test: add a regression test for the WebSocket BroadcastToUser key mismatch

[cypriannwokolo2-creator]

Summary

The BroadcastToUser key-mismatch bug (hub keyed by client.ID vs userID lookup) has no test — deliverability regressions go undetected.

Acceptance Criteria

• Test asserting user-targeted broadcast reaches the connection
• Multi-connection per user case
• Run in CI

Complexity

Medium.

[Sensei-Victor]

@Sensei-Victor has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

THIS IS MY DOMINANT FIELD

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[Stephan-Thomas]

@Stephan-Thomas has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi, i would like to work on this.

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[paulpeter32-coder]

@paulpeter32-coder has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi maintainer I'm a fullstack developer and I would love to work on this issue

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[Bigdaddyobamo]

@Bigdaddyobamo has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi Maintainer, I have done something similar. Please kindly assign.

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[achiever2110]

@achiever2110 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

please assign to me

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