Hermes

Hermes loads the xmsg plugin (extensions/hermes/plugin.yaml and extensions/hermes/__init__.py) from $HERMES_HOME/plugins/ when plugins.enabled includes "xmsg". Like opencode, the Hermes plugin holds one multiplexed register.sock connection per Hermes process.

Registration and tools

• Registration: A session registers at the first pre_llm_call hook or xmsg tool call that carries its session_id.
• Delegates (delegate_task): A delegate_task subagent (whose pre_llm_call names its parent) acts as its root conversation P and does not bind a separate sub-address.
• Tools (xmsg toolset): Exposes xmsg_list, xmsg_send, xmsg_reply, and xmsg_replies, sent as frames on register.sock under the calling session_id. Because Hermes defers plugin tools behind its Tool Search bridge (tools.tool_search) by default, models discover and invoke them through tool_search and tool_call.

Session lifecycle and compaction

• Ending a session (on_session_finalize): Closing a desktop session, running /new, or exiting the CLI releases the session’s address (410 gone). Any late tool call from an ended session’s background delegate returns gone without re-registering the old session.
• Switching sessions in the CLI: /new ends the old session and registers the new one (on_session_reset). For /resume and /branch (which fire no plugin hook), the plugin detects the changed session_id on the next hook, tool call, or push and releases the old address so one session’s message is never injected into another.
• Compression (continues): Hermes’s default in-place compaction preserves session_id and its xmsg address. When compression.in_place: false is used, compression creates a new session_id; the plugin reads SessionDB(read_only=True).get_compression_chain and sends a continues frame on register.sock to move the xmsg address to the new session ID.

Push delivery and busy modes

• Classic CLI: While a turn is running, delivered messages route through the CLI’s busy-input handler according to display.busy_input_mode (or /busy): queue runs it as the next turn, interrupt redirects the running turn, and steer injects it after the current tool call. When idle, it starts a new turn.
• TUI and desktop host: Hermes’s inject_message queues incoming messages on the session in all busy modes so a notification never cancels in-flight work. Requires plugins.entries.xmsg.allow_gateway_injection: true in Hermes settings.
• Acknowledgments: The plugin sends ack only after Hermes accepts the message.

Home Manager switch

Set programs.xmsg.harnesses.hermes.enable = true (requires services.hermes-agent enabled) to link the plugin into services.hermes-agent.extraPlugins, append "xmsg" to settings.plugins.enabled, enable allow_gateway_injection, and install the xmsg skill. See NixOS & Home Manager.