The inbound path hardcoded Nostr kind 9 at both the WebSocket
subscription filter and the dispatch gate (which runs before mention
gating), so Buzz forum channels — kind 45001 thread roots and 45003
comment replies — were silently never dispatched to the agent; chat and
stream channels worked, making the gap invisible (#90309). Block's own
ACP harness documents the forum kinds explicitly.
Introduce _DISPATCH_KINDS = {9, 45001, 45003} for the subscription
filter and dispatch gate. The stream kinds (46010/40007/45002) stay out
of scope until their dispatch semantics are confirmed.
_is_direct_message_event deliberately keeps its kind-9-only check:
widening it would let a p-tagged forum post be reclassified as a DM and
bypass mention gating. The send path already works unchanged (send()
omits --kind and threads via --reply-to).
Fixes#90309
liuhao1024