Merge pull request #202 from levineuwirth/reap-ledger-silent-failures

Make the reap ledger's silent kill failures testable
2026-07-31 00:58:04 +00:00 · 2026-07-31 00:58:04 +00:00 · fbcf235cec
parent 22df6ab11a 7df13f2257
commit fbcf235cec
4 changed files with 1186 additions and 9 deletions
--- a/docs/active-work.md
+++ b/docs/active-work.md
@ -333,6 +333,94 @@ compatible.
    githubsucks/test-ambient-config-isolation
  ```
 ## Reap-ledger silent failures — IMPLEMENTED, PR OPEN
 - **Branch `reap-ledger-silent-failures`**, worktree
  `../pmacs-reap-ledger`, based on `githubsucks/main` @ `22df6ab`.
  `docs/reap-ledger-silent-failures-framing.md`, **revision 4**;
  approved at revision 3 after two review rounds (round 1: three
  blocking, two major; round 2: two blocking, two major; all accepted).
  Revision 4 records implementation findings, not a new design round.
 - **All four bets resolved.** Bet 1 (every site takes a directed
  outcome) and Bet 2 (every consequence is reachable) hold. **Bet 3
  resolves the shutdown coupling as real and measured** — under 500ms
  with a failed force-kill plus an errored probe, versus the full 2s
  bound with only the force-kill failing. **Bet 4 is falsified: no
  reporting channel exists**, so reporting becomes its own lane.
 - **The in-drain pin's first fixture was vacuous, and the bite caught
  it.** `poll_one` TERMs the group on leader exit, so an untrapped
  descendant died before writing its late marker — absent on *both*
  paths. With the seam reverted the pin failed only the consumed-plan
  check, never the content assertion. Fixed with `trap '' TERM` behind
  the readiness gate.
 - **Gates: 10/10 green** on the pushed tree, all five bootstrap-storage
  variables controlled — fmt, diff-check, clippy, `--lib` (1888),
  `--lib --features crdt` (2073), compile-mode (67), copy-mode in both
  feature configurations (18/19), M4 with the basedpyright skip (149),
  required GPU (221). The five new process pins ran **15/15** as a
  repetition set, since supervisor tests are load-sensitive.
 - **Unparked from PR #200's §5.** #200 retired the premise that
  justified the ledger's leniency and deliberately changed no
  disposition; this lane owns what it refused.
 - **Four sites, not the two #200 named.** In the persistent ledger: a
  probe error of any errno drops the entry and cancels escalation; a
  failed escalating `SIGKILL` is marked as succeeded, so **no later tick
  retries it**; and `shutdown()` discards its own force-kill result the
  same way — on the path that exists specifically to stop a leak at
  editor exit. Those last two are **distinct, not cumulative**:
  `shutdown()` force-kills every entry with no `!entry.killed` guard, so
  a failed escalation still gets one attempt at exit, while a failed
  force-kill leaks the group past exit with nothing left to try.
  **Plus the in-drain
  twin** `final_drain_runtime`, which collapses every errno to "dead"
  while no tick runs; a false "dead" there cancels the readers, so its
  failure mode is truncated output rather than a leaked process.
 - **The blast radius is exactly what the ledger exists for:** a
  TERM-ignoring descendant that outlived its leader with output
  redirected. Neither leader state nor reader state can see it; only
  group liveness can. A silent drop leaks the one process nothing else
  is watching. **Journey step 9 (build/test), not step 8** — the ledger
  arms only for `spec.group`, which spawn rejects for PTY mode, so no
  terminal reaches it; compile mode is the only production caller.
 - **`shutdown()`'s final loop terminates when the ledger empties**,
  which happens via the same silent drop — so the probe error that hides
  a leak can also end the cleanup loop early. That coupling is why the
  probe cannot be made strict on its own. **Its precondition is
  `any_running()` already false**, so the fixture must be a leader that
  exited leaving a survivor; any other shape tests the other arm of the
  disjunction.
 - **None of the three has been observed.** #200 saw an explicit
  `SIGTERM` fail in `signal()`, not a ledger call. The premise is
  falsified and the path exposed; the occurrence is not evidence these
  fire.
 - **They are also untestable today**: `tick_reap_ledger` and
  `shutdown()` call `nix` directly and consult no injection seam, unlike
  `signal()`'s `forced_kill_errno`. All five existing ledger tests
  exercise the success path only. The seam must be **site-directed and
  multi-outcome**: `shutdown()` calls `self.signal()` before its ledger
  force-kill, so a single global slot would be consumed by the wrong
  call, and the coupling test needs two pending outcomes at once. The
  in-drain probe repeats every 1 ms but only cancels readers after 50 ms
  of false "dead", so it needs a directed full-drain override rather
  than a one-shot error. Test state is per-supervisor and shared into
  the drain context, never global; teardown proves its intended site was
  reached. The in-drain SIGKILL's local flag has no independently
  observable outer-path consequence, so it is named but not given a
  dead injection seam. The first PR is the seam **plus** the tests that
  exercise it — a seam without tests does not show it reaches the
  intended calls.
 - **Diagnosis first, no disposition change proposed.** Stage A of the
  signal lane had three tolerance rules rejected across three revisions
  for the same shape of error on the same data structure.
 - Recovery from a clean checkout:
  ```sh
  git fetch githubsucks
  git worktree add ../pmacs-reap-ledger \
    -b reap-ledger-silent-failures \
    githubsucks/reap-ledger-silent-failures
  ```
 ## Folding lane (Arc 6) — Stages 1 and 2 MERGED; Stage 3 (GPU) is next
 Both shipped stages are on `main`; nothing in this arc is in flight. Stage 3
--- a/docs/agent-handoff.md
+++ b/docs/agent-handoff.md
@ -257,6 +257,69 @@ commands, read `docs/active-work.md` immediately after this file.
    disagree — and it still establishes no identity, because it is read
    inside the same read-then-act window and no portable mechanism closes
    that for a *group* (`pidfd` covers a process; macOS has neither).
 - **Reap-ledger silent failures — DIAGNOSTIC, in flight**
  (`docs/reap-ledger-silent-failures-framing.md`). The lane #200's
  framing §5 parked and its evidence unparked. **Four `kill(2)` results
  are discarded in the group reap ledger**, and each discard has its own
  consequence — three in the persistent ledger, one in the in-drain
  twin:
  - `tick_reap_ledger`'s probe cannot tell `ESRCH` (the group is gone —
    correct) from any other errno (we could not ask — not correct), and
    `retain` deletes the entry either way, cancelling escalation.
  - The deadline escalation sets `killed = true` whether or not the
    `SIGKILL` landed, so **no later tick retries it** — that arm is
    guarded by `!entry.killed` and never fires again for the group.
  - `shutdown()`'s force-kill discards its result the same way, on the
    path written specifically to stop a leak at editor exit. **It is not
    the same failure**, and the difference is the retry: `shutdown()`
    iterates the ledger with *no* `!entry.killed` guard, so it does
    re-kill an entry the escalation arm marked. A failed escalation
    leaks the group until editor exit, where one more attempt is made; a
    failed force-kill leaks it *past* editor exit, with nothing left to
    try. Saying the escalation is "never retried by anything" collapses
    the two.
  - `final_drain_runtime`'s twin collapses every errno into "dead",
    which quiesces the drain and **cancels the readers** — truncated
    output rather than a leaked process, and terminal for that drain
    where a later tick could revisit the ledger.
  - **None of the four has been observed to fire.** #200's evidence is an
    explicit `SIGTERM` failing in `signal()`, not any ledger call. What
    it retires is the *reason* ("EPERM cannot happen for our own
    children"), not the behaviour.
  - **`shutdown()`'s loop exit depends on the silent drop, and this is
    now measured.** It runs while `any_running() || !reap_ledger.is_empty()`,
    so an early exit needs the ledger empty **and** no live managed
    record — the leader-exited-survivor case the ledger exists to serve.
    With a failed force-kill followed by an errored probe it exits in
    under 500ms instead of holding its 2s bound, having concluded
    cleanup finished because the probe failed. Making the probe strict
    without touching the loop converts that silent early exit into a
    guaranteed 2s stall at every editor exit that hits it: **the two
    cannot be changed independently.**
  - **There is no channel for a background tick to report on.**
    `ProcessEvent` is keyed by `ProcessId`, while the ledger is keyed by
    pgid and is deliberately independent of managed records, so in the
    case that matters there is no id to attribute to. Every production
    consumer polls `take_events(id)` per known id; `take_all_events`
    would sidestep the keying but **has no production consumer at all**
    (two test call sites only). `pmacs.error` is dead. Reporting is
    therefore its own lane, as the framing's Bet 4 anticipated.
  - **A test seam for a background loop has to be directed.**
    `shutdown()` signals every managed process before it reaches its
    ledger force-kill, so one undirected "next kill fails" slot is eaten
    by the wrong call and the test passes while proving nothing. The
    persistent sites take a FIFO each (the coupling pin needs two
    outcomes pending at once); the in-drain site needs one outcome that
    **repeats for a whole drain**, because a one-shot is consumed by the
    next 1ms probe and can never survive the 50ms window `quiesced`
    requires.
  - **An absence assertion needs a fixture that could have produced the
    thing.** The in-drain pin's first fixture had no `trap '' TERM`, so
    `poll_one`'s leader-exit group TERM killed the descendant before it
    wrote its late marker: the marker was absent on *both* paths and the
    pin would have stayed green with the collapse fixed. The bite caught
    it — the reverted seam failed only the consumed-plan check, not the
    content assertion. That is what the consumed-plan check is for.
 - **Lean 4 arc (Arc 8) — stages 1, 2, 3a, 3b, 4a, 4b ALL LANDED**
  (`docs/lean4-mode-framing.md`; #160, #161, #167, #170, #179, #181). pmacs edits Lean 4: `arborium-lean` highlighting, a
  `lean4` major mode, `⟨⟩ ⦃⦄ ⟮⟯` pairs, and a `lake serve` language
--- a/docs/reap-ledger-silent-failures-framing.md
+++ b/docs/reap-ledger-silent-failures-framing.md
@ -0,0 +1,500 @@
 # Framing — group cleanup fails silently at four sites
 **Revision 4.** Status: **APPROVED at revision 3; implemented.** Lane
 `reap-ledger-silent-failures`, worktree `../pmacs-reap-ledger`, based on
 `githubsucks/main` @ `22df6ab`. Revision 4 records what implementation
 found; it is not a new design round.
 **Parked by PR #200's framing §5 and unparked by its evidence.** #200
 retired the premise that justified the ledger's leniency; it deliberately
 changed no disposition, and said so. This lane owns what it refused.
 ## Revision history
 **Revision 3 → 4**, found **while implementing**, not a new design
 round. Every bet resolved; one acceptance turned out to be satisfiable
 vacuously.
 - **Acceptance 2's in-drain clause could be met by a vacuous fixture,
  and was.** "The live descendant's named late output absent" says
  nothing about how the descendant stays live — and `poll_one` sends
  `SIGTERM` to the whole group on leader exit, so an untrapped
  descendant dies before it can write. The marker was then absent on
  *both* paths and the pin would have stayed green with the collapse
  fixed. The bite is what caught it: with the seam reverted, the pin
  failed only the consumed-plan check, never the content assertion. The
  fixture now uses `trap '' TERM` behind `survivor_script`'s readiness
  gate. **The lesson generalises past this pin: an absence assertion is
  only as good as the fixture's ability to produce the thing.**
 - **Bet 1 holds.** All four sites took a directed outcome with no
  restructuring. `final_drain_runtime` — the one §3 named as at risk,
  being a free function — needed only a shared handle on the context it
  already receives.
 - **Bet 2 holds, in the direction that keeps the lane.** All four
  consequences are reachable; none was already foreclosed by an earlier
  guard. The lane does not shrink.
 - **Bet 3 resolves: the coupling is real and measured.** With a failed
  force-kill and an errored probe, `shutdown()` returns in **under
  500ms** instead of holding its 2s bound, with the survivor alive. With
  only the failed force-kill it burns the full bound. §1.3's warning
  stands: making the probe strict without touching the loop converts a
  silent early exit into a guaranteed 2s stall.
 - **Bet 4 is falsified, exactly as its own clause anticipated: no
  channel exists.** `ProcessEvent` is keyed by `ProcessId` while the
  ledger is keyed by pgid and is deliberately independent of managed
  records, so in the leader-exited-survivor case there is no id to
  attribute to. Every production consumer polls `take_events(id)` per
  known id (`lua_bindings/mod.rs:8933`, `:10731`, `mcp.rs:361`).
  `take_all_events` would sidestep the keying but **has no production
  consumer at all** — its only two call sites are tests, despite a doc
  comment naming a `*processes*` buffer. `pmacs.error` was already
  known dead. **Reporting becomes its own lane** (§5), and this PR ships
  instrumentation plus tests without it, which is what §7 said it would
  do in this case.
 - **The in-drain `SIGKILL` is still unpinned**, as §1.2a promised. Its
  `group_killed` flag stays local and the persistent ledger retries in
  the same outer tick, so pinning the local non-retry still needs a
  call-count assertion or a direct free-function test. Unchanged, and
  restated here so a later reader does not mistake the shipped seam for
  covering it.
 **Revision 2 → 3**, after review round 2 (two blocking, two major).
 All four accepted; all four verified in the code first.
 - **The new in-drain test could not fire under the specified seam.** The
  drain initializes `last_data` on entry and probes again after each 1 ms
  sleep; `quiesced` needs a false result for the full 50 ms
  `READER_SEND_POLL_INTERVAL`. A one-shot error is therefore gone before
  reader cancellation. The in-drain override now returns its selected
  result for that one `GroupDrainCtx`, and the acceptance requires named
  late output to prove the cancellation through `poll_one`.
 - **The in-drain SIGKILL had no outer-path discriminator.** Its local
  `group_killed` flag is followed by the persistent ledger's retry in the
  same outer tick; testing it would require a call-count assertion or a
  direct free-function test. It remains an explicit code fact but is
  outside this diagnostic PR's injection seam.
 - **The seam needed a lifetime owner.** A context-local queue cannot be
  asserted at fixture teardown and a global one crosses test fixtures.
  The test state is now specified as per-supervisor and shared into the
  production `GroupDrainCtx`; an unconsumed outcome proves the intended
  site was never reached.
 - **The four-site scope had stale "three" language.** Acceptance and
  handoff obligations now distinguish the three persistent-ledger paths
  from the in-drain probe twin.
 **Revision 1 → 2**, after review round 1 (three blocking, two major).
 All five accepted; all five verified in the code first.
 - **§0 named the wrong journey step.** It claimed step 8, "Open a
  terminal", while Q#RL5 in the same document says the ledger is
  unreachable for PTY children. Both cannot be true. The only production
  `group = true` caller is compile mode
  (`builtin/runtime/compile.lua:820`), so this is **step 9, build/test**,
  plus general pipe-process cleanup.
 - **A fourth site was missed.** `final_drain_runtime` (`:2331`) probes
  `kill(-pgid, None)`, treats every error as dead, discards its `SIGKILL`
  result and sets its own `group_killed` flag — and it enforces the
  ledger deadline *while no tick runs*. It is now in scope (§1.2a).
 - **The staging contradicted itself.** "Bet 1 ships alone" against an
  acceptance requiring three failure-path tests, under one-branch /
  one-PR. A seam with no tests does not even prove it reaches the
  production calls. §7 now scopes the first PR as seam **plus**
  behaviour-preserving tests, which is still diagnosis-only.
 - **A generic seam is the wrong shape.** `shutdown()` calls
  `self.signal(*id, SIGKILL)` *before* its ledger force-kill, so a single
  "next kill errno" would be eaten by the wrong call. The seam is now
  site-directed (§3 Bet 1).
 - **§1.3 overstated the loop coupling.** Early exit needs the ledger
  empty **and** `any_running()` already false; a live managed record
  keeps the loop going regardless. The precondition is now stated.
 **Diagnosis first. No disposition change is proposed in this revision.**
 §2 asks whether one is warranted; §5 parks every candidate until the
 lane's own evidence exists. That ordering is not caution for its own
 sake — Stage A of the signal lane had three tolerance rules rejected
 across three revisions, each because it concluded something about one
 entity from something that was not about that entity, and this is the
 same shape of problem on the same data structure.
 ## 0. Coherence impact (COHERENCE §20)
 - **Journey step 9, "Build and test"** — every compile and grep run,
  plus general pipe-process cleanup. **Not step 8:** the ledger arms
  only for `proc.spec.group`, which spawn *rejects* for PTY mode, so no
  terminal ever reaches it (Q#RL5). The only production `group = true`
  caller is compile mode (`builtin/runtime/compile.lua:820`).
  **No grade change proposed.**
 - **Serves §9 (worker model), failure attribution.** The ledger is the
  one mechanism that can see a survivor nothing else can, and today it
  cannot report that it failed to.
 - **Interaction islands: none. Config registry: not adopted.
  Background-work attribution: unchanged.**
 - **No audited claim in COHERENCE.md changes**; under §25 no COHERENCE
  edit rides this PR.
 ## 1. Ground truth (verified at `22df6ab`)
 ### 1.1 What the ledger is for
 `tick_reap_ledger` (`src/process.rs:1472`) exists for one case its own
 doc names: **a TERM-ignoring descendant that survived its leader's clean
 exit with its output redirected.** Neither leader state nor reader state
 can see that survivor — `try_wait` reports the leader, and the readers
 see a closed pipe. Only group liveness can (Q#CM3, round-3 finding 1).
 That is the blast radius. A silent failure here leaks *precisely* the
 process the mechanism exists to catch, and nothing else in the
 supervisor is looking.
 ### 1.2 Three silent failures in the persistent ledger
 ```rust
 // (a) any probe error drops the entry
 if nix::sys::signal::kill(Pid::from_raw(-*pgid), None).is_err() {
    return false;
 }
 // (b) the escalating SIGKILL's result is discarded, and the entry is
 //     marked killed regardless
 if now >= entry.deadline && !entry.killed {
    let _ = nix::sys::signal::kill(Pid::from_raw(-*pgid), Some(Signal::SIGKILL));
    entry.killed = true;
 }
 ```
 **(a)** `retain` returning `false` deletes the entry, so escalation is
 cancelled. The comment is honest that this is a *bounded-growth policy*
 rather than a claim the group is gone — #200 corrected it — but the
 behaviour is unchanged: an `EPERM` probe is indistinguishable from
 `ESRCH`.
 **(b)** A failed `SIGKILL` is recorded as a successful one. The entry
 then satisfies `!entry.killed == false` forever, so **no later tick
 retries it** — the escalation arm is guarded by `!entry.killed` and
 never fires again for that group.
 **Scoped to ticks, and the scope matters.** `shutdown()`'s force-kill
 loop (c) iterates the ledger with **no `!entry.killed` guard**, so it
 *does* re-kill an entry this arm marked. The two failure modes are
 therefore distinct rather than cumulative:
 | Failure | Survivor lives until |
 |---|---|
 | escalation `SIGKILL` fails | editor exit, where `shutdown()` gets one more attempt |
 | `shutdown()` force-kill fails | past editor exit — nothing else tries |
 Saying (b) is "never retried by anything" would collapse that
 distinction and overstate it: the one remaining attempt is exactly what
 (c) is, and (c)'s own failure is a different and worse outcome.
 **(c) `shutdown()` has the same discard** (`:1763-1766`), on the path
 that exists specifically to stop a leak at editor exit:
 ```rust
 for (pgid, entry) in &mut self.reap_ledger {
    let _ = nix::sys::signal::kill(Pid::from_raw(-*pgid), Some(Signal::SIGKILL));
    entry.killed = true;
 }
 ```
 Its own comment says it is there because "a pre-deadline ledger ... would
 be silently discarded at Drop and leak the member". The fix for one
 silent leak was written with a discarded result of its own.
 ### 1.2a A fourth site: the in-drain twin
 `final_drain_runtime` (`:2331`, called once from `:1573`) runs the same
 pattern on the same pgid, while **no tick is running**:
 ```rust
 let group_alive = nix::sys::signal::kill(Pid::from_raw(-ctx.pgid), None).is_ok();
 if group_alive && now >= ctx.deadline && !group_killed {
    let _ = nix::sys::signal::kill(Pid::from_raw(-ctx.pgid), Some(Signal::SIGKILL));
    group_killed = true;
 }
 ```
 `is_ok()` collapses every errno into "dead", exactly as the persistent
 ledger's `is_err()` does — and the consequence differs. Once that false
 "dead" persists for one quiescent `READER_SEND_POLL_INTERVAL`, it makes
 `quiesced` true, which sets `rt.cancel` and **cancels the readers**, so
 the failure mode is truncated output rather than a leaked process. One
 false probe is not enough: the loop probes again every millisecond, and
 `last_data` starts at the drain's entry.
 **It is not identical to the persistent ledger and the framing does not
 claim it is.** A later `tick` can retry the ledger entry; this decision
 is terminal for that drain. It is in scope because it is the same
 collapse on the same data with its own consequence, not because it is
 the same bug.
 The ignored in-drain `SIGKILL` is a real code fact, but not an
 independently observable acceptance in this diagnostic PR. Its
 `group_killed` flag is local; when the drain returns, the same outer
 `tick` reaches the persistent ledger and can retry the group. Proving
 the local non-retry without a call-count assertion would mean testing
 the free function directly rather than its production caller. This lane
 therefore tests the probe-collapse consequence above and does **not**
 promise an injection seam for the in-drain `SIGKILL`. Any later retry
 policy must re-scout that local flag with the persistent ledger.
 **It constrains the seam.** `final_drain_runtime` is a free function
 taking `&RuntimeHandles` and `Option<GroupDrainCtx>` — there is no
 `&mut self` to hang a supervisor field on. Test-only injection state
 therefore remains owned by the `ProcessSupervisor` and is shared into
 `GroupDrainCtx` at the `:1573` production call site. It is never global:
 fixture teardown can then assert the planned outcome was consumed, even
 when unit tests run in parallel.
 ### 1.3 The shutdown loop's exit condition depends on the silent drop
 `shutdown()`'s final loop (`:1773-1775`) runs while
 `self.any_running() || !self.reap_ledger.is_empty()`, bounded at 2s, and
 calls `tick()` — which calls `tick_reap_ledger`.
 So the loop terminates when the ledger empties, and **the ledger empties
 via (a)**. On `ESRCH` that is correct: the group is gone. On any other
 errno the loop exits *early*, having concluded cleanup finished because
 the probe failed.
 **The precondition matters and revision 1 omitted it.** The condition is
 a disjunction: `any_running() || !reap_ledger.is_empty()`. An early exit
 therefore needs the ledger empty **and** `any_running()` already false —
 a live managed record keeps the loop running whatever the ledger does.
 The coupling is real for the case the ledger exists to serve, the
 leader-exited survivor, and Bet 3 must build exactly that fixture rather
 than any group.
 This coupling is the reason (a) cannot be changed casually: making the
 probe strict without touching the loop converts a silent early exit into
 a guaranteed 2-second stall at every editor exit that hits it.
 ### 1.4 None of the three has been observed
 **#200 observed an explicit `SIGTERM` failing in `signal()`, not any
 ledger call.** What it established is narrower and still sufficient to
 open this lane: a group-directed `kill` computed from the spawn-time
 `pgid == pid` assumption returned `EPERM` while the leader was alive, on
 macOS, intermittently
 ([run 30553376486](https://github.com/levineuwirth/pmacs/actions/runs/30553376486/job/90907461258)).
 That retires "EPERM cannot happen for our own children" as a *reason* to
 discard an arbitrary group error. It does **not** show that any of (a),
 (b) or (c) has fired. This lane must not claim otherwise, and §3's bets
 are built to find out rather than to assume.
 ### 1.5 The ledger's kills have no injection seam
 `signal()` consults `forced_kill_errno` (Q#PD4), which is how #176 and
 #200 tested failure paths without provoking real errnos.
 **`tick_reap_ledger` calls `nix` directly and consults nothing.** Same
 for `shutdown()`'s loop.
 So all three failure paths are, today, **untestable**. That is the
 first thing this lane has to fix, and it is a prerequisite for any
 disposition change rather than a nicety: a disposition change whose
 failure path cannot be exercised is a rule nobody can falsify.
 ### 1.6 What is tested today
 `liveness_probe_reaps_term_ignoring_survivor_after_leader_exit`
 (`:4274`), `repeated_terminate_does_not_extend_ledger_deadline`
 (`:4314`), `shutdown_force_kills_outstanding_ledger_groups` (`:4350`),
 `leader_exit_reap_bounds_drain_with_pipe_holding_descendant` (`:4415`),
 and `setsid_escapee_is_not_reaped_and_teardown_reclaims_readers`
 (`:4450`).
 Every one exercises the **success** path. None injects a probe or
 `SIGKILL` failure, because §1.5 makes that impossible.
 *`repeated_terminate_does_not_extend_ledger_deadline` is also the test
 that flaked on macOS in #191 — the occurrence that produced §1.4's
 evidence. It is load-sensitive and unrelated to what this lane changes;
 noted so a red run on it is not mistaken for this lane's doing.*
 ### 1.7 Limits of the evidence
 - **Not reproduced.** No ledger probe or `SIGKILL` has been seen to
  fail, on any platform.
 - **The mechanism is not established.** Why a group-directed `kill` can
  return `EPERM` against a live owned child is still unknown — #200
  narrowed it and explicitly did not solve it.
 - **Group identity remains unprovable** (#200 §1.5). Nothing this lane
  measures can distinguish the original group from a recycled one; a
  `pidfd` covers a process, not a group, and macOS has neither.
 ## 2. Questions
 - **Q#RL1** — Should the probe distinguish `ESRCH` from other errnos?
  *Unknown, and deliberately not proposed yet. It is the obvious change
  and it directly trades bounded growth (the stated original reason) for
  correctness, while §1.3 shows it also changes editor-exit timing. It
  needs evidence and its own review.*
 - **Q#RL2** — Should a failed escalation be retried, and how many times?
  *Unknown. `killed = true` on a failed `SIGKILL` is clearly wrong as
  bookkeeping; what should replace it is a policy question, not an
  obvious fix.*
 - **Q#RL3** — How does a background tick report anything? **ANSWERED at
  revision 4: it cannot, today.** `ProcessEvent` is keyed by
  `ProcessId`; the ledger is keyed by pgid and is deliberately
  independent of managed records, so in the leader-exited-survivor case
  — the one the mechanism exists for — there is no id to attribute to.
  All three production consumers poll `take_events(id)` per known id
  (`lua_bindings/mod.rs:8933`, `:10731`, `mcp.rs:361`).
  `take_all_events` would sidestep the keying but has **no production
  consumer**; its only call sites are two tests, notwithstanding a doc
  comment naming a `*processes*` buffer. `pmacs.error` was already dead
  at 15 sites. Reporting is therefore parked as its own lane (§5).
 - **Q#RL4** — Does the `shutdown()` loop need its own termination
  condition if (a) becomes strict? *Almost certainly (§1.3), and that
  coupling is why the two cannot be changed independently.*
 - **Q#RL5** — Is the ledger reachable for PTY children? **No** —
  `spec.group` is rejected at spawn for PTY mode, so the ledger is a
  pipe-path mechanism only. Stated because #200 revision 2 got this
  exact relationship wrong in the opposite direction.
 ## 3. Bets
 - **Bet 1 — the four sites can be made injectable, site by site,
  without changing behaviour.** Not a generic "next kill errno":
  `shutdown()` calls `self.signal(*id, SIGKILL)` *before* its ledger
  force-kill, so a single shared one-shot would be consumed by the wrong
  call and the test would pass while proving nothing.
  The persistent-ledger and shutdown outcomes are **directed and
  one-shot**. The in-drain probe instead needs a directed result for one
  complete drain: a one-shot error is consumed by its next 1 ms probe and
  cannot reach `quiesced`'s 50 ms interval. The test mode must therefore
  return the selected error for every in-drain probe until that
  `GroupDrainCtx` ends, while leaving the later persistent-ledger probe
  real.
  The independently addressable outcomes are:
  | Site | What is injected |
  |---|---|
  | `tick_reap_ledger` probe | the `kill(-pgid, None)` result |
  | `tick_reap_ledger` escalation | the `SIGKILL` result |
  | `shutdown()` force-kill | the `SIGKILL` result |
  | `final_drain_runtime` probe | one selected result for the complete drain, via `GroupDrainCtx` (§1.2a) |
  Bet 3's coupling test needs **two at once** — a failed shutdown
  force-kill *and* a failed subsequent probe — so the seam must express
  more than one pending outcome. A typed queue per site, or a per-site
  slot, either is acceptable; a single global slot is not.
  **Fixture cleanup is part of the seam, not an afterthought.** Test
  state is per-supervisor, not global. An unconsumed planned outcome
  proves the fixture missed its intended production site; each finite
  outcome is consumed on use and asserted empty at fixture teardown, and
  the in-drain override records that it was used before its context ends.
  - *Falsified if* a site cannot take a directed outcome without
    restructuring the code under test — which would make the test a test
    of the restructuring. `final_drain_runtime` is the one at risk,
    being a free function.
 - **Bet 2 — each silent consequence is demonstrable once injectable.**
  With the seam: an `EPERM` probe drops an entry whose group is still
  alive; a failed `SIGKILL` leaves `killed = true` so no later **tick**
  retries it; `shutdown()`'s discard leaks the group past editor exit,
  which is a different and worse outcome; and a continuously false
  in-drain probe cancels readers before a live descendant's deliberately
  late output can arrive.
  - *Falsified if* any of the three turns out to be unreachable in
    practice — for instance if some earlier guard makes the entry
    already absent. **That would be a genuinely good outcome** and would
    shrink this lane rather than embarrass it.
 - **Bet 3 — the shutdown coupling is real and measurable.** A test shows
  the final loop exiting early when the probe errors, rather than
  running to its 2s bound.
  - **The fixture must have `any_running()` already false** (§1.3): a
    leader that has exited leaving a group survivor. Any other shape
    tests the disjunction's other arm and proves nothing about the
    coupling.
  - *Falsified if* the loop still runs to its bound with the ledger
    emptied and no managed record live — in which case §1.3 overstates
    the coupling and the two changes can be separated after all.
 - **Bet 4 — a failure here is reportable at all.** Q#RL3 has no answer
  yet. This bet is a scouting obligation, not a design: find every
  channel a background tick could use, and say plainly if none exists.
  - *Falsified if* the only available channel is one already known dead
    (`pmacs.error`) — in which case reporting becomes its own lane and
    this one ships instrumentation plus tests without it.
 ## 4. Acceptance
 1. A **directed, multi-outcome** injection seam covering the three
   persistent-ledger paths plus the in-drain probe of §3 Bet 1, on
   Q#PD4's terms: result only, everything else production code. The
   in-drain result lasts only for its one production `GroupDrainCtx`.
   Finite outcomes are consumed on use and asserted empty at teardown.
 2. A test per silent consequence, each asserting the observable consequence
   — entry dropped while the group lives; `killed` set after a failed
   kill; the same at shutdown; readers cancelled after a false "dead" in
   the drain and the live descendant's named late output absent — rather
   than that a function was called.
 3. Each new test falsified by an actual revert, both directions
   recorded in the PR body.
 4. The `shutdown()` coupling of §1.3 pinned by a test, whichever way
   Bet 3 resolves.
 5. **No disposition change.** `retain` still drops on any error;
   `killed` is still set unconditionally. This lane makes the failures
   visible and testable; changing them is §5's.
 6. Q#RL3 answered in the PR body with the channels actually found, or
   an explicit statement that none exists.
 7. `docs/agent-handoff.md` records the three persistent-ledger paths and
   the in-drain probe twin, and that none has been observed — the
   distinction #200 had to make twice.
 ## 5. Parked
 - **Q#RL1's strict-`ESRCH` probe**, **Q#RL2's retry policy**, and any
  other disposition change. Each needs this lane's evidence.
 - **Reporting**, if Bet 4 finds no channel.
 - **Retargeting to the measured pgid**, and any EPERM/ESRCH tolerance
  rule in `signal()` — still parked from #200, unchanged.
 - **`signal_target`'s read-then-kill of `tcgetpgrp`** on the PTY path —
  Stage A's "most likely real fix site", still unframed, still not this.
 - **Why a group-directed `kill` can return `EPERM` against a live owned
  child.** The mechanism is unknown; this lane instruments the
  consequences, not the cause.
 ## 6. Gates
 Standard suite, each its own step with a real exit status and nothing
 after the command that could mask it: `cargo fmt --check`; `cargo clippy
 --workspace --all-targets -- -D warnings`; `cargo test --lib`; `cargo
 test --lib --features crdt`; `compile_mode_acceptance`;
 `terminal_copy_mode_acceptance` (both feature configurations); `cargo
 test --test m4_acceptance -- --skip basedpyright`;
 `PMACS_REQUIRE_GPU=1 cargo test -p pmacs-gpu`; `git diff --check`.
 **All five bootstrap-storage variables controlled locally** —
 `XDG_CONFIG_HOME`, `XDG_DATA_HOME`, `XDG_STATE_HOME`, `XDG_CACHE_HOME`,
 `PMACS_STATE_HOME` — per the ambient-root framing merged as #201.
 Isolating only the config root leaves the data-root write path open.
 **Process-supervisor tests are load-sensitive**; the PR body records
 repetition counts rather than a single green.
 ## 7. Branch plan
 One branch, one PR: **the seam together with the tests that exercise
 it.** Revision 1 said "Bet 1 ships alone", which contradicted an
 acceptance requiring failure-path tests under one-branch/one-PR — and
 was wrong on its own terms, because a seam with no tests does not even
 demonstrate that it reaches the intended production calls.
 This is still diagnosis-only: every test pins **current** behaviour,
 including the behaviour that is wrong. Nothing in this PR changes what
 the supervisor does.
 If Bet 2 finds a path unreachable, the lane shrinks and says so rather
 than manufacturing a failure to justify itself. If Q#RL3 finds no
 reporting channel, reporting becomes its own lane and this PR ships
 instrumentation plus tests without it.
--- a/src/process.rs
+++ b/src/process.rs
@ -48,7 +48,7 @@
 //! `unsafe` block — see [`build_pty_command`] for the full
 //! rationale.
-use std::collections::HashMap;
+use std::collections::{HashMap, VecDeque};
 use std::io::{Read, Write};
 use std::path::PathBuf;
 use std::sync::atomic::{AtomicBool, AtomicU64, AtomicUsize, Ordering};
@ -480,6 +480,17 @@ pub struct ProcessSupervisor {
    /// Test seam for the PTY foreground-group lookup (see
    /// `force_next_pty_lookup`). Always `None` outside tests.
    forced_pty_lookup: Option<Result<i32, PtyLookupFailure>>,
    /// Directed test seam for the reap ledger's **own** `kill(2)` calls
    /// (see [`ReapKillFaults`]). Always empty in production: the only
    /// ways to add an outcome are `#[cfg(test)]`.
    ///
    /// Shared behind an `Arc` because `final_drain_runtime` is a free
    /// function taking `&RuntimeHandles` — there is no `&mut self` to
    /// reach — so the plan travels into it through [`GroupDrainCtx`].
    /// It is owned by the supervisor rather than living in a global, so
    /// fixture teardown can assert its plan was consumed even when unit
    /// tests run in parallel.
    reap_kill_faults: Arc<Mutex<ReapKillFaults>>,
 }
 /// One armed group in the reap ledger.
@ -491,6 +502,104 @@ struct GroupReap {
    killed: bool,
 }
 /// Which of the reap ledger's `kill(2)` calls a planned test outcome
 /// belongs to.
 ///
 /// **The seam is directed, and that is the whole point.** `shutdown()`
 /// signals every managed process through [`ProcessSupervisor::signal`]
 /// *before* it reaches its ledger force-kill, so a single undirected
 /// "next kill fails" slot would be eaten by the wrong call and the test
 /// would report a pass while proving nothing.
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
 enum ReapKillSite {
    /// `tick_reap_ledger`'s liveness probe, `kill(-pgid, None)`.
    LedgerProbe,
    /// `tick_reap_ledger`'s deadline escalation, `kill(-pgid, SIGKILL)`.
    LedgerEscalation,
    /// `shutdown()`'s pre-loop force-kill, `kill(-pgid, SIGKILL)`.
    ShutdownForceKill,
 }
 /// Planned failures for the reap ledger's own `kill(2)` calls. Empty in
 /// production; populated only by `#[cfg(test)]` helpers.
 ///
 /// Two shapes, because the sites need different lifetimes:
 ///
 /// * The three persistent-ledger paths take a **FIFO of one-shot**
 ///   outcomes each, since one tick makes one call per site. A queue
 ///   rather than a slot because the shutdown-coupling pin needs a failed
 ///   force-kill *and* a failed subsequent probe pending at once.
 /// * The in-drain probe takes **one outcome that repeats for one whole
 ///   drain**. A one-shot cannot work there: `final_drain_runtime` probes
 ///   again every millisecond and `quiesced` needs a false answer to
 ///   persist across a full [`READER_SEND_POLL_INTERVAL`], so a one-shot
 ///   error is long gone before reader cancellation can be reached.
 #[derive(Default)]
 struct ReapKillFaults {
    /// Per-site queue; each entry is consumed by one call at that site.
    queued: HashMap<ReapKillSite, VecDeque<nix::errno::Errno>>,
    /// The errno every probe inside the one claiming `GroupDrainCtx`
    /// reports, for that drain's whole lifetime.
    in_drain: Option<nix::errno::Errno>,
    /// Set once a drain has claimed `in_drain`, so a second drain in the
    /// same test probes for real instead of inheriting the fault.
    in_drain_claimed: bool,
    /// Set the first time the claiming drain actually reported the
    /// fault. Teardown asserts it: an armed-but-never-reported plan
    /// proves the fixture never reached the site it aimed at.
    #[cfg(test)]
    in_drain_used: bool,
 }
 impl ReapKillFaults {
    /// Consume one planned failure for `site`, if any.
    fn take(&mut self, site: ReapKillSite) -> Option<nix::errno::Errno> {
        self.queued.get_mut(&site)?.pop_front()
    }
    /// Claim the armed in-drain fault for one `GroupDrainCtx`. Returns
    /// `false` in production, where `in_drain` is always `None`.
    fn claim_in_drain(&mut self) -> bool {
        if self.in_drain.is_none() || self.in_drain_claimed {
            return false;
        }
        self.in_drain_claimed = true;
        true
    }
    /// The errno the claiming drain's probe should report.
    fn in_drain_report(&mut self) -> Option<nix::errno::Errno> {
        let errno = self.in_drain?;
        #[cfg(test)]
        {
            self.in_drain_used = true;
        }
        Some(errno)
    }
 }
 /// The reap ledger's own `kill(2)`, with the directed seam of
 /// [`ReapKillSite`] applied first.
 ///
 /// On Q#PD4's terms: the injection replaces the **result only**. The
 /// branch it feeds, the ledger bookkeeping, and every other syscall run
 /// as production code.
 fn reap_kill(
    faults: &Mutex<ReapKillFaults>,
    site: ReapKillSite,
    pgid: i32,
    signal: Option<Signal>,
 ) -> nix::Result<()> {
    if let Some(errno) = faults
        .lock()
        .expect("reap fault plan is never held across a panic")
        .take(site)
    {
        return Err(errno);
    }
    nix::sys::signal::kill(Pid::from_raw(-pgid), signal)
 }
 struct ManagedProcess {
    spec: ProcessSpec,
    state: ProcessState,
@ -1140,6 +1249,55 @@ impl ProcessSupervisor {
            group_term_grace: GROUP_TERM_GRACE,
            forced_kill_errno: None,
            forced_pty_lookup: None,
            reap_kill_faults: Arc::new(Mutex::new(ReapKillFaults::default())),
        }
    }
    /// Plan a one-shot failure for the reap ledger's `kill(2)` at
    /// `site`. Queued per site (see [`ReapKillFaults`]), so a plan for
    /// one site can never be consumed by another's call.
    #[cfg(test)]
    fn plan_reap_kill_failure(&mut self, site: ReapKillSite, errno: nix::errno::Errno) {
        self.reap_kill_faults
            .lock()
            .expect("reap fault plan")
            .queued
            .entry(site)
            .or_default()
            .push_back(errno);
    }
    /// Plan the in-drain probe failure: the *next* group drain to start
    /// claims it and reports `errno` from every probe for that drain's
    /// whole lifetime. See [`ReapKillFaults`] for why this one is not a
    /// one-shot.
    #[cfg(test)]
    fn plan_in_drain_probe_failure(&mut self, errno: nix::errno::Errno) {
        self.reap_kill_faults
            .lock()
            .expect("reap fault plan")
            .in_drain = Some(errno);
    }
    /// Fixture teardown: every planned outcome must have been consumed
    /// by the production site it was aimed at. An unconsumed plan means
    /// the fixture never reached that site, which would otherwise leave
    /// a test asserting the *absence* of an effect it never provoked.
    #[cfg(test)]
    fn assert_reap_faults_consumed(&self) {
        let faults = self.reap_kill_faults.lock().expect("reap fault plan");
        for (site, queue) in &faults.queued {
            assert!(
                queue.is_empty(),
                "{} planned {site:?} failure(s) were never consumed — the fixture did not reach that production site",
                queue.len()
            );
        }
        if faults.in_drain.is_some() {
            assert!(
                faults.in_drain_used,
                "the in-drain probe fault was armed but never reported — the fixture did not reach final_drain_runtime's probe"
            );
        }
    }
@ -1471,6 +1629,8 @@ impl ProcessSupervisor {
    /// see that survivor; only group liveness can).
    fn tick_reap_ledger(&mut self) {
        let now = Instant::now();
        // Cloned out before `retain` takes `&mut self.reap_ledger`.
        let faults = Arc::clone(&self.reap_kill_faults);
        self.reap_ledger.retain(|pgid, entry| {
            // ESRCH: no such group — done. Any other probe error is
            // also treated as "nothing left we can reach", so the
@ -1491,11 +1651,16 @@ impl ProcessSupervisor {
            // Both are known and deliberately unchanged here: the
            // diagnostic lane that found them does not alter
            // disposition. Fixing it is its own lane.
-            if nix::sys::signal::kill(Pid::from_raw(-*pgid), None).is_err() {
+            if reap_kill(&faults, ReapKillSite::LedgerProbe, *pgid, None).is_err() {
                return false;
            }
            if now >= entry.deadline && !entry.killed {
-                let _ = nix::sys::signal::kill(Pid::from_raw(-*pgid), Some(Signal::SIGKILL));
+                let _ = reap_kill(
                    &faults,
                    ReapKillSite::LedgerEscalation,
                    *pgid,
                    Some(Signal::SIGKILL),
                );
                entry.killed = true;
            }
            true
@ -1564,13 +1729,19 @@ impl ProcessSupervisor {
                GroupDrainCtx {
                    pgid,
                    deadline: entry.deadline,
                    faults: Arc::clone(&self.reap_kill_faults),
                    in_drain_fault_claimed: self
                        .reap_kill_faults
                        .lock()
                        .expect("reap fault plan is never held across a panic")
                        .claim_in_drain(),
                }
            })
        } else {
            None
        };
        let now = Instant::now();
-        let final_output = final_drain_runtime(runtime, group_ctx);
+        let final_output = final_drain_runtime(runtime, group_ctx.as_ref());
        let (termination, event) = match status {
            Ok(Some(TermStatus::Exited(code))) => (
                Termination::Exited {
@ -1760,8 +1931,14 @@ impl ProcessSupervisor {
        // (leader exited promptly, TERM-ignoring group member alive)
        // would be silently discarded at Drop and leak the member
        // (Q#CM3, round-4 finding 1).
        let faults = Arc::clone(&self.reap_kill_faults);
        for (pgid, entry) in &mut self.reap_ledger {
-            let _ = nix::sys::signal::kill(Pid::from_raw(-*pgid), Some(Signal::SIGKILL));
+            let _ = reap_kill(
                &faults,
                ReapKillSite::ShutdownForceKill,
                *pgid,
                Some(Signal::SIGKILL),
            );
            entry.killed = true;
        }
        // Final reap loop. SIGKILL is delivered immediately by the
@ -1805,6 +1982,15 @@ impl ProcessSupervisor {
    fn reap_ledger_len(&self) -> usize {
        self.reap_ledger.len()
    }
    /// Whether the ledger has recorded a SIGKILL as sent for `pgid`.
    /// `None` if no entry is armed. The whole point of the
    /// failed-escalation pin is that this reads `true` after a kill
    /// that never happened.
    #[cfg(test)]
    fn reap_ledger_killed(&self, pgid: i32) -> Option<bool> {
        self.reap_ledger.get(&pgid).map(|e| e.killed)
    }
 }
 impl Drop for ProcessSupervisor {
@ -2322,13 +2508,40 @@ fn drain_runtime_output(rt: &RuntimeHandles) -> Vec<ProcessEventKind> {
 /// ledger's deadline for this group: the drain enforces it from
 /// inside its loop because no other tick runs while the drain
 /// blocks the frame.
 #[derive(Clone, Copy)]
 struct GroupDrainCtx {
    pgid: i32,
    deadline: Instant,
    /// The supervisor's fault plan (empty in production), carried here
    /// because this drain runs in a free function with no `&mut self`.
    faults: Arc<Mutex<ReapKillFaults>>,
    /// True when this drain claimed the armed in-drain probe fault at
    /// construction. Exactly one drain can claim it.
    in_drain_fault_claimed: bool,
 }
-fn final_drain_runtime(rt: &RuntimeHandles, group: Option<GroupDrainCtx>) -> Vec<ProcessEventKind> {
+/// The in-drain liveness probe, with the seam of §1.2a applied first.
 ///
 /// The injected errno is *returned*, and the caller's `.is_ok()` then
 /// discards it — which is the collapse under test, left exactly as it
 /// is. This function changes what the probe reports, never what the
 /// drain does with the report.
 fn in_drain_probe(ctx: &GroupDrainCtx) -> nix::Result<()> {
    if ctx.in_drain_fault_claimed
        && let Some(errno) = ctx
            .faults
            .lock()
            .expect("reap fault plan is never held across a panic")
            .in_drain_report()
    {
        return Err(errno);
    }
    nix::sys::signal::kill(Pid::from_raw(-ctx.pgid), None)
 }
 fn final_drain_runtime(
    rt: &RuntimeHandles,
    group: Option<&GroupDrainCtx>,
 ) -> Vec<ProcessEventKind> {
    let deadline = Instant::now() + EXIT_OUTPUT_DRAIN_TIMEOUT;
    let mut out = Vec::new();
    // Group drains get tighter bounds than the plain byte-flush
@ -2358,9 +2571,9 @@ fn final_drain_runtime(rt: &RuntimeHandles, group: Option<GroupDrainCtx>) -> Vec
        if rt.readers.iter().all(std::thread::JoinHandle::is_finished) && !drained_any {
            return out;
        }
-        if let Some(ctx) = &group {
+        if let Some(ctx) = group {
            let now = Instant::now();
-            let group_alive = nix::sys::signal::kill(Pid::from_raw(-ctx.pgid), None).is_ok();
+            let group_alive = in_drain_probe(ctx).is_ok();
            if group_alive && now >= ctx.deadline && !group_killed {
                let _ = nix::sys::signal::kill(Pid::from_raw(-ctx.pgid), Some(Signal::SIGKILL));
                group_killed = true;
@ -4374,6 +4587,319 @@ mod tests {
        );
    }
    // -----------------------------------------------------------------
    // Reap-ledger silent failures (framing §4).
    //
    // Every pin below asserts the *consequence* of a discarded kill(2)
    // result — a live group the ledger stopped tracking, a survivor the
    // ledger records as killed, output cancelled before it arrived —
    // and never that a function was called. All five pin CURRENT
    // behaviour, including the behaviour that is wrong: this lane
    // changes no disposition (§7).
    //
    // Each ends with `assert_reap_faults_consumed`, which is not
    // ceremony: a planned failure that was never consumed means the
    // fixture never reached the production site, and an
    // absence-assertion under those conditions is vacuous.
    // -----------------------------------------------------------------
    /// Kill a leaked fixture descendant that a pin deliberately let
    /// survive. Called after the assertions, never before them.
    fn reap_fixture_survivor(pid: i32) {
        let _ = nix::sys::signal::kill(Pid::from_raw(pid), Some(Signal::SIGKILL));
    }
    #[test]
    fn an_unreachable_probe_drops_an_entry_whose_group_is_still_alive() {
        // §1.2 (a). `retain` returning false deletes the entry, so
        // escalation is cancelled — and the probe cannot tell ESRCH
        // ("the group is gone", correct) from any other errno ("we
        // could not ask", not correct).
        let dir = tempfile::tempdir().expect("tempdir");
        let mut sup = ProcessSupervisor::new();
        // Long enough that the escalation cannot fire and confuse the
        // reading: the only thing that empties the ledger here is (a).
        sup.set_group_term_grace(Duration::from_secs(30));
        let (script, pidfile) = survivor_script(dir.path(), true);
        let id = sup
            .spawn(sh_group_spec("probe-eperm", &script))
            .expect("spawn");
        let _ = drain_until(&mut sup, id, Duration::from_secs(5), has_exited);
        let survivor = wait_pidfile(&pidfile);
        assert!(pid_alive(survivor), "survivor alive before the probe");
        assert_eq!(sup.reap_ledger_len(), 1, "ledger armed before the probe");
        sup.plan_reap_kill_failure(ReapKillSite::LedgerProbe, nix::errno::Errno::EPERM);
        sup.tick();
        assert_eq!(
            sup.reap_ledger_len(),
            0,
            "an EPERM probe drops the entry exactly as ESRCH would"
        );
        assert!(
            pid_alive(survivor),
            "and the group it stopped tracking is still alive — this is the leak"
        );
        sup.assert_reap_faults_consumed();
        reap_fixture_survivor(survivor);
    }
    #[test]
    fn a_failed_escalation_is_recorded_as_a_successful_one() {
        // §1.2 (b). `entry.killed = true` runs unconditionally, so a
        // SIGKILL that never landed satisfies `!entry.killed == false`
        // forever. The consequence is not bookkeeping: **no later tick
        // retries it**, so the survivor outlives every escalation the
        // ledger will ever attempt during the session.
        //
        // Scoped to ticks deliberately. `shutdown()`'s force-kill loop
        // iterates the ledger with **no `!entry.killed` guard**, so it
        // does re-kill an entry this arm marked — which is why that
        // failure mode is distinct and has its own pin. This one ticks
        // and never calls `shutdown`, so what it asserts is exactly
        // what it says.
        let dir = tempfile::tempdir().expect("tempdir");
        let mut sup = ProcessSupervisor::new();
        sup.set_group_term_grace(Duration::from_millis(150));
        let (script, pidfile) = survivor_script(dir.path(), true);
        let id = sup
            .spawn(sh_group_spec("kill-eperm", &script))
            .expect("spawn");
        let events = drain_until(&mut sup, id, Duration::from_secs(5), has_exited);
        let pgid = i32::try_from(started_pid(&events).expect("leader pid")).expect("pgid fits");
        let survivor = wait_pidfile(&pidfile);
        sup.plan_reap_kill_failure(ReapKillSite::LedgerEscalation, nix::errno::Errno::EPERM);
        // Past the grace, so the escalation arm is the one that runs.
        std::thread::sleep(Duration::from_millis(250));
        sup.tick();
        assert_eq!(
            sup.reap_ledger_killed(pgid),
            Some(true),
            "the entry records a SIGKILL that returned EPERM as sent"
        );
        // The retry that `killed = true` forecloses: keep ticking well
        // past the grace and the survivor is still there.
        let stop = Instant::now() + Duration::from_millis(600);
        while Instant::now() < stop {
            sup.tick();
            std::thread::sleep(Duration::from_millis(20));
        }
        assert!(
            pid_alive(survivor),
            "no tick ever retries the failed SIGKILL, so the survivor outlives the ledger's only escalation"
        );
        assert_eq!(
            sup.reap_ledger_len(),
            1,
            "the entry is retained, and inert to every subsequent tick"
        );
        sup.assert_reap_faults_consumed();
        reap_fixture_survivor(survivor);
    }
    #[test]
    fn shutdown_still_force_kills_a_group_a_failed_escalation_marked_killed() {
        // The boundary of the pin above, and the reason its claim is
        // "no later TICK retries it" rather than "nothing retries it".
        //
        // `shutdown()`'s force-kill loop iterates the ledger with no
        // `!entry.killed` guard, so the one thing that still acts on an
        // entry the escalation arm gave up on is editor exit. That
        // keeps the two failure modes distinct: a failed escalation
        // leaks the group until exit; a failed force-kill leaks it
        // past exit.
        //
        // No fault is planned for the shutdown site here — the whole
        // point is that this force-kill really lands.
        let dir = tempfile::tempdir().expect("tempdir");
        let mut sup = ProcessSupervisor::new();
        sup.set_group_term_grace(Duration::from_millis(150));
        let (script, pidfile) = survivor_script(dir.path(), true);
        let id = sup
            .spawn(sh_group_spec("escalation-then-shutdown", &script))
            .expect("spawn");
        let events = drain_until(&mut sup, id, Duration::from_secs(5), has_exited);
        let pgid = i32::try_from(started_pid(&events).expect("leader pid")).expect("pgid fits");
        let survivor = wait_pidfile(&pidfile);
        sup.plan_reap_kill_failure(ReapKillSite::LedgerEscalation, nix::errno::Errno::EPERM);
        std::thread::sleep(Duration::from_millis(250));
        sup.tick();
        assert_eq!(
            sup.reap_ledger_killed(pgid),
            Some(true),
            "precondition: the entry is marked killed by a SIGKILL that failed"
        );
        assert!(pid_alive(survivor), "precondition: the survivor is alive");
        sup.shutdown();
        assert!(
            !pid_alive(survivor),
            "shutdown force-kills every armed entry, marked or not — so an escalation \
             failure is not the survivor's last reprieve"
        );
        assert_eq!(sup.reap_ledger_len(), 0, "and the entry probes to ESRCH");
        sup.assert_reap_faults_consumed();
    }
    #[test]
    fn a_failed_shutdown_force_kill_leaks_the_group_and_burns_the_bound() {
        // §1.2 (c). The path that exists specifically to stop a leak at
        // editor exit discards its own kill result — and because it
        // still sets `killed`, the final loop can never escalate again.
        // It therefore runs to its full 2s bound and exits with the
        // member alive.
        let dir = tempfile::tempdir().expect("tempdir");
        let mut sup = ProcessSupervisor::new();
        // The ledger must not be able to reap on its own; only
        // shutdown's force-kill could have.
        sup.set_group_term_grace(Duration::from_secs(30));
        let (script, pidfile) = survivor_script(dir.path(), true);
        let id = sup
            .spawn(sh_group_spec("shutdown-eperm", &script))
            .expect("spawn");
        let _ = drain_until(&mut sup, id, Duration::from_secs(5), has_exited);
        let survivor = wait_pidfile(&pidfile);
        assert!(pid_alive(survivor), "survivor alive pre-shutdown");
        sup.plan_reap_kill_failure(ReapKillSite::ShutdownForceKill, nix::errno::Errno::EPERM);
        let t0 = Instant::now();
        sup.shutdown();
        let elapsed = t0.elapsed();
        assert!(
            pid_alive(survivor),
            "the group survives editor exit — the leak this path was written to prevent"
        );
        assert_eq!(
            sup.reap_ledger_len(),
            1,
            "the entry never reaches ESRCH, so the loop holds it to the bound"
        );
        assert!(
            elapsed >= Duration::from_millis(1900),
            "the final loop runs to its 2s bound rather than converging; took {elapsed:?}"
        );
        sup.assert_reap_faults_consumed();
        reap_fixture_survivor(survivor);
    }
    #[test]
    fn a_probe_error_after_a_failed_force_kill_exits_the_shutdown_loop_early() {
        // Bet 3, and §1.3's coupling. The loop runs while
        // `any_running() || !reap_ledger.is_empty()`, so an early exit
        // needs BOTH: the fixture is a leader that has already exited
        // (any_running() false) leaving a group survivor, which is
        // exactly the case the ledger exists to serve.
        //
        // This is also the pin that justifies a multi-outcome seam:
        // it needs a failed force-kill AND a failed subsequent probe
        // pending at the same time.
        let dir = tempfile::tempdir().expect("tempdir");
        let mut sup = ProcessSupervisor::new();
        sup.set_group_term_grace(Duration::from_secs(30));
        let (script, pidfile) = survivor_script(dir.path(), true);
        let id = sup
            .spawn(sh_group_spec("coupling", &script))
            .expect("spawn");
        let _ = drain_until(&mut sup, id, Duration::from_secs(5), has_exited);
        let survivor = wait_pidfile(&pidfile);
        assert!(
            !sup.any_running(),
            "the leader has exited: the other arm of the disjunction is already false"
        );
        sup.plan_reap_kill_failure(ReapKillSite::ShutdownForceKill, nix::errno::Errno::EPERM);
        sup.plan_reap_kill_failure(ReapKillSite::LedgerProbe, nix::errno::Errno::EPERM);
        let t0 = Instant::now();
        sup.shutdown();
        let elapsed = t0.elapsed();
        assert_eq!(
            sup.reap_ledger_len(),
            0,
            "the errored probe empties the ledger"
        );
        assert!(
            elapsed < Duration::from_millis(500),
            "and the loop then exits early, concluding cleanup finished because the probe failed; took {elapsed:?}"
        );
        assert!(
            pid_alive(survivor),
            "while the survivor it concluded about is alive"
        );
        sup.assert_reap_faults_consumed();
        reap_fixture_survivor(survivor);
    }
    #[test]
    fn a_collapsed_in_drain_probe_cancels_readers_before_late_output() {
        // §1.2a, the fourth site. `is_ok()` collapses every errno into
        // "the group is dead", which makes `quiesced` true and cancels
        // the readers. Unlike the persistent ledger, no later tick can
        // revisit this: the decision is terminal for that drain, and
        // the failure mode is truncated output rather than a leak.
        //
        // The fault repeats for the whole drain because a one-shot
        // cannot reach `quiesced`: the loop probes again every 1ms and
        // the quiescent window is a full READER_SEND_POLL_INTERVAL.
        let dir = tempfile::tempdir().expect("tempdir");
        let pidfile = dir.path().join("pid");
        let mut sup = ProcessSupervisor::new();
        // Far enough out that the real path would wait, and the drain's
        // own 2s EXIT_OUTPUT_DRAIN_TIMEOUT would still collect the late
        // marker at ~500ms. That is what makes the absence meaningful.
        sup.set_group_term_grace(Duration::from_secs(3));
        // The descendant keeps fd1, so the readers stay open after the
        // leader exits. EARLY is written before the leader exits, so it
        // is in the pipe before the drain begins.
        //
        // **`trap '' TERM` is load-bearing, and its absence made the
        // first draft of this pin vacuous.** `poll_one` TERMs the whole
        // group on leader exit, so an untrapped descendant dies before
        // its 0.5s sleep ends — the late marker then never arrives on
        // *either* path, and "LATE-MARKER is absent" holds for a reason
        // that has nothing to do with the probe. The bite caught it:
        // with the seam reverted the pin still passed both content
        // assertions and failed only the consumed-plan check.
        //
        // The readiness gate is `survivor_script`'s, for its reason: a
        // slow scheduler can otherwise deliver the group TERM before
        // the subshell's `trap` runs.
        let ready = dir.path().join("ready");
        let script = format!(
            "echo EARLY; ( trap '' TERM; : > {ready}; sleep 0.5; echo LATE-MARKER; sleep 5 ) & \
             echo $! > {pid}; while [ ! -e {ready} ]; do sleep 0.01; done",
            ready = ready.display(),
            pid = pidfile.display(),
        );
        sup.plan_in_drain_probe_failure(nix::errno::Errno::EPERM);
        let id = sup
            .spawn(sh_group_spec("in-drain", &script))
            .expect("spawn");
        let events = drain_until(&mut sup, id, Duration::from_secs(5), has_exited);
        let survivor = wait_pidfile(&pidfile);
        // Positive control on the fixture itself. Without it, "LATE is
        // absent" would also hold if the pipe never carried anything.
        assert!(
            stdout_contains(&events, b"EARLY"),
            "the fixture's pipe must actually deliver output; events: {events:?}"
        );
        assert!(
            !stdout_contains(&events, b"LATE-MARKER"),
            "a probe that reports EPERM as 'dead' quiesces the drain and cancels the readers \
             before the live descendant's later output can arrive; events: {events:?}"
        );
        sup.assert_reap_faults_consumed();
        reap_fixture_survivor(survivor);
        sup.shutdown();
    }
    #[test]
    fn maybe_restart_inert_once_shut_down() {
        let mut sup = ProcessSupervisor::new();