid] for rid in runner_order
+                )
+
+                # 5. Write gathered data to runner: [uint32 total_size][total_size bytes]
+                total_size = len(ordered_data)
+                response = struct.pack("<I", total_size) + ordered_data
+                await to_thread.run_sync(partial(_pipe_write_all, write_fd, response))
+
+                logger.info(
+                    f"JACCL pipe relay: wrote {total_size} bytes to runner, seq={sequence}"
+                )
+                sequence += 1
+        except OSError as e:
+            logger.warning(f"JACCL pipe relay: OS error: {e}")
+        except Exception as e:
+            logger.opt(exception=e).error("JACCL pipe relay: unexpected error")
+
+    def notify_gathered(self, event: JacclSideChannelGathered) -> None:
+        """Called by the worker when a JacclSideChannelGathered event arrives."""
+        seq = event.sequence
+        if seq not in self._gathered_waiters:
+            logger.warning(f"JACCL: received gathered event for unknown sequence {seq}")
+            return
+        waiter, _ = self._gathered_waiters[seq]
+        self._gathered_waiters[seq] = (waiter, event)
+        waiter.set()
+
     def __del__(self) -> None:
         if self.runner_process.is_alive():
             logger.warning("RunnerSupervisor was not stopped cleanly.")
@@ -191,7 +381,7 @@ class RunnerSupervisor:
         logger.info("Checking runner's status")
         if self.runner_process.is_alive():
             logger.info("Runner was found to be alive, attempting to join process")
-            await to_thread.run_sync(self.runner_process.join, 5)
+            await to_thread.run_sync(self.runner_process.join, 1)
         rc = self.runner_process.exitcode
         logger.info(f"RunnerSupervisor exited with exit code {rc}")
         if rc == 0:

src/exo/worker/runner/tool_parsers.py

@@ -1,72 +0,0 @@
-import json
-from dataclasses import dataclass
-from typing import Any, Callable
-
-from exo.shared.types.api import ToolCallItem
-
-
-@dataclass
-class ToolParser:
-    start_parsing: str
-    end_parsing: str
-    parse_tool_calls: Callable[[str], list[ToolCallItem] | None]
-
-
-def make_mlx_parser(
-    tool_call_start: str,
-    tool_call_end: str,
-    tool_parser: Callable[[str], dict[str, Any] | list[dict[str, Any]]],
-) -> ToolParser:
-    def parse_tool_calls(text: str) -> list[ToolCallItem] | None:
-        try:
-            text = text.removeprefix(tool_call_start)
-            text = text.removesuffix(tool_call_end)
-            parsed = tool_parser(text)
-            if isinstance(parsed, list):
-                return [ToolCallItem.model_validate(_flatten(p)) for p in parsed]
-            else:
-                return [ToolCallItem.model_validate(_flatten(parsed))]
-
-        except Exception:
-            return None
-
-    return ToolParser(
-        start_parsing=tool_call_start,
-        end_parsing=tool_call_end,
-        parse_tool_calls=parse_tool_calls,
-    )
-
-
-# TODO / example code:
-def _parse_json_calls(text: str) -> list[ToolCallItem] | None:
-    try:
-        text = text.removeprefix("<tool_call>")
-        text = text.removesuffix("</tool_call>")
-        top_level = {
-            k: json.dumps(v) if isinstance(v, (dict, list)) else v
-            for k, v in json.loads(text).items()  # pyright: ignore[reportAny]
-        }
-        return [ToolCallItem.model_validate(top_level)]
-    except Exception:
-        return None
-
-
-def _flatten(p: dict[str, Any]) -> dict[str, str]:
-    return {
-        k: json.dumps(v) if isinstance(v, (dict, list)) else str(v)  # pyright: ignore[reportAny]
-        for k, v in p.items()  # pyright: ignore[reportAny]
-    }
-
-
-json_tool_parser = ToolParser(
-    start_parsing="<tool_call>",
-    end_parsing="</tool_call>",
-    parse_tool_calls=_parse_json_calls,
-)
-
-
-def infer_tool_parser(chat_template: str) -> ToolParser | None:
-    """Attempt to auto-infer a tool parser from the chat template."""
-    if "<tool_call>" in chat_template and "tool_call.name" in chat_template:
-        return json_tool_parser
-    return None

src/exo/worker/tests/unittests/test_runner/test_parse_tool_calls.py

@@ -5,13 +5,12 @@ from typing import Any
 
 from exo.shared.types.worker.runner_response import GenerationResponse, ToolCallResponse
 from exo.worker.runner.runner import parse_tool_calls
-from exo.worker.runner.tool_parsers import make_mlx_parser
 
 
 def _make_responses(
     texts: list[str],
     finish_on_last: bool = True,
-) -> Generator[GenerationResponse]:
+) -> Generator[GenerationResponse | ToolCallResponse]:
     """Create a sequence of GenerationResponses from text strings."""
     for i, text in enumerate(texts):
         is_last = i == len(texts) - 1
@@ -23,13 +22,10 @@ def _make_responses(
         )
 
 
-def _dummier_parser(text: str) -> dict[str, Any]:
+def _dummy_parser(text: str) -> dict[str, Any]:
     return {"name": "test_fn", "arguments": {"arg": text}}
 
 
-_dummy_parser = make_mlx_parser("<tool_call>", "</tool_call>", _dummier_parser)
-
-
 class TestParseToolCalls:
     """Tests for parse_tool_calls generator."""
 
@@ -39,6 +35,8 @@ class TestParseToolCalls:
         results = list(
             parse_tool_calls(
                 _make_responses(texts, finish_on_last=False),
+                "<tool_call>",
+                "</tool_call>",
                 _dummy_parser,
             )
         )
@@ -52,6 +50,8 @@ class TestParseToolCalls:
         results = list(
             parse_tool_calls(
                 _make_responses(texts),
+                "<tool_call>",
+                "</tool_call>",
                 _dummy_parser,
             )
         )
@@ -76,7 +76,9 @@ class TestParseToolCalls:
         results = list(
             parse_tool_calls(
                 _make_responses(texts, finish_on_last=False),
-                make_mlx_parser("<tool_call>", "</tool_call>", _failing_parser),
+                "<tool_call>",
+                "</tool_call>",
+                _failing_parser,
             )
         )
 

uv.lock

@@ -367,6 +367,7 @@ version = "0.3.0"
 source = { editable = "." }
 dependencies = [
     { name = "aiofiles", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
+    { name = "aiohttp", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
     { name = "anyio", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
     { name = "exo-pyo3-bindings", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
     { name = "fastapi", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
@@ -376,8 +377,8 @@ dependencies = [
     { name = "hypercorn", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
     { name = "loguru", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
     { name = "mflux", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
-    { name = "mlx", version = "0.30.6", source = { registry = "https://pypi.org/simple" }, extra = ["cpu"], marker = "sys_platform == 'linux'" },
-    { name = "mlx", version = "0.30.7.dev20260218+14841977", source = { git = "https://github.com/rltakashige/mlx-jaccl-fix-small-recv.git?branch=address-rdma-gpu-locks#1484197707f35186ad3bd614357c7c47fdf86ebc" }, marker = "sys_platform == 'darwin'" },
+    { name = "mlx", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
+    { name = "mlx", extra = ["cpu"], marker = "sys_platform == 'linux'" },
     { name = "mlx-lm", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
     { name = "msgspec", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
     { name = "openai-harmony", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
@@ -388,6 +389,7 @@ dependencies = [
     { name = "rustworkx", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
     { name = "tiktoken", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
     { name = "tomlkit", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
+    { name = "types-aiofiles", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
     { name = "zstandard", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
 ]
 
@@ -404,6 +406,7 @@ dev = [
 [package.metadata]
 requires-dist = [
     { name = "aiofiles", specifier = ">=24.1.0" },
+    { name = "aiohttp", specifier = ">=3.12.14" },
     { name = "anyio", specifier = "==4.11.0" },
     { name = "exo-pyo3-bindings", editable = "rust/exo_pyo3_bindings" },
     { name = "fastapi", specifier = ">=0.116.1" },
@@ -413,9 +416,9 @@ requires-dist = [
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     { name = "loguru", specifier = ">=0.7.3" },
     { name = "mflux", specifier = "==0.15.5" },
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+    { name = "mlx", marker = "sys_platform == 'darwin'", specifier = "==0.30.6" },
     { name = "mlx", extras = ["cpu"], marker = "sys_platform == 'linux'", specifier = "==0.30.6" },
-    { name = "mlx-lm", specifier = "==0.30.7" },
+    { name = "mlx-lm", specifier = "==0.30.6" },
     { name = "msgspec", specifier = ">=0.19.0" },
     { name = "openai-harmony", specifier = ">=0.0.8" },
     { name = "pillow", specifier = ">=11.0,<12.0" },
@@ -425,6 +428,7 @@ requires-dist = [
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     { name = "tiktoken", specifier = ">=0.12.0" },
     { name = "tomlkit", specifier = ">=0.14.0" },
+    { name = "types-aiofiles", specifier = ">=24.1.0.20250708" },
     { name = "zstandard", specifier = ">=0.23.0" },
 ]
 
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+    { name = "mlx", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
+    { name = "mlx", extra = ["cuda13"], marker = "sys_platform == 'linux'" },
     { name = "numpy", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
     { name = "opencv-python", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
     { name = "piexif", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
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 version = "0.30.6"
 source = { registry = "https://pypi.org/simple" }
-resolution-markers = [
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@@ -1062,14 +1072,6 @@ cuda13 = [
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 ]
 
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 [[package]]
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 version = "0.30.6"
@@ -1096,20 +1098,30 @@ wheels = [
 
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