Send Draft

Convert a draft to a sent message via the API's transport.

The draft's from_handle becomes the message's from_handle. The signed_by attribution defaults to the from_handle's prefix unless overridden in the request body. This is the point where the human's approval is formally recorded — the MCP client calls this only after the user clicks 'send' in Claude's UI.

Optional body: { "signed_by": "brian" # short-form attribution override }