# Row 47 (#1533): Mr flows test and the leftover shim

Dewey, 2026-10-10. Brief: `docs/plans/2026-10-10_s5-follow-up-and-hygiene.md`
§ "S5 follow-up". Base 21e0f1a3. The candidate touches five test files in
`packages/conversation/tests/` and this file. No `src/` file and no README
changes.

## Mr

`flows.test.mjs` gains "terminal: a hold inside held input holds again, and
once it is drained later input and Ctrl-C still reach the terminal (Darkwing
note 1 on #1522)". It is the draft in `~/dewey-scratch/s5/mr-test.patch`
unchanged. Under Mr (`holds = this.held !== null;` after the re-parse in
`#run` becomes `holds = false;`) it is the only failing test, 164/165.

## Why the shim outlived the suite

- `src/shim.mjs` ignores SIGTERM and SIGHUP (line 188) and exits only on the
  `release` op once `engine` reports `populated 0` (line 160).
- No `src/` code sends `release`. `forceStopCohort` (`src/cohort.mjs:150`)
  runs term, freeze, members and kill, then returns its proof. Controller
  close doesn't release either. So after a force stop the scope stays up
  with its shim, reparented to the systemd user manager, until something
  SIGKILLs the unit.
- Two claim tests force-stop a scope and leave it: W5's probe fixture
  (the traced release run) and W13. Both relied on the file's `after`
  hook, whose `reap` sends `systemctl --user kill` and `stop` with a 5 s
  timeout and checks neither result.
- On 7ab2f92d with logging added (scratch only,
  `~/dewey-scratch/s5/probe-instrumentation.diff`), the W5 probe unit was
  `active` from probe close (03:29:14.783Z) to the start of `after`
  (03:29:43.671Z), and `inactive` after `reap` (03:29:44.211Z).
- In Filbert's row 41 round 2 gate the shim left running was
  `chat03-nWFPcN/f55`, unit `mosaic-chat-cd9f5111af2b95a6b6110b9a1`. That is
  the W5 probe: f55 is the probe fixture in claim.test, and the `afterleak`
  mutant below leaks the same fixture. The user journal shows it started at
  20:43:51.093 local and never killed.

Limit of the evidence: that journal has no `mosaic-chat` lines after
20:43:56 local, though W5 ran 33.7 s and passed
(`~/filbert-scratch/s6-logs/gate-r2/node-conversation.txt`). The system
journal isn't readable to me. So I can show the probe was left for `after`
and that `after`'s kill didn't land in that run, but not why the
`systemctl` call missed.

## The change

- `harness.mjs`: `liveShims(root)` lists running shims whose socket is
  under `root`, from `/proc` cmdline and cgroup. `killShims(root)` SIGKILLs
  each one's scope and then the shim by PID. `shimsGone(root, ms)` waits up
  to 5 s and returns what is left. `reap(fx)` ends with
  `killShims(fx.base)`, so a shim the records don't name, or one the
  unchecked `systemctl` calls missed, is still killed.
- `claim.test.mjs`: W5 reaps its probe and W13 reaps its fixture as soon
  as they close, not in `after`.
- `cohort.test.mjs` K19: if its own kill or release fails, the `finally`
  SIGKILLs the scope before asserting, so a failure doesn't leave the
  shim for `after`.
- claim, cohort and races (the files that launch scopes): `after` reaps,
  sweeps with `killShims()`, waits with `shimsGone()`, and then asserts
  that no shim is left ("no shim outlives this file (#1533)"). A failing
  `after` hook fails the file in node:test, with exit 1. Each file also
  ends with a test "no shim from this file's tests is left running for the
  after hook", which names the test's leak before `after` cleans it up.
  `tmp` is per process, so each file checks only its own shims.

The shim keeps ignoring SIGTERM. That is deliberate (README, force stop:
"so that a stray TERM never drops the scope's anchor"), so the fix is in the
tests that spawn it.

## Finding for Sage (out of scope, not fixed)

A force-stopped scope never ends on its own: nothing in `src/` sends
`release`, so its shim and the empty scope stay up until something kills the
unit. In tests that is now handled. In a running controller each force stop
leaves one `mosaic-chat-*.scope` with an idle node shim. This is in
`cohort.mjs`/`controller.mjs`, which the brief puts out of scope, so I
haven't touched it. I recommend a follow-up row: after a proven force stop
(and on close of a stopped binding), send `release`, with a test that the
unit is gone afterwards.

## Mutation check

Scratch copies of the working tree, the full conversation suite per mutant
(`~/dewey-scratch/s5/mut-tools/run.sh`). After each run the runner lists
any shim left under the mutant's TMPDIR, then SIGKILLs its scope and PID.

| Mutant | Change | Result | Shims left after the suite | Killed by |
|---|---|---|---|---|
| base | none | 165/165 | none | (baseline) |
| Mr | `holds = false;` after re-parsing held text | killed, 164/165 | none | terminal: a hold inside held input holds again … |
| noprobe | W5 doesn't reap its probe | killed, 164/165 | none | claim: no shim from this file's tests is left running for the after hook |
| now13 | W13 doesn't reap its fixture | killed, 164/165 | none | the same test |
| afterleak | noprobe, and `after` doesn't reap or sweep | killed, 164 pass, 2 fail | 1 (`mosaic-chat-c719df56e9490f21f5919fe8e`, killed by the runner) | the same test, and the claim file's `after` hook |

The `afterleak` hook failure:

```
✖ .../packages/conversation/tests/claim.test.mjs (5101.703413ms)
  AssertionError [ERR_ASSERTION]: no shim outlives this file (#1533)
  + [
  +   {
  +     pid: 3106581,
  +     socket: '/home/jwoltje/dewey-scratch/s5/tmp/chat03-S6WdOu/f55/sock/shim-c719df56e949.sock',
  +     unit: 'mosaic-chat-c719df56e9490f21f5919fe8e'
  +   }
  + ]
  - []
```

That run is the round 2 leak reproduced on purpose: the probe's shim
outlives the suite. With the candidate's `after` hook it can't.

## Gate

Sequential, on a detached worktree of 21e0f1a3 with the candidate's test
changes applied (patch sha256 `f57759e0…41df9d`), 03:42:59Z to 03:47:11Z,
output in `~/dewey-scratch/s5/r47-gate/out/`:

- conversation 165/0, webui 22/0
- test-auth 15/0, test-conductor 17/0, test-config 24/0, test-discord 66/0,
  test-extension-package 18/0, test-foundation 44/0, test-release 14/0,
  test-task 98/0
- test-queue 27/0 (node 148/0). Its canonical-root check skips in a
  worktree, as it does in every worktree gate.

No shim was running after the gate.