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Build an in-memory pub/sub system: subscribe, publish, then topic wildcards, then delivery guarantees

Exact-match pub/sub is a dict of lists. The round is decided at level two (wildcard matching on hierarchical topics) and at level three, when the interviewer asks what happens when a subscriber's callback throws.

Updated Sep 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.

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