ACP clients don't show the session plan — plan sessionUpdate is never emitted #40745

Problem

When OpenCode runs as an ACP agent (Zed, JetBrains, Neovim via ACP), the session todo list that the TUI renders is never shown in the client. ACP defines a first-class plan sessionUpdate for this, but OpenCode's ACP adapter never emits it.

The state is already published as a todo.updated event (packages/schema/src/session-todo.ts, packages/core/src/session/todo.ts) on the same event stream the adapter consumes (sdk.global.event() in packages/opencode/src/acp/event.ts). The handle() switch has no case "todo.updated", so the data is dropped before reaching the client.

The todowrite tool result is visible in ACP clients as a raw tool-call payload, but there is no plan panel — that only comes from sessionUpdate: "plan".

Proposal

Map todo.updated → session/update with sessionUpdate: "plan" in event.ts. Todo.Info (content/priority/status) maps 1:1 onto ACP PlanEntry.

Verification

• event.ts emits agent_message_chunk, agent_thought_chunk, tool_call(_update), usage_update, available_commands_update — no plan.

• SessionTodo.Event.Updated (type: "todo.updated", properties: { sessionID, todos }) is published on EventV2 and surfaces in the global event stream.

• A standalone ACP agent emitting the equivalent plan updates renders a live plan panel in Zed — the client side is ready.

• I have verified this behavior is missing