Agent runtime architecture — openclaw

OpenClaw owns the built-in agent runtime. Runtime code lives under src/agents/, model/provider transport lives under src/llm/, and plugin-facing contracts are exposed through openclaw/plugin-sdk/* barrels.

Runtime Layout

Path	Owns
`src/agents/embedded-agent-runner/`	Built-in attempt loop (`run.ts`, `run/`), model selection and provider normalization (`model.ts`), per-provider request params (`extra-params.`), compaction, transcript and session wiring.
`src/agents/sessions/`	Session persistence (`session-manager.ts`), resource discovery (`package-manager.ts`, `resource-loader.ts`), in-session `extensions` loading, prompt templates, skills, themes, and TUI-backed tool renderers (`tools/`).
`packages/agent-core/`	Reusable agent core (`@openclaw/agent-core`): agent loop, harness types, messages, compaction helpers, prompt templates, skills, and session storage contracts.
`src/agents/runtime/`	OpenClaw facade that wires `@openclaw/agent-core` to the plugin SDK LLM runtime and re-exports it plus local proxy utilities.
`src/agents/agent-tools*.ts`	OpenClaw-owned tool definitions, parameter schemas, tool policy, before/after tool-call adapters, and host/sandbox edit tools.
`src/agents/agent-hooks/`	Built-in runtime hooks: compaction safeguard, compaction instructions, context pruning.
`src/agents/harness/`	Harness registry, selection policy, and lifecycle for the built-in and plugin-registered harnesses.
`src/llm/`	Model/provider registry, transport helpers, and provider-specific stream implementations (`src/llm/providers/`).

Boundaries

Core calls the built-in runtime through OpenClaw modules and SDK barrels; no external agent framework packages remain. Plugins use documented openclaw/plugin-sdk/* entrypoints and do not import src/** internals.

@earendil-works/pi-tui remains a third-party dependency: a terminal component toolkit used by the local TUI and session tool renderers. Internalizing it would be a separate vendoring effort.

Manifests

Resource packages declare OpenClaw resources in package.json metadata. Entries are file paths or globs relative to the package root:

{
  "openclaw": {
    "extensions": ["extensions/index.ts"],
    "skills": ["skills/*.md"],
    "prompts": ["prompts/*.md"],
    "themes": ["themes/*.json"]
  }
}

Resource types not listed in a manifest fall back to discovery of conventional extensions/, skills/, prompts/, and themes/ directories.

Runtime Selection

The built-in runtime id is openclaw. The legacy alias pi normalizes to openclaw; codex-app-server normalizes to codex.
Plugin harnesses register additional runtime ids (for example codex).
Runtime policy is model/provider-scoped agentRuntime.id config (model entry wins over provider entry). Unset or default resolves to auto.
auto selects a registered plugin harness that supports the effective provider route, otherwise the built-in OpenClaw runtime. A provider or model prefix alone never selects a harness.
OpenAI may select codex implicitly only for an exact official HTTPS Platform Responses or ChatGPT Responses route with no authored request override. Completions adapters, custom endpoints, and routes with authored request behavior stay on openclaw; plaintext official HTTP endpoints are rejected. See OpenAI implicit agent runtime.

Source: docs/agent-runtime-architecture.md

Runtime Layout

Boundaries

Manifests

Runtime Selection

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