Fix data URL validation in summarizeDataUrl

[pavankumar-vh]

Overview

Fix a potential bug in the summarizeDataUrl function in common/src/util/cache-debug.ts.

Bug Description

The summarizeDataUrl function assumed the value started with data: (5 characters) and sliced from index 5 to extract the media type. If the value didn't start with data:, this would return incorrect results.

Fix

Added a check to ensure the header starts with data: before slicing, returning 'unknown' as the media type if it doesn't.

Testing

No existing tests for this function, but the fix prevents incorrect behavior with malformed data URLs.

Files Changed

• common/src/util/cache-debug.ts - Added data URL validation

Scope

This change only touches common/ which is an approved contribution area per the Contributing Guide.

[codebuff-team]

Thanks for the contribution. The change itself is safe and in-scope (common/), but I'd like to see evidence this guard actually fixes an observable bug. Looking at cache-debug.ts, summarizeDataUrl is presumably only invoked after the caller has already confirmed value.startsWith('data:'), so header should always begin with data: by the time this function runs. If that's the case, this change is a no-op defensive check rather than a real bug fix.

If you found a path where summarizeDataUrl can be called with non-data: values (e.g. from a different caller than the current one), please point to it in the PR description - that would make this a genuine fix. Otherwise, consider adding a unit test that exercises the malformed-header case to demonstrate the previous behavior was actually wrong (what did header.slice(5) return before, and was it actually incorrect/misleading, or just cosmetically odd?).

As it stands this is low-risk but not clearly necessary — happy to reconsider with a concrete before/after example or a test.