ci(test-tiers): per-PR gate for a package that adopts a *.e2e.test.* or *.live.test.* file without reading OS_TEST_TIERS

[claude]

Filed by the skills lane seat (session session_019RfFHiRCSs3JXLK4cwcfox, os-steve) at the landing of #16455 (flight X, PR #16481), 2026-09-07T04:3xZ, under the finding-admission threshold: a silent class (tier files leaking back into the queue) that nothing makes red on the pull request that introduces it. Surface owner stays domain:devx.

What

A pull request that adds a *.e2e.test.* or *.live.test.* file to a package whose vitest configuration does not read OS_TEST_TIERS goes red on that pull request, not only on the nightly.

Measured (from the #16455 delivery, PR #16481 at 770dd18)

• 72 standalone vitest.config.ts files, none sharing a config, no root config or workspace; today exactly one package (packages/cli) owns tier-named files (60 *.e2e.test.ts) and zero *.live.test.* files exist anywhere.
• scripts/nightly-tiers.mjs --check refuses to run past a tier-owning package that ignores the switch, but only on the nightly. Nothing makes that red on the pull request that introduces the file, so such a file runs in the queue (the cost ci: e2e and live tiers move to a nightly run on main; PR and queue runs keep unit, integration and conformance (maintainer-directed, part B tiering) #16455 moved out) until the next nightly notices, and the nightly's refusal then blocks the whole tier run for one package's omission.

Ruling

1. One per-PR gate: a check:* script under scripts/ (or nightly-tiers.mjs --check's pure judge over a static walk, whichever needs no vitest boot) wired into lint.yml beside the other gates, with a self-test covering at least: a tier file in a package that reads the switch (green); a tier file in a package that does not (red, naming the package and the file); no tier files on disk (green, printing the zero count).
2. No test file is changed and no package is made to read the switch by this card: the gate reports, the adopting pull request fixes.
3. Clause-②: no. The gate only narrows what a pull request may merge.

Acceptance

• Self-test green; the gate's own red case shown once in the PR with a scratch tier file in a non-reading package, then removed (one-time proof, no permanent test file).
• pnpm check:pm-dispatch-gates accepts the new family.

Blocked-by: #16455 (the script it wires lands there).

Refs #16455.

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