copilot --acp doesn't send modes like plan mode, accept edits during initialisation

[carlos-algms]

Describe the bug

When running copilot --acp to integrate with an IDE, during the initialisation, it's sending the list of models, but not the list of modes it can operate.

Schema described here: https://agentclientprotocol.com/protocol/session-modes

Affected version

v0.0.400

Steps to reproduce the behavior

1. run copilot --acp
2. send the initialise JSON
3. observe copilot's response

Expected behavior

Copilot should send the modes it supports, along with the available models, in the initialisation response.

Additional context

No response