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

@@ -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.
@@ -724,14 +724,38 @@ 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:
             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()
 
@@ -2317,6 +2341,9 @@ 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 []
 

tests/test_hermes_state.py

@@ -1,11 +1,35 @@
 """Tests for hermes_state.py — SessionDB SQLite CRUD, FTS5 search, export."""
 
+import sqlite3
 import time
 import pytest
 
 from hermes_state import SessionDB
 
 
+class _NoFtsCursor(sqlite3.Cursor):
+    """Simulate a SQLite build without the fts5 module."""
+
+    def execute(self, sql, parameters=()):
+        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 "USING fts5" in sql_script:
+            raise sqlite3.OperationalError("no such module: fts5")
+        return super().executescript(sql_script)
+
+
+class _NoFtsConnection(sqlite3.Connection):
+    def cursor(self, factory=None):
+        return super().cursor(factory or _NoFtsCursor)
+
+
 @pytest.fixture()
 def db(tmp_path):
     """Create a SessionDB with a temp database file."""
@@ -135,6 +159,33 @@ class TestSessionLifecycle:
         child = db.get_session("child")
         assert child["parent_session_id"] == "parent"
 
+    def test_db_initializes_without_fts5_module(self, tmp_path, monkeypatch):
+        real_connect = sqlite3.connect
+
+        def connect_without_fts(*args, **kwargs):
+            kwargs["factory"] = _NoFtsConnection
+            return real_connect(*args, **kwargs)
+
+        monkeypatch.setattr("hermes_state.sqlite3.connect", connect_without_fts)
+
+        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")
+
+            messages = db.get_messages("s1")
+            assert len(messages) == 1
+            assert messages[0]["content"] == "hello from sqlite without fts"
+            assert db.search_messages("hello") == []
+        finally:
+            db.close()
+
 
 # =========================================================================
 # Message storage