Handle PostgreSQL self-restart demotion preflight

tests/test-demote-database.py

@@ -137,3 +137,56 @@ assert result["reason"] == "successor_unreachable"
 print("successor_unreachable    rejected")
 
 print("DEMOTE_DATABASE_FAILURE_TEST_PASS=1")
+
+print()
+print("===== SELF-RESTART DATABASE GATE =====")
+
+plugin.monitor = lambda config, runtime_state: {
+    "ha": {"ocf_rc": plugin.OCF_RUNNING_PROMOTED},
+    "primary": {"current_wal_lsn": "14/1C07A920"},
+}
+
+self_restart_state = {
+    "postgresql": {
+        "notification": {
+            "type": "pre",
+            "operation": "demote",
+            "demote_uname": "david-prodesk",
+            "promote_uname": "david-prodesk",
+            "promoted_uname": "david-prodesk",
+            "unpromoted_uname": "david-eve",
+            "received_at": time.time(),
+        },
+    },
+}
+
+connect_called = False
+
+def must_not_connect(**kwargs):
+    global connect_called
+    connect_called = True
+    raise AssertionError(
+        "self-restart demotion must not probe a remote successor"
+    )
+
+plugin.psycopg2.connect = must_not_connect
+
+result = plugin.demote_database(
+    config,
+    self_restart_state,
+    {},
+)
+
+assert result["ocf_rc"] == 0
+assert result["ready"] is True
+assert result["mutation"] is False
+assert result["final_handoff_required"] is False
+assert result["handoff_mode"] == "local_restart"
+assert result["reason"] == "local_restart_demotion_ready"
+assert result["successor_node"] == "david-prodesk"
+assert result["checks"]["local_primary"] is True
+assert result["checks"]["remote_handoff_required"] is False
+assert connect_called is False
+
+print("self_restart_database     accepted")
+print("remote_probe_skipped      accepted")