Make Matrix agent registry immutable

adapter/matrix/agent_registry.py

@@ -19,8 +19,8 @@ class AgentDefinition:
 
 class AgentRegistry:
     def __init__(self, agents: list[AgentDefinition]) -> None:
-        self.agents = agents
-        self._by_id = {agent.agent_id: agent for agent in agents}
+        self.agents = tuple(agents)
+        self._by_id = {agent.agent_id: agent for agent in self.agents}
 
     def get(self, agent_id: str) -> AgentDefinition:
         try:

tests/adapter/matrix/test_agent_registry.py

@@ -22,6 +22,23 @@ def test_load_agent_registry_reads_yaml_entries(tmp_path: Path):
     assert registry.get("agent-1").label == "Analyst"
 
 
+def test_agent_registry_agents_sequence_is_immutable(tmp_path: Path):
+    path = tmp_path / "agents.yaml"
+    path.write_text(
+        "agents:\n"
+        "  - id: agent-1\n"
+        "    label: Analyst\n",
+        encoding="utf-8",
+    )
+
+    registry = load_agent_registry(path)
+
+    with pytest.raises(AttributeError):
+        registry.agents.append(  # type: ignore[attr-defined]
+            registry.agents[0]
+        )
+
+
 def test_load_agent_registry_rejects_duplicate_ids(tmp_path: Path):
     path = tmp_path / "agents.yaml"
     path.write_text(
@@ -136,3 +153,22 @@ def test_load_agent_registry_rejects_null_id_or_label(tmp_path: Path, content: s
 
     with pytest.raises(AgentRegistryError, match="each agent entry requires id and label"):
         load_agent_registry(path)
+
+
+@pytest.mark.parametrize(
+    "content",
+    [
+        "agents:\n"
+        "  - id: '   '\n"
+        "    label: Analyst\n",
+        "agents:\n"
+        "  - id: agent-1\n"
+        "    label: '   '\n",
+    ],
+)
+def test_load_agent_registry_rejects_blank_id_or_label(tmp_path: Path, content: str):
+    path = tmp_path / "agents.yaml"
+    path.write_text(content, encoding="utf-8")
+
+    with pytest.raises(AgentRegistryError, match="each agent entry requires id and label"):
+        load_agent_registry(path)