validate-pr: Diff-Derived Test Plan

Generate and self-execute a validation plan matched to what actually changed in a PR. Replaces generic "tests pass" with area-targeted evidence and revert-test quality checks that prove tests catch regressions.

When To Use

• End of /fix-pr Step 5 (Validate), before Step 6 (Complete)
• Standalone after any PR fix, to generate targeted validation evidence
• When you need proof that revert-tests are genuine guards

When NOT To Use

• --scope minor with only formatting or doc changes (no logic changed)
• No diff available (clean branch, nothing changed)
• --skip-validate passed to /fix-pr

Algorithm