fix(react): Add transaction name guards for rapid lazy-route navigations

[onurtemizkan]

Following up on #18098 and #18155

Fixes a race condition where rapid navigations between lazy routes cause transaction names to be incorrectly assigned or corrupted.

This occurs when async lazy handlers resolve after the user already navigated to a different route. The root cause was captureCurrentLocation() was reading window.location at the time of handler invocation, but during patchRoutesOnNavigation, the browser URL hasn't actually updated yet. So when handlers invoked during navigation A resolve later, they would capture navigation B's location (or whatever the current URL is), leading to incorrect span updates.

The fix introduces a navigation context mechanism that captures both the correct targetPath and the active span at the start of patchRoutesOnNavigation, making them available to async handler proxies during invocation. This ensures handlers always use the navigation context they were invoked with, not the current browser state.

The navigation context uses a stack to properly handle overlapping/concurrent patchRoutesOnNavigation calls. If a second navigation starts before the first one's handlers complete, each navigation maintains its own captured context.

[Copilot]

Pull request overview

This PR adds transaction name guards to prevent corruption when users rapidly navigate between lazy routes before lazy handlers complete resolution. The fix captures the location at the time a lazy handler is invoked and verifies it still matches the current location before updating transaction names.

• Captures window location when lazy route handlers are invoked
• Adds guard logic to skip span updates if user has navigated away
• Includes comprehensive e2e tests for various rapid navigation scenarios

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
packages/react/src/reactrouter-compat-utils/lazy-routes.tsx	Added captureCurrentLocation() function and modified proxy to capture location at invocation time, passing it through to processResolvedRoutes
packages/react/src/reactrouter-compat-utils/instrumentation.tsx	Added guard logic to compare captured location with current window location, skipping span updates when they don't match
packages/react/test/reactrouter-compat-utils/lazy-routes.test.ts	Updated test expectations to include new currentLocation parameter and added test for null-to-undefined conversion
dev-packages/e2e-tests/test-applications/react-router-7-lazy-routes/tests/transactions.test.ts	Added seven new e2e tests covering rapid navigation, zero-wait navigation, browser back, and multiple overlapping handlers
dev-packages/e2e-tests/test-applications/react-router-7-lazy-routes/src/pages/SlowFetchLazyRoutes.tsx	New test page with 500ms delay and top-level await to simulate slow lazy route loading
dev-packages/e2e-tests/test-applications/react-router-7-lazy-routes/src/pages/Index.tsx	Added navigation link to slow-fetch route for testing
dev-packages/e2e-tests/test-applications/react-router-7-lazy-routes/src/pages/DelayedLazyRoute.tsx	Added navigation links for testing rapid navigation between routes
dev-packages/e2e-tests/test-applications/react-router-7-lazy-routes/src/index.tsx	Added slow-fetch route configuration with lazy handler

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[Copilot]

The location key is computed twice: once using computeLocationKey() for currentLocation, and once manually for windowLocation. This duplicates the logic and increases the risk of inconsistency. Consider using computeLocationKey() for both, or extracting the manual computation into a reusable helper that accepts a window.location-like object.

Suggested change

	const currentKey = `${windowLocation.pathname}${windowLocation.search || ''}${windowLocation.hash || ''}`;
	const currentKey = computeLocationKey(windowLocation);

[Copilot]

The test name "should pass null location when currentLocation is null" is misleading because the test actually verifies that null is converted to undefined when passed to processResolvedRoutes. Consider renaming to "should convert null location to undefined for processResolvedRoutes" to better reflect what is being tested.

Suggested change

	it('should pass null location when currentLocation is null', () => {
	it('should convert null location to undefined for processResolvedRoutes', () => {

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated no new comments.

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[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

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