docs(skill): clarify regression verification triggers

shared/skills/verification/regression-verification/SKILL.md

@@ -1,10 +1,18 @@
 ---
 name: regression-verification
-description: Check that existing behavior was not unintentionally broken.
+description: Use after a code or configuration change when adjacent existing behavior may have regressed; select and run focused checks, then report results and gaps.
 ---
 
 # Regression Verification
 
-Identify the affected existing behavior and run proportionate regression checks.
+Use after a change when existing behavior may have been affected.
 
-Report results and any unverified areas. Do not claim checks that were not run.
+## Workflow
+
+1. List the user-visible behaviors and contracts adjacent to the change, including sibling callers that share modified logic.
+2. Select existing tests or short scenarios that exercise those behaviors and their important boundaries.
+3. Run checks at the narrowest useful level. Expand only when shared components, persisted data, security boundaries, or integration paths justify it.
+4. Compare failures with the baseline and distinguish regressions from pre-existing or environment-specific failures.
+5. Check generated output or compatibility artifacts when the source change feeds them.
+
+Report behaviors checked, exact checks run, results, and any gaps. Never imply that unrun tests passed.