fix(agent): polish interrupt-resume flow for merge readiness

backend/src/v1/agent/router.py

@@ -2,7 +2,7 @@ from __future__ import annotations
 
 from typing import Annotated
 
-from fastapi import APIRouter, Depends, HTTPException
+from fastapi import APIRouter, Depends, HTTPException, Path
 from fastapi.responses import StreamingResponse
 
 from v1.agent.dependencies import get_agent_service
@@ -25,7 +25,7 @@ async def create_run(
 
 @router.post("/runs/{run_id}/resume")
 async def resume_run(
-    run_id: str,
+    run_id: Annotated[str, Path(min_length=1, max_length=255)],
     input_data: RunAgentInput,
     service: Annotated[AgentChatService, Depends(get_agent_service)],
 ) -> StreamingResponse:
@@ -34,6 +34,7 @@ async def resume_run(
             status_code=409,
             detail=f"run_id mismatch: path={run_id}, body={input_data.runId}",
         )
+    await service.prepare_resume(run_id, input_data)
     return StreamingResponse(
         service.stream_resume(run_id, input_data),
         media_type="text/event-stream",