pi-acp-agents

ACP agent client for pi — spawn and control ACP-compatible agents from within pi.

What it does

This pi extension registers tools that let the pi LLM communicate with external ACP (Agent Client Protocol) compatible agents like Gemini CLI, Claude, or any custom command that speaks ACP over stdio JSON-RPC.

Tools

Tool	Description
acp_prompt	Send a prompt to an ACP agent, get the text response
acp_status	Show configured agents, active sessions, circuit breaker state
acp_session_new	Create a new isolated session with an agent
acp_session_load	Load an existing session by ID
acp_session_set_model	Change the model for an active session
acp_session_set_mode	Change the mode (thinking level) for an active session
acp_cancel	Cancel an ongoing prompt
acp_delegate	Delegate a task (short-lived session, auto-disposed)
acp_broadcast	Send same prompt to multiple agents in parallel
acp_compare	Get responses from multiple agents and compare them

Configuration

Config file: ~/.pi/acp-agents/config.json

{
  "agents": {
    "gemini": {
      "command": "gemini",
      "args": ["--acp"],
      "defaultModel": "gemini-2.5-pro"
    }
  },
  "defaultAgent": "gemini"
}

Fields

Field	Default	Description
agents	{ gemini: {...} }	Map of agent name → config
defaultAgent	"gemini"	Agent used when not specified
staleTimeoutMs	900000 (15 min)	Session staleness threshold
healthCheckIntervalMs	30000 (30s)	Background health polling interval
circuitBreakerMaxFailures	3	Consecutive failures before circuit opens
circuitBreakerResetMs	60000 (60s)	Time before circuit half-opens
stallTimeoutMs	300000 (5 min)	Per-operation timeout

Per-agent config

Field	Required	Description
command	yes	Executable to spawn
args	no	Arguments (e.g., ["--acp"])
env	no	Extra environment variables
cwd	no	Working directory override
defaultModel	no	Default model ID

Resilience

• Circuit breaker: Opens after N consecutive failures, auto-recovers after timeout
• Stall timeout: Prompts that receive no activity are auto-cancelled
• Health polling: Background monitor tracks lastActivityAt per session
• Busy mutex: Prevents concurrent prompts on same session
• Process safeguards: SIGTERM → SIGKILL escalation, EPIPE error handlers
• Non-blocking: All tool errors return as tool error results, never throw

Architecture

Adapter pattern:
  AcpAgentAdapter (abstract base)
  ├── GeminiAcpAdapter  — gemini --acp defaults
  └── CustomAcpAdapter  — any user-defined ACP command

Client layer:
  AcpClient — wraps @agentclientprotocol/sdk ClientSideConnection

Resilience:
  AcpCircuitBreaker — wraps all tool execute calls
  HealthMonitor — background session health polling

Coordination:
  AgentCoordinator — multi-agent delegate/broadcast/compare

Logs

Central logs: ~/.pi/acp-agents/logs/

• main.log — general log
• session-{id}/trace.jsonl — per-session JSON-RPC traces

Prerequisites

• Gemini CLI installed and authenticated: gemini --version + gemini (login)
• ACP TypeScript SDK: bundled as dependency

References

• ACP Protocol: https://agentclientprotocol.com/protocol/overview
• ACP TypeScript SDK: @agentclientprotocol/sdk
• Gemini ACP docs: https://geminicli.com/docs/cli/acp-mode/