Fixes#17971
When initSessionState() reads the session store, use skipCache: true
to ensure fresh data from disk. The session store cache is process-local
and uses mtime-based invalidation, which can fail in these scenarios:
1. Multiple gateway processes (each has separate in-memory cache)
2. Windows file system where mtime granularity may miss rapid writes
3. Race conditions between messages 6-8 seconds apart
Symptoms: 134+ orphaned .jsonl transcript files, each with only 1
exchange. Session rotates on every incoming message even when
sessionKey is stable.
Root cause: loadSessionStore() returns stale cache → entry not found
for sessionKey → new sessionId generated → new transcript file.
The fix ensures session identity (sessionId) is always resolved from
the latest on-disk state, not potentially-stale cache.
16ddbbc628