fix(remote-workspace): observe Pi prompt failures before acknowledgement - #761

Summary

A Pi child can fail while its prompt acknowledgement is still pending. The runtime created a separate turn-settlement promise but did not observe it until after awaiting that acknowledgement. A process exit, malformed RPC output, or early extension error could therefore reject both promises while only the command rejection was handled. Even a caller that caught handle.prompt() still received a process-level unhandledRejection.

Observe prompt admission and turn settlement concurrently with Promise.all. Either failure rejects the prompt immediately, and success still requires both a successful prompt response and the turn's settlement event. Clear only the active settlement owned by this prompt. Process launch, remote permissions, tool admission, cleanup and replay policy are unchanged.

Add seven isolated synthetic RPC scenarios covering child exit, malformed output, extension errors before/after acknowledgement, explicit rejection, and successful completion in either order. The fixture records process-level unhandled rejections without changing the test runner's rejection policy. Update the architecture contract and English/Korean guide.

This is a pre-existing application lifetime bug reproduced on official Bun 1.4.3 and 1.4.4, not a newly introduced Bun 1.4.4 regression. The daemon's crash guard may absorb an unhandled rejection; this PR does not claim that every occurrence terminates the daemon.

Verification

Base: fork dev at c4d4bb2da2162e23c314befafc5ec104292902a0. Local execution: Linux x64. Tests use the repository's normal preload/shared lock in the host PID namespace.

Reproduction and regression

On untouched base, a real synthetic child exiting with code 7 before acknowledging a prompt produced both:

• caught prompt error: Pi RPC exited with code 7;
• one unhandled rejection with the same message.

This was reproduced on both Bun versions. Early extension failure and malformed RPC output independently produced the same double-reporting shape on Bun 1.4.4. With this patch, the prompt still rejects with the relevant error and the fixture records zero unhandled rejections.

The fixture accepts an absolute source path, so the exact same probe can target a baseline worktree:

bun tests/fixtures/pi-prompt-lifetime.ts /absolute/base/src/remote-control/workspace-pi-runtime.ts exit-before-ack
bun tests/fixtures/pi-prompt-lifetime.ts /absolute/base/src/remote-control/workspace-pi-runtime.ts extension-before-ack
bun tests/fixtures/pi-prompt-lifetime.ts /absolute/base/src/remote-control/workspace-pi-runtime.ts malformed-before-ack

Commands and results

The focused subprocess fixture is explicitly invoked because changed-mode import analysis cannot follow the source filename passed to a child. The broad repository suite was not rerun under the documented constrained-worktree/resource exception; validation covers the changed runtime and connected client/CLI paths plus explicit session, documentation and size guards. Exact-head hosted CI remains separate. Native Windows/macOS execution, real Pi/provider execution, and live CLI confinement are unverified; opt-in skips are not counted as passing evidence.

Independent source/test/documentation review by a separate agent found no material issue. This is an agent review, not a maintainer approval or hosted bot review.

Checklist

• Scope stays focused and avoids unrelated cleanup.
• Docs or release notes were updated when needed.
• Security-sensitive changes were reviewed for secrets, auth, and unsafe defaults. The patch changes promise observation only; it does not change credentials, process argv, approved roots, remote capabilities, tool execution, or automatic replay. Privacy scan passed.

Co-authored-by: luvs01 27862058+luvs01@users.noreply.github.com

Summary by CodeRabbit

• Bug Fixes

  • Remote workspace sessions now report prompt-start failures promptly if Pi exits or an extension encounters an error, without waiting for a turn acknowledgment.
  • A prompt is considered successful only after both Pi accepts it and the turn settles, helping prevent failures from going unreported.

• Documentation

  • Updated remote workspace guidance in English and Korean to explain how prompt failures are reported.