## Problem
On host-mode Windows runners, a job can leave processes running after it finishes,
and those leftovers hold file handles that block deletion of the workspace.
Today a step's tree is only torn down when the step is *cancelled*
(`process.Killer`). A step that completes leaves whatever it spawned alive, and
the existing workspace scan in `terminateRunningProcesses` misses two shapes of
leftover: orphans whose parent already exited (no tree to walk, and their
executable often lives outside the workspace), and processes that merely *run in*
the workspace but reference no path from it — `Win32_Process` exposes no working
directory, so the scan cannot match them.
## Solution
Two additions in `internal/pkg/process`, both no-ops outside Windows:
- **`process.Group`** — a job-scoped Windows Job Object created with
`JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE`. Step processes are assigned to it before
they get their own `Killer`, so the step's job nests inside the job's:
cancellation still kills exactly the step's tree, while `Remove` closing the
group makes the kernel terminate everything still assigned, whatever its
parentage. The kernel also drops the handle when the runner exits, so a crashed
runner cannot strand processes.
- **`process.KillProcessesWithCWDUnder`** — a best-effort net for processes that
never joined the job (started via a service or scheduled task). It reads each
process's working directory from its PEB and terminates those under a workspace
dir. Processes it cannot open are skipped.
---------
Co-authored-by: silverwind <me@silverwind.io>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1080
Reviewed-by: silverwind <2021+silverwind@noreply.gitea.com>
