mockpeer

Overview ¶

Package main builds mockpeer: a small, real ACP agent used as a scriptable test peer. It is spawned as a subprocess (over acp/transport/stdio) by acp/client's tests and by mockpeer_test.go here; it is never imported as a library.

mockpeer speaks the agent role of the Agent Client Protocol directly on protocol.Conn (via Conn.Handle/HandleNotify with the generated method-name constants and request/response types) rather than through a typed "server-side AgentConn" wrapper, because no such wrapper exists yet — that lands in Phase 2 as the real agent facade.

Behavior is scripted entirely through environment variables, read once at startup and validated defensively (see envBool and envExitCode): garbage values fail closed with exitInvalidEnv rather than being silently ignored or causing a panic.

• ACP_MOCK_EXIT_CODE=n: exit immediately with code n, before any protocol activity.
• ACP_MOCK_MALFORMED_OUTPUT=1: write one non-JSON line to stdout before starting the connection, then continue serving normally.
• ACP_MOCK_DIE_AFTER_INIT=1: behave normally through the "initialize" response, then exit the instant that response has been flushed to stdout — simulating a peer that crashes right after the handshake.
• Default (none set): answer "initialize", "session/new", and "session/prompt"; a prompt streams a fixed "session/update" sequence (an agent message chunk, an agent thought chunk, a tool call, a tool call update, and a plan) and issues one "session/request_permission" call back to the peer.

Note on elicitation: the task this package implements (docs/plans/2026-07-23-acp-bridge-implementation.md, Task 1.8) also calls for mockpeer to "issue ... one elicitation when told to." The pinned v1.20.0 ACP schema this module generates from (see protocol/methods_gen.go) has no elicitation method at all — it was already confirmed absent during Task 1.7 (protocol/acp.go has no ClientConn.Elicit either, for the same reason). Per the plan's own precedence rule ("when a generated-schema detail conflicts with this plan's exact constant names, the pinned artifact wins"), elicitation is omitted here rather than invented.