fix-rollbar (7266/464932643616): Guard against undefined week in exercise editor

[astashovai]

Summary

• Add defensive null checks when accessing evaluatedProgram.weeks[index].days in exercise editing UI components
• Protect against stale week/day indices that reference positions no longer existing in the re-evaluated program
• Affected files: screenEditProgramExercise.tsx, editProgramExerciseDay.tsx, editProgramExerciseDaysList.tsx, editProgramExerciseAcrossAllWeeks.tsx, editProgramUiHelpers.ts

Rollbar

https://app.rollbar.com/a/astashov/fix/item/liftosaur/7266/occurrence/464932643616

Decision

Fixed — the error has 230 occurrences in production on Android, affects normal user flows (editing exercise programs), and the fix is minimal defensive null checking.

Root Cause

When a user edits a program exercise on Android (React Native), state changes can cause the evaluated program to be recomputed with a different week/day structure. Components that access evaluatedProgram.weeks[index].days without null guards crash with "Cannot read property 'days' of undefined" when the index points to a week that no longer exists in the re-evaluated program.

Test plan

• Edit a program exercise with multiple weeks
• Delete a week while on the exercise editing screen
• Verify no crash occurs and the UI recovers gracefully
• Unit tests pass (804 passing)
• Build succeeds