Voice messages, scheduled sends and a full-screen editor

When the composer is empty, its send button is a microphone: record a voice message and send it in one press; the other side gets a player with its waveform. Press and hold Send to schedule a message for later.

Formatting shows as you type — bold, lists, quotes and code. Past four lines the field grows, and one more press opens a full-screen editor with smart lists and a live preview.