Cowork's Read_and_Send_iMessages connector doesn't match this repo's documented tools / lacks group chat support

In Cowork (Claude desktop app), the connected iMessage integration is named `Read_and_Send_iMessages` and exposes: `read_imessages(phone_number, limit)`, `search_contacts(query)`, `get_unread_imessages(limit)`, `send_imessage`.

This repo's README (`external_plugins/imessage/README.md`) documents a different tool surface — `reply` and `chat_messages` — with explicit group chat support via `chat_guid` ("Omit chat_guid to see every allowlisted chat at once, or pass one to drill in").

I tried passing a group chat identifier (`chat860122946619699955`, and `any;+;chat860122946619699955`) into `read_imessages`'s `phone_number` parameter to fetch a family group chat's history — both returned an empty array, with no way to retrieve group messages at all through the connected tools.

Could someone clarify: is Cowork running a different/older iMessage integration than this plugin, or should this plugin's group-chat support (`chat_guid`) be reaching Cowork sessions and isn't? Either way, it'd help to have this documented, since right now group chats silently return nothing rather than an explicit "unsupported" error.

Start by reading external_plugins/imessage/README.md and compare its documented reply and chat_messages tools with the Read_and_Send_iMessages tools exposed in Cowork. Determine whether chat_guid group-chat support is available in Cowork; document the actual support and make the silent unsupported case explicit if appropriate.

索引モデルが issue の本文から書いたものです。