## Summary
Fixes issue #21677 where `Bun.serve()` was adding redundant Date headers
when users provided their own Date header in the response.
The root cause was that the HTTP server was writing user-provided Date
headers and then µWebSockets was automatically adding its own Date
header without checking if one already existed.
## Changes
- **Added Date header detection in `NodeHTTP.cpp`**: When a user
provides a Date header (either in common or uncommon headers), the code
now sets the `HTTP_WROTE_DATE_HEADER` flag to prevent µWebSockets from
automatically adding another Date header
- **Case-insensitive header matching**: Uses
`WTF::equalIgnoringASCIICase` for proper header name comparison in
uncommon headers
- **Comprehensive test coverage**: Added regression tests that verify no
duplicate Date headers in all scenarios (static responses, dynamic
responses, proxy responses)
## Test Plan
- [x] Added comprehensive regression test in
`test/regression/issue/21677.test.ts`
- [x] Tests verify only one Date header exists in all response scenarios
- [x] Tests fail with current main branch (confirms bug exists)
- [x] Tests pass with this fix (confirms bug is resolved)
- [x] Existing Date header tests still pass (no regression)
## Testing
The reproduction case from the issue now works correctly:
**Before (multiple Date headers):**
```
HTTP/1.1 200 OK
Date: Thu, 07 Aug 2025 17:02:24 GMT
content-type: text/plain;charset=utf-8
Date: Thu, 07 Aug 2025 17:02:23 GMT
```
**After (single Date header):**
```
HTTP/1.1 200 OK
Date: Thu, 07 Aug 2025 17:02:23 GMT
content-type: text/plain;charset=utf-8
```
🤖 Generated with [Claude Code](https://claude.ai/code)
---------
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
