fix(state): fail fast on non-contention flock errors and retry deferred FTS rebuilds in-process (salvage #100130)

Two pieces of PR #100130 (@HexLab98) re-applied on top of the orphaned-flock
break (894fc35337) and fail-closed admission (#100895) that landed since:

* `is_advisory_lock_contention` (hermes_state_common): only EAGAIN /
  EWOULDBLOCK / EACCES / EDEADLK mean "another process holds the lock".
  ESTALE / ENOTSUP / ENOLCK / EIO from flock or msvcrt.locking are
  environment failures that polling cannot fix — `_acquire_db_flock` and
  both Windows msvcrt loops (FTS rebuild admission, state.db repair lock)
  now defer immediately with the real errno instead of burning the full
  120s / holder timeout and then logging a fake "held by another process".

* `retry_deferred_fts_recovery` (hermes_state_schema): a SessionDB whose
  open-time `_recover_stale_fts` deferred (foreign holders or busy rebuild
  lock) stayed `_fts_stale` — LIKE-only search — until the process
  reopened state.db. Short-lived CLIs reopen every run; the gateway opens
  once and stays up for days, so the deferral was effectively permanent
  (#100108). The retry runs from the EXISTING gateway housekeeping tick
  (`_start_gateway_housekeeping`, 60s) against the shared SessionDB
  instances via `hermes_state_registry.live_shared_session_dbs()`:
  non-blocking admission (`fts_rebuild_admission(timeout_seconds=0)`),
  bounded backoff 60s -> 1h, no new thread, still fails closed on live
  holders. `fts_rebuild_admission` gains the `timeout_seconds` kwarg.

* WAL-reset warning names `sys.executable` so a "linked SQLite 3.45.1"
  line can be matched to the interpreter that actually linked it
  (#100108 point 3).

Deliberately NOT carried from #100130: the "leftover lock file = holder"
premise (a 0-byte lock file never blocked flock; the real cause was the
fork-inherited fd, fixed in 894fc35337) and the `_rebuild_fts_once`
one-shot rework.

Co-authored-by: HexLab98 <liruixinch@outlook.com>

hermes_state_registry.py

@@ -42,7 +42,7 @@ from __future__ import annotations
 import logging
 import threading
 from pathlib import Path
-from typing import TYPE_CHECKING, Dict, Optional, Tuple
+from typing import TYPE_CHECKING, Dict, List, Optional, Tuple
 
 if TYPE_CHECKING:  # pragma: no cover - import cycle guard, typed only
     from hermes_state import SessionDB
@@ -289,6 +289,18 @@ def close_all() -> int:
     return closed
 
 
+def live_shared_session_dbs() -> List["SessionDB"]:
+    """Snapshot of every live (non-retired) shared SessionDB in this process.
+
+    For periodic in-process maintenance (the gateway housekeeping tick's
+    deferred-FTS retry). Refcounts are NOT touched: the caller only invokes
+    a method on an instance that some holder already keeps alive; a
+    concurrent final release closes it and the callee sees ``_conn is None``.
+    """
+    with _lock:
+        return [g.db for g in _generations.values() if not g.retired]
+
+
 def stats() -> Dict[str, int]:
     """Registry census for tests and diagnostics (no locks held long)."""
     with _lock: