Tracker /v1/network/assign now accepts an optional `hf_repo` query param
to restrict assignment to a specific model, and returns `gap_found: bool`
so callers know whether they received a real gap vs a redundancy slot.
Node startup with --model-id (no explicit shard args) now queries the
tracker first for an uncovered gap for that model before defaulting to
full coverage (0..n-1). This means a second node with --model-id will
serve only the missing layers, not the whole model again.
Auto-join fallback (no --model-id) now prints why it fell through
instead of silently switching to stub-model.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
