feat(public-api): add /v1/sessions/:id/runs endpoint for AG-UI prompt delivery #753
Description
Problem
The public API has no endpoint for sending prompts to a running session. The only way to deliver a prompt to a runner is:
- Through the frontend's backend proxy at
/api/projects/:name/agentic-sessions/:id/agui/run - Directly to the runner pod on port 8001 via port-forward or in-cluster access
Option 1 requires a browser. Option 2 bypasses the UI entirely — the frontend never sees the AG-UI event stream, so work happens invisibly.
Impact
- The MCP server (
ambient-code/mcp) and CLI (acpctl) cannot send prompts to sessions through any API - The
acp-compileworkflow (submit a plan for autonomous execution) has no proper delivery mechanism - Direct pod access creates invisible work that the UI can't display
Proposed Solution
Add POST /v1/sessions/:id/runs to the public API that proxies to the runner's AG-UI endpoint, similar to how the backend already proxies at /api/projects/:name/agentic-sessions/:id/agui/run.
This enables:
- MCP server to send prompts via API
- CLI to submit work via
acpctl - Any API client to interact with sessions
The endpoint should:
- Accept the same AG-UI
RunAgentInputJSON body the runner expects - Stream SSE events back to the caller
- Require the same auth (Bearer token + X-Ambient-Project header)
Context
Discovered while trying to use the acp-compile skill to submit a plan to a running session on a kind cluster. The only way to deliver the prompt was curl directly to the pod, which cut the UI out completely.