fix(session): degrade gracefully when SQLite lacks FTS5

hermes_state.py

@@ -380,6 +380,7 @@ class SessionDB:
 
         self._lock = threading.Lock()
         self._write_count = 0
+        self._fts_enabled = False
         try:
             self._conn = sqlite3.connect(
                 str(self.db_path),
@@ -388,7 +389,6 @@ class SessionDB:
                 # handles contention instead of sitting in SQLite's internal
                 # busy handler for up to 30s.
                 timeout=1.0,
-                # Autocommit mode: Python's default isolation_level=""
                 # auto-starts transactions on DML, which conflicts with our
                 # explicit BEGIN IMMEDIATE.  None = we manage transactions
                 # ourselves.
@@ -724,8 +724,22 @@ class SessionDB:
         # FTS5 setup (separate because CREATE VIRTUAL TABLE can't be in executescript with IF NOT EXISTS reliably)
         try:
             cursor.execute("SELECT * FROM messages_fts LIMIT 0")
-        except sqlite3.OperationalError:
-            cursor.executescript(FTS_SQL)
+            self._fts_enabled = True
+        except sqlite3.OperationalError as exc:
+            if "no such table" not in str(exc).lower():
+                raise
+            try:
+                cursor.executescript(FTS_SQL)
+                self._fts_enabled = True
+            except sqlite3.OperationalError as fts_exc:
+                err = str(fts_exc).lower()
+                if "fts5" not in err and "no such module" not in err:
+                    raise
+                logger.warning(
+                    "SQLite FTS5 unavailable for %s; full-text search disabled: %s",
+                    self.db_path,
+                    fts_exc,
+                )
 
         # Trigram FTS5 for CJK/substring search
         try:
@@ -2317,6 +2331,9 @@ class SessionDB:
         ignores ``sort``. The trigram CJK path honours ``sort`` like the main
         FTS5 path.
         """
+        if not self._fts_enabled:
+            return []
+
         if not query or not query.strip():
             return []