Summary

Add long-lived sandboxed ACP subagents to Hermes so work can continue across turns instead of forcing everything through synchronous delegate_task runs.

Motivation

Today Hermes subagents are one-shot and synchronous:

• start a sandbox
• run the child task
• wait for the final summary
• tear it down

That works for bounded delegation, but it blocks longer-running agent workflows where Hermes should be able to:

• start a coding/research subagent and move on
• see which background agents are still open on later turns
• send follow-up instructions later
• poll buffered progress/output
• get nudged when a background agent finishes or dies

Proposed behavior

• Keep delegate_task unchanged.
• Add explicit background-subagent tools:
  • spawn_background_subagent
  • list_background_subagents
  • send_background_subagent
  • poll_background_subagent
  • get_background_subagent_status
  • stop_background_subagent
• Run each background subagent as one persistent ACP peer session inside one Hermes-managed sandbox container.
• Show the parent agent, every turn, which background subagents are still open, their purpose, cwd, status, and unread output count.
• Buffer ACP updates until the parent explicitly polls them.
• Enforce an idle timeout and an absolute max lifetime.
• Send a hidden nudge on the next parent turn when a subagent finishes, times out, errors, or loses its channel.

Design notes

• ACP-first, standards-compliant over stdio JSON-RPC.
• One live ACP session per sandbox container.
• In-memory only for v1; no restart reattachment.
• Primary target is opencode acp.
• Keep the runtime extensible for future Hermes-to-Hermes ACP and gated reverse requests from child to parent.

Related work

• feat: delegate_task ACP transport override — spawn ACP child agents from non-ACP parent #2653
• A2A follow-up: adopt named-instance runtime for inter-agent sessions and per-instance identity #2883
• feat: Add inter-profile orchestration with conversation history #3754
• feat(acp): register client-provided MCP servers as agent tools #4705
• Feature: A2A (Agent-to-Agent) Protocol Support — Remote Agent Discovery, Communication & Interoperability #514