shell: detached Windows process leaves parent session stuck running #43910

Description

On OpenCode V2 (opencode2) on Windows, a TUI session remained permanently running after a shell tool launched a long-lived GUI process with PowerShell Start-Process. The direct PowerShell process had exited, but the tool remained running, preventing the parent session from consuming completed subagent notifications and queued user input.

This was server state, not only stale TUI rendering:

GET /api/session/active
parent session: running
both child sessions: absent (idle)

parent tool state: running
tool: shell
direct pwsh process: no longer present

GET /api/session/{parent}/inbox
2 synthetic subagent completion messages
2 queued user messages

Both child sessions already contained final assistant messages with finish: stop. Sending POST /interrupt to either child correctly behaved as an idle no-op, despite the TUI presenting the child as still in progress.

The workaround was:

POST /api/session/{parent}/background

It immediately changed the outer shell tool state to completed, emptied the inbox, and allowed the parent to resume. The detached GUI process remained alive and responsive, as intended.

Plugins: opencode-ponytail, opencode-gemini-auth@latest, ponytail-v2.mjs; local integration plugins for After Effects, Blender, Microsoft 365, Resolve, and Unreal.

OpenCode version: 0.0.0-beta-17793 (build commit 4d22d4e75fb949db5a6302cc605e9af87ea671bf)

Steps to reproduce

The same failure has occurred twice. These are the exact observed steps; a controlled reproduction has not yet been run, so the frequency is currently intermittent.

1. In a parent TUI session on Windows, start two subagents.
2. Run a PowerShell shell tool that uses Start-Process -PassThru with redirected stdout/stderr to launch a long-lived GUI executable, then checks that the GUI is alive and listening.
3. Allow the direct PowerShell process to exit while the detached GUI remains running.
4. Allow both subagents to finish and submit additional user messages to the parent.
5. Observe that both child sessions have final answers and are absent from /api/session/active, while the parent and its shell tool remain running and completion/user messages accumulate in the parent inbox.
6. Call POST /api/session/{parent}/background; observe that the tool completes and the parent immediately consumes its inbox.

Relevant observed transition:

{
  "before": {
    "toolState": "running",
    "runningToolProcessPresent": false,
    "parentInboxItems": 4
  },
  "afterBackground": {
    "toolState": "completed",
    "toolResult": "The command was moved to the background.",
    "metadataStatus": "running",
    "parentInboxItems": 0
  }
}

Expected: once the direct shell process exits, the tool should complete or transition to background observation without retaining foreground ownership of the parent session. Completed subagents and queued input should then be consumed normally.

Actual: foreground ownership remained attached to the stale shell tool for about 27 minutes, until the explicit /background request.

Screenshot and/or share link

Unavailable: the affected session is private. API state was captured above.

Operating System

Windows 11, build 10.0.26200.9168, x64

Terminal

TUI with TERM=xterm-256color; terminal application unavailable from the environment. Shell: PowerShell 7.6.5 (ComSpec=C:\WINDOWS\system32\cmd.exe).