Fix agent runtime queue races

[canvascoding]

Summary

• Serialize state-changing chat WebSocket actions per user/session so follow-ups cannot overtake runtime startup.
• Keep follow-up queue ownership in the runtime and attach only one item to agent-core at a time.
• Make Steer suspend all remaining follow-ups, so only the selected message enters the active runtime.
• Add regression tests for WebSocket session ordering and runtime queue consumption.

Verification

• npm run lint
• npm run build
• npm run test:websocket:session-queue
• npm run test:pi:queue

Notes

• No UI change; no Playwright run was started under the repository explicit-approval rule.

Greptile Summary

This PR changes how Pi runtime and WebSocket queues preserve chat action order. The main changes are:

• Runtime-owned follow-up and steering queues in RuntimeMessageQueues.
• One-at-a-time follow-up attachment to agent-core.
• Per-user/session WebSocket action serialization.
• Regression scripts for runtime queue and WebSocket ordering behavior.

Confidence Score: 4/5

The runtime queue promotion path can leave remaining follow-ups stuck.

• Promoting one queued follow-up clears agent-core's follow-up queue.
• Remaining runtime-owned follow-ups stay suspended after the steering message is consumed.
• WebSocket session serialization and import changes look contained.

app/lib/pi/runtime-queue.ts

Important Files Changed

Filename	Overview
app/lib/pi/runtime-queue.ts	Adds runtime-owned queue management, with a stuck suspended-follow-up path after steering promotion.
app/lib/pi/live-runtime.ts	Delegates follow-up, steering, remove, replace, and consume behavior to the new queue controller.
server/websocket-session-queue.ts	Adds a per-user/session promise queue for ordered WebSocket action handling.
server/websocket-server.ts	Wraps session-scoped chat actions in the new WebSocket session queue.
scripts/pi-runtime-queue-test.ts	Adds coverage for one-at-a-time runtime queue attachment and steering promotion behavior.
scripts/websocket-session-queue-test.ts	Adds coverage for FIFO session actions, cross-session parallelism, and recovery after failures.
package.json	Adds npm scripts for the new queue tests.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  A[Multiple follow-ups queued] --> B[One follow-up attached to agent-core]
  A --> C[User promotes a queued follow-up]
  C --> D[Agent follow-up queue is cleared]
  D --> E[Remaining follow-ups stay runtime-owned]
  E --> F[followUpsSuspended remains true]
  C --> G[Promoted message enters steering]
  G --> H[Steering message is consumed]
  H --> I[Remaining follow-ups are not re-attached]

Loading

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flowchart TD
  A[Multiple follow-ups queued] --> B[One follow-up attached to agent-core]
  A --> C[User promotes a queued follow-up]
  C --> D[Agent follow-up queue is cleared]
  D --> E[Remaining follow-ups stay runtime-owned]
  E --> F[followUpsSuspended remains true]
  C --> G[Promoted message enters steering]
  G --> H[Steering message is consumed]
  H --> I[Remaining follow-ups are not re-attached]

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_{Reviews (1): Last reviewed commit: "Prevent Steer from draining queued follo..." | Re-trigger Greptile}

Greptile also left 1 inline comment on this PR.

Context used (3)

• Context used - CLAUDE.md (source)
• Context used - AGENTS.md (source)
• Context used - seed_sys_prompts/AGENTS.md (source)

[greptile-apps]

Suspended Follow-Ups Stay Stuck

When one follow-up is promoted while others remain queued, this clears agent-core's follow-up queue and leaves followUpsSuspended set to true. The promoted steering message is consumed from the steering queue, so the remaining follow-ups are never re-attached to agent-core; they stay visible in status but do not run unless the user manually removes or clears them.