feat(acp): accept signed events through a local forward socket

[Gforce10-design]

Summary

Allow a local gateway to deliver original signed Buzz events to ACP through an opt-in Unix socket, while preserving the existing author, mention, thread/session, queue, and steering decisions. --relay-input false disables data subscriptions while retaining membership notifications and outbound publishing.

The socket checks native peer UID, event signature, channel membership, canonical channel ID, and dedupe key. Both sources enter one typed admission function. Explicit state storage, frame/read/concurrency limits, and startup path checks bound the local interface. Forward input is Unix-only; default relay operation remains available on other platforms.

accepted means admission or intentional policy filtering with persisted occupancy, not completed work. Queues remain in memory and the bounded occupancy history does not provide exactly-once delivery. See crates/buzz-acp/FORWARDING.md for protocol and failure semantics.

This branch is based directly on upstream ef2aa1ae38fadcc0bc22b8bf6ed96b35933146be; it does not carry the original prototype's unrelated ancestor commits.

Related issue

N/A. Searched existing block/buzz issues and PRs for "forward socket"; none found. Companion gateway implementation: NousResearch/hermes-agent#116264.

Testing

• Linux (isolated Alpine test container): cargo test -p buzz-acp, 993 passed, 1 ignored, including native peer credentials, shared admission, concurrent persistence and socket path preservation.
• macOS: serial cargo test -p buzz-acp, 993 passed, 1 ignored, with the rustdoc phase passing. An earlier rustdoc dependency-artifact failure during concurrent builds did not recur in this serial run.
• just ci: exit 0, covering repository checks and Rust, desktop, web and mobile test/build gates. After the final narrow review fixes, the affected crate tests, Clippy (--all-targets -- -D warnings), workspace formatting and file-size checks were revalidated and passed.
• Independent ECC review: two rounds APPROVE_WITH_NOTES; required constant/persistence/protocol findings resolved.
• Windows compilation is not locally verified. No live deployment is included.

[github-actions]

🔐 Codex Security Review

Status: review required for the current range.

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