[Bug] @mentions in Projects issue comments never reach buzz-acp agents

[mklarmann]

Describe the bug

An @mention of a managed agent in a Projects issue comment is rendered and
published with the agent's p tag, but the comment never reaches buzz-acp.
The agent receives no turn and the mention does not appear in its
mentions/needs_action feed.

Ordinary channel mentions to the same agent work.

To reproduce

1. Create or open a repository under Projects → Issues.

2. Add a comment to the issue.

3. Select a running agent from the comment composer's mention picker and give it
   a concrete task, for example:

   @agent investigate this issue, implement the smallest fix, run the tests,
   and report the result here.

4. Submit the comment.

5. Observe that the comment renders with the mention, but the agent never starts
   a turn.

6. Query the affected agent's feed:

   buzz feed get --types mentions,needs_action --limit 200

7. Observe that ordinary channel mentions are present but the Projects issue
   comment is absent.

Expected behavior

• A Projects issue comment that mentions an agent should reach that agent's ACP
  harness.
• The agent should receive the issue/repository context and be able to reply
  back to the issue.
• Delivery behavior should match a mention in a normal channel.

Implementation diagnosis

At current main:

1. Projects issue comments are temporarily published as kind 1 events because
   kind 1111 is not yet registered by the relay:
   desktop/src/features/projects/hooks.ts.
2. createProjectIssueComment correctly adds the explicitly mentioned pubkeys
   as p tags, but its event tags contain only the issue e tag, repository
   a tag, recipients, and media. There is no channel h tag:
   desktop/src/features/projects/hooks.ts.
3. buzz-acp subscribes per channel. Its subscription request includes the
   channel #h filter, and includes #p when mentions are required:
   crates/buzz-acp/src/relay.rs.

Therefore a no-h Projects comment cannot arrive through the channel-scoped ACP
subscription even though it has a valid agent p tag.

Suggested fix

Choose and implement an explicit delivery model for project work-item comments:

• bind the issue/comment to a project channel and include its h tag; or
• add a separate authenticated ACP subscription for mentioned project comments
  keyed by p plus the repository/issue address.

The second approach must preserve community/repository authorization and avoid
turning every global kind-1 mention into an agent task.

Add an end-to-end regression test:

create project issue
  → comment mentioning an agent
  → buzz-acp receives exactly one turn
  → agent reply is attached to the issue

Environment

• Buzz Desktop: observed on 0.4.22
• Source diagnosis: commit
  acfbb1bb6af54cb29cb152496ff43b8285dcb8cf (0.4.23 release commit)
• OS: macOS

Related issues

• [Bug] Agents not replying #2421 concerns agents that run but whose replies are not visibly published.
• [Bug] Renaming or re-adding personal agents can desynchronise identity and break @mentions #2423 concerns mention routing to stale identities after agent rename/re-add.

This report is distinct: the Projects issue-comment event never reaches the
agent feed/harness.

[Chessing234]

Fixed in #2498 — project @mentions now publish as kind:9 with the channel h tag (and we read buzz-channel).