[BUG] Remote Control spawned sessions exit with "Process exited with error" mid-task; app reports host offline

Summary

Sessions spawned by claude remote-control --spawn worktree exit mid-task with Session failed: Process exited with error cse_…, followed by kept worktree … · session crashed. The project thread in the Claude app then reports that the host "went offline partway through the build", even though the Remote Control server process stayed up and Ready the whole time.

Environment

• Claude Code 2.1.296, macOS 27.0.1 (Apple silicon), always-on Mac
• Remote Control servers run as LaunchAgents: claude remote-control --name "<host> · <project>" --spawn worktree --permission-mode bypassPermissions --no-create-session-in-dir
• Sessions are started from a cloud project thread in the Claude desktop app (the cloud session spawns a helper on the Mac)

What happened

Three spawned sessions on one server died this way in one afternoon (local times 12:28:47, 13:26:17, 13:31:33). In the clearest case:

1. The helper started a long xcodebuild in the background and armed a Monitor / until-loop on it.
2. About 6 seconds later, the transcript just stops: no error entry, no API error, nothing after the last tool result.
3. The server log shows Session failed: Process exited with error, the background build is reported killed, and the worktree is kept.

Shortly before, that helper had written "the build restarted after the container reset". That suggests the cloud side had already reset once, and that a cloud-side reset or turn end may be tearing down the Mac-side helper mid-task. This is not verified.

No crash report was written, there was no memory pressure (about 60% free), and no OOM or jetsam log entries. The server process itself never restarted.

Expected

• A helper waiting on a background build should keep running, or at least exit with a reason that's logged.
• The app should not report the host as offline when the server is up and only the helper exited.

Repro (approximate)

1. Run a Remote Control server with --spawn worktree on a Mac.
2. From a cloud project thread, have the spawned session run a multi-minute xcodebuild in the background and wait on it with a Monitor.
3. The session process exits within about 1–2 minutes with "Process exited with error".

Evidence

Session IDs: cse_01EWQssnVLXWEz58ChQhRUEj, cse_01WAwgw2bTqXyMqh3me4YtbM, cse_01DTSZSoMiKJCCewLpDgG98s (2026-10-13). Logs are available on request.