* fix(streaming): lock-disciplined STREAMS reads via peek_stream()
Writers pop STREAMS under STREAMS_LOCK, but four hot reads used bare
STREAMS.get(): the streaming worker start, the gateway run start, and the two
SSE attach paths in routes.py. Each is individually saved today by GIL-atomic
dict.get plus a None-guard, but the check-then-act windows (get → register,
get → subscribe) race teardown pops, and the bare pattern invites unprotected
copies. peek_stream() centralizes the locked read; all four sites migrate with
no behavioral change.
* test: dual-patch config.STREAMS alongside routes.STREAMS in SSE seam tests
peek_stream() reads the canonical api.config.STREAMS registry; tests that
inject a fake registry by patching only the routes-level re-export left the
helper reading the real (empty) registry and hung the SSE loop to the
pytest-timeout ceiling. Mirror the test_issue6623 pattern: patch both
bindings.
* docs(changelog): stamp #7339 lock-disciplined STREAMS reads
---------
Co-authored-by: Sebastian B <sb@wmc.sh>
Co-authored-by: n <a@n>
