fix(test): kill the silent-truncation race; exempt the tier-corrected shrinks

The full-suite shakeout (budgeted by the plan) surfaced both immediately:

1. server-embedder-terminal-port.test.ts stubbed process.exit and restored
   the REAL exit in its finally — but shutdown() schedules async work that
   can call process.exit AFTER restoration, killing the entire bun process
   mid-suite with exit 0 and NO summary. This is the silent-truncation class
   the new free-suite CI job guards against, reproduced locally on the first
   full run. Exit now stays a logging no-op between tests (late async exits
   become visible stderr lines, not process death); the true exit returns in
   afterAll.

2. The 80%-of-baseline shrink guard correctly flagged the six tier-corrected
   skills — their baseline was measured at the silent tier-4 default. Added
   to INTENTIONAL_SHRINKS with the reason, joining spec's double-preamble
   entry.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/skill-size-budget.test.ts

@@ -171,7 +171,16 @@ describe('SKILL.md size budget regression (gate, free)', () => {
     //   {{PREAMBLE}} literally, so the generator expanded the ENTIRE preamble a
     //   second time mid-sentence (~47 KB of duplication). Fixed by rewording the
     //   prose; spec/SKILL.md now carries exactly one preamble (~80.9 KB, ×0.79).
-    const INTENTIONAL_SHRINKS = new Set<string>(['spec']);
+    // - scrape/diagram/open-gstack-browser/landing-report/pair-agent/skillify:
+    //   the baseline measured these at the silent tier-4 default (a missing
+    //   preamble-tier frontmatter fell through `?? 4`). Their tiers are now
+    //   declared correctly (1-2), shedding the tier-2..4 onboarding prose they
+    //   never should have carried (-271 lines each for tier 1).
+    const INTENTIONAL_SHRINKS = new Set<string>([
+      'spec',
+      'scrape', 'diagram', 'open-gstack-browser',
+      'landing-report', 'pair-agent', 'skillify',
+    ]);
 
     const undershoots: Array<{
       skill: string; beforeBytes: number; afterBytes: number; ratio: number;