The Event That Fired Twice

Payments team sees duplicate charge attempts whenever the stream client reconnects. Logs show one event id, two handler invocations. The reconnect path calls ensureSubscribed again without removing the previous listener.

Initial failing signalReconnect double-invokes handlerExpected behavior: Reconnect invokes the handler exactly once. · actual behavior: Reconnect invokes the handler twice.

Progress

1Reproduce the bugRun checks

2Edit the fixOpen

3Pass checksOpen

4Submit fixOpen

Reproduction Steps

Subscribe a counter handler.
Call ensureSubscribed a second time (reconnect).
Emit once — handler should run once.

Focus Mode

Start

src/subscriber.ts
src/bus.ts

Likely area

src/subscriber.ts
src/bus.ts
src/client.ts

Challenge Coach

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

TopicEvents & Concurrency

DifficultyMedium

Est. time15 min

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Evidence Map

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