Debug a Stale Insurance Eligibility Status
Company: Headway
Role: Software Engineer
Category: Software Engineering Fundamentals
Difficulty: medium
Interview Round: Onsite
# Debug a Stale Insurance Eligibility Status
A patient list shows a cached `eligibility_status` from `UserInsurance`, while each insurance record has timestamped `EligibilityLookup` snapshots. Some rows display success although the latest lookup is not successful. Diagnose and repair the full-stack behavior.
### Constraints & Assumptions
- The latest lookup is the current source of truth.
- Existing records may already contain stale cached values.
### Clarifying Questions to Ask
- How are equal timestamps ordered?
- Where and when is the cache updated?
### What a Strong Answer Covers
- Reproduction, query ordering, cache update atomicity, backfill, and UI verification.
- Regression tests for no lookup, ties, and out-of-order completion.
### Follow-up Questions
- Would you remove the cache?
- How would concurrent lookups be reconciled?
Quick Answer: A patient list shows a cached `eligibility_status` from `UserInsurance`, while each insurance record has timestamped `EligibilityLookup` snapshots. Make the API or object boundaries explicit, then cover invariants, edge cases, testing strategy, and operational trade-offs.