Incident Dossier

Idempotency fingerprint key-order sensitive

Two identical payment requests with the same logical body produce two charges. The access logs show both requests reached the server, but the dedupe layer did not recognise the second one as a replay because the inner objects happened to serialise in a different order.

Initial failing signalReversed key order misses the dedupe cacheExpected behavior: store.hasSeen({currency, amount}) returns true after remembering {amount, currency} · actual behavior: store.hasSeen returns false

Progress

1Reproduce the bugRun checks

2Edit the fixOpen

3Pass checksOpen

4Submit fixOpen

Reproduction Steps

Run npm test.
Find the function that builds the dedupe fingerprint.
Notice it relies on JSON.stringify, whose key order is implementation-defined per insertion order.
Replace it with a canonical serialisation that sorts keys at every level.

Focus Mode

Start

src/fingerprint.js

Likely area

src/fingerprint.js

Challenge Coach

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

TopicData Integrity

DifficultyMedium

Est. time22 min

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Evidence Map

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workspace

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