fix(reconcile): retire workflow session rows whose owners are no longer live

Implement a sanctioned session lifecycle for post-restart reconciliation so
active session rows with dead or reused owner PIDs can be terminalized
without deleting history. Protect live owners, live leases, and live
client-managed sessions; record durable session_retired audit events; keep
cleanup idempotent under concurrent reconciles.

Closes #969

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

tests/test_control_plane_db.py

@@ -37,7 +37,7 @@ class ControlPlaneDBTest(unittest.TestCase):
             rows = dict(conn.execute("SELECT key, value FROM schema_meta").fetchall())
         finally:
             conn.close()
-        self.assertEqual(rows["schema_version"], "5")
+        self.assertEqual(rows["schema_version"], "6")
         self.assertIn("DB coordinates", rows["architecture"])
         self.assertIn("bridge", rows["architecture"].lower())
 
@@ -868,7 +868,7 @@ class SessionCheckpointTest(unittest.TestCase):
             conn.close()
         self.assertIn("session_checkpoints", names)
         record = self._write()
-        self.assertEqual(record["checkpoint_schema_version"], 5)
+        self.assertEqual(record["checkpoint_schema_version"], 6)
 
     # AC2 — checkpoints written for multi-role session fixtures.
     def test_multi_role_fixtures_each_get_a_row(self) -> None: