A page driven entirely by Datastar: on load it opens one
long-lived stream (/ds/feed) that the server pushes state through, and every button below is a short
SSE stream of its own that answers with patches and ends. Element patches (outer, inner, append), signal patches,
signals sent both as query and as JSON body, a stream that keeps going for a while, and broadcasts to every tab.
Open it twice and use one tab; state is shared by everyone, on purpose.
A signal patch a second, broadcast on the feed.
Broadcast when a feed opens or closes: close a tab and watch it drop.
POST, signals as JSON body. The server bumps the count and patches the signal to every tab.
The text travels as the message signal; the server appends a list item to every tab
(patch-elements, mode append) and clears the input by patching the signal back to empty.
One request whose stream stays open for a few seconds, patching the bar as it goes (mode inner). The button is disabled by Datastar's indicator signal while the stream is open.