[MBL-19559][Student] Fix New Quizzes error handling for expired assignments

[kristofnemere]

Test plan:

1. As a teacher, create a New Quiz assignment in a course
2. Set an "until date" that is in the past (e.g., yesterday)
3. As a student enrolled in the course, submit the quiz before the until date expires
4. After the until date has passed, log in as the student in the Canvas Android app
5. Navigate to the course grades and tap on the quiz assignment
6. Verify that an error toast is displayed instead of the app attempting to navigate with a null LTI tool
7. Expected: Error message "An unexpected error occurred." should appear as a toast
8. Verify the app doesn't crash and remains functional

refs: MBL-19559
affects: Student
release note: Fixed issue where students couldn't view New Quizzes submissions after the assignment's until date had passed

Checklist

• Follow-up e2e test ticket created or not needed
• Run E2E test suite
• Tested in dark mode
• Tested in light mode
• Test in landscape mode and/or tablet
• A11y checked
• Approve from product

[claude]

Review Summary

This PR improves error handling for external tool launch URLs by changing from exception-based error handling to nullable return values. This is a good architectural improvement that makes error handling more explicit and prevents crashes.

Key Changes

• Changed getExternalToolLaunchUrl return type from LTITool to LTITool? in the repository interface and network data source
• Updated error handling from dataOrThrow to dataOrNull in AssignmentDetailsNetworkDataSource
• Added null check in AssignmentDetailsViewModel to gracefully handle failures with a user-friendly error message
• Updated tests to reflect the new behavior (returns null instead of throwing exception)
• Added new test case for the null LTI tool scenario in the ViewModel

Positive Aspects

✅ Consistent with existing code: The LocalDataSource already returns null for this method, so this change makes the network implementation consistent
✅ Better user experience: Users now see a friendly error message instead of a crash
✅ Proper test coverage: Both the data source test and ViewModel test were updated to cover the new null-handling behavior
✅ Follows Kotlin idioms: Using nullable types is more idiomatic than throwing exceptions for expected failure cases
✅ Clean implementation: The null check is straightforward and handles the error case appropriately

Suggestions for Improvement

• Consider adding error logging: Track when this failure occurs to understand its frequency in production (see inline comment on AssignmentDetailsViewModel.kt:691)
• Consider more specific error message: The generic "unexpected error" message could be replaced with something more specific like "Unable to load external tool" (see inline comment on AssignmentDetailsViewModel.kt:691)

Code Quality Assessment

• Architecture: ✅ Good - follows repository pattern correctly
• Error Handling: ✅ Good - graceful degradation instead of crashes
• Test Coverage: ✅ Good - both unit tests updated appropriately
• Code Style: ✅ Good - follows Kotlin conventions and project patterns
• Performance: ✅ No concerns
• Security: ✅ No concerns

Overall, this is a solid improvement to error handling. The suggestions above are minor enhancements and not blocking issues.

[github-actions]

📊 Code Coverage Report

✅ Student

• PR Coverage: 42.80%
• Master Coverage: 42.80%
• Delta: +0.00%

✅ Teacher

• PR Coverage: 25.44%
• Master Coverage: 25.44%
• Delta: +0.00%

✅ Pandautils

• PR Coverage: 22.63%
• Master Coverage: 22.61%
• Delta: +0.02%

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📈 Overall Average

• PR Coverage: 30.29%
• Master Coverage: 30.29%
• Delta: +0.01%

[github-actions]

Teacher Install Page

[github-actions]

Student Install Page