Forum thread mentions never reach managed agents

Start in crates/buzz-acp/src/config.rs at SubscribeMode::Mentions and compare the defaults in build_channel_filters with the dynamic single-channel path; then inspect crates/buzz-acp/src/filter.rs to confirm the kind filter precedes require_mention. Add the two forum kinds to both defaults and verify forum-thread mentions arrive while existing stream kinds and p-tag filtering still work.

Describe the bug

A managed agent that is a member of a forum channel never responds to an @mention posted inside a forum thread. It stays silent, logs nothing, and reports no error, so the agent looks perfectly healthy while ignoring every mention.

The cause is the subscription filter. In crates/buzz-acp/src/config.rs, SubscribeMode::Mentions builds a fixed kind list:

let kinds = config.kinds_override.clone().unwrap_or_else(|| {
    vec![KIND_STREAM_MESSAGE, KIND_WORKFLOW_APPROVAL_REQUESTED, KIND_STREAM_REMINDER]
});

That is 9, 46010, 40007. Forum posts (45001) and forum comments (45003) are absent. In crates/buzz-acp/src/filter.rs an event whose kind is not in the list is rejected before the require_mention p-tag check ever runs, so the mention is discarded at the transport layer.

Neither forum kind appears anywhere in the buzz-acp crate.

Steps to reproduce

1. Create a forum channel and add a managed agent to it as a bot
2. Create a thread and mention the agent inside it
3. The agent never wakes up. Its log shows no incoming event.
4. Mention the same agent in a stream channel: it responds normally

Expected behavior

Mentioning an agent in a forum thread should reach it, same as in a stream channel. The UI lets you add agents to forum channels, so the mention path should work there.

Workaround

Setting the environment variable below restores it. The variable replaces the default list rather than extending it, so the three original kinds have to be repeated:

BUZZ_ACP_KINDS=9,40007,46010,45001,45003

This is safe: require_mention stays enabled and its p-tag check is kind-agnostic, so agents still only wake when tagged.

Suggested fix

Add KIND_FORUM_POST and KIND_FORUM_COMMENT to the SubscribeMode::Mentions defaults in both places they are constructed (build_channel_filters and the dynamic single-channel path). Routing on the p-tag rather than on kind would close the whole class of problem, but adding the two kinds is the minimal change.

Version and platform

• Buzz version: 0.5.6
• OS: Windows 11 (10.0.26200)

Additional context

Two follow-on effects are visible once mentions do arrive, filed separately: typing indicators and the persistent agent audience are both stream-only in the desktop UI.