Codex CORE findings on the fingerprint: (1) default busy timeout could stall
/api/sessions ~10s on a locked state.db; (2) COUNT(*) forced a full messages
table SCAN (~16-22ms/refresh on 200k rows). Fix: open file:...?mode=ro with
timeout=0.05 + PRAGMA busy_timeout=50 (returns fast, falls back to stat stamp on
lock), and use index-only MAX(rowid) per table (no COUNT, no scan). Verified:
EXPLAIN shows SEARCH not SCAN, 0.36ms on 200k msgs, 0.16ms while EXCLUSIVE-locked.
Fingerprint shape is now (sessions_max_rowid, messages_max_rowid); regression
tests updated.
Codex root-cause consult confirmed: the CLI-session cache (_CLI_SESSIONS_CACHE,
5s TTL) and session-list cache were keyed on (st_mtime_ns, st_size) of state.db
+ WAL sidecars. Under WAL-mode writes those stamps collide (same mtime-ns bucket
+ WAL frame size after checkpoint), serving a stale cache -> freshly-committed
gateway/CLI session intermittently absent from /api/sessions (the recurring
test_gateway_sync flake AND a real up-to-5s sidebar delay for gateway writes).
PRAGMA data_version is NOT usable here (fresh per-request connection always
reports its own initial value, never advances — verified). Fix = a cheap
content fingerprint (COUNT/MAX(rowid) over sessions+messages) read on a fresh
connection, which DOES advance on every commit and is immune to mtime
granularity. Wired into _sqlite_file_stat_cache_key (models) + the routes-layer
source stamp. + 3 regression tests + corrected the earlier false root-cause
comments.
nesquena-hermes