Mention autocomplete never offers remotely-hosted agents (shared relay agent eligibility is unreachable) #3971

Version: 0.5.2 (also present on current main)

Setup: An ACP agent hosted on machine A (via buzz-acp with NIP-OA owner attestation), and Buzz Desktop on machine B owned by the same user. The agent is a member of a shared channel, publishes a kind-0 profile, appears in the member list with the agent chip ("managed by you"), is registered in the relay agent directory, and advertises respond_to=anyone.

Bug: The @ mention autocomplete on machine B never offers the agent, so there is no way to send it a p-tag mention from the UI. The members panel shows it; the composer refuses to.

Root cause: In desktop/src/features/messages/lib/useMentions.ts, addCandidate drops any candidate flagged isAgent that is not in the local managed-agent list:

if (!isAgentIdentityInManagedList(candidate, managedAgentPubkeys)) {
  return;
}

This runs before shouldHideAgentFromMentions, whose mentionableAgentPubkeys set (built from relayAgentIsSharedWithUser — directory agents with respond_to=anyone/allowlist sharing a channel) is meant to make exactly these agents mentionable. Because the earlier filter only consults the local list, that machinery is unreachable dead code for any agent hosted on another machine.

Suggested fix: let mentionable relay agents through the first filter:

if (
  !isAgentIdentityInManagedList(candidate, managedAgentPubkeys) &&
  !mentionableAgentPubkeys.has(pubkey)
) {
  return;
}

Impact: Any multi-device / team setup where an agent runs on one machine and users chat from another. Current workarounds are thread replies (reply p-tags the parent author) or agent-side content-matching rules instead of real mentions.