LibWeb: Release discarded navigation redirect requests

[gmta]

Since f454515, document navigation requests have been retained in RequestServer so they can be handed to the UI process if a response becomes a download. Intermediate redirect responses never reach download handling, however, and replacing FetchController's pending request left each retained response pipe open. Repeated redirects eventually exhausted RequestServer's file descriptors.

The Fetch specification does not account for this lifecycle. RequestServer transfer retention is a Ladybird implementation detail, not web-observable Fetch state. Release the transfer hold before discarding an intermediate redirect response, and stop its request when it is still active.

Cover this with a focused http_redirect_fetch() test that records the release of a synthetic intermediate response. An end-to-end regression would have to lower the process file limit and perform hundreds of navigations, making it slow and dependent on test-runner arguments and process timing. The unit test directly protects the missing ownership step.

This is one of the potential sources for FD leaks that we're seeing on our WPT runner.

[coderabbitai]

📝 Walkthrough

Walkthrough

HTTP redirect fetching now releases intermediate response transfer state and stops associated requests when no location URL is produced. The fetch function is exported, and a LibWeb test verifies transfer release during redirect processing.

Changes

Redirect cleanup

Layer / File(s)	Summary
Redirect cleanup and API export Libraries/LibWeb/Fetch/Fetching/Fetching.h, Libraries/LibWeb/Fetch/Fetching/Fetching.cpp	http_redirect_fetch is exported and releases the intermediate response transfer hold, stopping an associated RequestServer request before returning when no location URL is available.
Transfer-release test coverage Tests/LibWeb/CMakeLists.txt, Tests/LibWeb/TestFetchResponse.cpp	The test target links LibRequests and LibURL; a tracking response and redirect test verify that transfer release occurs.

Estimated code review effort: 2 (Simple) | ~10 minutes

Suggested reviewers: atkinssj

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
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	The description matches the patch, describing redirect request cleanup, transfer release, and the new focused http_redirect_fetch test.

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