`_committed_session_ids` is a permanent per-sid latch, and
`_session_needs_commit` checks it before the turn counter by design — a
racing sync_turn can re-increment `_turn_count` after commit+reset, so
the guard must win to stop a double-commit.
That is correct for a session being left behind. It is wrong for one
that keeps its id. `compress_context()` commits before rewriting the
transcript in both modes, and with `compression.in_place: true` (the
default) `on_session_switch` receives the same id and does not rotate.
The latch then rejects every later commit for a still-live session — the
next compression, /new, normal session end, startup recovery — so every
post-compression turn is silently never extracted.
Rotation mode is unaffected because a fresh child id is minted and
starts clean, which is what confirms the latch's intent was only ever to
dedupe the departing id.
Clear the latch when compression completes without rotation. Turns
arriving after that point are genuinely new, and this is a defined
moment rather than a race. The rotation path is untouched, so the old
id stays latched and its _finalize_session_async still dedupes against
the compression commit.
Fixes#74695
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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