Fix speculative temp: use request temperature, not global env var

The speculative cycle was using EXO_SPECULATIVE_TEMP (global) instead
of the request's actual temperature. This caused greedy decoding in
speculative while the model sampled at T=0.7, producing different
(shorter) output and missing responses after </think>.

Now passes task_params.temperature from submit() to MTPBatchGenerator
per-request via _request_temp[uid]. Falls back to self.temp (env var)
if not set.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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

@@ -332,6 +332,11 @@ class ExoBatchGenerator:
 
         uid = uids[0]
 
+        # Pass request temperature to speculative cycle
+        if hasattr(self._exo_gen, '_request_temp'):
+            request_temp = task_params.temperature if task_params.temperature is not None else 0.7
+            self._exo_gen._request_temp[uid] = request_temp
+
         self._active_tasks[uid] = _EngineTask(
             uid=uid,
             task_params=task_params,

src/exo/worker/engines/mlx/speculative/mtp_batch_generator.py

@@ -45,6 +45,7 @@ class MTPBatchGenerator(BatchGenerator):
         self._captured = {}            # pre_norm / prompt_pre_norm from norm wrapper
         self._mtp_pre_norm = {}        # uid → (B, 1, D) pre-norm hidden state
         self._mtp_prefilled = set()    # uids with MTP cache prefilled
+        self._request_temp = {}        # uid → temperature from request
 
         self._setup_hidden_capture()
 
@@ -134,7 +135,7 @@ class MTPBatchGenerator(BatchGenerator):
             return super()._next()
 
         gamma = self.gamma
-        temp = self.temp
+        temp = self._request_temp.get(uid, self.temp)
         alpha = self.alpha
 
         # 1. Draft γ tokens (lazy chain, no eval)
@@ -303,3 +304,4 @@ class MTPBatchGenerator(BatchGenerator):
         self._mtp_pre_norm.pop(uid, None)
         self._mtp_prefilled.discard(uid)
         self._token_buffer.pop(uid, None)
+        self._request_temp.pop(uid, None)