Port ACP support to V2 core and APIs #35457

Priority

Low — the V2 protocol/server/client APIs are still being completed, so this should wait until the required surfaces settle.

Current state

ACP exists on the \�0v2\�0 branch, but it has not been ported to the V2 core/API stack end-to-end.

At \�0f9d1d3b259cf6c1f2195068214941fc7a19cfd11\�0:

• \�0packages/opencode/src/acp/service.ts\�0 still uses \�0@opencode-ai/sdk/v2\�0 and calls the compatibility \�0sdk.session.*\�0 APIs.
• Those routes are still backed by the legacy app services such as \�0SessionPrompt\�0, \�0Session\�0, and the legacy event/permission bridge.
• The V2 protocol/client and core surfaces needed by ACP have been landing incrementally, so copying the existing adapter onto the branch is not the same as running ACP on V2 execution semantics.

Goal

Port \�0opencode acp\�0 to V2 sessions, execution, events, and public APIs without routing through the legacy session stack.

Scope

• Define the ACP-to-V2 boundary: use the generated V2 client/protocol where appropriate, or direct V2 services when the ACP subprocess owns the runtime.
• Port session lifecycle: new, load/resume, list, close, fork, and cancel.
• Port prompt admission/execution to durable V2 session semantics.
• Map V2 message/tool/permission/session events to ordered ACP \�0session/update\�0 notifications.
• Preserve model, agent/mode, variant/effort, usage, and session config-option behavior.
• Port per-session MCP setup once the V2 MCP API is ready.
• Keep slash-command behavior aligned with the V2 command API rather than the legacy command path.
• Remove ACP's dependency on legacy \�0@opencode-ai/sdk/v2\�0 compatibility routes when the port is complete.

Acceptance criteria

• \�0opencode acp\�0 creates and drives V2 sessions end-to-end.
• Prompt, streaming text/thoughts, tool updates, permissions, cancel, reload/resume, and fork have ACP integration coverage against V2.
• ACP turn completion is ordered after all turn updates.
• Existing ACP subprocess tests run against the V2 implementation.
• No legacy session execution path is required by ACP.

Dependencies

Track this after the remaining V2 API work needed for session lifecycle, command execution, MCP, permissions/events, and generated clients is stable.

Source: https://discord.com/channels/1391832426048651334/1447692703549755466/1523384646195216384