Sub-agent concurrency, recovery, and stopping

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Concurrency

Sub-agents use a dedicated in-process queue lane:

• Lane name: subagent
• Concurrency: agents.defaults.subagents.maxConcurrent (default 8)

Suspended completion deliveries do not block new work. Native subagents, ACP sessions, and visible sessions retain their normal active-run limits and authorization checks independently of the delivery backlog. Operators can inspect, retry, or dismiss retained deliveries with openclaw tasks. OpenClaw warns when the delivery backlog reaches 25. Within a Gateway process, unchanged backlog counts do not repeat the warning every sweep. A count change at or above 25, or a return to that threshold after recovery, produces a new warning. The backlog size does not discard results or change their retention.

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Liveness and recovery

OpenClaw does not treat endedAt absence as permanent proof that a sub-agent is still alive. When the reading process can verify a current execution owner or an exact queued collector reservation, an unended run keeps counting regardless of age. Persisted metadata alone does not establish that ownership in another process. Other unended runs stop counting as active/pending after the stale-run window (2 hours, or the configured run timeout plus a short grace period, whichever is longer). These retained counts govern /subagents list, status summaries, descendant completion gating, and per-session concurrency checks; they are not proof that an executor is live. After a Gateway restart, the parent owns continuation of the user’s task. Interrupted sub-agents are finalized through their normal completion path instead of automatically relaunched. Their results tell the parent that execution was interrupted and that partially completed actions need checking. A parent waiting for its child batch receives the settled results, including children that finished before the restart, and decides what work remains. Recovery handles both sessions marked abortedLastRun: true and hard kills that prevented the shutdown marker from being written. For a hard kill, the child session must still identify the exact run from the retired Gateway, with no newer run or admitted work owning that session. Live executions and queued collectors keep their existing owners. Orphaned runs settle their background task before cleanup, so retained child sessions do not leave phantom running activity. If the task update fails, completion remains available for retry. The parent can inspect a retained child transcript and use sessions_send to continue that session, or spawn a replacement after confirming the old execution has stopped. Reusing a child restores its conversation context; it does not replay an interrupted command. Existing cleanup and retention settings still apply. When a detached cleanup attempt logs subagent cleanup finalize failed, its retries use bounded backoff in the current Gateway process. If those retries are exhausted, the run remains recorded with incomplete cleanup; inspect the warning to identify the failing operation. Unrelated sub-agent completions do not restart failed cleanup or reset its retry budget. Descendant completion still wakes the current requester ancestors waiting on that work. These cleanup retries are separate from completion delivery.

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Stopping

An explicit Stop targeting a parent run cancels the children associated with that run and their descendants, including ordinary sub-agents and Swarm collectors. Successful cancellation keeps selected queued collectors from starting while running children stop. Exact-run cancellation does not cancel unrelated turns or clear unrelated session-wide queues. For Gateway callers, chat.abort with a runId uses this exact-parent scope. sessions.abort with a runId also targets that run. When it resolves a recovered native run without a chat controller, it cancels children only if the captured active parent accepts Stop; a declined or no-active-run result, including an already-finalizing parent, leaves those children alone. Sending /stop in the requester chat has broader scope: it aborts requester session work, clears its queues, and cancels its active child tree. Session-wide sessions.abort also requests descendant cancellation; clearing queued follow-ups requires clearQueued: true. Ordinary chat.abort without a runId does not cascade to children. These operations retain their normal authorization checks. A typed /stop sent through chat.send honors expectedLeafEntryId and, when that branch check is present, sessionId. If the check fails during descendant cancellation, the Gateway refuses further cancellation and reports active-leaf-changed. Cancellation already accepted by a child still settles. Incomplete cancellation is reported as an error, not a clean success. /stop reports actual stopped and failed child counts. Inspect the remaining background tasks and retry their cancellation; request acknowledgment does not mean all runtime cleanup is instantaneous. Accepted children remain independent after ordinary parent completion, yield, or timeout. Those events do not automatically cancel them.

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Limitations

• Direct announce attempts are best-effort, but admitted session-queued completion handoffs and their owner/task projections survive gateway restarts in the shared SQLite state database.
• Sub-agents still share the same gateway process resources; treat maxConcurrent as a safety valve.
• sessions_spawn returns { status: "accepted", runId, childSessionKey } when startup is accepted, without waiting for the child task to finish. Cloud-worker spawns can wait for provisioning before returning this receipt.
• Sub-agent context only injects AGENTS.md (no SOUL.md, IDENTITY.md, USER.md, MEMORY.md, or BOOTSTRAP.md). Its ## Tools section carries environment-specific notes. Codex-native subagents follow the same boundary through native AGENTS.md discovery, while parent-only persona, identity, and user files are injected as turn-scoped collaboration instructions so children do not clone them.
• Recursive spawning is enabled through depth 5 by default. Set maxSpawnDepth from 1 through 5 to lower the boundary.
• maxChildrenPerAgent caps active children per session (default 5, range 1-20).