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WriteAsync published one awaited QoS 1 round-trip per request, so 50 writes to a stalled broker cost 50 publish deadlines. Different topics now publish concurrently (at most 8 in flight); same-topic writes stay in request order. A caller cancel still fills every slot. A successful publish advances LastSuccessfulRead. MiniBroker now frames packets properly and records/PUBACKs PUBLISHes. Refs #744 Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT