pr-test-analyzer: add 'weakened-to-pass / gate-gaming' critical-gap class #5

Parent

#1 — PRD: Loop Engineering adoption

What to build

In the pr-test-analyzer agent's "Identify Critical Gaps" list, add a named "Weakened-to-pass / gate-gaming" gap class with the explicit taxonomy (lifted from the corpus):

Weakened-to-pass tests — the suite is made green without fixing the code: deleting tests, loosening assertions, wrapping in try/catch to silence errors, marking tests skipped/xfail.

Include two operational additions:

• Inspect diffs for touched test files even when the suite is green (the cheat hides in test edits, not source).
• Gate-rot variant — a test that still passes but no longer catches the failure mode it was written for.

The bullet(s) stay under the agent's existing 1-10 behavioral-criticality + file:line paper-trail ritual — they do NOT bypass that format (this gap class is typically 7-9 criticality). External support: "current approaches place excessive faith in AI-generated tests, currently inadequate for behavior verification."

Acceptance criteria

• A named weakened-to-pass / gate-gaming gap class is added to "Identify Critical Gaps," matching sibling noun-phrase style.
• The taxonomy (delete / loosen / try-catch-silence / skip-mark) is present, plus the "inspect touched test files even when green" instruction and the gate-rot variant.
• The bullet remains subject to the agent's existing 1-10 rating + file:line paper-trail ritual (no instruction to omit them).
• Green bar: bash skills/harness-audit/scripts/audit.sh clean vs baseline AND claude plugin validate --strict exits 0.

Blocked by

None — can start immediately.