Stale-while-revalidate serves stale forever Debugging Lab

Stale-while-revalidate serves stale foreverCaching & PerformanceMediumPreparing workspaceAutosaved

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Incident Dossier

Stale-while-revalidate serves stale forever

A profile cache serves stale data indefinitely. After the upstream profile is updated, every read returns the original value because the background revalidation never runs.

Initial failing signalStale branch returns cached value without refreshingExpected fetcher invoked twice (initial + revalidation) · received fetcher invoked only once

Progress

1Reproduce the bugRun checks

2Edit the fixOpen

3Pass checksOpen

4Submit fixOpen

Reproduction Steps

Run npm test.
Advance the clock past the TTL and trace what happens on a second read.
Compare the fresh branch to the stale branch and decide which fields each reads.
Make the stale branch fetch and store a fresh value while still returning the cached one.

Focus Mode

Start

src/cache.js

Likely area

src/cache.js

Progressive hints

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

TopicCaching & Performance

DifficultyMedium

Est. time20 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...