When models.json changes, the front recomputed the per-engine assignment and
immediately POSTed /internal/reload-config to every engine. If an engine was
mid-generation it was GIL-busy, so the push blocked and timed out, stalling the
front's poll thread ("reload-config push to 'nvidia' failed: timed out").

Now the front updates its local router instantly but queues the reload push per
engine, and _flush_pending_reloads() delivers it only once that engine's
inflight count drops to 0 (generation finished). Failed pushes are requeued.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011DDv7BchtZQWsnPG6Jm49m