feat(ui): authenticated POST->SSE reader

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

public/sse.js

@@ -0,0 +1,33 @@
+// Authenticated POST -> SSE reader. Calls onEvent({ type, ...data }) per frame.
+const TOKEN_KEY = 'void_token';
+
+export async function streamTurn(path, body, onEvent) {
+  const res = await fetch(path, {
+    method: 'POST',
+    headers: {
+      'Authorization': 'Bearer ' + (localStorage.getItem(TOKEN_KEY) || ''),
+      'Content-Type': 'application/json'
+    },
+    body: JSON.stringify(body)
+  });
+  if (!res.ok || !res.body) throw new Error('stream failed: ' + res.status);
+
+  const reader = res.body.getReader();
+  const decoder = new TextDecoder();
+  let buf = '';
+  for (;;) {
+    const { value, done } = await reader.read();
+    if (done) break;
+    buf += decoder.decode(value, { stream: true });
+    const frames = buf.split('\n\n');
+    buf = frames.pop();                       // keep the trailing partial
+    for (const frame of frames) {
+      let event = 'message', data = '';
+      for (const line of frame.split('\n')) {
+        if (line.startsWith('event:')) event = line.slice(6).trim();
+        else if (line.startsWith('data:')) data += line.slice(5).trim();
+      }
+      if (data) onEvent({ type: event, ...JSON.parse(data) });
+    }
+  }
+}