ACP Protocol

The Agent Client Protocol (ACP) adapter exposes an Awaken runtime over stdio using the official agent-client-protocol Rust SDK. Unlike the HTTP protocols, ACP is a process/stdio integration: a host launches the Awaken-backed process, then exchanges ACP JSON-RPC messages over stdin/stdout.

Feature gate: server

Runtime entry points

API	Purpose
awaken_server::protocols::acp::stdio::serve_stdio(runtime)	Serve ACP on process stdin/stdout.
awaken_server::protocols::acp::stdio::serve_stdio_io(runtime, input, output)	Serve ACP over caller-provided async I/O; used by tests and embedders.
awaken_server::protocols::acp::encoder::AcpEncoder	Transcode AgentEvent values into ACP session updates.

Session behavior

• initialize returns the requested protocol version, awaken-acp agent info, and prompt capabilities for text plus image/audio/embedded-context blocks.
• newSession requires an absolute cwd. mcpServers in the request are rejected; register MCP servers through Awaken config instead.
• The adapter selects the default agent when present. If no default agent exists, the runtime must have exactly one registered agent.
• Each ACP session maps to a fresh Awaken thread id. prompt appends the user content to that thread and runs the selected agent through AgentRuntime.
• Tool permission requests are bridged to the ACP client and converted back into Awaken HITL resume decisions.

Relationship to HTTP adapters

ACP is backed by the same AgentRuntime and AgentEvent stream as the other protocol adapters. Each adapter projects or collects those events according to its own wire semantics; ACP does not add a separate agent execution path.