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ACP agents

Agent Client Protocol (ACP) sessions let Velaclaw run external coding harnesses (for example Pi, Claude Code, Codex, Cursor, Copilot, Velaclaw ACP, OpenCode, Gemini CLI, and other supported ACPX harnesses) through an ACP backend plugin. If you ask Velaclaw in plain language to “run this in Codex” or “start Claude Code in a thread”, Velaclaw should route that request to the ACP runtime (not the native sub-agent runtime). Each ACP session spawn is tracked as a background task. If you want Codex or Claude Code to connect as an external MCP client directly to existing Velaclaw channel conversations, use velaclaw mcp serve instead of ACP.

Which page do I want?

There are three nearby surfaces that are easy to confuse:

Does this work out of the box?

Usually, yes.
  • Fresh installs now ship the bundled acpx runtime plugin enabled by default.
  • The bundled acpx plugin prefers its plugin-local pinned acpx binary.
  • On startup, Velaclaw probes that binary and self-repairs it if needed.
  • Start with /acp doctor if you want a fast readiness check.
What can still happen on first use:
  • A target harness adapter may be fetched on demand with npx the first time you use that harness.
  • Vendor auth still has to exist on the host for that harness.
  • If the host has no npm/network access, first-run adapter fetches can fail until caches are pre-warmed or the adapter is installed another way.
Examples:
  • /acp spawn codex: Velaclaw should be ready to bootstrap acpx, but the Codex ACP adapter may still need a first-run fetch.
  • /acp spawn claude: same story for the Claude ACP adapter, plus Claude-side auth on that host.

Fast operator flow

Use this when you want a practical /acp runbook:
  1. Spawn a session:
    • /acp spawn codex --bind here
    • /acp spawn codex --mode persistent --thread auto
  2. Work in the bound conversation or thread (or target that session key explicitly).
  3. Check runtime state:
    • /acp status
  4. Tune runtime options as needed:
    • /acp model <provider/model>
    • /acp permissions <profile>
    • /acp timeout <seconds>
  5. Nudge an active session without replacing context:
    • /acp steer tighten logging and continue
  6. Stop work:
    • /acp cancel (stop current turn), or
    • /acp close (close session + remove bindings)

Quick start for humans

Examples of natural requests:
  • “Bind this Discord channel to Codex.”
  • “Start a persistent Codex session in a thread here and keep it focused.”
  • “Run this as a one-shot Claude Code ACP session and summarize the result.”
  • “Bind this iMessage chat to Codex and keep follow-ups in the same workspace.”
  • “Use Gemini CLI for this task in a thread, then keep follow-ups in that same thread.”
What Velaclaw should do:
  1. Pick runtime: "acp".
  2. Resolve the requested harness target (agentId, for example codex).
  3. If current-conversation binding is requested and the active channel supports it, bind the ACP session to that conversation.
  4. Otherwise, if thread binding is requested and the current channel supports it, bind the ACP session to the thread.
  5. Route follow-up bound messages to that same ACP session until unfocused/closed/expired.

ACP versus sub-agents

Use ACP when you want an external harness runtime. Use sub-agents when you want Velaclaw-native delegated runs. See also Sub-agents.

How ACP runs Claude Code

For Claude Code through ACP, the stack is:
  1. Velaclaw ACP session control plane
  2. bundled acpx runtime plugin
  3. Claude ACP adapter
  4. Claude-side runtime/session machinery
Important distinction:
  • ACP Claude is a harness session with ACP controls, session resume, background-task tracking, and optional conversation/thread binding.
  • CLI backends are separate text-only local fallback runtimes. See CLI Backends.
For operators, the practical rule is:
  • want /acp spawn, bindable sessions, runtime controls, or persistent harness work: use ACP
  • want simple local text fallback through the raw CLI: use CLI backends

Bound sessions

Current-conversation binds

Use /acp spawn <harness> --bind here when you want the current conversation to become a durable ACP workspace without creating a child thread. Behavior:
  • Velaclaw keeps owning the channel transport, auth, safety, and delivery.
  • The current conversation is pinned to the spawned ACP session key.
  • Follow-up messages in that conversation route to the same ACP session.
  • /new and /reset reset the same bound ACP session in place.
  • /acp close closes the session and removes the current-conversation binding.
What this means in practice:
  • --bind here keeps the same chat surface. On Discord, the current channel stays the current channel.
  • --bind here can still create a new ACP session if you are spawning fresh work. The bind attaches that session to the current conversation.
  • --bind here does not create a child Discord thread or Telegram topic by itself.
  • The ACP runtime can still have its own working directory (cwd) or backend-managed workspace on disk. That runtime workspace is separate from the chat surface and does not imply a new messaging thread.
  • If you spawn to a different ACP agent and do not pass --cwd, Velaclaw inherits the target agent’s workspace by default, not the requester’s.
  • If that inherited workspace path is missing (ENOENT/ENOTDIR), Velaclaw falls back to the backend default cwd instead of silently reusing the wrong tree.
  • If the inherited workspace exists but cannot be accessed (for example EACCES), spawn returns the real access error instead of dropping cwd.
Mental model:
  • chat surface: where people keep talking (Discord channel, Telegram topic, iMessage chat)
  • ACP session: the durable Codex/Claude/Gemini runtime state Velaclaw routes to
  • child thread/topic: an optional extra messaging surface created only by --thread ...
  • runtime workspace: the filesystem location where the harness runs (cwd, repo checkout, backend workspace)
Examples:
  • /acp spawn codex --bind here: keep this chat, spawn or attach a Codex ACP session, and route future messages here to it
  • /acp spawn codex --thread auto: Velaclaw may create a child thread/topic and bind the ACP session there
  • /acp spawn codex --bind here --cwd /workspace/repo: same chat binding as above, but Codex runs in /workspace/repo
Current-conversation binding support:
  • Chat/message channels that advertise current-conversation binding support can use --bind here through the shared conversation-binding path.
  • Channels with custom thread/topic semantics can still provide channel-specific canonicalization behind the same shared interface.
  • --bind here always means “bind the current conversation in place”.
  • Generic current-conversation binds use the shared Velaclaw binding store and survive normal gateway restarts.
Notes:
  • --bind here and --thread ... are mutually exclusive on /acp spawn.
  • On Discord, --bind here binds the current channel or thread in place. spawnAcpSessions is only required when Velaclaw needs to create a child thread for --thread auto|here.
  • If the active channel does not expose current-conversation ACP bindings, Velaclaw returns a clear unsupported message.
  • resume and “new session” questions are ACP-session questions, not channel questions. You can reuse or replace runtime state without changing the current chat surface.

Thread-bound sessions

When thread bindings are enabled for a channel adapter, ACP sessions can be bound to threads:
  • Velaclaw binds a thread to a target ACP session.
  • Follow-up messages in that thread route to the bound ACP session.
  • ACP output is delivered back to the same thread.
  • Unfocus/close/archive/idle-timeout or max-age expiry removes the binding.
Thread binding support is adapter-specific. If the active channel adapter does not support thread bindings, Velaclaw returns a clear unsupported/unavailable message. Required feature flags for thread-bound ACP:
  • acp.enabled=true
  • acp.dispatch.enabled is on by default (set false to pause ACP dispatch)
  • Channel-adapter ACP thread-spawn flag enabled (adapter-specific)
    • Discord: channels.discord.threadBindings.spawnAcpSessions=true
    • Telegram: channels.telegram.threadBindings.spawnAcpSessions=true

Thread supporting channels

  • Any channel adapter that exposes session/thread binding capability.
  • Current built-in support:
    • Discord threads/channels
    • Telegram topics (forum topics in groups/supergroups and DM topics)
  • Plugin channels can add support through the same binding interface.

Channel specific settings

For non-ephemeral workflows, configure persistent ACP bindings in top-level bindings[] entries.

Binding model

  • bindings[].type="acp" marks a persistent ACP conversation binding.
  • bindings[].match identifies the target conversation:
    • Discord channel or thread: match.channel="discord" + match.peer.id="<channelOrThreadId>"
    • Telegram forum topic: match.channel="telegram" + match.peer.id="<chatId>:topic:<topicId>"
    • BlueBubbles DM/group chat: match.channel="bluebubbles" + match.peer.id="<handle|chat_id:*|chat_guid:*|chat_identifier:*>" Prefer chat_id:* or chat_identifier:* for stable group bindings.
    • iMessage DM/group chat: match.channel="imessage" + match.peer.id="<handle|chat_id:*|chat_guid:*|chat_identifier:*>" Prefer chat_id:* for stable group bindings.
  • bindings[].agentId is the owning Velaclaw agent id.
  • Optional ACP overrides live under bindings[].acp:
    • mode (persistent or oneshot)
    • label
    • cwd
    • backend

Runtime defaults per agent

Use agents.list[].runtime to define ACP defaults once per agent:
  • agents.list[].runtime.type="acp"
  • agents.list[].runtime.acp.agent (harness id, for example codex or claude)
  • agents.list[].runtime.acp.backend
  • agents.list[].runtime.acp.mode
  • agents.list[].runtime.acp.cwd
Override precedence for ACP bound sessions:
  1. bindings[].acp.*
  2. agents.list[].runtime.acp.*
  3. global ACP defaults (for example acp.backend)
Example:
Behavior:
  • Velaclaw ensures the configured ACP session exists before use.
  • Messages in that channel or topic route to the configured ACP session.
  • In bound conversations, /new and /reset reset the same ACP session key in place.
  • Temporary runtime bindings (for example created by thread-focus flows) still apply where present.
  • For cross-agent ACP spawns without an explicit cwd, Velaclaw inherits the target agent workspace from agent config.
  • Missing inherited workspace paths fall back to the backend default cwd; non-missing access failures surface as spawn errors.

Start ACP sessions (interfaces)

From sessions_spawn

Use runtime: "acp" to start an ACP session from an agent turn or tool call.
Notes:
  • runtime defaults to subagent, so set runtime: "acp" explicitly for ACP sessions.
  • If agentId is omitted, Velaclaw uses acp.defaultAgent when configured.
  • mode: "session" requires thread: true to keep a persistent bound conversation.
Interface details:
  • task (required): initial prompt sent to the ACP session.
  • runtime (required for ACP): must be "acp".
  • agentId (optional): ACP target harness id. Falls back to acp.defaultAgent if set.
  • thread (optional, default false): request thread binding flow where supported.
  • mode (optional): run (one-shot) or session (persistent).
    • default is run
    • if thread: true and mode omitted, Velaclaw may default to persistent behavior per runtime path
    • mode: "session" requires thread: true
  • cwd (optional): requested runtime working directory (validated by backend/runtime policy). If omitted, ACP spawn inherits the target agent workspace when configured; missing inherited paths fall back to backend defaults, while real access errors are returned.
  • label (optional): operator-facing label used in session/banner text.
  • resumeSessionId (optional): resume an existing ACP session instead of creating a new one. The agent replays its conversation history via session/load. Requires runtime: "acp".
  • streamTo (optional): "parent" streams initial ACP run progress summaries back to the requester session as system events.
    • When available, accepted responses include streamLogPath pointing to a session-scoped JSONL log (<sessionId>.acp-stream.jsonl) you can tail for full relay history.

Resume an existing session

Use resumeSessionId to continue a previous ACP session instead of starting fresh. The agent replays its conversation history via session/load, so it picks up with full context of what came before.
Common use cases:
  • Hand off a Codex session from your laptop to your phone — tell your agent to pick up where you left off
  • Continue a coding session you started interactively in the CLI, now headlessly through your agent
  • Pick up work that was interrupted by a gateway restart or idle timeout
Notes:
  • resumeSessionId requires runtime: "acp" — returns an error if used with the sub-agent runtime.
  • resumeSessionId restores the upstream ACP conversation history; thread and mode still apply normally to the new Velaclaw session you are creating, so mode: "session" still requires thread: true.
  • The target agent must support session/load (Codex and Claude Code do).
  • If the session ID isn’t found, the spawn fails with a clear error — no silent fallback to a new session.

Operator smoke test

Use this after a gateway deploy when you want a quick live check that ACP spawn is actually working end-to-end, not just passing unit tests. Recommended gate:
  1. Verify the deployed gateway version/commit on the target host.
  2. Confirm the deployed source includes the ACP lineage acceptance in src/gateway/sessions-patch.ts (subagent:* or acp:* sessions).
  3. Open a temporary ACPX bridge session to a live agent (for example razor(main) on jpclawhq).
  4. Ask that agent to call sessions_spawn with:
    • runtime: "acp"
    • agentId: "codex"
    • mode: "run"
    • task: Reply with exactly LIVE-ACP-SPAWN-OK
  5. Verify the agent reports:
    • accepted=yes
    • a real childSessionKey
    • no validator error
  6. Clean up the temporary ACPX bridge session.
Example prompt to the live agent:
Notes:
  • Keep this smoke test on mode: "run" unless you are intentionally testing thread-bound persistent ACP sessions.
  • Do not require streamTo: "parent" for the basic gate. That path depends on requester/session capabilities and is a separate integration check.
  • Treat thread-bound mode: "session" testing as a second, richer integration pass from a real Discord thread or Telegram topic.

Sandbox compatibility

ACP sessions currently run on the host runtime, not inside the Velaclaw sandbox. Current limitations:
  • If the requester session is sandboxed, ACP spawns are blocked for both sessions_spawn({ runtime: "acp" }) and /acp spawn.
    • Error: Sandboxed sessions cannot spawn ACP sessions because runtime="acp" runs on the host. Use runtime="subagent" from sandboxed sessions.
  • sessions_spawn with runtime: "acp" does not support sandbox: "require".
    • Error: sessions_spawn sandbox="require" is unsupported for runtime="acp" because ACP sessions run outside the sandbox. Use runtime="subagent" or sandbox="inherit".
Use runtime: "subagent" when you need sandbox-enforced execution.

From /acp command

Use /acp spawn for explicit operator control from chat when needed.
Key flags:
  • --mode persistent|oneshot
  • --bind here|off
  • --thread auto|here|off
  • --cwd <absolute-path>
  • --label <name>
See Slash Commands.

Session target resolution

Most /acp actions accept an optional session target (session-key, session-id, or session-label). Resolution order:
  1. Explicit target argument (or --session for /acp steer)
    • tries key
    • then UUID-shaped session id
    • then label
  2. Current thread binding (if this conversation/thread is bound to an ACP session)
  3. Current requester session fallback
Current-conversation bindings and thread bindings both participate in step 2. If no target resolves, Velaclaw returns a clear error (Unable to resolve session target: ...).

Spawn bind modes

/acp spawn supports --bind here|off. Notes:
  • --bind here is the simplest operator path for “make this channel or chat Codex-backed.”
  • --bind here does not create a child thread.
  • --bind here is only available on channels that expose current-conversation binding support.
  • --bind and --thread cannot be combined in the same /acp spawn call.

Spawn thread modes

/acp spawn supports --thread auto|here|off. Notes:
  • On non-thread binding surfaces, default behavior is effectively off.
  • Thread-bound spawn requires channel policy support:
    • Discord: channels.discord.threadBindings.spawnAcpSessions=true
    • Telegram: channels.telegram.threadBindings.spawnAcpSessions=true
  • Use --bind here when you want to pin the current conversation without creating a child thread.

ACP controls

Available command family:
  • /acp spawn
  • /acp cancel
  • /acp steer
  • /acp close
  • /acp status
  • /acp set-mode
  • /acp set
  • /acp cwd
  • /acp permissions
  • /acp timeout
  • /acp model
  • /acp reset-options
  • /acp sessions
  • /acp doctor
  • /acp install
/acp status shows the effective runtime options and, when available, both runtime-level and backend-level session identifiers. Some controls depend on backend capabilities. If a backend does not support a control, Velaclaw returns a clear unsupported-control error.

ACP command cookbook

/acp sessions reads the store for the current bound or requester session. Commands that accept session-key, session-id, or session-label tokens resolve targets through gateway session discovery, including custom per-agent session.store roots.

Runtime options mapping

/acp has convenience commands and a generic setter. Equivalent operations:
  • /acp model <id> maps to runtime config key model.
  • /acp permissions <profile> maps to runtime config key approval_policy.
  • /acp timeout <seconds> maps to runtime config key timeout.
  • /acp cwd <path> updates runtime cwd override directly.
  • /acp set <key> <value> is the generic path.
    • Special case: key=cwd uses the cwd override path.
  • /acp reset-options clears all runtime overrides for target session.

acpx harness support (current)

Current acpx built-in harness aliases:
  • claude
  • codex
  • copilot
  • cursor (Cursor CLI: cursor-agent acp)
  • droid
  • gemini
  • iflow
  • kilocode
  • kimi
  • kiro
  • velaclaw
  • opencode
  • pi
  • qwen
When Velaclaw uses the acpx backend, prefer these values for agentId unless your acpx config defines custom agent aliases. If your local Cursor install still exposes ACP as agent acp, override the cursor agent command in your acpx config instead of changing the built-in default. Direct acpx CLI usage can also target arbitrary adapters via --agent <command>, but that raw escape hatch is an acpx CLI feature (not the normal Velaclaw agentId path).

Required config

Core ACP baseline:
Thread binding config is channel-adapter specific. Example for Discord:
If thread-bound ACP spawn does not work, verify the adapter feature flag first:
  • Discord: channels.discord.threadBindings.spawnAcpSessions=true
Current-conversation binds do not require child-thread creation. They require an active conversation context and a channel adapter that exposes ACP conversation bindings. See Configuration Reference.

Plugin setup for acpx backend

Fresh installs ship the bundled acpx runtime plugin enabled by default, so ACP usually works without a manual plugin install step. Start with:
If you disabled acpx, denied it via plugins.allow / plugins.deny, or want to switch to a local development checkout, use the explicit plugin path:
Local workspace install during development:
Then verify backend health:

acpx command and version configuration

By default, the bundled acpx backend plugin (acpx) uses the plugin-local pinned binary:
  1. Command defaults to the plugin-local node_modules/.bin/acpx inside the ACPX plugin package.
  2. Expected version defaults to the extension pin.
  3. Startup registers ACP backend immediately as not-ready.
  4. A background ensure job verifies acpx --version.
  5. If the plugin-local binary is missing or mismatched, it runs: npm install --omit=dev --no-save acpx@<pinned> and re-verifies.
You can override command/version in plugin config:
Notes:
  • command accepts an absolute path, relative path, or command name (acpx).
  • Relative paths resolve from Velaclaw workspace directory.
  • expectedVersion: "any" disables strict version matching.
  • When command points to a custom binary/path, plugin-local auto-install is disabled.
  • Velaclaw startup remains non-blocking while the backend health check runs.
See Plugins.

Automatic dependency install

When you install Velaclaw globally with npm install -g velaclaw, the acpx runtime dependencies (platform-specific binaries) are installed automatically via a postinstall hook. If the automatic install fails, the gateway still starts normally and reports the missing dependency through velaclaw acp doctor.

Plugin tools MCP bridge

By default, ACPX sessions do not expose Velaclaw plugin-registered tools to the ACP harness. If you want ACP agents such as Codex or Claude Code to call installed Velaclaw plugin tools such as memory recall/store, enable the dedicated bridge:
What this does:
  • Injects a built-in MCP server named velaclaw-plugin-tools into ACPX session bootstrap.
  • Exposes plugin tools already registered by installed and enabled Velaclaw plugins.
  • Keeps the feature explicit and default-off.
Security and trust notes:
  • This expands the ACP harness tool surface.
  • ACP agents get access only to plugin tools already active in the gateway.
  • Treat this as the same trust boundary as letting those plugins execute in Velaclaw itself.
  • Review installed plugins before enabling it.
Custom mcpServers still work as before. The built-in plugin-tools bridge is an additional opt-in convenience, not a replacement for generic MCP server config.

Runtime timeout configuration

The bundled acpx plugin defaults embedded runtime turns to a 120-second timeout. This gives slower harnesses such as Gemini CLI enough time to complete ACP startup and initialization. Override it if your host needs a different runtime limit:
Restart the gateway after changing this value.

Permission configuration

ACP sessions run non-interactively — there is no TTY to approve or deny file-write and shell-exec permission prompts. The acpx plugin provides two config keys that control how permissions are handled: These ACPX harness permissions are separate from Velaclaw exec approvals and separate from CLI-backend vendor bypass flags such as Claude CLI --permission-mode bypassPermissions. ACPX approve-all is the harness-level break-glass switch for ACP sessions.

permissionMode

Controls which operations the harness agent can perform without prompting.

nonInteractivePermissions

Controls what happens when a permission prompt would be shown but no interactive TTY is available (which is always the case for ACP sessions).

Configuration

Set via plugin config:
Restart the gateway after changing these values.
Important: Velaclaw currently defaults to permissionMode=approve-reads and nonInteractivePermissions=fail. In non-interactive ACP sessions, any write or exec that triggers a permission prompt can fail with AcpRuntimeError: Permission prompt unavailable in non-interactive mode. If you need to restrict permissions, set nonInteractivePermissions to deny so sessions degrade gracefully instead of crashing.

Troubleshooting