fix(state-db): skip read indexes an older schema can't hold instead of rolling back the rest

On a pre-2026-07-28 Agent schema, sessions has no last_activity_at, so the
fingerprint index's CREATE failed inside the single BEGIN IMMEDIATE and rolled
back idx_messages_session too, leaving messages unindexed: the exact older-agent
case the troubleshooting doc says the tool fixes. Gate each index on its columns
being present and report 'skipped'. (Opus advisor SHOULD-FIX on #7445.)

scripts/ensure_state_db_read_indexes.py

@@ -92,6 +92,14 @@ def ensure_read_indexes(db_path, *, confirmed_drained=False, lock_file=None):
             db.execute("BEGIN IMMEDIATE")
             try:
                 for name, (table, keys) in INDEXES.items():
+                    # An older Agent schema can lack a column one index keys on
+                    # (sessions.last_activity_at is newer than
+                    # messages.timestamp). Skip that index instead of letting its
+                    # CREATE fail and roll back the ones this schema supports.
+                    present = {r[1] for r in db.execute(f"PRAGMA table_info({table})")}
+                    if any(col not in present for col, _ in keys):
+                        statuses[name] = "skipped"
+                        continue
                     existing = db.execute("SELECT tbl_name FROM sqlite_master WHERE name=?", (name,)).fetchone()
                     if existing:
                         actual = tuple((r[2], r[4]) for r in db.execute(f"PRAGMA index_xinfo({name})") if r[5])

tests/test_pr7445_readonly_review_followups.py

@@ -248,6 +248,30 @@ def _maintenance_schema(path):
         )
 
 
+def test_maintenance_skips_indexes_an_older_schema_cannot_hold(tmp_path, maintenance_without_fcntl):
+    """A legacy ``sessions`` table without ``last_activity_at`` must not roll back
+    the message indexes the schema does support."""
+    module = maintenance_without_fcntl
+    path = tmp_path / "state.db"
+    with closing(sqlite3.connect(str(path))) as conn:
+        conn.executescript(
+            """
+            CREATE TABLE sessions(source TEXT, id TEXT, message_count INTEGER);
+            CREATE TABLE messages(session_id TEXT, timestamp REAL, role TEXT);
+            """
+        )
+    result = module.ensure_read_indexes(path, confirmed_drained=True)
+    assert result == {
+        "idx_messages_session": "created",
+        "idx_messages_session_role": "created",
+        "idx_sessions_webui_fingerprint": "skipped",
+    }
+    with closing(sqlite3.connect(str(path))) as conn:
+        names = {r[0] for r in conn.execute("SELECT name FROM sqlite_master WHERE type='index'")}
+    assert {"idx_messages_session", "idx_messages_session_role"} <= names
+    assert "idx_sessions_webui_fingerprint" not in names
+
+
 @pytest.fixture
 def maintenance_without_fcntl(monkeypatch):
     """Import the maintenance module as a platform without ``fcntl`` sees it."""