[BUG] Claude Desktop (Windows) silently kills run_in_background tasks after 15-min idle — WarmLifecycle taskkills the embedded CLI process tree

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

On Claude Desktop for Windows (build 1.12603.1, bundled Claude Code agent 2.1.170), any task started with run_in_background is silently killed after the session has been idle (tab/window hidden) for ~15 minutes. No error is shown, and the Desktop background-task list still reports the task as running. Only tasks started inside Desktop are affected — the same task started from the standalone CLI (~/.local/bin/claude, v2.1.177) or via OS-level scheduling survives.

Root cause (traced in …\Claude_1.12603.1…\app\resources\app.asar): the Desktop wraps the embedded CLI in a WarmLifecycle manager instantiated with idleTimeoutMs: 900*1e3 (15 min), timeoutOnHidden: true, armOnTurnComplete: "when-hidden". When the session tab is hidden and the idle timer fires, it runs:

onDisconnect → pauseSession → teardownSession(id, "pause") → teardownQuery → query.close()

On Windows, query.close() terminates the spawned claude.exe via taskkill /pid <pid> /T /F. The /T flag kills the entire process tree, so the CLI's run_in_background child processes are force-killed along with it. Re-interacting calls warmSession, which spawns a fresh CLI with a new PID (the PID change confirms this). Because teardownQuery only nulls the async handles (activeWorkflows, pendingGitBashIds, …) without reconciling task state, the background-task list keeps showing running (related: #18390, #59962).

This is a design behavior of Desktop's idle session-recycling, not a transient crash. macOS is likely affected too via the process.kill(-pid, "SIGTERM") branch (process-group kill).

What Should Happen?

Idle session recycling should not silently destroy work the user explicitly backgrounded. Either:

1. Don't tear down the CLI process tree while it has live run_in_background tasks, or
2. Detach run_in_background children from the CLI process group so they survive a WarmLifecycle pause/re-warm, and/or
3. At minimum, when the process tree is killed, reconcile background-task state to failed/killed instead of leaving it stuck at running, and surface a notification to the user.

Error Messages/Logs

No error is produced — the silent kill IS the bug. Relevant Desktop-side evidence:

Analytics/log event emitted on the idle path:
  desktop_ccd_session_idle_paused { trigger: "idle_timeout", idle_timeout_ms: 900000, ... }

Decompiled code (app.asar, build 1.12603.1):
  new eWA({ idleTimeoutMs: 900*1e3, timeoutOnHidden: true,
            onDisconnect: t => this.pauseSession(t),
            onWarmUp: t => this.warmSession(t), ... })

  scheduleIdleTimeout(e,t){ e.idleTimeoutId = setTimeout(async()=>{
      if(this.config.armOnTurnComplete==="when-hidden" && e.isTabVisible) return;
      ... // → onDisconnect → pauseSession
  }, t) }

  teardownSession(e,t){ ... if(s.query){ this.teardownQuery(s); if(t==="pause"){ ...emit "paused" } } }

  teardownQuery(e){ try{ e.query?.close() }catch{} ; e.activeWorkflows=void 0; e.pendingGitBashIds=void 0; ... }

  // Windows process teardown inside query.close():
  process.platform==="win32"
    ? spawn("taskkill",["/pid",String(pid),"/T","/F"],{windowsHide:true})
    : process.kill(-pid,"SIGTERM")

Steps to Reproduce

1. Open Claude Desktop for Windows (build 1.12603.1), start a Code session in any project.
2. Have Claude start a long-running background task, e.g.:

run_in_background a loop that appends a timestamp to a log file every 10s
(PowerShell: while($true){ (Get-Date).ToString('o') | Out-File -Append .\timer.log; Start-Sleep 10 }).

1. Note the PID of the spawned claude.exe and its child shell process in Task Manager.
2. Switch to another app so the Claude Desktop session tab/window is hidden; leave it idle.
3. After ~15 minutes of idle (hidden), observe:

• The background task's child process is gone from Task Manager; the claude.exe PID has changed.
• timer.log stops growing — no error anywhere.
• The Desktop background-task list still shows the task as "running".

Control: run the exact same task from the standalone CLI (claude in a terminal) or via Windows Task Scheduler → it keeps running indefinitely. Only the Desktop-spawned path is affected.

Claude Model

Not sure / Multiple models

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Claude Desktop 1.12603.1 (Windows); bundled Claude Code agent 2.1.170.

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

_No response_