tooling(pm): derive the line ratchet's lane roster from the lanes/ directory - #16437

Fixes #15965

The self-test's lane-roster case was an .every over eight literal lane names, so the ninth lane file (lanes/triage.md, landed by #15958) was pinned by nothing: a ceiling row put there for it kept the case green without the case ever naming it, and deleting that row again was caught only by the map-wide cases, which say nothing about a row that is simply gone.

The roster is now read from the lanes/ directory (readdirSync, every *.md, sorted) and held against CEILINGS, so the tree and the map are two independent sources checked against one another. A new lane file is pinned by construction: no list to extend, and no count in the label to keep in step with the list.

A derived roster has one failure mode of its own, and it is the same shape as the defect it repairs — every() over an empty array is true, so an unreadable directory would report perfect coverage of nothing. The verdict refuses an empty roster outright, and each red path carries a fixture case beside the live one, because a red path that stopped working runs green forever.

One file, self-test only: scripts/pm/check-skill-line-ratchet.mjs. No ceiling row changed.

Every move, named

The pinned case label and its expectation-table entry moved together in the same commit — that table is half of the duplicate-label refusal. One case became three: the live derived-roster case, plus one fixture case per red path. Nothing else in the battery-floor machinery, the H-rows or the pins was touched.

Reverse verification

Run against the committed implementation, on scratch copies placed at scripts/pm/ depth so REPO_ROOT still resolves. Each mutation was proved on disk by occurrence count before and after, not by an editor's exit code; the copies were removed afterwards, git diff HEAD is empty, and the worktree blob b7db6099e4 is identical to the HEAD blob.

(a) the defect. Pre-edit file, with lanes/triage.md's ceiling row and its table-row pin both removed (occurrences (1,1) on disk before, (0,0) after) — the realistic shape of deleting a lane's coverage:

LEG_A2_EXIT=0
  ✓ all eight lane/seat job descriptions are covered
✓ check-skill-line-ratchet self-test: 155 cases pass.
--- reds --- (NONE)

The ninth lane file leaves the map entirely, the self-test exits 0, and the roster case whose job this is stays green.

Removing only the ceiling row and leaving the pin row behind reds a different case (and the pin map names no file the ceiling map does not cover) on the asymmetry alone — the roster case stays green there too, which is why the both-rows leg above is the honest demonstration rather than the one-row leg.

(b) the fix. Edited file, same both-rows removal:

LEG_B2_EXIT=1
  ✗ every lane/seat job description in the tree carries a ceiling row
✗ check-skill-line-ratchet self-test: 1 failure(s) (cases and floor).

It is the only red, and its verdict message names the file:

.claude/skills/pm-dispatch/references/lanes/triage.md — lane job description(s) in the tree
carrying no ceiling row, so the ratchet does not read them at all. Give each one a row keyed
by that path, or take the lane file out of the tree.

(c) restored. ✓ check-skill-line-ratchet self-test: 157 cases pass. at exit 0, and the live gate run at exit 0 with zero ✗ lines — every pin holding, pm-dispatch/SKILL.md at 811 lines against its ceiling of 811, lanes/triage.md at 7 against 7.

Serial merge-tree proof

Both PRs were read from the API at proof time: #15955 and #16357 are open, not merged, at exactly the heads this proof targets. So the proof ran as ruled — twice, against HEAD 2c9c1a5282, the second pass with the custom merge driver disabled, because a driver's exit 0 only means the driver took the file.

The driver-disabled runs produce byte-identical trees, so no exit 0 above is a driver having absorbed the file. In both merged trees scripts/pm/check-skill-line-ratchet.mjs carries zero conflict markers and keeps this change intact (SELF_TEST_BATTERY_FLOOR = 157 present in each).

Gates

Derived with dispatch-gates.mjs --commands --repo objectstack-ai/objectstack on the final one-file list (the tool takes its own change set from the merge base ac76425f0, three-dot). All 31 ran, each exit captured by redirecting before any pipe:

• 31 of 31 exit 0. Reconciled: ✓ dispatch-gates --ran: 31 derived famil(ies) accounted for — 31 run, 0 NOT-MEASURED.
• ratchet self-test exit 0 (157 cases) · ratchet live run exit 0, zero reds
• check-clause2-carriers --self-test exit 0 (190 cases)
• check-governed-merges --test scripts/pm/check-skill-line-ratchet.mjs exit 0 — ✅ NOT governed — ordinary queue landing applies to a PR with exactly this file list.
• check-nul-bytes exit 0 (8078 text files, no raw control bytes), plus a direct control-byte scan of the edited file: no hits
• whole-repo pnpm lint (eslint . --no-inline-config) through scripts/pm/os-verify-lock.sh, slot issue-15965: VERDICT command-exit 0 · held the lock 99s · waited 0s
• the artifact-roster gates whose roster sits under scripts/ or scripts/pm/ were run rather than read as silent: check-published-list-mirrors, check:pm-label-desc-cap, check:pm-governed-prose, check:single-claim-paths, check:skills-token-ratchet — all exit 0

check:ratchet-remedy-authority is worth calling out: it classifies this very file as excluded, and its OFFER_VERB grammar would have reclassified it had the new verdict message spelled its remedy with an expanding verb next to a declared registry name. The message is worded to stay out of that grammar; the gate and its self-test both stay green.

No changeset — repo tooling only, nothing published from any package; skip-changeset applied.

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