The Update That Forgot Its Pin Debugging Lab

The Update That Forgot Its PinData IntegrityHardPreparing workspaceAutosaved

00:00

Incident Dossier

The Update That Forgot Its Pin

Two concurrent callers each read version 1 of a record and submit updates pinned at version 1. Both succeed and the second write silently overwrites the first; the caller of the first update never learns it was lost.

Initial failing signaltwo pinned updates both succeedExpected exactly 1 success · received 2 successes, version jumps to 3

Progress

1Reproduce the bugRun checks

2Edit the fixOpen

3Pass checksOpen

4Submit fixOpen

Reproduction Steps

Run npm test.
Notice that update accepts an expectedVersion but never compares it.
Two concurrent callers both observe version 1, both pin version 1, both write.
Add the version comparison inside the critical section and reject mismatches.

Focus Mode

Start

src/update.js

Likely area

src/update.js

Progressive hints

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

TopicData Integrity

DifficultyHard

Est. time25 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...