Follow-up fixes for salvaged PR #65637:
1. Clear _dirty_transcripts in rewrite_transcript + rewind_session —
stale pending messages were re-inserted after /retry, /undo, /compress.
2. Narrow _is_fts_corruption_error to specific SQLite error strings —
bare 'fts' substring matched 'shifts', 'gifts', etc.
3. Move DB write outside _transcript_retry_lock — holding the lock
during writes serialized all sessions' transcript appends and blocked
during FTS rebuild. Now the lock guards only the pending queue.
4. Push rebuild_fts() into SessionDB — SessionStore was reaching into
_conn/_lock private attrs. SessionDB.rebuild_fts() follows the same
pattern as optimize_fts().
5. Cap pending per session at 200 — prevents unbounded memory growth
when DB is persistently broken. Oldest messages dropped with warning.
Added 4 new tests: dirty-clear on rewrite/rewind, FTS matcher false
positives, pending cap enforcement.
kshitijk4poor
a9cc17fd80