Dedupe stuck on failure Debugging Lab

Dedupe stuck on failureEvents & ConcurrencyHardPreparing workspaceAutosaved

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Incident Dossier

Dedupe stuck on failure

A payment provider retries a webhook whose first attempt returned a 500 from a downstream service. The dedupe entry was already written before the side effect ran, so the retry is now treated as a duplicate and the side effect never executes — the customer's payment is never recorded.

Initial failing signalRetry of a failed event is suppressed as a duplicateExpected handle(event) returns { status: 'ok' } on the retry after a failed first attempt · received handle(event) returns { status: 'duplicate' } on the retry after a failed first attempt

Progress

1Reproduce the bugRun checks

2Edit the fixOpen

3Pass checksOpen

4Submit fixOpen

Reproduction Steps

Run npm test.
Find where the dedupe set is mutated.
Notice the mutation happens before the side effect runs and is not undone on error.
Move the mutation to after the side effect succeeds.

Focus Mode

Start

src/handler.js

Likely area

src/handler.js

Progressive hints

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

TopicEvents & Concurrency

DifficultyHard

Est. time24 min

Workspacecreating

Explorer

Preparing workspace files…

Evidence Map

Failing signal loaded from challenge API
Workspace files loaded from workspace API
Results rendered only after API run/submit

Autosaved

workspace

Outputread-onlyready$ workspace boot

Workspace booting...