A gateway process opened state.db from ~12 call sites, each minting its
own writer connection, self._lock, close-time WAL checkpoint, and
token-writer thread. With N independent writers on one WAL file, one
connection's close-time checkpoint could race another's growth — the
lost/reordered-page-write signature across 11+ incidents (#90837).
Adds hermes_state_registry.py: a process-wide, per-path, refcounted
shared registry owning the writer boundary.
- acquire(path): same resolved path returns the same instance (one
writer connection, one lock, one token-writer thread) for every
long-lived in-process caller (gateway runner, SessionStore, per-agent
lazy recall, cron per-job, mirror, channel_directory, slash_commands,
shutdown_flush, session_search, react_to_message, delegate, mcp_serve,
auto_archive, tui_gateway).
- close() on a shared instance is a NO-OP — the registry owns the
lifecycle, so one caller's close can never tear down a writer other
callers still hold.
- Generation-aware retirement on inode change: a replaced state.db
RETIRES the live generation (never lent again) but keeps it alive for
existing holders; release is object-keyed so holders of the old
generation drain it independently of the new one. The old
generation's own write path still fails with the typed
StateDbReplacedError (existing protection, unchanged).
- Replacement-open failure leaves NO registry entry for the path —
the next acquire retries fresh, never hands out a closed stale object.
- All teardown runs OUTSIDE the registry lock: a final release's WAL
checkpoint can never stall acquisition for every state.db.
- close_shared_session_dbs() at gateway shutdown drains every
generation (live + retired) as the final safety net.
CLI one-shots, recovery flows, and read-only cross-profile opens keep
using SessionDB() directly with their own close() — only long-lived
in-process sites route through the registry.
References #90837 (root-cause tracker stays open: the #10 EOF signature
and the WAL-lifecycle A/B verdict remain under investigation there).
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