Cursor built from a non-unique column Debugging Lab

Cursor built from a non-unique columnHTTP/APIMediumPreparing workspaceAutosaved

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Incident Dossier

Cursor built from a non-unique column

Customers syncing their event log via keyset pagination report that some rows appear twice in a row, then are missing entirely on the next page. The endpoint uses an opaque cursor but its anchor column isn't unique.

Initial failing signalsecond page re-emits a row from the first pageExpected [3, 4] · received [2, 3]

Progress

1Reproduce the bugRun checks

2Edit the fixOpen

3Pass checksOpen

4Submit fixOpen

Reproduction Steps

Run npm test.
Inspect how the cursor is encoded and decoded.
Notice the cursor encodes a single column, while the lookup uses both columns.
Make the cursor unambiguous by combining the unique id with the status.

Focus Mode

Start

src/cursor.js

Likely area

src/cursor.js

Progressive hints

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

TopicHTTP/API

DifficultyMedium

Est. time16 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...