fix(router): avoid restarting fetcher revalidations

[dogxii]

Summary:

• Fix Revalidating fetchers incorrectly reloading on GET navigations #14115
• Track in-flight fetcher revalidations so a subsequent GET navigation does not abort and restart the same fetcher load
• Update the fetcher interruption regression test and add a patch change file

Testing:

• pnpm test packages/react-router/tests/router/fetchers-test.ts
• pnpm test packages/react-router/tests/router
• pnpm prettier --check packages/react-router/lib/router/router.ts packages/react-router/tests/router/fetchers-test.ts packages/react-router/.changes/patch.fetcher-revalidation-navigation.md
• git diff --check
• pnpm run typecheck
• pnpm build

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Prevents GET navigations from aborting/restarting fetcher revalidations that are already in-flight (typically triggered by action submissions), allowing the original revalidation to complete.

Changes:

• Track in-flight fetcher revalidations via revalidatingFetchersInFlight and thread it through getMatchesToLoad
• Skip restarting a fetcher load during navigation revalidation when the same fetcher is already revalidating in-flight (unless it was explicitly cancelled)
• Update fetcher test expectations and add a patch changes entry

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
packages/react-router/lib/router/router.ts	Adds and uses an in-flight revalidation tracking set to avoid restarting fetcher revalidations during GET navigations
packages/react-router/tests/router/fetchers-test.ts	Updates test to assert in-flight action revalidation fetchers are not aborted/restarted by navigation
packages/react-router/.changes/patch.fetcher-revalidation-navigation.md	Documents the patch-level behavior change

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