Add read-only PostgreSQL demotion preparation

plugins/postgresql/manifest.json

@@ -5,7 +5,8 @@
   "actions": [
     "monitor",
     "notify",
-    "notify.target"
+    "notify.target",
+    "demote.prepare"
   ],
   "required_config": [
     "PGHOST",

plugins/postgresql/plugin.py

@@ -529,3 +529,114 @@ def notify_target(config, runtime_state, request_parameters):
         "node": node_name,
         "age_seconds": age,
     }
+
+
+def demote_prepare(config, runtime_state, request_parameters):
+    """
+    Read-only demotion preparation.
+
+    Validates the latest Pacemaker demotion notification against this local
+    daemon and reports the successor. PostgreSQL mutation remains outside this
+    action until candidate and WAL checks are migrated.
+    """
+    del request_parameters
+
+    node_name = str(
+        config.get("PACEMAKER_NODE_NAME", "")
+    ).strip().lower()
+
+    if not node_name:
+        raise ValueError(
+            "PACEMAKER_NODE_NAME is required for demote.prepare"
+        )
+
+    notification = _postgres_runtime_state(
+        runtime_state
+    ).get("notification")
+
+    if not isinstance(notification, dict):
+        return {
+            "ocf_rc": 1,
+            "ready": False,
+            "reason": "notification_missing",
+            "node": node_name,
+        }
+
+    if notification.get("type") != "pre":
+        return {
+            "ocf_rc": 1,
+            "ready": False,
+            "reason": "notification_type_invalid",
+            "node": node_name,
+        }
+
+    if notification.get("operation") != "demote":
+        return {
+            "ocf_rc": 1,
+            "ready": False,
+            "reason": "notification_operation_invalid",
+            "node": node_name,
+        }
+
+    received_at = notification.get("received_at")
+
+    if not isinstance(received_at, (int, float)):
+        return {
+            "ocf_rc": 1,
+            "ready": False,
+            "reason": "notification_timestamp_invalid",
+            "node": node_name,
+        }
+
+    age = time.time() - received_at
+
+    if age < 0 or age > NOTIFY_TARGET_MAX_AGE_SECONDS:
+        return {
+            "ocf_rc": 1,
+            "ready": False,
+            "reason": "notification_stale",
+            "age_seconds": age,
+            "node": node_name,
+        }
+
+    target_node = str(
+        notification.get("demote_uname", "")
+    ).strip().lower()
+
+    successor_node = str(
+        notification.get("promote_uname", "")
+    ).strip().lower()
+
+    if target_node != node_name:
+        return {
+            "ocf_rc": 1,
+            "ready": False,
+            "reason": "local_node_not_target",
+            "node": node_name,
+            "target_node": target_node,
+            "successor_node": successor_node,
+        }
+
+    if not successor_node:
+        return {
+            "ocf_rc": 1,
+            "ready": False,
+            "reason": "successor_missing",
+            "node": node_name,
+        }
+
+    return {
+        "ocf_rc": 0,
+        "ready": True,
+        "mutation": False,
+        "node": node_name,
+        "target_node": target_node,
+        "successor_node": successor_node,
+        "age_seconds": age,
+        "checks": {
+            "notification": True,
+            "local_target": True,
+            "successor_selected": True,
+            "postgresql_mutated": False,
+        },
+    }