Studio: prevent long streaming Markdown stalls

studio/frontend/src/components/assistant-ui/markdown-text.tsx

@@ -24,7 +24,12 @@ import { HugeiconsIcon } from "@hugeicons/react";
 import { createMathPlugin } from "@streamdown/math";
 import { mermaid } from "@streamdown/mermaid";
 import { useEffect, useMemo, useRef, useState } from "react";
-import { Block, type BlockProps, Streamdown } from "streamdown";
+import {
+  Block,
+  type BlockProps,
+  Streamdown,
+  type StreamdownProps,
+} from "streamdown";
 import { createCodePlugin } from "./code-plugin";
 import "katex/dist/katex.min.css";
 import { AudioPlayer } from "./audio-player";
@@ -36,6 +41,15 @@ const code = createCodePlugin({
 });
 const { withSmoothContextProvider } = INTERNAL;
 
+// Streamdown 2.5 schedules ordinary streaming blocks in an interruptible React
+// transition. A continuous token stream can starve that transition for seconds.
+// Its animated path commits every block update directly; zero duration preserves
+// that scheduling behavior without adding a visible text animation.
+const STREAMDOWN_IMMEDIATE_UPDATES = {
+  duration: 0,
+  stagger: 0,
+} satisfies NonNullable<StreamdownProps["animated"]>;
+
 const STREAMDOWN_COMPONENTS = {
   a: ({ href, children, ...props }: React.ComponentProps<"a">) => (
     <a
@@ -395,6 +409,7 @@ const MarkdownTextImpl = () => {
         key={messageId}
         mode="streaming"
         isAnimating={status.type === "running"}
+        animated={STREAMDOWN_IMMEDIATE_UPDATES}
         plugins={{ code, math, mermaid }}
         components={STREAMDOWN_COMPONENTS}
         urlTransform={safeMarkdownUrl}

studio/frontend/tests/markdown-streaming-scheduling.test.ts

@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+// Copyright 2026-present the Unsloth AI Inc. team. All rights reserved. See /studio/LICENSE.AGPL-3.0
+
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import test from "node:test";
+
+import ts from "typescript";
+
+const MARKDOWN_TEXT_PATH = new URL(
+  "../src/components/assistant-ui/markdown-text.tsx",
+  import.meta.url,
+);
+const source = ts.createSourceFile(
+  MARKDOWN_TEXT_PATH.pathname,
+  readFileSync(MARKDOWN_TEXT_PATH, "utf8"),
+  ts.ScriptTarget.ESNext,
+  true,
+  ts.ScriptKind.TSX,
+);
+
+function findImmediateUpdateConfig(): ts.ObjectLiteralExpression | null {
+  let config: ts.ObjectLiteralExpression | null = null;
+  const visit = (node: ts.Node): void => {
+    if (
+      ts.isVariableDeclaration(node) &&
+      node.name.getText(source) === "STREAMDOWN_IMMEDIATE_UPDATES" &&
+      node.initializer &&
+      ts.isSatisfiesExpression(node.initializer) &&
+      ts.isObjectLiteralExpression(node.initializer.expression)
+    ) {
+      config = node.initializer.expression;
+    }
+    node.forEachChild(visit);
+  };
+  source.forEachChild(visit);
+  return config;
+}
+
+function findChatStreamdown(): ts.JsxOpeningLikeElement | null {
+  let streamdown: ts.JsxOpeningLikeElement | null = null;
+  const visit = (node: ts.Node): void => {
+    if (
+      (ts.isJsxOpeningElement(node) || ts.isJsxSelfClosingElement(node)) &&
+      node.tagName.getText(source) === "Streamdown"
+    ) {
+      streamdown = node;
+    }
+    node.forEachChild(visit);
+  };
+  source.forEachChild(visit);
+  return streamdown;
+}
+
+function jsxAttribute(
+  opening: ts.JsxOpeningLikeElement,
+  name: string,
+): ts.JsxAttribute | null {
+  for (const attribute of opening.attributes.properties) {
+    if (
+      ts.isJsxAttribute(attribute) &&
+      attribute.name.getText(source) === name
+    ) {
+      return attribute;
+    }
+  }
+  return null;
+}
+
+test("chat streaming bypasses Streamdown's starvable transition without visible animation", () => {
+  const config = findImmediateUpdateConfig();
+  assert.ok(config, "STREAMDOWN_IMMEDIATE_UPDATES is missing");
+
+  const values = new Map(
+    config.properties.flatMap((property) => {
+      if (
+        !(
+          ts.isPropertyAssignment(property) &&
+          ts.isNumericLiteral(property.initializer)
+        )
+      ) {
+        return [];
+      }
+      return [
+        [property.name.getText(source), Number(property.initializer.text)],
+      ];
+    }),
+  );
+  assert.equal(values.get("duration"), 0);
+  assert.equal(values.get("stagger"), 0);
+
+  const streamdown = findChatStreamdown();
+  assert.ok(streamdown, "chat <Streamdown> is missing");
+  assert.equal(
+    jsxAttribute(streamdown, "mode")?.initializer?.getText(source),
+    '"streaming"',
+  );
+  assert.equal(
+    jsxAttribute(streamdown, "animated")?.initializer?.getText(source),
+    "{STREAMDOWN_IMMEDIATE_UPDATES}",
+  );
+});