can1357--oh-my-pi/docs/rpc.md

RPC Protocol Reference

RPC mode runs the coding agent as a newline-delimited JSON protocol over stdio.

• stdin: commands (RpcCommand), extension UI responses, and host-tool updates/results
• stdout: a ready frame, command responses (RpcResponse), session/agent events, extension UI requests, host-tool requests/cancellations

Primary implementation:

• src/modes/rpc/rpc-mode.ts
• src/modes/rpc/rpc-types.ts
• src/session/agent-session.ts
• packages/agent/src/agent.ts
• packages/agent/src/agent-loop.ts

Startup

omp --mode rpc [regular CLI options]

Behavior notes:

• @file CLI arguments are rejected in RPC mode.
• RPC mode disables automatic session title generation by default to avoid an extra model call.
• RPC mode resets workflow-altering todo.*, task.*, memory.backend/memories.enabled, advisor.*, async.*, and bash.autoBackground.* settings to their built-in defaults instead of inheriting user overrides.
• The process reads stdin as JSONL (readJsonl(Bun.stdin.stream())).
• At startup it writes { "type": "ready" } before processing commands.
• When stdin closes, pending host-tool calls and host-URI requests are rejected and the process exits with code 0.
• Responses/events are written as one JSON object per line.

Transport and Framing

Each frame is a single JSON object followed by \n.

There is no envelope beyond the object shape itself.

Outbound frame categories (stdout)

1. Ready frame ({ type: "ready" })
2. RpcResponse ({ type: "response", ... })
3. AgentSessionEvent objects (agent_start, message_update, etc.)
4. RpcExtensionUIRequest ({ type: "extension_ui_request", ... })
5. Host tool requests/cancellations (host_tool_call, host_tool_cancel)
6. Host URI requests/cancellations (host_uri_request, host_uri_cancel)
7. Extension errors ({ type: "extension_error", extensionPath, event, error })
8. Available-commands updates ({ type: "available_commands_update", commands }), emitted at startup and whenever command metadata changes
9. Prompt lifecycle hints ({ type: "prompt_result", id?, agentInvoked }) for scheduled prompts that later resolve without invoking the agent
10. Subagent frames (subagent_lifecycle, subagent_progress, subagent_event), gated by set_subagent_subscription
11. Builtin slash-command side channels (command_output, session_info_update, config_update)

Inbound frame categories (stdin)

1. RpcCommand
2. RpcExtensionUIResponse ({ type: "extension_ui_response", ... })
3. Host tool updates/results (host_tool_update, host_tool_result)
4. Host URI results (host_uri_result)

Request/Response Correlation

All commands accept optional id?: string.

• If provided, normal command responses echo the same id.
• RpcClient relies on this for pending-request resolution.

Important edge behavior from runtime:

• Unknown command responses are emitted with id: undefined (even if the request had an id).
• Parse/handler exceptions in the input loop emit command: "parse" with id: undefined.
• prompt and abort_and_prompt return immediate success, then may emit a later error response with the same id if async prompt scheduling fails.
• prompt success responses may include data.agentInvoked. false means the prompt completed locally without an agent turn; true means the prompt produced agent lifecycle events; omitted means the host must rely on session events for completion.
• abort_and_prompt does not currently emit data.agentInvoked or prompt_result; hosts should treat it as the legacy abort-then-schedule path and rely on session events or same-id scheduling errors.

Command Schema (canonical)

RpcCommand is defined in src/modes/rpc/rpc-types.ts:

Prompting

• { id?, type: "prompt", message: string, images?: ImageContent[], streamingBehavior?: "steer" | "followUp" }
• { id?, type: "steer", message: string, images?: ImageContent[] }
• { id?, type: "follow_up", message: string, images?: ImageContent[] }
• { id?, type: "abort" }
• { id?, type: "abort_and_prompt", message: string, images?: ImageContent[] }
• { id?, type: "new_session", parentSession?: string }

State

• { id?, type: "get_state" }
• { id?, type: "get_available_commands" }
• { id?, type: "set_todos", phases: TodoPhase[] }
• { id?, type: "set_host_tools", tools: RpcHostToolDefinition[] }
• { id?, type: "set_host_uri_schemes", schemes: RpcHostUriSchemeDefinition[] }
• { id?, type: "set_subagent_subscription", level: "off" | "progress" | "events" }
• { id?, type: "get_subagents" }
• { id?, type: "get_subagent_messages", subagentId?: string, sessionFile?: string, fromByte?: number }

Model

• { id?, type: "set_model", provider: string, modelId: string }
• { id?, type: "cycle_model" }
• { id?, type: "get_available_models" }

Thinking

• { id?, type: "set_thinking_level", level: ThinkingLevel }
• { id?, type: "cycle_thinking_level" }

Queue modes

• { id?, type: "set_steering_mode", mode: "all" | "one-at-a-time" }
• { id?, type: "set_follow_up_mode", mode: "all" | "one-at-a-time" }
• { id?, type: "set_interrupt_mode", mode: "immediate" | "wait" }

Compaction

• { id?, type: "compact", customInstructions?: string }
• { id?, type: "set_auto_compaction", enabled: boolean }

Retry

• { id?, type: "set_auto_retry", enabled: boolean }
• { id?, type: "abort_retry" }

Bash

• { id?, type: "bash", command: string }
• { id?, type: "abort_bash" }

bash is dispatched concurrently: the RPC server continues reading commands while the shell command runs, so abort_bash (or any other command) sent during a long-running bash is handled without waiting for it to finish on its own. The bash response is emitted when the command completes; hosts correlate it via id. Ordering across concurrent commands is not guaranteed — clients MUST match responses on id, not on emission order.

Session

• { id?, type: "get_session_stats" }
• { id?, type: "export_html", outputPath?: string }
• { id?, type: "switch_session", sessionPath: string }
• { id?, type: "branch", entryId: string }
• { id?, type: "get_branch_messages" }
• { id?, type: "get_last_assistant_text" }
• { id?, type: "set_session_name", name: string }
• { id?, type: "handoff", customInstructions?: string }

Messages

• { id?, type: "get_messages" }

Login

• { id?, type: "get_login_providers" }
• { id?, type: "login", providerId: string }

Response Schema

All command results use RpcResponse:

• Success: { id?, type: "response", command: <command>, success: true, data?: ... }
• Failure: { id?, type: "response", command: string, success: false, error: string }

Data payloads are command-specific and defined in rpc-types.ts.

prompt payload

prompt is acknowledged after the command is accepted, not after a model turn finishes:

{
  "id": "req_1",
  "type": "response",
  "command": "prompt",
  "success": true,
  "data": { "agentInvoked": false }
}

data.agentInvoked: false is a completion signal for local-only prompts, including slash commands that produce output without starting an agent turn. data.agentInvoked: true means the prompt produced agent lifecycle events; those events can be emitted before or after the prompt response depending on the command path. Older runtimes may omit data; hosts should then rely on agent_end, custom message completion, or prompt_result.

prompt_result is emitted when a prompt was accepted immediately but later resolves as local-only:

{ "type": "prompt_result", "id": "req_1", "agentInvoked": false }

Local-only slash commands may emit command_output frames before completing via data.agentInvoked: false or a later prompt_result. They do not emit agent_end.

get_state payload

{
  "model": { "provider": "...", "id": "..." },
  "thinkingLevel": "off|minimal|low|medium|high|xhigh|max",
  "isStreaming": false,
  "isCompacting": false,
  "steeringMode": "all|one-at-a-time",
  "followUpMode": "all|one-at-a-time",
  "interruptMode": "immediate|wait",
  "sessionFile": "...",
  "sessionId": "...",
  "sessionName": "...",
  "autoCompactionEnabled": true,
  "messageCount": 0,
  "queuedMessageCount": 0,
  "todoPhases": [
    {
      "id": "phase-1",
      "name": "Todos",
      "tasks": [
        {
          "id": "task-1",
          "content": "Map the tool surface",
          "status": "in_progress"
        }
      ]
    }
  ],
  "systemPrompt": ["..."],
  "dumpTools": [
    {
      "name": "read",
      "description": "Read files and URLs",
      "parameters": {}
    }
  ],
  "contextUsage": {
    "tokens": 1100,
    "contextWindow": 200000,
    "percent": 0.55
  }
}

set_todos payload

Replaces the in-memory todo state for the current session and returns the normalized phase list:

{
  "id": "req_2",
  "type": "set_todos",
  "phases": [
    {
      "id": "phase-1",
      "name": "Evaluation",
      "tasks": [
        {
          "id": "task-1",
          "content": "Map the read tool surface",
          "status": "in_progress"
        },
        {
          "id": "task-2",
          "content": "Exercise edit operations",
          "status": "pending"
        }
      ]
    }
  ]
}

This is useful for hosts that want to pre-seed a plan before the first prompt.

set_host_tools payload

Replaces the current set of host-owned tools that the RPC server may call back into over stdio:

{
  "id": "req_3",
  "type": "set_host_tools",
  "tools": [
    {
      "name": "echo_host",
      "label": "Echo Host",
      "description": "Echo a value from the embedding host",
      "parameters": {
        "type": "object",
        "properties": {
          "message": { "type": "string" }
        },
        "required": ["message"],
        "additionalProperties": false
      }
    }
  ]
}

The response payload is:

{
  "toolNames": ["echo_host"]
}

These tools are added to the active session tool registry before the next model call. Re-sending set_host_tools replaces the previous host-owned set.

set_host_uri_schemes payload

Replaces the current set of host-owned URL schemes the RPC server should dispatch reads/writes through:

{
  "id": "req_4",
  "type": "set_host_uri_schemes",
  "schemes": [
    {
      "scheme": "db",
      "description": "Virtual db row files",
      "writable": true,
      "immutable": false
    }
  ]
}

The response payload is:

{
  "schemes": ["db"]
}

Schemes are case-insensitive on the wire and normalized to lowercase before the response is sent. Re-sending set_host_uri_schemes replaces the entire previous set — schemes missing from the new list are unregistered.

Event Stream Schema

RPC mode forwards AgentSessionEvent objects from AgentSession.subscribe(...).

Common event types:

• agent_start, agent_end
• turn_start, turn_end
• message_start, message_update, message_end
• tool_execution_start, tool_execution_update, tool_execution_end
• auto_compaction_start, auto_compaction_end
• auto_retry_start, auto_retry_end
• ttsr_triggered
• todo_reminder
• todo_auto_clear

Extension runner errors are emitted separately as:

{
  "type": "extension_error",
  "extensionPath": "...",
  "event": "...",
  "error": "..."
}

message_update includes streaming deltas in assistantMessageEvent (text/thinking/toolcall deltas).

Prompt/Queue Concurrency and Ordering

This is the most important operational behavior.

Immediate ack vs completion

prompt and abort_and_prompt are acknowledged immediately:

{ "id": "req_1", "type": "response", "command": "prompt", "success": true }

That means:

• command acceptance != run completion
• agent turns complete via agent_end
• local-only prompts complete via data.agentInvoked: false on the response or via a later prompt_result

While streaming

AgentSession.prompt() requires streamingBehavior during active streaming:

• "steer" => queued steering message (interrupt path)
• "followUp" => queued follow-up message (post-turn path)

If omitted during streaming, prompt fails.

Queue defaults

From packages/agent/src/agent.ts defaults:

• steeringMode: "one-at-a-time"
• followUpMode: "one-at-a-time"
• interruptMode: "immediate"

Mode semantics

• set_steering_mode / set_follow_up_mode
  • "one-at-a-time": dequeue one queued message per turn
  • "all": dequeue entire queue at once
• set_interrupt_mode
  • "immediate": tool execution checks steering between tool calls; pending steering can abort remaining tool calls in the turn
  • "wait": defer steering until turn completion

Extension UI Sub-Protocol

Extensions in RPC mode use request/response UI frames.

Outbound request

RpcExtensionUIRequest (type: "extension_ui_request") methods:

• select, confirm, input, editor, cancel
• notify, setStatus, setWidget, setTitle, set_editor_text
• open_url (emitted by RPC login flows)

Runtime note:

• Automatic session title generation is disabled in RPC mode, and setTitle UI requests are also suppressed by default because most hosts do not have a meaningful terminal-title surface. Set PI_RPC_EMIT_TITLE=1 to opt back in to the UI event only.

Example:

{
  "type": "extension_ui_request",
  "id": "123",
  "method": "confirm",
  "title": "Confirm",
  "message": "Continue?",
  "timeout": 30000
}

Inbound response

RpcExtensionUIResponse (type: "extension_ui_response"):

• { type: "extension_ui_response", id: string, value: string }
• { type: "extension_ui_response", id: string, confirmed: boolean }
• { type: "extension_ui_response", id: string, cancelled: true, timedOut?: boolean }

If a dialog has a timeout, RPC mode resolves to a default value when timeout/abort fires.

Host Tool Sub-Protocol

RPC hosts can expose custom tools to the agent by sending set_host_tools, then serving execution requests over the same transport.

Outbound request

When the agent wants the host to execute one of those tools, RPC mode emits:

{
  "type": "host_tool_call",
  "id": "host_1",
  "toolCallId": "toolu_123",
  "toolName": "echo_host",
  "arguments": { "message": "hello" }
}

If the tool execution is later aborted, RPC mode emits:

{
  "type": "host_tool_cancel",
  "id": "host_cancel_1",
  "targetId": "host_1"
}

Inbound updates and completion

Hosts can optionally stream progress:

{
  "type": "host_tool_update",
  "id": "host_1",
  "partialResult": {
    "content": [{ "type": "text", "text": "working" }]
  }
}

Completion uses:

{
  "type": "host_tool_result",
  "id": "host_1",
  "result": {
    "content": [{ "type": "text", "text": "done" }]
  }
}

Set top-level isError: true on host_tool_result to reject the pending host tool call and surface the returned text content as a tool error.

Host URI Sub-Protocol

RPC hosts can also own custom URL schemes (virtual files). After set_host_uri_schemes, every read of <scheme>://… and write of <scheme>://… (when registered as writable) is bounced back to the host over the same transport.

Outbound request

When a session tool resolves a host-owned URL, RPC mode emits:

{
  "type": "host_uri_request",
  "id": "uri_1",
  "operation": "read",
  "url": "db://users/42"
}

Writes look the same with "operation": "write" and an additional "content": "..." field carrying the full replacement bytes.

If the request is later aborted (caller cancels, session ends), RPC mode emits:

{
  "type": "host_uri_cancel",
  "id": "uri_cancel_1",
  "targetId": "uri_1"
}

Inbound result

For successful reads:

{
  "type": "host_uri_result",
  "id": "uri_1",
  "content": "id=42\nname=Alice\n",
  "contentType": "text/plain",
  "notes": ["fresh from cache"],
  "immutable": false
}

For successful writes, omit content:

{ "type": "host_uri_result", "id": "uri_1" }

To reject the request, set isError: true and either populate error with a message or fall back to content for textual error surfacing:

{
  "type": "host_uri_result",
  "id": "uri_1",
  "isError": true,
  "error": "row 42 not found"
}

Constraints

• The agent's edit tool does not target host URIs. Hosts that want to mutate virtual files expose write and let the model use the write tool with replacement content.
• Schemes are global to the process; set_host_uri_schemes replaces the previous set, unregistering anything not in the new list.
• Schemes are normalized to lowercase before registration.

Error Model and Recoverability

Command-level failures

Failures are success: false with string error.

{
  "id": "req_2",
  "type": "response",
  "command": "set_model",
  "success": false,
  "error": "Model not found: provider/model"
}

Recoverability expectations

• Most command failures are recoverable; process remains alive.
• Malformed JSONL / parse-loop exceptions emit a parse error response and continue reading subsequent lines.
• Empty set_session_name is rejected (Session name cannot be empty).
• Extension UI responses with unknown id are ignored.
• Process termination conditions are stdin close or explicit extension-triggered shutdown after the current command.

Compact Command Flows

1) Prompt and stream

stdin:

{ "id": "req_1", "type": "prompt", "message": "Summarize this repo" }

stdout sequence (typical):

{ "id": "req_1", "type": "response", "command": "prompt", "success": true }
{ "type": "agent_start" }
{ "type": "message_update", "assistantMessageEvent": { "type": "text_delta", "delta": "..." }, "message": { "role": "assistant", "content": [] } }
{ "type": "agent_end", "messages": [] }

2) Prompt during streaming with explicit queue policy

stdin:

{
  "id": "req_2",
  "type": "prompt",
  "message": "Also include risks",
  "streamingBehavior": "followUp"
}

3) Inspect and tune queue behavior

stdin:

{ "id": "q1", "type": "get_state" }
{ "id": "q2", "type": "set_steering_mode", "mode": "all" }
{ "id": "q3", "type": "set_interrupt_mode", "mode": "wait" }

4) Extension UI round trip

stdout:

{
  "type": "extension_ui_request",
  "id": "ui_7",
  "method": "input",
  "title": "Branch name",
  "placeholder": "feature/..."
}

stdin:

{ "type": "extension_ui_response", "id": "ui_7", "value": "feature/rpc-host" }

Notes on RpcClient helper

src/modes/rpc/rpc-client.ts is a convenience wrapper, not the protocol definition.

Current helper characteristics:

• Spawns bun <cliPath> --mode rpc
• Correlates responses by generated req_<n> ids
• Dispatches recognized core AgentEvent types to listeners
• Supports host-owned custom tools via setCustomTools() and automatic handling of host_tool_call / host_tool_cancel
• Wraps common protocol commands including OAuth getLoginProviders() / login(...); use raw protocol frames for any surface not wrapped by the helper.

Use raw protocol frames if you need complete surface coverage.