Incident Dossier

Dedupe cache evicts too eagerly

During a flash sale the payments endpoint sees 500 unique webhook events in a few seconds. The dedupe cache evicts the first ones as new events arrive, and any retry for those early events runs the side effect a second time.

Initial failing signalFirst event of a burst is no longer in the dedupe cacheExpected behavior: dedupe.hasSeen('evt_1') returns true after 60 unique marks · actual behavior: dedupe.hasSeen('evt_1') returns false after 60 unique marks

Progress

1Reproduce the bugRun checks

2Edit the fixOpen

3Pass checksOpen

4Submit fixOpen

Reproduction Steps

Run npm test.
Mark 60 unique event ids and then look up the first one.
Trace the eviction policy inside createDedupe.
Replace the tiny capacity with a default that survives realistic bursts.

Focus Mode

Start

src/cache.js

Likely area

src/cache.js

Challenge Coach

Hints reveal broad direction first, then narrow toward the suspect path without showing hidden tests or exact solution code.

TopicReliability

DifficultyMedium

Est. time18 min

Workspacepreparing

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Evidence Map

Failing signal loaded from challenge API
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workspace

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