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Sub-agents

Sub-agents are background agent runs spawned from an existing agent run. They run in their own session (agent:<agentId>:subagent:<uuid>) and, when finished, announce their result back to the requester chat provider. Primary goals:
  • Parallelize “research / long task / slow tool” work without blocking the main run.
  • Keep sub-agents isolated by default (session separation + optional sandboxing).
  • Keep the tool surface hard to misuse: sub-agents do not get session tools by default.
  • Avoid nested fan-out: sub-agents cannot spawn sub-agents.

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Tool

Use sessions_spawn:
  • Starts a sub-agent run (deliver: false, global lane: subagent)
  • Then runs an announce step and posts the announce reply to the requester chat provider
Tool params:
  • task (required)
  • label? (optional)
  • agentId? (optional; spawn under another agent id if allowed)
  • model? (optional; overrides the sub-agent model; invalid values are skipped and the sub-agent runs on the default model with a warning in the tool result)
  • runTimeoutSeconds? (default 0; when set, the sub-agent run is aborted after N seconds)
  • cleanup? (delete|keep, default keep)
Allowlist:
  • routing.agents.<agentId>.subagents.allowAgents: list of agent ids that can be targeted via agentId (["*"] to allow any). Default: only the requester agent.
Discovery:
  • Use agents_list to see which agent ids are currently allowed for sessions_spawn.
Auto-archive:
  • Sub-agent sessions are automatically archived after agent.subagents.archiveAfterMinutes (default: 60).
  • Archive uses sessions.delete and renames the transcript to *.deleted.<timestamp> (same folder).
  • cleanup: "delete" archives immediately after announce (still keeps the transcript via rename).
  • Auto-archive is best-effort; pending timers are lost if the gateway restarts.
  • runTimeoutSeconds does not auto-archive; it only stops the run. The session remains until auto-archive.

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Announce

Sub-agents report back via an announce step:
  • The announce step runs inside the sub-agent session (not the requester session).
  • If the sub-agent replies exactly ANNOUNCE_SKIP, nothing is posted.
  • Otherwise the announce reply is posted to the requester chat provider via the gateway send method.
Announce payloads include a stats line at the end:
  • Runtime (e.g., runtime 5m12s)
  • Token usage (input/output/total)
  • Estimated cost when model pricing is configured (models.providers.*.models[].cost)
  • sessionKey, sessionId, and transcript path (so the main agent can fetch history via sessions_history or inspect the file on disk)

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Tool Policy (sub-agent tools)

By default, sub-agents get all tools except session tools:
  • sessions_list
  • sessions_history
  • sessions_send
  • sessions_spawn
Override via config: 
{
  agent: {
    subagents: {
      maxConcurrent: 1,
      tools: {
        // deny wins
        deny: ["gateway", "cron"],
        // if allow is set, it becomes allow-only (deny still wins)
        // allow: ["read", "bash", "process"]
      }
    }
  }
}

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Concurrency

Sub-agents use a dedicated in-process queue lane:
  • Lane name: subagent
  • Concurrency: agent.subagents.maxConcurrent (default 1)

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Limitations

  • Sub-agent announce is best-effort. If the gateway restarts, pending “announce back” work is lost.
  • Sub-agents still share the same gateway process resources; treat maxConcurrent as a safety valve.
  • sessions_spawn is always non-blocking: it returns { status: "accepted", runId, childSessionKey } immediately.