Mobile: Fix Joplin Cloud login failing when Android kills the app during OAuth

[laurent22]

Fixed an issue where the Joplin Cloud login would fail on Android if the system killed the app while the user was authorising in the browser.

The app now saves the authentication request before opening the browser and, on next startup, checks if the authorisation was completed on the server. Previously, the credentials were lost when the app was killed, requiring the user to re-authorise repeatedly.

Possible fix for https://discourse.joplinapp.org/t/joplin-cloud-credentials-are-invalid-cant-sync-android-app-with-windows/49610/5

TODO

• Needs to be tested properly on all platforms

[coderabbitai]

📝 Walkthrough

Walkthrough

This pull request introduces a mechanism to persist and recover pending Joplin Cloud authentication by storing an application auth ID in settings and completing the authentication flow during application startup on both desktop and mobile platforms.

Changes

Cohort / File(s)	Summary
Application Startup Integration packages/app-desktop/app.ts, packages/app-mobile/utils/buildStartupTasks.ts	Added new startup tasks that invoke completePendingAuthentication() to handle recovery of interrupted Joplin Cloud authentication flows on application launch.
Login Screen Updates packages/app-desktop/gui/JoplinCloudLoginScreen.tsx, packages/app-mobile/components/screens/JoplinCloudLoginScreen.tsx	Updated login screens to call saveApplicationAuthId() when users initiate authorization, persisting the generated auth identifier for recovery purposes.
Core Authentication Services packages/lib/services/joplinCloudUtils.ts, packages/lib/models/settings/builtInMetadata.ts	Added new setting sync.10.pendingAuthId to store pending authentication state, introduced saveApplicationAuthId() and completePendingAuthentication() functions, and updated checkIfLoginWasSuccessful() to clear the pending auth ID upon successful completion.

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Important

Pre-merge checks failed

Please resolve all errors before merging. Addressing warnings is optional.

❌ Failed checks (1 error)

Check name	Status	Explanation	Resolution
Pr Description Must Follow Guidelines	❌ Error	Pull request lacks required Test Plan section detailing manual testing on Android, automated test cases, and verification steps as mandated by technical_spec.md guidelines.	Add Test Plan section documenting manual OAuth flow testing on Android, automated test coverage for saveApplicationAuthId() and completePendingAuthentication() functions, and reviewer verification steps.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main change: fixing Joplin Cloud login on Android when the OS kills the app during OAuth authentication.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description check	✅ Passed	The PR description accurately relates to the changeset, explaining the issue (Joplin Cloud login failure when Android kills the app during OAuth), the solution (saving authentication request before browser opening), and the impact (checking on startup if authorisation completed).

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch mobile_oauth_login_fix

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