The editor page posted its full `innerHTML` on every input event and its
formatting state on every selection change, which fires on every
keystroke too. Each message re-rendered the whole composer, where a
`JSON.stringify` snapshot of the body ran on every render (PF8).
- typing now posts at most one `change` per 400 ms: the first keystroke
at once, so the composer knows it is dirty, then the latest content
when the window ends; toolbar commands and blur post straight away
- the formatting state is posted only when it changes
- the empty-placeholder check no longer serializes the body per
keystroke, and the dirty-tracking snapshot is memoized
- autosave reads the live editor DOM, like send, save-and-close and the
format switch already do, so the throttle can't make it save a
slightly older body
The body stays in state rather than a ref: the Send button and the
close guard render from it.
Linus Rath
fc00781b47