fix(web): keep streamed replies painting incrementally

tests/test_static_vendor.py

@@ -199,6 +199,14 @@ class StaticVendorTests(unittest.TestCase):
         self.assertIn('p > 1 ? "100%+"', src)
         self.assertIn("cache_hit_tokens", src)
 
+    def test_sse_consumer_yields_for_streaming_text_paints(self) -> None:
+        chat_js = (JS_DIR / "chat.js").read_text(encoding="utf-8")
+
+        self.assertIn("renderEventsSincePaint", chat_js)
+        self.assertIn("renderEventsSincePaint >= 24", chat_js)
+        self.assertIn("await yieldToStreamPaint()", chat_js)
+        self.assertIn('document.visibilityState === "hidden"', chat_js)
+
     def test_custom_task_name_is_optional_with_explicit_directory(self) -> None:
         html = DEV_HTML.read_text(encoding="utf-8")
         newtask_js = (JS_DIR / "newtask.js").read_text(encoding="utf-8")

web/static/js/chat.js

@@ -2975,6 +2975,7 @@ async function consumeSseStream(url, asstCard, ctx) {
   const reader = r.body.getReader();
   const dec = new TextDecoder();
   let buf = "";
+  let renderEventsSincePaint = 0;
   setRunHint(ctx, "接收中…");
   while (true) {
     const { value, done } = await reader.read();
@@ -2988,15 +2989,40 @@ async function consumeSseStream(url, asstCard, ctx) {
       const ev = parseSseFrame(frame);
       if (!ev) continue;
       handleSseEvent(ev, asstCard, ctx);
+      if ((ev.event === "text" || ev.event === "reasoning") && ev.data && ev.data.delta) {
+        renderEventsSincePaint++;
+      }
       if (ev.event === "done" || ev.event === "error") {
         ctx.terminal = true;
+        // 正文高速到达时,同一个 ReadableStream chunk 里可能塞进大量 SSE frame。
+        // handleSseEvent 的 DOM 更新由 rAF 节流；若这里直接一路吃到 done 并 return，
+        // 浏览器始终拿不到绘制机会，用户就只会在收尾时看到整段正文。终态前先让
+        // 已排队的 rAF 落一次屏，保持最后一批文字也按流式过程可见。
+        if (renderEventsSincePaint) await yieldToStreamPaint();
         refreshProcs();  // run 收尾顺手校正后台进程条(run 中可能起了/杀了 proc)
         return;
       }
+      // 限制一次同步消费的渲染事件数。Flash 正文 token 很密时主动给主线程背压，
+      // 让 Markdown rAF 与自动滚底能逐帧执行；隐藏标签页无需等待不会触发的 rAF。
+      if (renderEventsSincePaint >= 24) {
+        await yieldToStreamPaint();
+        renderEventsSincePaint = 0;
+      }
+    }
+    // 即使单个网络 chunk 不到阈值，也在读取下一批前兑现本批 DOM 更新。部分浏览器
+    // 会从内部缓冲连续 resolve reader.read()，只依赖网络 await 仍可能长期饿死绘制。
+    if (renderEventsSincePaint) {
+      await yieldToStreamPaint();
+      renderEventsSincePaint = 0;
     }
   }
 }
 
+function yieldToStreamPaint() {
+  if (document.visibilityState === "hidden") return Promise.resolve();
+  return new Promise(resolve => requestAnimationFrame(resolve));
+}
+
 function parseSseFrame(frame) {
   const lines = frame.split("\n");
   let event = "msg"; let dataLines = [];