Bug: `is_group` field missing from JSON output

[clawbunny]

Summary

When using imsg history --json or imsg watch --json, messages from group chats do not include an is_group field. This makes it impossible for consumers to distinguish group messages from direct messages based on the JSON output alone.

Current Behavior

{
  "id": 1234,
  "chat_id": 4,
  "sender": "user@example.com",
  "text": "Hello",
  "is_from_me": false,
  "guid": "ABC-123",
  "created_at": "2026-02-16T12:00:00.000Z",
  "attachments": [],
  "reactions": []
}

No is_group field is present, regardless of whether the message is from a group chat or a DM.

Expected Behavior

Messages should include is_group: true for group chats and is_group: false for DMs:

{
  "id": 1234,
  "chat_id": 4,
  "sender": "user@example.com",
  "text": "Hello",
  "is_from_me": false,
  "is_group": true,
  "guid": "ABC-123",
  "created_at": "2026-02-16T12:00:00.000Z",
  "attachments": [],
  "reactions": []
}

Root Cause

The macOS Messages SQLite database (chat.db) stores chat type in the chat.style column:

• Style 43 = group chat (multi-party)
• Style 45 = direct message (1:1)

This information is available via a JOIN between the message, chat_message_join, and chat tables, but imsg does not currently expose it in the JSON output.

Suggested Fix

When building the JSON output for a message, JOIN against the chat table and set is_group based on chat.style:

SELECT 
  m.*,
  CASE WHEN c.style = 43 THEN 1 ELSE 0 END AS is_group
FROM message m
JOIN chat_message_join cmj ON m.ROWID = cmj.message_id
JOIN chat c ON cmj.chat_id = c.ROWID

Then include "is_group": true/false in the JSON output.

Impact

Downstream consumers (automation tools, bots, AI gateways) that process iMessage via imsg cannot reliably determine if a message came from a group chat. They must resort to workarounds like maintaining a separate config-based allowlist of known group chat IDs.

Environment

• imsg version: 0.4.0
• macOS: 15.x (Sequoia)
• Architecture: arm64 (Apple Silicon)