[No QA] Fix onboarding modal guard redirect causing infinite navigation loop

[TMisiukiewicz]

Explanation of Change

When a navigation guard redirects to a modal route (e.g. OnboardingModalNavigator or MigratedUserModalNavigator), the REDIRECT handler in RootStackRouter.ts was calling CommonActions.reset() with only the redirect state's routes. This wiped out all existing base app routes (like ReportsSplitNavigator).

With no base routes present, React Navigation continuously generated PUSH actions to reconcile the missing routes — creating an infinite loop.

The fix detects whether the redirect target is a modal navigator. If it is, the redirect routes are merged with the existing state routes instead of replacing them. Non-modal redirects (e.g. to HOME) still perform a full replace as before.

Fixed Issues

$ #85454
PROPOSAL:

Tests

1. Login with @gmail.com domain
2. When in work email validation path, run the following code in the console:

// Set the exact NVP_ONBOARDING state from the bug report
window.Onyx.merge('nvp_onboarding', {
    hasCompletedGuidedSetupFlow: false,
    shouldValidate: true,
    signupQualifier: 'individual'
    // Note: isMergeAccountStepCompleted is intentionally absent
});

3. Refresh the page
4. Verify the onboarding step opened correctly
5. Verify you are able to complete the onboarding

• Verify that no errors appear in the JS console

Offline tests

N/A

QA Steps

Same as tests

• Verify that no errors appear in the JS console

PR Author Checklist

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Screenshots/Videos

Android: Native

Android: mWeb Chrome

iOS: Native

iOS: mWeb Safari

MacOS: Chrome / Safari

Screen.Recording.2026-04-01.at.11.37.44.mov

[codecov]

Codecov Report

❌ Looks like you've decreased code coverage for some files. Please write tests to increase, or at least maintain, the existing level of code coverage. See our documentation here for how to interpret this table.

Files with missing lines	Coverage Δ
...igator/createRootStackNavigator/RootStackRouter.ts	66.66% <11.11%> (-7.11%)	⬇️
... and 46 files with indirect coverage changes

[melvin-bot]

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[chatgpt-codex-connector]

Preserve updated modal route state during redirect

When isModalRedirect is true, the merge path drops any redirect route whose name already exists (existingRouteNames), so an existing ONBOARDING_MODAL_NAVIGATOR/MIGRATED_USER_MODAL_NAVIGATOR entry is never replaced with the new redirectState version. That makes guard redirects a no-op when only the nested state/params changed (same route name), even though guards like OnboardingGuard compute a step-specific redirect route repeatedly. In that case users can remain on a stale onboarding step because resetRoutes reuses state.routes instead of applying the newly computed modal route state.

Useful? React with 👍 / 👎.

[TMisiukiewicz]

Closing in favor of #86390