fix(session): surface silent SessionDB failures that cause session data loss (#2999)

* fix(session): surface silent SessionDB failures that cause session data loss

SessionDB initialization and operation failures were logged at debug level
or silently swallowed, causing sessions to never be indexed in the FTS5
database. This made session_search unable to find affected conversations.

In practice, ~48% of sessions can be lost without any visible indication.
The JSON session files are still written (separate code path), but the
SQLite/FTS5 index gets nothing — making session_search return empty results
for affected sessions.

Changes:
- cli.py: Log warnings (not debug) when SessionDB init fails at both
  __init__ and _start_session entry points
- run_agent.py: Log warnings on create_session, append_message, and
  compression split failures
- run_agent.py: Set _session_db = None after create_session failure to
  fail fast instead of silently dropping every message for the session

Root cause: When gateway restarts or DB lock contention occurs during
SessionDB() init, the exception is caught and swallowed. The agent
continues running normally — JSON session logs are written to disk —
but no messages reach the FTS5 index.

* fix: use module logger instead of root logging for SessionDB warnings

Follow-up to cherry-picked PR #2939 — the original used logging.warning()
(root logger) instead of logger.warning() (module logger) in the 5 new
warning calls. Module logger preserves the logger hierarchy and shows the
correct module name in log output.

---------

Co-authored-by: LucidPaths <lc77@outlook.de>

cli.py

@@ -1186,8 +1186,8 @@ class HermesCLI:
         try:
             from hermes_state import SessionDB
             self._session_db = SessionDB()
-        except Exception:
-            pass
+        except Exception as e:
+            logger.warning("Failed to initialize SessionDB — session will NOT be indexed for search: %s", e)
         
         # Deferred title: stored in memory until the session is created in the DB
         self._pending_title: Optional[str] = None
@@ -1852,7 +1852,7 @@ class HermesCLI:
                 from hermes_state import SessionDB
                 self._session_db = SessionDB()
             except Exception as e:
-                logger.debug("SQLite session store not available: %s", e)
+                logger.warning("SQLite session store not available — session will NOT be indexed: %s", e)
         
         # If resuming, validate the session exists and load its history.
         # _preload_resumed_session() may have already loaded it (called from