test: update delegation tests for YAML-driven agent IDs

Old hardcoded IDs (seer, forge, echo, helm, quill) replaced with
YAML-defined IDs (orchestrator, researcher, coder, writer, memory,
experimenter). Added test that old names are explicitly rejected.

src/timmy/tools_intro/__init__.py

@@ -219,25 +219,26 @@ def get_task_queue_status() -> dict[str, Any]:
 
 
 def get_agent_roster() -> dict[str, Any]:
-    """Get the agent roster from the orchestrator's sub-agent definitions.
+    """Get the agent roster from agents.yaml config.
 
     Returns:
         Dict with agent list and summary.
     """
     try:
-        from timmy.agents.timmy import _PERSONAS
+        from timmy.agents.loader import list_agents
 
-        roster = []
-        for persona in _PERSONAS:
-            roster.append(
-                {
-                    "id": persona["agent_id"],
-                    "name": persona["name"],
-                    "status": "available",
-                    "capabilities": ", ".join(persona.get("tools", [])),
-                    "role": persona.get("role", ""),
-                }
-            )
+        agents = list_agents()
+        roster = [
+            {
+                "id": a["id"],
+                "name": a["name"],
+                "status": a.get("status", "available"),
+                "capabilities": ", ".join(a.get("tools", [])),
+                "role": a.get("role", ""),
+                "model": a.get("model", ""),
+            }
+            for a in agents
+        ]
 
         return {
             "agents": roster,