bash tool: timeout kills the shell but does not abandon the stdio read — call duration is unbounded

Description

Summary

The bash tool's timeout terminates the shell process on schedule, but then keeps reading its
stdout/stderr pipe. If the command spawned a process that inherited those handles, EOF never arrives
while that process lives — so the call blocks well past the timeout, unbounded for a long-lived server.

The returned message is also misleading: it says the command was terminated at the timeout, when in fact
substantially more wall-clock time elapsed before the call returned.

• Bounded, reproducible: timeout: 5000 → call returned after 25.79 s
• Observed in practice: timeout: 120000 → call returned after 1842.5 s (30.7 min), and only
  because the process tree was killed externally

Suggested fix

On timeout, stop awaiting stream EOF: resolve from process exit and drain stdio with a deadline, so
timeout is a hard upper bound on the call regardless of stream state. Optionally also kill the
process group / job object so descendants don't survive the timeout — they currently do, and are
never reaped.

Plugins

OMO

OpenCode version

1.18.30

Steps to reproduce

Part A — the mechanism (standalone, no opencode needed, ~25 s)

Paste into PowerShell. It appears to freeze for ~25 s; that freeze is the bug, and it self-terminates.

$inner = Join-Path $env:TEMP 'pipedemo-inner.ps1'
@'
Start-Process -FilePath "powershell.exe" `
  -ArgumentList @("-NoProfile", "-Command", "Start-Sleep -Seconds 25") `
  -WindowStyle Hidden `
  -RedirectStandardOutput "$env:TEMP\hang-o.log" `
  -RedirectStandardError "$env:TEMP\hang-e.log" | Out-Null
"INNER_SCRIPT_DONE at $(Get-Date -Format o)"
'@ | Set-Content -LiteralPath $inner -Encoding utf8

$sw  = [System.Diagnostics.Stopwatch]::StartNew()
$psi = [System.Diagnostics.ProcessStartInfo]::new()
$psi.FileName  = 'powershell.exe'
$psi.Arguments = "-NoProfile -File `"$inner`""
$psi.RedirectStandardOutput = $true
$psi.UseShellExecute = $false
$p = [System.Diagnostics.Process]::Start($psi)
$null = $p.WaitForExit(60000); $exitedAt = $sw.Elapsed.TotalSeconds
$out  = $p.StandardOutput.ReadToEnd(); $eofAt = $sw.Elapsed.TotalSeconds
"child process EXITED: $([math]::Round($exitedAt,2)) s"
"child stdout EOF    : $([math]::Round($eofAt,2)) s"
Remove-Item -LiteralPath $inner -Force -ErrorAction SilentlyContinue

Measured (Windows 11 build 26200, PowerShell 7.6.6):

child process EXITED: 0.26 s
child stdout EOF    : 25.41 s

25.15 s of blocking after the child had already exited. Running the inner script directly in a
console returns in 0.58 s — the hang only appears when stdout is a pipe being read to EOF, which is
why it never reproduces interactively.

Part B — the timeout does not bound the call (through the bash tool, ~25 s)

Invoke the bash tool with timeout: 5000 and this command:

$inner = Join-Path $env:TEMP 'to-test.ps1'
@'
Start-Process -FilePath "powershell.exe" -ArgumentList @("-NoProfile","-Command","Start-Sleep -Seconds 25") -WindowStyle Hidden -RedirectStandardOutput "$env:TEMP\to-o.log" -RedirectStandardError "$env:TEMP\to-e.log" | Out-Null
"CHILD_SPAWNED"
'@ | Set-Content -LiteralPath $inner -Encoding utf8
& powershell.exe -NoProfile -File $inner
"script finished at $(Get-Date -Format o)"

Expected: the call returns at ~5 s.
Actual: it returns at 25.79 s (recorded state.time.end - state.time.start), i.e. when the
detached child exits and EOF finally arrives — while reporting:

shell tool terminated command after exceeding timeout 5000 ms

The timeout did fire and did kill the shell; it simply did not stop the read. With a server in place
of Start-Sleep 25, the call never returns at all.

Screenshot and/or share link

No response

Operating System

Windows 11 Pro build 26200, AMD64

Terminal

PowerShell 7.6.6