Reject non-mapping agent registry entries

adapter/matrix/agent_registry.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 from dataclasses import dataclass
+from collections.abc import Mapping
 from pathlib import Path
 
 import yaml
@@ -37,6 +38,8 @@ def load_agent_registry(path: str | Path) -> AgentRegistry:
     agents: list[AgentDefinition] = []
     seen: set[str] = set()
     for entry in entries:
+        if not isinstance(entry, Mapping):
+            raise AgentRegistryError("each agent entry requires id and label")
         agent_id = str(entry.get("id", "")).strip()
         label = str(entry.get("label", "")).strip()
         if not agent_id or not label: