feat(sync): add typed broadcast primitive

req: sync/004

examples/kanban/src/main.rs

@@ -15,6 +15,7 @@ use hemx_axum::{
 use hemx_kanban_example::ui::board::{self as board};
 use hemx_kanban_example::ui::board_card as card_board;
 use hemx_kanban_example::ui::{self, board as board_ui};
+use hemx_sync::{Channel, SyncEffect};
 use serde::{Deserialize, Serialize};
 use std::collections::BTreeMap;
 use std::convert::Infallible;
@@ -498,6 +499,7 @@ async fn main() {
     let ordinary_routes = Router::new()
         .route("/", get(home).post(interact))
         .route("/events", get(events))
+        .route("/sync/broadcast", get(sync_broadcast))
         .route("/sync-demo", get(sync_demo))
         .route("/sync.js", get(sync_js))
         .route("/sync/context", get(sync_context))
@@ -579,6 +581,24 @@ async fn interact(
 }
 
 // req: push/001 req: push/003 req: examples/001
+async fn sync_broadcast(Query(params): Query<BTreeMap<String, String>>) -> Response {
+    let Some(channel) = params
+        .get("channel")
+        .and_then(|channel| Channel::new(channel).ok())
+    else {
+        return (StatusCode::BAD_REQUEST, "missing or invalid sync channel").into_response();
+    };
+    if channel.as_str() != "board" {
+        return StatusCode::NOT_FOUND.into_response();
+    }
+    let batch = board::presence
+        .put(&Presence { count: 7 })
+        .into_batch(ui::BUILD_FINGERPRINT);
+    let broadcast = SyncEffect::broadcast(channel, batch);
+    let (_channel, effect_batch) = broadcast.into_parts();
+    sse(stream::iter([Ok::<_, Infallible>(effect_batch)]).boxed()).into_response()
+}
+
 async fn events(Query(params): Query<BTreeMap<String, String>>) -> impl IntoResponse {
     if params.contains_key("once") {
         let effect = board::presence.put(&Presence { count: 1 });