Messaging · Messages: messages in runs, threads, the unread line and receipts

ChatMessage sets a message under its author's picture, name and clock
time. The next by the same author within five minutes, on the same day,
joins the run: only its words, the time in the gutter on hover.
UnreadDivider marks where unread messages start. MessageThread tells who
replied, how many and when the last came; with a handler it opens on a
press, Enter or Space. ThreadPanel holds the first message, a rule
counting the replies, the replies and a composer, its body scrolling.
ReadReceipt says sending, sent, delivered or read, and who saw it in a
group. MessageReactions and TypingIndicator point to collab and motion.

gpui recolors nothing on hover: text takes its color at layout. The
gutter time rests invisible and turns visible through a group hover.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

AGENTS.md

@@ -47,6 +47,7 @@ Ely GPUI Component. A component library for GPUI, in light and dark.
 - `ely_gpui_component::init` binds Tab and Shift-Tab to `FocusNext` and `FocusPrev`. Wrap the root in `FocusScope` with `.root()` and focus its handle. A root scope takes focus when the focused element leaves the tree, as a toast's or an alert's button does.
 - gpui's `Window::dispatch_event` returns a private type, so the gallery scripts mouse input by posting `NSEvent`s to its own queue.
 - `hover()` needs an element id.
+- gpui applies hover and group-hover styles once an element has a hitbox, in prepaint and paint, but text takes its color at layout, so a hover cannot recolor text. What shows on hover rests `invisible()` and turns `visible()` through `group_hover` (`chat::ConversationItem`, `messaging::ChatMessage`).
 - `occlude()` blocks the pointer for everything painted before it, its own ancestors too. Put it on the outermost box that should stop the pointer, as the toast stack does, or the ancestors' hover never fires.
 - A drag that pans, turns or slides goes through gpui's drag, whose moves reach the owner in or out of its box; `on_mouse_move` stops at the box's edge. gpui sends a drag's moves to every listener of its type, so each payload carries its owner's `EntityId` and handlers check it.
 - gpui 0.2.2 paints pictures without a transform, so a picture turns by its pixels: `media::turn` turns decoded frames by quarter turns off the main thread, an asset keyed by the picture and the turn.