Windows: background job cancellation fails without a process identity

[pj991207]

Summary

On native Windows, a running background task records pidIdentity: null. The cancel command then refuses to stop the task and marks it as cancel_failed.

Reproduction

I ran a real background task through the companion CLI on Windows, with a prompt that starts node -e "setTimeout(() => {}, 120000)" and does not edit files:

node scripts/claude-companion.mjs task --background --write --json

While claude.exe and its Bash child were still running, the job state contained:

{
  "status": "running",
  "pid": 27956,
  "pidIdentity": null
}

Cancelling it returned:

{
  "status": "cancel_failed",
  "note": "Refusing to cancel a stored process without a PID identity."
}

The process tree was still alive afterward and had to be terminated manually.

Root cause

getProcessIdentity() handles macOS separately and otherwise reads /proc/<pid>/stat. On Windows that resolves to a path such as D:\proc\<pid>\stat and fails with ENOENT. Callers treat identity collection as best-effort, so the job continues with a null identity, but cancellation deliberately requires one.

The Windows CI job currently runs the curated test:cross-platform list, which does not include tests/process.test.mjs. That test file also uses echo and cat as standalone executables, so it is not portable to native Windows yet.

Expected behavior

Windows jobs should store a stable process-birth identity and pass the same PID-reuse check used on the other platforms. tests/process.test.mjs should run in the Windows CI job.

Environment

• Windows 11
• Node.js 24.17.0
• cc-plugin-codex 1.5.0 (19e5651)
• Claude Code 2.1.263

[pj991207]

I hit a second Windows-specific path while verifying the fix: once the PID identity was available, cancellation still used the Unix negative-PID signal path and treated the failure as "Process not found". #111 fixes both parts by storing the Windows process start time and routing cancellation through the existing taskkill /T /F helper.

I also verified it against a live background job: the claude.exe process and its Bash/Node children were gone after cancellation.