Report malformed percent-escapes in Google resource URLs

[snowyukitty]

What does this change?

Binding a Google resource from a URL containing a bare % throws an unhandled URIError: URI malformed instead of the explanatory errors every sibling validation path in getGatekeeperClassFor() raises. https://mail.google.com/mail/u/0/#search/50%off is the reproduction reported in #55.

This adds a decodeResourceUrlPart() helper — decodeURIComponent() in a try, rethrowing as Invalid <part>: it cannot be percent-decoded. Encode a literal "%" as "%25". — and uses it at the four bare decode sites in getGatekeeperClassFor(): the Gmail #search/ query, the Gmail #label/ name, the Google Calendar path segment, and the BigQuery path segments.

#55 notes the same bare-decode pattern in other gatekeeper packages; this PR deliberately stays on the reported backend path to remain a small, single-concern change.

Fixes #55

Why is this obviously correct and trivially verifiable?

The success path returns exactly what decodeURIComponent() returned, unchanged. The only behavioral difference is that a thrown URIError becomes an Error whose message follows the wording style of the sibling validation messages in the same function. There are no control-flow, dependency, or API changes.

Verified on Windows 11 (Node 22.22.3, pnpm 11.17.0) against 4288713: tsc -p packages/gatekeeper-google and full pnpm lint pass.

AI tools authored this patch under human direction, and an independent AI review approved it before submission; the verification commands above were run locally.

Checklist

Checking every item does not guarantee acceptance. Maintainers determine whether
a pull request meets the contribution policy.

• This is a small, concrete change; it is not a feature, refactor, or low-value cleanup.
• I understand that maintainers decide whether the change is obviously correct and trivially verifiable.
• I have read and followed the contribution guidelines.

🤖 Generated with Claude Code

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.

[snowyukitty]

Closing this myself: CONTRIBUTING asks contributors to keep PRs to "a dozen or so lines" and this one is +16/-4, which is over that line. #221 was the right size and I should have kept to it here.

Leaving the report behind in case it is useful: in packages/gatekeeper-google/src/google.ts, decodeURIComponent is called on parts of a Google resource URL, so an unescaped literal % — a Gmail search or label like "50% off" — throws a bare URIError that does not say which part of the URL failed to decode.

I am not reopening this as a smaller PR. Splitting a change to fit the size guideline would be evading it.