2 · Live counter

live.live-counter — live_counter.clj, live_counter_controller.clj.

A connected component. The home page mounts it with @get('/ds/nds-connect/…/init'), so the INIT render arrives on an SSE stream that stays open.

State machine

stateDiagram-v2
  direction LR
  [*] --> displayed : INIT / read the server count
  displayed --> displayed : INCREMENT · RESET (change the server count, push to everyone)

What to look at

• No data-signals on the root: the count is an atom on the server, put into top-level ctx by the INIT action. Nothing is the client's to round-trip.
• INCREMENT is an ordinary one-shot @post. Its action bumps the atom and calls ds/send-ui! with a :broadcast effect, which reaches every stream registered under the component-id. The clicking tab also gets the one-shot response; both patch the same id.
• The buttons append ?user='+$user from a page-level signal, because the examples app identifies users by that query param — stand-in for real authentication, which would set [:params :logged-user] from a session.

Try it: open the live-counter page as ?example=live-counter&user=alice and …&user=bob side by side; click in one, watch the other. From a REPL on port 7789:

(taia.ds.datastar.interface/send-ui! "live1" "alice"
  [[:broadcast [:div#live1 [:h2 "pushed"]] {:d*/selector "#live1"}]])

Caveat: pushing from a transition action keeps the example in one file; in an application the push comes from the thing that knows something changed (a job, an agent, a use case).

Spec: block 2 in examples_test.clj (the count is in ctx, not :memory; a different user sees the same number).