test(mock): cover SnapshotAgent excludeUrls playback

[maruthang]

This relates to...

Fixes #4663

Rationale

Issue #4663 reported that SnapshotAgent in playback mode threw "No snapshot found" for URLs matched by excludeUrls, even though excluded URLs are meant to pass through to the real network.

The underlying bug was already fixed on main by PR #4670 (commit 5024d1b7), which routes excluded URLs through kRealAgent.dispatch before findSnapshot is consulted (see lib/mock/snapshot-agent.js:85-88). However, the issue was never formally closed and no regression test was added for this specific playback-mode path.

This PR adds a focused regression test so the excludeUrls playback short-circuit cannot silently regress. It reproduces the exact scenario from the issue and also covers a RegExp pattern that only matches during playback, which exercises the dispatch branch end-to-end.

Changes

Add test/mock/issue-4663.js with two cases:

1. String excludeUrls entry — excluded URL is fetched live during playback.
2. RegExp excludeUrls entry — excluded URL is fetched live during playback.

Features

N/A

Bug Fixes

N/A — the bug itself was fixed in #4670. This PR adds regression coverage only.

Breaking Changes and Deprecations

N/A

Status

• I have read and agreed to the Developer's Certificate of Origin
• Tested (test/mock/issue-4663.js; all snapshot-* and mock-* tests pass)
• Benchmarked (optional)
• [S] Documented
• Review ready
• In review
• Merge ready

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.10%. Comparing base (ec60a7c) to head (2404ffa).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5080   +/-   ##
=======================================
  Coverage   93.10%   93.10%           
=======================================
  Files         110      110           
  Lines       35807    35807           
=======================================
  Hits        33339    33339           
  Misses       2468     2468           

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[mcollina]

WHy is the test included in #4670 not enough?

[maruthang]

Fair point @mcollina — the excluded URLs should not error in playback mode test added in #4670 already covers the exact #4663 scenario (string-form excludeUrls, playback, excluded URL passes through to the real server). The only delta in this PR is exercising the same codepath with a RegExp-form excludeUrls (the existing regex test at test/snapshot-testing.js:1240 only covers record mode). Given isUrlExcluded normalizes both string and RegExp into the same branch inside dispatch(), the incremental coverage is thin.

Happy to close this if you'd prefer to keep the suite lean — the issue is already functionally closed by #4670. If you think the RegExp-in-playback case is worth pinning separately I can leave it, but otherwise just say the word and I'll close.

[maruthang]

Friendly nudge — approved by @metcoder95, all 35 checks green. Tests-only change covering the SnapshotAgent excludeUrls playback-mode regex form. @mcollina — happy for this to land whenever you have a moment. Thanks!