fix(sessions): restore trigram after deferred bootstrap

hermes_state_schema.py

@@ -547,10 +547,12 @@ class SessionSchemaMixin:
         """Body of :meth:`_recover_stale_fts`; caller holds rebuild authority. One write
         transaction, so no canonical writer slips between rebuild and trigger restoration."""
         try:
-            include_trigram = self._fts_table_probe(cursor, "messages_fts_trigram") is True
+            trigram_present = self._fts_table_probe(cursor, "messages_fts_trigram") is True
         except (sqlite3.DatabaseError, UnicodeDecodeError):
             # A corrupt vtable may fail even a LIMIT 0 probe; still include it in the drop-and-recreate.
             include_trigram = True
+        else:
+            include_trigram = trigram_present or (not legacy and self._trigram_tokenizer_available(cursor))
 
         drop_sql = "".join(f"DROP TRIGGER IF EXISTS {trigger};" for trigger in _FTS_TRIGGERS)
         if include_trigram:
@@ -590,6 +592,21 @@ class SessionSchemaMixin:
         logger.warning("Rebuilt stale state.db FTS indexes from canonical messages and restored sync triggers.")
         return True
 
+    def _trigram_tokenizer_available(self, cursor: sqlite3.Cursor) -> bool:
+        """Probe trigram support without publishing a persistent FTS object."""
+        probe = "temp.hermes_fts5_trigram_probe"
+        cursor.execute(f"DROP TABLE IF EXISTS {probe}")
+        try:
+            cursor.execute(f"CREATE VIRTUAL TABLE {probe} USING fts5(content, tokenize='trigram')")
+        except sqlite3.OperationalError as exc:
+            if not self._is_trigram_unavailable_error(exc):
+                raise
+            self._warn_trigram_unavailable(exc)
+            return False
+        finally:
+            cursor.execute(f"DROP TABLE IF EXISTS {probe}")
+        return True
+
     # ── Declarative column reconciliation ──────────────────────────────────
 
     @staticmethod

tests/state/test_fts_fresh_bootstrap_admission.py

@@ -1,5 +1,6 @@
 """Fresh state.db FTS bootstrap must honor cross-process rebuild admission."""
 
+import sqlite3
 import subprocess
 import sys
 from pathlib import Path
@@ -22,6 +23,17 @@ with fts_rebuild_admission(Path(sys.argv[1]), timeout_seconds=0) as acquired:
 """
 
 
+def _trigram_supported() -> bool:
+    conn = sqlite3.connect(":memory:")
+    try:
+        conn.execute("CREATE VIRTUAL TABLE trigram_probe USING fts5(content, tokenize='trigram')")
+    except sqlite3.OperationalError:
+        return False
+    finally:
+        conn.close()
+    return True
+
+
 def test_fresh_fts_bootstrap_does_not_publish_schema_without_admission(tmp_path, monkeypatch):
     """A fresh opener that loses admission leaves no partially initialized FTS surface."""
     db_path = tmp_path / "state.db"
@@ -53,6 +65,11 @@ def test_fresh_fts_bootstrap_does_not_publish_schema_without_admission(tmp_path,
     try:
         assert recovered._fts_stale is False
         assert recovered._fts_enabled is True
+        if _trigram_supported():
+            assert recovered._trigram_available is True
+            assert recovered._conn.execute(
+                "SELECT 1 FROM sqlite_master WHERE name = 'messages_fts_trigram'"
+            ).fetchone() is not None
         recovered.create_session("s1", source="test")
         recovered.append_message("s1", "user", "fresh bootstrap recovered")
         assert recovered.search_messages("recovered")