fix(devx): check-regen-pending refuses on an unmet prerequisite instead of reading a crash as a stale artifact (#15722) (#15785)

* fix(devx): check-regen-pending refuses on an unmet prerequisite instead of calling the artifact stale

`check-regen-pending` does not regenerate and does not compare bytes: it spawns
each deferred artifact's `check:` gate and reads the exit status. Every reason a
gate has for exiting non-zero therefore arrived wearing the same clothes, and all
of them were printed as one word — `stale` — over three lines of whatever the
child said. On a checkout with no `node_modules` that is a verdict about a file
nothing read.

Grade the failure instead. A gate that could not LOAD is reported in #11557's
landed frame — `reportPrerequisiteNotMet`, `EXIT_PREREQUISITE_NOT_MET`, both
imported from `scripts/import-prerequisite.mjs`, never restated — and the run
exits 3. Three shapes, all measured live on an uninstalled tree across the 14
registered paths: the runner missing (`sh: 1: tsx: not found`, 10), a raw
`ERR_MODULE_NOT_FOUND` link failure (1), and a child that already refused with
`PREREQUISITE NOT MET` and exited 3 (1) — the landed fix undone one process
boundary out.

Nothing is loosened. The refusal is still a refusal, the marker still keeps every
deferred path, and a gate that RAN and failed still reads `stale` and exits 1.
The prerequisite branch sits BELOW `defer`, so a merge commit that cannot run its
gates still defers rather than being refused — putting that back would restore
the #8047 defect whose learned workaround was skipping the whole hook.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012zGPuVVX3deAx9LdjK8jCk

* fix(devx): join the prerequisite headline with a colon, not a second em dash

The shared frame already spells `PREREQUISITE NOT MET — <headline>`, so a second
em dash inside the headline read as one sentence broken twice.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012zGPuVVX3deAx9LdjK8jCk

* fix(devx): count the unmeasured artifacts past three instead of listing them

The shared frame inlines the `measures` clause into a sentence it does not wrap,
so a fourteen-path list there buries the clause that carries the reading.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012zGPuVVX3deAx9LdjK8jCk

* test(devx): assert the DIAGNOSIS, not the echoed child line

Two of the new fixture assertions matched a string the raw child output carries
either way, so they passed against the pre-fix code — measured under ablation A1,
where their parent cases went red and they stayed green. They now assert the text
only the refusal produces.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012zGPuVVX3deAx9LdjK8jCk

* docs(scripts): the mirror gate's export count follows the module it describes

check-regen-pending.mjs now exports eight functions, not seven; the count is
prose in check-declaration-mirrors.mjs, not a pin, and the gate stays green
either way — but a stale number there is a lie this change introduced.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012zGPuVVX3deAx9LdjK8jCk

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: claude[bot]

scripts/check-declaration-mirrors.mjs

@@ -71,7 +71,7 @@
 // design.
 //
 // ⛔ One direction is deliberately NOT fatal: a module export that the
-// declaration omits. `check-regen-pending.mjs` exports seven functions and
+// declaration omits. `check-regen-pending.mjs` exports eight functions and
 // declares three, on purpose -- its declaration says "The surface is three
 // functions". That partial mirror cannot fail green: a consumer importing an
 // undeclared name gets `TS2305`, which is loud, red and immediate. Failing on