iMessage media and attachments

• inbound attachment ingestion is off by default — set channels.imessage.includeAttachments: true to forward photos, voice memos, video, and other attachments to the agent. With it disabled, attachment-only iMessages are dropped before reaching the agent and may produce no Inbound message log line at all.
• remote inbound attachment paths can be fetched via SCP when remoteHost is set
• outbound files are staged into an owner-only temporary path on the configured or auto-detected Messages Mac, passed to imsg by that remote path, and cleaned up best-effort after success, failure, or timeout; cleanup failure emits a warning and can leave owner-only residue
• attachment paths must match allowed roots:
  • channels.imessage.attachmentRoots (local)
  • channels.imessage.remoteAttachmentRoots (remote SCP mode)
  • configured roots extend the default root pattern /Users/*/Library/Messages/Attachments (merged, not replaced)
• SCP uses strict host-key checking (StrictHostKeyChecking=yes)
• outbound media size uses channels.imessage.mediaMaxMb (default 16 MB)

• text chunk limit: channels.imessage.textChunkLimit (default 4000)
• chunk mode: channels.imessage.streaming.chunkMode
  • length (default)
  • newline (paragraph-first splitting)
• outbound markdown bold/italic/underline/strikethrough is converted to native styled text (macOS 15+ recipients render the styling; older recipients see plain text without the markers); markdown tables are converted per the channel markdown table mode
• channels.imessage.sendTransport (auto default, bridge, applescript) selects how imsg delivers sends

Preferred explicit targets:

• chat_id:123 (recommended for stable routing)
• chat_guid:...
• chat_identifier:...

Direct handles are also supported:

• +1555...
• tel:+1555...
• imessage:+1555...
• sms:+1555...
• user@example.com

Use a service-qualified target for a contact name or mixed alphanumeric alias:

• auto:<contact> lets Messages choose iMessage or SMS
• imessage:<contact> requires iMessage
• sms:<contact> requires SMS

Bare contact names and mixed alphanumeric aliases are rejected instead of being converted to a phone number. If an existing automation uses one, add auto:, imessage:, or sms: to make the intended delivery service explicit.

imsg chats --limit 20