Preserve and verify full mutation gates

[jonbaldie]

Parent

#21

What to build

Complete the diff-aware mutation workflow by proving that globally relevant changes and release paths still run the full suite. Test changes, mutation-infrastructure changes, unsafe PR metadata, main builds, and release builds must retain comprehensive mutation coverage and the existing thresholds.

This final tracer bullet verifies every selector mode in real CI and confirms that the optimization cannot create a false green release.

Acceptance criteria

• Any test-suite change triggers the complete production mutation suite in both engines.
• Changes to mutation configuration, runners, threshold enforcement, or mutation CI orchestration trigger the complete suite.
• Missing or ambiguous PR metadata, target-fetch failures, and merge-base failures log the problem and trigger the complete suite.
• Builds on main run the complete mutation suite.
• Release/tag builds run the complete mutation suite.
• Full runs preserve current engine versions, test commands, concurrency, and per-file thresholds.
• Ordinary compilation and tests remain prerequisites in the existing job order.
• CI logs clearly distinguish intentional full runs from fail-closed fallback runs.
• A test-change or mutation-infrastructure tracer-bullet PR demonstrates full mode with both checks green.
• A main or release tracer bullet demonstrates full mode with both checks green.
• The docs/tooling skip, selected-source, and full-suite tracer bullets collectively verify all three modes.

Blocked by

• Scope both mutation engines to changed production files #24