Remove Redis TTL for static quiz and QA caches

[ViktorSvertoka]

• Remove TTL configuration for quiz answers cache.
• Store QA cache entries without expiration.
• Keep Redis reads as the primary source for static data.

Summary by CodeRabbit

• Chores
  • Cleaned up inline comments across Q&A and quiz components for improved code maintainability.
  • Removed cache time-to-live (TTL) configuration, allowing cached data to persist without automatic expiration.

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[coderabbitai]

📝 Walkthrough

Walkthrough

This PR removes TTL (time-to-live) cache expiration logic from quiz and Q&A caching modules, along with cleanup of inline comments throughout the codebase. The changes eliminate per-item cache expiration, making cached items persist indefinitely.

Changes

Cohort / File(s)	Summary
Comment cleanup frontend/components/q&a/AIWordHelper.tsx, frontend/components/q&a/SelectableText.tsx, frontend/lib/quiz/quiz-session.ts	Removed inline comments related to scrollbar handling, rate-limit UI branching, and TTL status without altering logic or control flow.
TTL and cache configuration removal frontend/lib/cache/qa.ts, frontend/lib/quiz/quiz-answers-redis.ts	Removed TTL constants (QA_CACHE_TTL_SECONDS, QUIZ_CACHE_TTL_SECONDS) and eliminated per-item expiration settings from cache operations; cache now persists indefinitely. Also removed public export qaCacheConfig object.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Possibly related issues

• (SP: 1) [Frontend] Remove redundant quiz files after Redis migration #262: Directly addresses Redis migration cleanup by removing legacy TTL-related code and constants from quiz/cache modules as part of the migration effort.

Possibly related PRs

• (SP: 5) [Quiz] Redis caching + guest session fix + cleanup #263: Conflicts with current PR's TTL removal, as the related PR adds Redis quiz-answer caching with a 12-hour TTL configuration.

Suggested labels

refactor

Suggested reviewers

• AM1007

Poem

A rabbit hops through caches bright,
Removing timers left and right,
No more TTLs to expire,
Comments cleaned like a morning fire,
Forever stored, without a care! 🐰⏱️

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The pull request title accurately summarizes the main objective: removing Redis TTL (time-to-live) configuration for static quiz and QA caches, which is reflected across all file changes.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch chore/remove-redis-ttl-static-caches

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[coderabbitai]

Actionable comments posted: 0

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

frontend/lib/cache/qa.ts (1)

45-50: ⚠️ Potential issue | 🔴 Critical

Cache invalidation mechanism is missing and dead code.

Removing TTL without implementing working invalidation is problematic: cache entries now persist indefinitely. While invalidateQaCacheByCategory and invalidateAllQaCache are exported, they are never imported or called anywhere. Since QA content is managed in Sanity CMS (separate system), there is no mechanism to invalidate the frontend cache when content changes. Users will see stale data indefinitely until the application restarts.

Either restore the TTL for automatic expiration, or implement a proper cache invalidation strategy when Sanity CMS content is published (e.g., via webhooks, scheduled revalidation, or revalidateTag).

🧹 Nitpick comments (1)

frontend/lib/quiz/quiz-answers-redis.ts (1)

59-60: Add invalidation function for quiz answer cache consistency.

The TTL has been removed from the cache set operation, making it consistent with the qa.ts module which also stores cache without expiration. However, unlike qa.ts which provides invalidateQaCacheByCategory() and invalidateAllQaCache(), this module lacks any invalidation mechanism.

While no production quiz update/delete endpoints were found, adding an invalidation function maintains defensive consistency with the qa.ts pattern and ensures the cached answers can be cleared if quiz content changes in the future. Additionally, the cachedAt timestamp is stored but never validated.

Consider adding:

export async function invalidateQuizAnswersCache(quizId: string): Promise<boolean> {
  const redis = getRedisClient();
  if (!redis) return false;
  
  const key = getCacheKey(quizId);
  await redis.del(key);
  return true;
}