* fix(engines): snapshot lazy registry keys so /engines can't 500 under concurrency
`list_backends()` runs in a FastAPI threadpool and iterates the lazy TTS/ASR
registries via `items()` → `__iter__`, which held a *live* `dict.__iter__(self)`
open across each engine's slow `is_available()` probe. Meanwhile the lazy
`__getitem__` resolves a deferred entry by mutating the dict (`self[key] = cls`).
A second concurrent `/engines` request (or any ASR op) materializing the lazy
`faster-whisper-isolated` entry therefore changed the dict size mid-iteration:
RuntimeError: dictionary changed size during iteration
asr_backend.py:1729 list_backends → _REGISTRY.items()
asr_backend.py:1665 __iter__ → for k in dict.__iter__(self)
Both `_LazyRegistry` (TTS) and `_LazyASRRegistry` (ASR) now snapshot their live
keys up front with `list(dict.__iter__(self))` — consumed atomically under the
GIL — so a concurrent lazy insert can no longer trip the iteration. The slow
per-engine probes then run over the snapshot, not the live iterator.
Deterministic fail-before/pass-after regression for both registries:
tests/backend/services/test_lazy_registry_concurrency.py.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
* docs(changelog): add the /engines concurrency fix under [Unreleased] (#940)
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
---------
Co-authored-by: mergetest <test@local>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
