openclaw/docs/concepts/agent-loop.md

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Agent loop lifecycle, streams, and wait semantics	You need an exact walkthrough of the agent loop or lifecycle events You are changing session queueing, transcript writes, or session write lock behavior	Agent loop

An agentic loop is the full "real" run of an agent: intake → context assembly → model inference → tool execution → streaming replies → persistence. It's the authoritative path that turns a message into actions and a final reply, while keeping session state consistent.

In OpenClaw, a loop is a single, serialized run per session that emits lifecycle and stream events as the model thinks, calls tools, and streams output. This doc explains how that authentic loop is wired end-to-end.

Entry points

• Gateway RPC: agent and agent.wait.
• CLI: agent command.

How it works (high-level)

1. agent RPC validates params, resolves session (sessionKey/sessionId), persists session metadata, returns { runId, acceptedAt } immediately.
2. agentCommand runs the agent:
   • resolves model + thinking/verbose/trace defaults
   • loads skills snapshot
   • calls runEmbeddedAgent (OpenClaw agent runtime)
   • emits lifecycle end/error if the embedded loop does not emit one
3. runEmbeddedAgent:
   • serializes runs via per-session + global queues
   • resolves model + auth profile and builds the OpenClaw session
   • subscribes to runtime events and streams assistant/tool deltas
   • enforces timeout -> aborts run if exceeded
   • for Codex app-server turns, aborts an accepted turn that stops producing app-server progress before a terminal event
   • returns payloads + usage metadata
4. subscribeEmbeddedAgentSession bridges agent runtime events to OpenClaw agent stream:
   • tool events => stream: "tool"
   • assistant deltas => stream: "assistant"
   • lifecycle events => stream: "lifecycle" (phase: "start" | "end" | "error")
5. agent.wait uses waitForAgentRun:
   • waits for lifecycle end/error for runId
   • returns { status: ok|error|timeout, startedAt, endedAt, error? }

Queueing + concurrency

• Runs are serialized per session key (session lane) and optionally through a global lane.
• This prevents tool/session races and keeps session history consistent.
• Messaging channels can choose queue modes (steer/followup/collect/interrupt) that feed this lane system. See Command Queue.
• Transcript writes are also protected by a session write lock on the session file. The lock is process-aware and file-based, so it catches writers that bypass the in-process queue or come from another process. Session transcript writers wait up to session.writeLock.acquireTimeoutMs before reporting the session as busy; the default is 60000 ms.
• Session write locks are non-reentrant by default. If a helper intentionally nests acquisition of the same lock while preserving one logical writer, it must opt in explicitly with allowReentrant: true.

Session + workspace preparation

• Workspace is resolved and created; sandboxed runs may redirect to a sandbox workspace root.
• Skills are loaded (or reused from a snapshot) and injected into env and prompt.
• Bootstrap/context files are resolved and injected into the system prompt report.
• A session write lock is acquired; SessionManager is opened and prepared before streaming. Any later transcript rewrite, compaction, or truncation path must take the same lock before opening or mutating the transcript file.

Prompt assembly + system prompt

• System prompt is built from OpenClaw's base prompt, skills prompt, bootstrap context, and per-run overrides.
• Model-specific limits and compaction reserve tokens are enforced.
• See System prompt for what the model sees.

Hook points (where you can intercept)

OpenClaw has two hook systems:

• Internal hooks (Gateway hooks): event-driven scripts for commands and lifecycle events.
• Plugin hooks: extension points inside the agent/tool lifecycle and gateway pipeline.

Internal hooks (Gateway hooks)

• agent:bootstrap: runs while building bootstrap files before the system prompt is finalized. Use this to add/remove bootstrap context files.
• Command hooks: /new, /reset, /stop, and other command events (see Hooks doc).

See Hooks for setup and examples.

Plugin hooks (agent + gateway lifecycle)

These run inside the agent loop or gateway pipeline:

• before_model_resolve: runs pre-session (no messages) to deterministically override provider/model before model resolution.
• before_prompt_build: runs after session load (with messages) to inject prependContext, systemPrompt, prependSystemContext, or appendSystemContext before prompt submission. Use prependContext for per-turn dynamic text and system-context fields for stable guidance that should sit in system prompt space.
• before_agent_start: legacy compatibility hook that may run in either phase; prefer the explicit hooks above.
• before_agent_reply: runs after inline actions and before the LLM call, letting a plugin claim the turn and return a synthetic reply or silence the turn entirely.
• agent_end: inspect the final message list and run metadata after completion.
• before_compaction / after_compaction: observe or annotate compaction cycles.
• before_tool_call / after_tool_call: intercept tool params/results.
• before_install: inspect built-in scan findings and optionally block skill or plugin installs.
• tool_result_persist: synchronously transform tool results before they are written to an OpenClaw-owned session transcript.
• message_received / message_sending / message_sent: inbound + outbound message hooks.
• session_start / session_end: session lifecycle boundaries.
• gateway_start / gateway_stop: gateway lifecycle events.

Hook decision rules for outbound/tool guards:

• before_tool_call: { block: true } is terminal and stops lower-priority handlers.
• before_tool_call: { block: false } is a no-op and does not clear a prior block.
• before_install: { block: true } is terminal and stops lower-priority handlers.
• before_install: { block: false } is a no-op and does not clear a prior block.
• message_sending: { cancel: true } is terminal and stops lower-priority handlers.
• message_sending: { cancel: false } is a no-op and does not clear a prior cancel.

See Plugin hooks for the hook API and registration details.

Harnesses may adapt these hooks differently. The Codex app-server harness keeps OpenClaw plugin hooks as the compatibility contract for documented mirrored surfaces, while Codex native hooks remain a separate lower-level Codex mechanism.

Streaming + partial replies

• Assistant deltas are streamed from the agent runtime and emitted as assistant events.
• Block streaming can emit partial replies either on text_end or message_end.
• Reasoning streaming can be emitted as a separate stream or as block replies.
• See Streaming for chunking and block reply behavior.

Tool execution + messaging tools

• Tool start/update/end events are emitted on the tool stream.
• Tool results are sanitized for size and image payloads before logging/emitting.
• Messaging tool sends are tracked to suppress duplicate assistant confirmations.

Reply shaping + suppression

• Final payloads are assembled from:
  • assistant text (and optional reasoning)
  • inline tool summaries (when verbose + allowed)
  • assistant error text when the model errors
• The exact silent token NO_REPLY / no_reply is filtered from outgoing payloads.
• Messaging tool duplicates are removed from the final payload list.
• If no renderable payloads remain and a tool errored, a fallback tool error reply is emitted (unless a messaging tool already sent a user-visible reply).

Compaction + retries

• Auto-compaction emits compaction stream events and can trigger a retry.
• On retry, in-memory buffers and tool summaries are reset to avoid duplicate output.
• See Compaction for the compaction pipeline.

Event streams (today)

• lifecycle: emitted by subscribeEmbeddedAgentSession (and as a fallback by agentCommand)
• assistant: streamed deltas from the agent runtime
• tool: streamed tool events from the agent runtime

Chat channel handling

• Assistant deltas are buffered into chat delta messages.
• A chat final is emitted on lifecycle end/error.

Timeouts

• agent.wait default: 30s (just the wait). timeoutMs param overrides.
• Agent runtime: agents.defaults.timeoutSeconds default 172800s (48 hours); enforced in runEmbeddedAgent abort timer.
• Cron runtime: isolated agent-turn timeoutSeconds is owned by cron. The scheduler starts that timer when execution begins, aborts the underlying run at the configured deadline, then runs bounded cleanup before recording the timeout so a stale child session cannot keep the lane stuck.
• Session liveness diagnostics: with diagnostics enabled, diagnostics.stuckSessionWarnMs classifies long processing sessions that have no observed reply, tool, status, block, or ACP progress. Active embedded runs, model calls, and tool calls report as session.long_running; active work with no recent progress reports as session.stalled; session.stuck is reserved for recoverable stale session bookkeeping, including idle queued sessions with stale ownerless model/tool activity. Stale session bookkeeping releases the affected session lane immediately after recovery gates pass; stalled embedded runs are abort-drained only after diagnostics.stuckSessionAbortMs (default: at least 5 minutes and 3x the warning threshold) so queued work can resume without cutting off merely slow runs. Recovery emits structured requested/completed outcomes, and diagnostic state is marked idle only if the same processing generation is still current. Repeated session.stuck diagnostics back off while the session remains unchanged.
• Model idle timeout: OpenClaw aborts a model request when no response chunks arrive before the idle window. models.providers.<id>.timeoutSeconds extends this idle watchdog for slow local/self-hosted providers, but it is still bounded by any lower agents.defaults.timeoutSeconds or run-specific timeout because those control the whole agent run. Otherwise OpenClaw uses agents.defaults.timeoutSeconds when configured, capped at 120s by default. Cron-triggered runs with no explicit model or agent timeout disable the idle watchdog and rely on the cron outer timeout.
• Provider HTTP request timeout: models.providers.<id>.timeoutSeconds applies to that provider's model HTTP fetches, including connect, headers, body, SDK request timeout, total guarded-fetch abort handling, and model stream idle watchdog. Use this for slow local/self-hosted providers such as Ollama before raising the whole agent runtime timeout, and keep the agent/runtime timeout at least as high when the model request needs to run longer.

Where things can end early

• Agent timeout (abort)
• AbortSignal (cancel)
• Gateway disconnect or RPC timeout
• agent.wait timeout (wait-only, does not stop agent)

Related

• Tools — available agent tools
• Hooks — event-driven scripts triggered by agent lifecycle events
• Compaction — how long conversations are summarized
• Exec Approvals — approval gates for shell commands
• Thinking — thinking/reasoning level configuration