(SP:2) [Frontend] Fix duplicated Q&A items after content updates

[ViktorSvertoka]

Summary

Fix duplicated questions in Q&A and make cache updates safer after content changes.

Changes

• Added Q&A cache key versioning (qa:v2:*)
• Added TTL for Q&A Redis cache
• Added deduplication in /api/questions/[category]
• Rewrites cache on HIT if duplicates are found
• Added Q&A cache invalidation after seed:questions
• Updated route tests for duplicate cases

Validation

• npm run test:run -- lib/tests/q&a/questions-route.test.ts passed

Closes #329

Summary by CodeRabbit

• Bug Fixes

  • Resolved duplicate questions appearing in API responses by ensuring returned lists contain unique entries.

• Improvements

  • Upgraded question caching with versioning and automatic expiration for more reliable, fresh results.
  • Improved cache behavior when the cache service is unavailable to avoid surprising errors.

• Chores

  • Automatically clears question cache after seeding/updating content.

• Tests

  • Added test coverage for question deduplication.

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Project	Deployment	Actions	Updated (UTC)
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[coderabbitai]

📝 Walkthrough

Walkthrough

Adds API-level deduplication and normalization for Q&A responses, versions and applies TTL to QA cache keys, returns numeric counts from cache invalidation, invalidates QA cache after seeding, and adds a test validating deduplication behavior.

Changes

Cohort / File(s)	Summary
Cache Infrastructure frontend/lib/cache/qa.ts	Added QA cache versioning prefix, introduced QA_CACHE_TTL_SECONDS, apply TTL on set, improved handling when Redis is unavailable (get returns null), and made invalidation functions return numeric deleted-key counts.
API Deduplication frontend/app/api/questions/[category]/route.ts	Introduced dedupeItems and normalizeResponse to remove duplicate items by id and locale+question text; applied normalization for both cached responses and newly built responses; updated cache writes to store normalized payloads.
Cache Invalidation (seed) frontend/db/seed-questions.ts	Calls invalidateAllQaCache after seeding questions, with console logging on success and warning on failure.
Deduplication Tests frontend/lib/tests/q&a/questions-route.test.ts	Added tests mocking duplicate question texts to assert API returns unique items and that setQaCache is called appropriately.

Sequence Diagram(s)

sequenceDiagram
    participant Client
    participant Route as Questions Route
    participant Cache as QA Cache (Redis)
    participant DB

    Client->>Route: GET /api/questions/:category?locale=...
    Route->>Cache: getQaCache(key=qa:v2:...)
    alt Cache hit
        Cache-->>Route: cachedPayload
        Route->>Route: normalizeResponse(cachedPayload)
        Route-->>Client: 200 normalizedPayload
    else Cache miss
        Route->>DB: query questions by category/locale
        DB-->>Route: rawItems
        Route->>Route: dedupeItems(rawItems) -> normalizedPayload
        Route->>Cache: setQaCache(key, normalizedPayload, TTL)
        Route-->>Client: 200 normalizedPayload
    end

Loading

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly Related PRs

• Remove Redis TTL for static quiz and QA caches #265: Changes to frontend/lib/cache/qa.ts around TTL and cache behavior — closely related to cache TTL/versioning changes here.
• feat(Blog):Adding pagination #244: Modifies the QA cache and questions route — overlaps with deduplication/normalization changes in the route.
• (SP: 2) [QA] Q&A Tests & Coverage #208: Updates tests and route behavior for Q&A — related test coverage adjustments.

Suggested Labels

backend

Suggested Reviewers

• AM1007

Poem

🐰 Hop, hop — I prune the duplicate leaves,
Keys now versioned, fresh answers weave,
TTL ticks softly, stale bits fall away,
Seed clears the cache to make room for play,
Rabbit cheers: unique Q&A today! 🥕✨

🚥 Pre-merge checks | ✅ 5 | ❌ 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 (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: fixing duplicated Q&A items after content updates, which is the core objective of the PR.
Linked Issues check	✅ Passed	The PR fully implements all coding requirements from issue #329: versioned cache keys, TTL for cache entries, API-side deduplication, cache invalidation after seeding, and route tests covering duplicate scenarios.
Out of Scope Changes check	✅ Passed	All changes are directly related to the linked issue #329 objectives: cache versioning, TTL implementation, deduplication logic, cache invalidation, and tests are all in scope.
Merge Conflict Detection	✅ Passed	✅ No merge conflicts detected when merging into develop

_{✏️ 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 bug/fix-qa

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[coderabbitai]

Actionable comments posted: 1

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)

59-59: ⚠️ Potential issue | 🔴 Critical

Bug: invalidateQaCacheByCategory prefix doesn't match versioned key format.

The key format was updated to qa:v2:category:${category}:… (Line 25), but this invalidation function still scans for qa:category:${category}:*. It will never match any v2 keys, making per-category invalidation silently broken.

🐛 Proposed fix

-  const prefix = `qa:category:${category.toLowerCase()}:`;
+  const prefix = `qa:${QA_CACHE_VERSION}:category:${category.toLowerCase()}:`;

🤖 Fix all issues with AI agents

In `@frontend/app/api/questions/`[category]/route.ts:
- Around line 53-63: normalizeResponse currently replaces data.items with
dedupeItems(data.items) but leaves data.total and data.totalPages unchanged;
update normalizeResponse (function normalizeResponse and the call to
dedupeItems) to recalculate total as uniqueItems.length and recompute totalPages
using the original page limit when available (e.g., totalPages = Math.ceil(total
/ limit)); if limit is not accessible in this scope, set total to
uniqueItems.length and either clear/undefine totalPages or emit a diagnostic log
indicating dedupe changed the count so callers can handle pagination. Also log
when deduplication reduces the count to help diagnose upstream duplication
issues.