ACP todo plan notifications are never sent because TodoListTool omits display block

Summary

The ACP adapter already has code to translate a todo_list tool display block into an ACP session/update of type plan, but the TodoListTool in agent-core never produces that display block. As a result, ACP clients never receive live todo/plan updates.

Where the wiring exists

• packages/acp-adapter/src/session.ts (around line 1039–1056) listens for tool.call.started events and calls planFromDisplayBlock(sessionId, event.turnId, event.display) when event.display is present.
• packages/acp-adapter/src/events-map.ts implements todoListToSessionUpdate / planFromDisplayBlock, which converts display.kind === 'todo_list' into an ACP plan session update.
• packages/protocol/src/display.ts defines the todo_list display schema.

The gap

packages/agent-core/src/tools/builtin/state/todo-list.ts TodoListTool.resolveExecution returns only description, approvalRule, and execute. It does not return a display field, so toolCallDisplayFieldsFromExecution in packages/agent-core/src/loop/tool-call.ts never attaches a todo_list display to the tool.call.started event.

Consequently, the ACP adapter’s Phase 9.3 branch is never triggered and no plan update is sent.

Impact

• External ACP clients cannot render the agent’s evolving todo list via plan session updates.
• The web UI path for todo_list display blocks (apps/kimi-web/src/composables/messagesToTurns.ts) is effectively dead for this tool.
• Only the TUI receives todo updates, and it does so by parsing tool-call arguments directly rather than through the ACP notification path.

Suggested fix

Update TodoListTool.resolveExecution to return a display block when the todo list is read or written:

display: {
  kind: 'todo_list',
  items: stored.map((todo) => ({ title: todo.title, status: todo.status })),
},

This would cause agent-core to attach the structured display to tool.call.started, which the ACP adapter already maps to a plan session update.

Related files

• packages/agent-core/src/tools/builtin/state/todo-list.ts
• packages/acp-adapter/src/session.ts
• packages/acp-adapter/src/events-map.ts
• packages/agent-core/src/loop/tool-call.ts
• packages/protocol/src/display.ts
• packages/acp-adapter/test/plan-and-commands.test.ts

Start with packages/agent-core/src/tools/builtin/state/todo-list.ts and trace how packages/agent-core/src/loop/tool-call.ts attaches display fields to tool.call.started events. Then inspect packages/acp-adapter/src/events-map.ts and test/plan-and-commands.test.ts to verify the ACP plan update path. Done means todo-list reads and writes produce the expected plan session updates without breaking existing display handling.