## Motivation
Download progress in the dashboard was broken: mainly treating all
download statuses as ongoing
## Changes
- Backend (apply.py): Deduplicate download progress events by model_id
instead of full shard_metadata, preventing duplicate entries per node
- Dashboard (+page.svelte): Extract shared collectDownloadStatus()
helper that both getModelDownloadStatus and getInstanceDownloadStatus
use, eliminating ~100 lines of duplicated logic. Adds proper handling
for
DownloadCompleted/DownloadFailed events, uses a Map to deduplicate
per-node entries, and introduces a typed NodeDownloadStatus with
explicit status states (downloading/completed/partial/pending)
- ModelCard: Replace single aggregate progress bar with per-node
download bars, each color-coded by status. Instance preview now scopes
download status to participating nodes only
## Why It Works
- Deduplicating by model_id in apply.py ensures each node has exactly
one download entry per model
- The perNodeMap in the frontend keeps only the latest event per node,
preventing duplicate bars
- Handling DownloadCompleted allows the UI to show finished downloads
instead of dropping them
- Scoping instance previews to assigned nodes avoids showing irrelevant
download progress
