Add invalid notification schema fixture

Author: Wonderforge-Lab

tests/fixtures/invalid/notification/record.json

@@ -0,0 +1,14 @@
+{
+  "record_type": "notification",
+  "schema_version": 1,
+  "notification_id": "20260902-sender-session-notice",
+  "created_at": "2026-09-02T12:00:00Z",
+  "from_visitor_id": "sender-session",
+  "to_visitor_id": "operator",
+  "message_id": "20260902-sender-session-fixture",
+  "status": "sent",
+  "path": "tests/fixtures/invalid/notification/artifact.md",
+  "needs_human_action": true,
+  "summary": "Invalid notification fixture.",
+  "notes": "Unsupported status."
+}