Add runtime SSE effect stream support

slhx-js/runtime/slhx.js

@@ -8,6 +8,7 @@
   const pending = new WeakMap();
   const queues = new WeakMap();
   const timers = new WeakMap();
+  const sseSources = new WeakMap();
   const atomStores = new WeakMap();
 
   function roots() {
@@ -402,6 +403,25 @@
     });
   }
 
+  function bindSse(root) {
+    const url = root.getAttribute("data-slhx-sse");
+    if (!url || sseSources.has(root) || typeof EventSource === "undefined") return;
+    const source = new EventSource(new URL(url, location.href).href);
+    source.addEventListener("slhx", (event) => applySseMessage(root, event));
+    source.addEventListener("message", (event) => applySseMessage(root, event));
+    source.addEventListener("error", () => emit(root, "slhx:sse-error", url));
+    sseSources.set(root, source);
+  }
+
+  function applySseMessage(root, event) {
+    try {
+      const bytes = base64UrlBytes(event.data);
+      applyBatch(bytes.buffer.slice(bytes.byteOffset, bytes.byteOffset + bytes.byteLength), root);
+    } catch (error) {
+      emit(root, "slhx:error", String(error));
+    }
+  }
+
   function duration(value) {
     if (!value) return 0;
     const match = String(value).trim().match(/^(\d+)(ms|s)?$/);
@@ -523,6 +543,7 @@
     roots().forEach((root) => {
       bootstrapState(root);
       bindRoot(root);
+      bindSse(root);
     });
     history.replaceState(history.state || { slhx: true }, "", location.href);
   }