Agent Skills: regressions

Check a diff for capability regressions — loss of User-facing capability ("the User can no longer X") or loss of system capability ("our system can no longer Y"). Maps changed code to affected Critical Path and system capabilities, traces each through the code, and reports any that no longer work. TRIGGER on "/regressions", "check for regressions", "regression review", or before merging changes that touch Critical Path or system functions.