Windows: bash tool call doesn't return until spawned descendant processes exit; stdio redirection is not a workaround (1.18.30) #48369

Description

On Windows, a bash tool call does not return when the command finishes if any process spawned during the call is still alive - even though the script itself exited and its output already streamed to the TUI. The turn stays wedged with no error until every descendant dies or the user aborts.

Key Windows detail: redirecting the child's stdout/stderr to files does NOT prevent this. Start-Process creates the child with handle inheritance enabled and no handle-list restriction, so the tool's stdout/stderr pipe write-handles leak to the child and its descendants regardless of redirection. There is no stdio-level workaround; the only reliable one we found is spawning long-lived processes out-of-tree via WMI (Win32_Process.Create - fresh handle table, outside the tool's process tree).

Measured with a controlled repro (no external tools involved):

Real-world case: an npm-installed CLI that self-daemonizes (agent-browser v0.37.1 - first command spawns a daemon + headless Chrome with a 1h idle lifetime). Every cold-start bash call wedges the primary session; after the abort the daemon survives, so later calls look fine - which made it look like "screenshots hang", because screenshot tasks are the typical first command. Killing the daemon releases the call.

This matches #47350 (macOS, EOF-vs-exit mechanism) and the "primary wedges too" case explicitly excluded from #47546. #44601 anchors completion on process exit instead of pipe EOF; its approach would resolve this. Filing to (1) confirm it still reproduces on 1.18.30 and (2) record that on Windows redirection cannot mask the bug. #44601 has been open since Aug 24 - would appreciate a review.

Plugins

None relevant (a TUI cache-meter plugin is installed; unrelated to the bash tool).

OpenCode version

1.18.30

Steps to reproduce

1. Windows 11, opencode 1.18.30 (bash tool runs PowerShell).

2. Have the agent run this bash command:

   $sw = [Diagnostics.Stopwatch]::StartNew()
   Start-Process pwsh -ArgumentList '-NoProfile','-c','Start-Sleep -Seconds 20' -WindowStyle Hidden
   "done in $($sw.ElapsedMilliseconds)ms"

3. Output appears immediately (~0.2 s), but the tool result returns only ~20 s later, when the hidden pwsh exits.

4. Same wedge with -RedirectStandardOutput <file> - redirection does not help on Windows.

5. Or reproduce with any self-daemonizing CLI: the first call wedges until abort; the surviving daemon makes subsequent calls fast until the next cold start.

Screenshot and/or share link

No response

Operating System

Windows 11 (10.0.26200)

Terminal

Windows Terminal