Slice 9 — User can hop into an active Run via SSE live stream

[safayavatsal]

What to build

Live observability into a Run, per ADR-0002's "async-default with hop-in" model.

• agent-orchestrator exposes GET /runs/:id/stream as Server-Sent Events. Events emitted: tool calls, tool results, model thoughts (when present), state transitions.
• Web UI: Run detail page subscribes to the stream and renders events in order. Includes a sticky "current state" badge.
• Backpressure / disconnect handling: the stream resumes from the last seen event id on reconnect.
• All events streamed are also persisted in agent.run_events so a user opening the page after the Run finished sees a complete trace.

Acceptance criteria

• Opening a running Run in the web UI shows new events appearing live (within ~1s of emission).
• Reloading the page mid-Run does not lose events; the trace catches up to the live edge.
• Opening a finished Run shows the full trace from agent.run_events.
• Closing the browser tab cleanly closes the SSE connection (no leaked connections on the server).
• No raw model API responses or sandbox secrets leak into the stream.

Blocked by

• Slice 7 — Wedge tracer: assign Issue to Agent → fake-but-real PR appears #7