Adds `crate::process_kill` — reliable SIGKILL-with-verify primitives used
across the server in place of the various ad-hoc kill paths that ignored
their kill-effective return values. The module exposes three pieces:
- `sigkill_pids_and_verify(pids)`: SIGKILL each pid and block (up to 2s)
until every pid is verified gone. Returns survivors if not.
- `pids_matching(pattern)`: pgrep -f wrapper.
- `descendant_pids(root)`: recursive pgrep -P walker for process trees.
Wires the watchdog's limit-termination path through it, and reorders the
protocol to fix the duplicate-coder bug observed on story 1086 (2026-05-15):
Before: check_agent_limits set status=Failed before the kill ran. The
kill itself was `portable_pty::ChildKiller::kill()`, which sends SIGHUP
on Unix — claude-code ignores SIGHUP, so the process kept running while
the agent record was already marked terminated. The idempotency check
in `start_agent` whitelists Running/Pending, so the next auto-assign
pass spawned a fresh agent alongside the still-alive prior one. Two
claude PIDs sharing one session_id, racing on the same worktree.
After: status update is moved OUT of check_agent_limits and into the
caller AFTER the kill is verified. The kill itself is now SIGKILL-the-
process-tree-in-the-worktree, with explicit verification that every pid
is gone. The idempotency window is closed.
The existing watchdog test suite (14 tests) still passes; 7 new tests
cover the process_kill primitives directly.
`agents/pool/process.rs`'s `kill_all_children` and `kill_child_for_key`
still use the old portable_pty SIGHUP path — they have the same bug but
in lower-impact code paths (shutdown, operator stop). They will be
migrated under a separate story to keep this commit focused.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Timmy
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