fix-rollbar (7424/464894116637): guard undefined week in playground handleFinish

[astashovai]

Summary

• Add optional chaining (?.) and early return guard to handleFinish in programPreviewPlayground.tsx to prevent crash when progresses[weekIndex] is undefined

Rollbar

https://app.rollbar.com/a/astashov/fix/item/liftosaur/7424/occurrence/464894116637

Decision

Fixed — the error is in our code and crashes the app during normal program preview/playground usage on Android.

Root Cause

In ProgramPreviewPlayground, the handleFinish callback accesses s.progresses[weekIndex].days[dayIndex] without checking if s.progresses[weekIndex] exists. On Android (React Native), the PagerView can fire callbacks with a weekIndex that is momentarily out of sync with the progresses array during state updates, causing s.progresses[weekIndex] to be undefined and the .days access to throw a TypeError.

Other code paths in the codebase already use optional chaining for the same access pattern (e.g., navModalPlaygroundUtils.ts, NavModalPlaygroundEditExercise.tsx, usePlaygroundModalBridges.ts).

Test plan

• Unit tests pass (803/803)
• Build succeeds
• TypeScript type check passes (no new errors)
• Verify playground week swiping on Android does not crash