fix(vc): treat unparseable expirationDate as expired (fail-closed)

[forumevi]

Problem

isExpired() in packages/vc/src/verification/is-expired.ts returns false when expirationDate cannot be parsed:

if (isNaN(expirationDate.getTime())) {
  // Expiration date is invalid, so we consider the credential not expired
  return false  // ← silently passes a credential with a malformed expiry
}

This means a credential with a malformed expirationDate (e.g. "not-a-date") passes every expiry check, bypassing the intended expiry boundary.

Inconsistency

This is inconsistent with the fail-closed approach used elsewhere in the same verification pipeline. resolveStatusListCredential (in is-revoked.ts) throws on an unreadable expirationDate rather than treating it as absent:

if (Number.isNaN(expiresAt)) {
  throw undetermined(
    `Status list credential from '${url}' has an unreadable expirationDate`,
  )
}

Fix

Return true instead of false when the date cannot be parsed, so a credential whose expiry cannot be established is rejected rather than silently accepted.

Updated the inline comment and JSDoc to reflect the new behaviour.

Test

Updated the existing "handles invalid date strings gracefully" test to assert the fail-closed behaviour (true instead of false) and renamed it to "treats invalid date strings as expired (fail-closed)" to make the intent explicit.

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Reviewing files that changed from the base of the PR and between fea568c and 1331714.

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• packages/vc/src/verification/is-expired.test.ts

Walkthrough

isExpired now returns true for an unparseable expiration date. Missing expiration dates still return false.

Changes

Expiration Date Validation

Layer / File(s)	Summary
Handle unparseable expiration dates packages/vc/src/verification/is-expired.ts	The documentation now describes unparseable expiration dates as expired. When parsing fails, isExpired returns true.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~5 minutes

Change: Bug fix

Merge Risk: 🟡 Moderate · up to fea56

The fail-closed behavior is intentional, but the test still expects malformed dates to pass. Update the test before merging.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: unparseable expirationDate values are treated as expired with fail-closed behavior.

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @packages/vc/src/verification/is-expired.ts:
- Line 27: Update the invalid-date case in the isExpired test to expect true and
describe invalid date strings as expired, matching the fail-closed behavior of
isExpired.

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• packages/vc/src/verification/is-expired.ts

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