A maximised composer goes position: fixed but stays a child of the dock,
and had no z-index of its own. The dock is a stacking context, so the
positioned parts of any composer later in the DOM (its recipients row, its
editor) painted straight over the full-screen one.
Give the maximised composer its own layer, and hide the other composers
while one is full screen: they cannot be reached anyway, and the 24px
inset would otherwise show their footers along the bottom edge. They stay
mounted, so nothing being written in them is lost.
Fixes#330
The body editor was told to focus itself with
autoFocus={d.to.length > 0 && Boolean(d.subject)}
and RichEditor ran that as an effect keyed on the prop. Typing the first
letter of a subject flipped Boolean(d.subject) false -> true, the effect fired,
and the caret jumped from the subject line into the message body.
autoFocus now means what it means on a DOM element: focus on mount. RichEditor
captures the prop in a ref and focuses once, and the composer decides where the
caret starts when it opens - recipients for a blank message, body for a reply
that already has recipients and a subject - instead of deriving it from state
that changes as the user types.
initialFocusTarget is extracted and exported so the rule is stated in one place
and tested. The regression test renders RichEditor and asserts it does not take
focus from a field being typed into; it fails against the previous effect.
jcoffey-dev