pm(check-expected-skips): derive the expected-skip roster from the workflows' job-level if: gates (#26648)

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Fixes #26439

Clause-②: no
Metadata-protocol: none

## 维护者速读

- 改了什么：`check-expected-skips` 不再手抄「允许 skip 的 job 名单」，改为直接读各 workflow 里每个
job 的 `if:` 推出名单；手抄的 16 行全部删除。
- 为什么改：手抄名单一漏就红（#26111 就是一次），新增或改名一个带门控的 job 都得来这里补一行；本 PR 实测 main
上已经又漏了两个（`Plan Test Core shards`、`Delete the reapable branches`）。
- 风险与回滚：只动一个 `scripts/pm` 脚本，不发布、不改
workflow；判错的方向是「多红」不是「放过」——不认识的写法一律拒收并点名。回滚即 revert 本 PR。
- 先看：`scripts/pm/check-expected-skips.mjs` 的 `gateTerm` /
`jobGate`（认哪几种写法）、`filterTermProblem`（filter 契约三条），再看自测里 ADD / RENAME /
UN-GATE 几条。
- 两分钟验证：`node scripts/pm/check-expected-skips.mjs --roster`，预期首行写 `20
expected-skip name(s), every one derived … none listed by hand`，且无 ⚠️
refused 行。
- 需要你做的：无，席位落地。

## What changes

`scripts/pm/check-expected-skips.mjs` only.

- **The hand roster is gone.** `EXPECTED_SKIPS` (16 rows), `GATE_KINDS`,
`gateSpellings`, the reason constants and `auditRoster` are deleted. The
roster is now derived from the tree on every run: `rosterFromTree` =
`deriveGatedSkips` (new) + `deriveNonPrEventSkips` (existing shape), off
one shared `scanWorkflowJobs` scan.
- **`deriveGatedSkips`** reads each job's job-level `if:`, splits it at
top-level `&&` (outside parentheses and literals), and admits the job
when at least one conjunct is a recognised gate term:
- `filter-output`: `needs.filter.outputs.OUTPUT != 'false'`, or a
parenthesised `||` whose every alternative is one;
- `pr-event`: `github.event_name != 'pull_request'` or `!=
'merge_group'` (the per-PR events; the full-battery jobs);
- `event-action`: `github.event.action != 'ACTION'` (a labeled /
unlabeled / edited run of the same head);
- `label`: `contains(github.event.pull_request.labels.*.name, 'LABEL')`
(opt-in) or its `!` negation (opt-out).
- The name is the job's `name:` verbatim (raw matrix template included),
so the hard-coded `/3`, `/8`, `/16` shard sizes disappear with the list:
GitHub reports a pre-expansion skip under the raw `name:`, never a size
read from `matrix:`.
- **Refusals (the skip stays exit 4, and `--roster` names it):** a
`filter` term whose output lacks the `|| 'true'` widening, is not
declared by the `filter` job, or sits on a job without `needs: filter`;
an `if:` that reads `needs.filter.outputs.` in any spelling the
recogniser does not read; a name two jobs carry; a name that cannot be
told. A job with no gate term at all is never admitted.
- Each derived row's reason is built from the terms the job spells
(queue-widened vs queue-read outputs, full battery, opt-in / opt-out
label, unread conjunct count, raw template).
- `judgeCheckRuns` and `renderRoster` now take the roster explicitly (no
hand-list default); `--roster` prints `gate: job-gate filter
core|crosspkg + pr-event pull_request|merge_group`-style lines.
- The header's "what the roster answers" section is rewritten for the
derivation at the same line count, so the `self-test-reads` declaration
stays at `:137` (pinned by `dispatch-gates.self-test.mjs`) — no edit
outside this file.

## Why

The card: the roster was a hand copy of ci.yml's `if:` gates and went
red on every new or renamed gated job until someone added a row (#26111:
`Build UI Deps`). Measured on `origin/main` `7c34e5dc2`, the class had
already recurred twice more on main:

| skipped check-run | job | main's roster | this PR |
|:---|:---|:---|:---|
| `Plan Test Core shards` | `ci.yml` › `test-plan` (gated on `core` \|\|
`crosspkg`, added with the shard planner) | exit 4 | exit 0 |
| `Delete the reapable branches` | `merged-branch-reaper.yml` › `reap`
(`!= 'pull_request'`, the workflow runs on PRs touching itself) | exit 4
| exit 0 |

## Tests

The self-test is rewritten in this file (no other test file moves): 173
→ 206 cases.

- **Recogniser** cases: top-level splitting, each term kind, and the
near-misses refused (`== 'true'`, a filter term inside a top-level `||`,
`(a) || (b)`, `!= 'push'`, `== 'pull_request'`, double-quoted labels,
status functions, two `${{ }}` blocks, unbalanced parentheses).
- **The measured heads (#18315, #20748) are judged against a frozen
fixture tree**, not this checkout's job names, so a gated job renamed in
a live workflow moves no case here. That also lets `MEASURED_18315` go
back to verbatim (`Test Core (… /6)`, the re-spelling to `/8` is
undone).
- **Acceptance fixtures on the fixture tree:** ADD (the #26111 shape: a
new gated job is expected on its first skip, nothing listed; the tree
without it reads ⛔), RENAME (new name expected, old name ⛔), DELETE,
UN-GATE (`if:` removed, `if: always()`, an ungated job added: each ⛔ — a
required job silently not run still reds), RE-GATE, the three
filter-contract refusals, the unread-spelling refusal, shared /
untellable names, an unreadable workflow refused once.
- **Live tree:** structural only — nothing refused, ci.yml's filter
contract read (at least one filter-gated row), every admitted row a real
job with a string `if:`, no bare status-function `if:` admitted, the
never-skipping sentinels out, the joined roster frozen and
duplicate-free. The CLI cases build their payloads from the live roster.

## Acceptance notes

- **Hypothesis 1 (the card): holds, with one correction.** Every one of
the 16 hand rows falls out of the rule — measured by `--roster`
before/after on `7c34e5dc2`: the 18 names before (16 listed + 2 derived)
are all present after, plus the two live misses above, 20 in all, 0
refused. The correction: shard sizes are not read from `matrix:` blocks;
the skipped check-run carries the raw `name:`, and ci.yml's `test`
matrix is `fromJSON(needs.test-plan.outputs.shards …)`, which has no
static size to read.
- **Hypothesis 2: holds.** The gate's real question survives:
`TypeScript Type Check` skipped still reds on both trees (below), and
the self-test keeps the un-gated cases.
- **`reap` is now expected.** Its `if:` conjoins `github.event_name !=
'pull_request'`, so its skip on a PR head is by construction; the
non-PR-event shape still refuses it (that case is kept).
- **Boundary kept:** the derivation is a recogniser of closed spellings,
never an evaluator; it answers the NAME question only, as before.
- The file's self-test carries the verdict handshake but not the
battery-name floor described in AGENTS.md § Writing a `--self-test`;
unchanged here (not this card), noted only.
- `node scripts/measure-self-test-floor.mjs --self-test` exits 1 on this
head naming `scripts/pm/check-prior-rulings.mjs` and
`scripts/pm/dispatch-gates.mjs` (handshake spelling census); neither
file is touched here and the script is not a wired check, so it reads
the same on `main`.

## Verification

All readings on head `98a3dc80`.

<details><summary>Acceptance proof on disk: add + rename a gated ci.yml
job (one-off, scratch worktrees)</summary>

In two scratch worktrees (main `7c34e5dc2` and this head), ci.yml was
edited: `build-docs` renamed to `Build Docs Site`, and a new job `Brand
New Gated Job` added with `if: ${{ !cancelled() &&
needs.filter.outputs.core != 'false' }}`. Then `--self-test` and
`--check-runs-json` on one-skip payloads:

| | main | this PR |
|:---|:---|:---|
| `--self-test` | exit 1 — `Build Docs: ci.yml job build-docs is named
"Build Docs Site" — the check-run name moved; correct the row` | exit 0,
206 cases |
| `Brand New Gated Job` skipped | exit 4 | exit 0 |
| `Build Docs Site` skipped | exit 4 | exit 0 |
| `Build Docs` (the old name) skipped | exit 0 (false OK) | exit 4 |

No file under `scripts/pm` was edited for the PR-side column.
</details>

<details><summary>The check still reds on the defect it was written
for</summary>

One-skip payloads, `--check-runs-json`, current tree:

| skipped | main | this PR |
|:---|:---|:---|
| `TypeScript Type Check` (no gate) | exit 4 | exit 4 |
| `Plan Test Core shards` | exit 4 | exit 0 |
| `Delete the reapable branches` | exit 4 | exit 0 |
| `Build UI Deps` (the #26111 job) | exit 0 | exit 0 |
</details>

<details><summary>Local gates (dispatch-gates --commands, 31
families)</summary>

- `pnpm check:pm-expected-skips` → `✓ check-expected-skips self-test:
206 cases pass`
- the 30 other derived commands: exit 0 each (list in the card report)
- `pnpm check:pm-dispatch-gates` → exit 0, `✓ dispatch-gates self-test
(fast tier): 1935 cases pass`
- `dispatch-gates --ran` → `31 derived famil(ies) accounted for — 31
run, 0 NOT-MEASURED (a DERIVED zero)`
- `pnpm check:ci-filter-parity` exit 0, `pnpm check:required-contexts`
exit 0 — neither reads this file (`git grep` for its name in both
scripts: 0 hits), so their output is unchanged by construction
- `eslint --no-inline-config scripts/pm/check-expected-skips.mjs` exit
0; `check:nul-bytes` exit 0
</details>

## Human Minimum

- [x] 1. Schemas start as Zod; `packages/spec` holds no runtime logic.
(not touched)
- [x] 2. Every name I added uses the casing for its kind.
- [x] 3. No formatter ran; `pnpm lint` passes. (eslint on the file
locally; repo-wide in CI)
- [x] 4. One issue, one branch off an up-to-date `main`, one pull
request.
- [x] 5. A change that publishes carries a changeset — nothing publishes
(`scripts/pm/**` only), `skip-changeset`; both declaration lines are
filled in above.
- [x] 6. `packages/spec` touched: n/a.
- [x] 7. No hand edits to `content/docs/references/`,
`packages/*/CHANGELOG.md` or `content/docs/releases/`.
- [x] 8. Title, body and comments are in English (the 维护者速读 block is the
required Chinese summary).
- [x] The *Before Submitting* list in CONTRIBUTING.md is done.

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