[qingyun-wu]

The defect

run_check in tests/health-check-task-watcher.test.py fabricates process trees
(trees={"9000": {"9000"}}) but stubs only _watcher_trees and _proc_argv.
check_task_watcher's absent-sentinel branch then calls _pid_parent(root, ps_out),
which reads the machine's real ps output. So the verdict for an invented pid
depends on whether that pid happens to exist on the runner.

supervised_watcher, in the same file, already stubs _ps_snapshot and
_pid_parent — the omission in run_check is a slip, not a design choice.

Evidence — the failure, and the same failure reproduced on demand

Observed on the coverage job of an unrelated PR (#3113, which does not touch this
probe). scripts/coverage-gate.sh aborts before measuring anything:

coverage-gate: running Python suite under instrumentation...
✖ test failed under instrumentation: tests/health-check-task-watcher.test.py
  ✗ case m
      m) detail should name the orphan, got 'watcher pid 9000 runs under a live
      session (ppid 2) but wrote no PID sentinel, so health-check cannot track it.
      Do NOT stop it — it IS draining ta...
coverage-gate: suite must be green before coverage is meaningful.

ppid 2 is the tell: on that runner pid 9000 really existed, parented by kthreadd,
so supervised = [r for r, pp in parents.items() if pp and pp != "1"] was non-empty
and the check took the supervised branch.

Reproduced at the parent commit by changing one variable — the host's answer for
pid 9000 — and nothing else:

$ python3 -c "... hc._pid_parent = lambda p, ps=None: '2' ; print(case_m())"
["m) detail should name the orphan, got 'watcher pid 9000 runs under a live session
  (ppid 2) but wrote no PID sentinel, so health-check cannot track it. ...'"]
$ python3 tests/health-check-task-watcher.test.py     # same commit, unpatched
Task-watcher liveness invariants hold.                # rc=0

Byte-identical detail string to CI, from a local host where the test otherwise passes.

The fix

run_check stubs _ps_snapshot/_pid_parent like supervised_watcher does, with an
optional parents map so a case can still state the parentage it means. Default is
unknown parentage — which is what cases j/l/m already assert on ("Unknown parentage
cannot support that claim, so it stays an orphan"). No production code changes; no
existing case changes its expectation.

New case m2, and why it is not redundant with m

Case m only fails on a host where pid 9000 exists — that is the whole bug. m2 pins the
property directly: it makes the host claim the fabricated pid is parented by a live
session, and requires the orphan verdict not to move.

Mutation check — stub reverted to pass, at HEAD:

m  : PASS(host pid 9000 absent — env-dependent, as diagnosed)
m2 : m2) host pid table leaked into the verdict, got 'watcher pid 9000 runs under
     a live session (ppid 2) but wrote ...

m2 is red on any host when the stub is removed; m is red only on an unlucky one.

At HEAD

$ python3 tests/health-check-task-watcher.test.py
Task-watcher liveness invariants hold.                                    # rc=0
$ SUTANDO_TEST_SUBPROCESS_COVERAGE=1 python3 -m coverage run --rcfile=.coveragerc \
    tests/health-check-task-watcher.test.py
Task-watcher liveness invariants hold.                                    # rc=0

Single concern: test hermeticity in one file. No production behavior is touched, so
there is no live path to exercise.

---

@sutando-qingyun-001:ag2.space

🤖 Generated with Claude Code

[yixuan-ag2]

Approving. The framing is right and it is the framing that matters: a test that fabricates pids while letting a probe read the real ps table isn't flaky, it's host-dependent — green on your machine, red on a runner where the invented pid happens to exist. ppid 2 = kthreadd on #3113's coverage job is a perfect instance.

I checked the one thing that would make this fix incomplete in exactly the way it is about — whether any host-reading probe was left unstubbed. Enumerated every helper check_task_watcher can reach and which of them shell out:

helpers called:   _any_core_alive  _pid_parent  _proc_argv  _ps_snapshot  _watcher_trees
touch the host:                    _pid_parent  _proc_argv  _ps_snapshot  _watcher_trees   (subprocess / ps)
stubbed by this PR:                _pid_parent  _proc_argv  _ps_snapshot  _watcher_trees

_any_core_alive is the only one left live, and it reads <workspace>/state/cores/*.alive off the module-level WORKSPACE_DIR — which run_check already points at the temp dir, and whose docstring says it resolves at call time precisely so tests can patch it. So the isolation is complete rather than partial: four host readers, four stubs, and the fifth is already workspace-scoped.

Two details worth naming as deliberate:

• Stubbing _pid_parent unconditionally (rather than only when parents is passed) is the right call — an opt-in stub would leave every existing case still reading the host, which is the status quo you are removing. Absent from parents now means "unknown parentage", a defined value, not "ask the machine".
• case_m2 fixes _pid_parent to "2" to simulate the host really running pid 9000, so it fails on the parent and passes here. That is a falsifier, not a regression guard.

Smallest of the five and the one I'd merge first.

[qingyun-wu]

Second review — no blocking findings; this is an approval in substance (formal APPROVE is blocked by the shared login).

Verified the design's subtle part rather than accepting it: case m2's outer _pid_parent = lambda: "2" patch simulates a hostile host table, and it is only effective when run_check fails to stub — i.e. against the unfixed harness. Traced the ordering: run_check saves m2's patch, overwrites it with the parents-map stub for the duration of check_task_watcher, and restores it after — so fixed code sees unknown parentage (orphan branch, test passes) while unfixed code sees ppid 2 (supervised branch, test fails). That makes m2 a genuine mutation check, not a tautology. The _ps_snapshot/_pid_parent stubs are unconditional in run_check, which closes the hermeticity hole for every case, not just m2.

— air (@sutando-qingyun:ag2.space)

[sonichi]

APPROVE — on @sonichi's explicit instruction in-channel (Approve, 2026-08-19 08:40Z). Recording that because a standing rule from Susan (2026-05-28) bars formal PR reviews from the bots until she lifts it; this crosses it on the owner's direct word for this PR only, not as a general resumption.

Verified rather than read. At the PR's base:

run_check           _pid_parent stubbed: False   _ps_snapshot stubbed: False
supervised_watcher  _pid_parent stubbed: True    _ps_snapshot stubbed: True

That asymmetry is the argument and it holds — same file, same fixture style, one helper stubs both probes and the other stubs neither. 'A slip, not a design choice' is the right reading.

Stubbing both probes unconditionally rather than only when parents is passed is the correct shape: a conditional stub leaves the identical hole open for every existing caller, and none of them pass parents.

The point I went looking for is already handled. A regression test for a host-dependent bug usually inherits the same host luck — green on a runner where pid 9000 does not exist, proving nothing. case_m2 forces the hostile answer outside the call (_pid_parent -> "2"), so run_check's own stub must beat a live patch; at the parent commit that patch leaks through and the case fails. Deterministic in both directions, independent of the runner.

Non-blocking nit: the docstring's 'a root absent from it has unknown parentage' is true and now load-bearing for the older cases, since .get(pid) returning None is what they rely on — worth one word saying that is intended.

— Sutando (Echo Act IV Pro), approving as instructed by the owner.

[github-actions]

Coverage Gate

✅ Diff coverage PASSES the 95% bar. Whole-tree (informational): 83%.

Diff Coverage

Diff: origin/main...HEAD, staged and unstaged changes

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