fix(session): extend no-FTS5 degradation to the trigram CJK index

The salvaged contributor commit guarded only messages_fts. Current main
also creates a second virtual table, messages_fts_trigram (CJK substring
search), whose CREATE VIRTUAL TABLE ... USING fts5 still raised
"no such module: fts5" on builds without FTS5 — re-crashing SessionDB
init. Wrap the trigram setup with the same guard, and broaden the test's
no-fts5 mock to fail BOTH tables so the regression test actually
exercises a faithful no-FTS5 build.

hermes_state.py

@@ -744,8 +744,18 @@ class SessionDB:
         # Trigram FTS5 for CJK/substring search
         try:
             cursor.execute("SELECT * FROM messages_fts_trigram LIMIT 0")
-        except sqlite3.OperationalError:
-            cursor.executescript(FTS_TRIGRAM_SQL)
+        except sqlite3.OperationalError as exc:
+            if "no such table" not in str(exc).lower():
+                raise
+            try:
+                cursor.executescript(FTS_TRIGRAM_SQL)
+            except sqlite3.OperationalError as fts_exc:
+                err = str(fts_exc).lower()
+                if "fts5" not in err and "no such module" not in err:
+                    raise
+                # Same FTS5-unavailable cause already warned about above for
+                # messages_fts; the trigram table is an additional CJK index,
+                # so just degrade silently here. CJK search falls back to LIKE.
 
         self._conn.commit()
 

tests/test_hermes_state.py

@@ -11,12 +11,16 @@ class _NoFtsCursor(sqlite3.Cursor):
     """Simulate a SQLite build without the fts5 module."""
 
     def execute(self, sql, parameters=()):
-        if sql.strip() == "SELECT * FROM messages_fts LIMIT 0":
-            raise sqlite3.OperationalError("no such table: messages_fts")
+        probe = sql.strip()
+        if probe in (
+            "SELECT * FROM messages_fts LIMIT 0",
+            "SELECT * FROM messages_fts_trigram LIMIT 0",
+        ):
+            raise sqlite3.OperationalError("no such table: " + probe.split()[-3])
         return super().execute(sql, parameters)
 
     def executescript(self, sql_script):
-        if "CREATE VIRTUAL TABLE IF NOT EXISTS messages_fts USING fts5" in sql_script:
+        if "USING fts5" in sql_script:
             raise sqlite3.OperationalError("no such module: fts5")
         return super().executescript(sql_script)
 
@@ -167,6 +171,10 @@ class TestSessionLifecycle:
         db = SessionDB(db_path=tmp_path / "state.db")
         try:
             assert db._fts_enabled is False
+            # Neither FTS5 virtual table should have been created on a build
+            # that lacks the fts5 module — both init paths must degrade.
+            assert db._fts_table_exists("messages_fts") is False
+            assert db._fts_table_exists("messages_fts_trigram") is False
 
             db.create_session(session_id="s1", source="cli")
             db.append_message("s1", role="user", content="hello from sqlite without fts")