fix: report outranked scan faults

[randomparity]

Summary

• preserve positive renumber and gate-existence verdicts when an earlier candidate scan faults
• emit deterministic warnings that retain the last fault path and exit status
• add mirrored regression coverage and record the four-outcome contract in ADR 0043

Verification

• ./.github/scripts/check-records-test.sh (210 passed, 0 failed)
• just records
• just verify
• pre-push verification suite

Closes #87

[randomparity]

verdict: approve
exit: none
findings: 0
iterations: 2
security: not triggered
delivered-head-sha: 4e4152a

Forge whole-branch review

forge review: not required (cast tasks share the same mirrored scripts and fixtures)