feat(agent-chat): complete core workflow and strengthen auth rate limiting

backend/src/core/agent_chat/events.py

@@ -0,0 +1,37 @@
+from __future__ import annotations
+
+from typing import Any
+
+
+def run_started(*, run_id: str) -> dict[str, Any]:
+    return {"type": "run.started", "run_id": run_id}
+
+
+def stage_completed(
+    *, run_id: str, stage: str, usage: dict[str, Any] | None = None
+) -> dict[str, Any]:
+    event: dict[str, Any] = {
+        "type": "stage.completed",
+        "run_id": run_id,
+        "stage": stage,
+    }
+    if usage is not None:
+        event["usage"] = usage
+    return event
+
+
+def run_completed(*, run_id: str, output: str, usage: dict[str, Any]) -> dict[str, Any]:
+    return {
+        "type": "run.completed",
+        "run_id": run_id,
+        "output": output,
+        "usage": usage,
+    }
+
+
+def run_failed(*, run_id: str, error: str) -> dict[str, Any]:
+    return {
+        "type": "run.failed",
+        "run_id": run_id,
+        "error": error,
+    }