Task 4.3: Implement API Retry Logic with Exponential Backoff

[rowantervelde]

Epic: #11 (Epic 4: Edge Cases, Performance & Testing)
Type: Enhancement
Priority: P2 (Medium)
Estimate: 0.5 day

Description

Add retry logic to API requests with exponential backoff to handle transient network failures and improve reliability.

Acceptance Criteria

• Retry failed API requests up to 3 times
• Use exponential backoff: 1s, 2s, 4s delays
• Only retry on network errors (not 4xx client errors)
• Show loading state during retries
• Display error message after max retries exceeded
• Log retry attempts for debugging

Technical Notes

• Add retry utility function in useSentiment.ts
• Check response status: retry on 5xx, timeout, network errors
• Don't retry on 4xx (client errors like 404, 400)
• Use setTimeout for delay between retries
• Consider abort controller for request cancellation

Dependencies

• Blocks: None
• Blocked by: None (can work in parallel with Epic 1)

Test Coverage

• Unit test: retry count, backoff timing
• Integration test: simulate network failures
• E2E test: TC-19 (API failure handling)

Related Files

• app/composables/useSentiment.ts
• specs/004-sentiment-detail/testplan.md (TC-19)

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Part of Feature 004: Sentiment Detail Breakdown Page