feat(control-ui): render Mermaid code fences in webchat

ui/package.json

@@ -12,7 +12,11 @@
     "@noble/ed25519": "3.0.1",
     "dompurify": "^3.3.3",
     "lit": "^3.3.2",
-    "marked": "^17.0.4"
+    "marked": "^17.0.4",
+    "mermaid": "11.13.0",
+    "signal-polyfill": "^0.2.2",
+    "signal-utils": "^0.21.1",
+    "vite": "8.0.0"
   },
   "devDependencies": {
     "@vitest/browser-playwright": "4.1.0",

ui/src/styles/chat.css

@@ -1,5 +1,6 @@
 @import "./chat/layout.css";
 @import "./chat/text.css";
+@import "./chat/mermaid.css";
 @import "./chat/grouped.css";
 @import "./chat/tool-cards.css";
 @import "./chat/sidebar.css";

ui/src/styles/chat/mermaid.css

@@ -0,0 +1,35 @@
+.chat-text :where(.mermaid-block) {
+  margin-top: 0.75em;
+  border: 1px solid var(--border);
+  border-radius: var(--radius-md);
+  overflow: hidden;
+  background: color-mix(in srgb, var(--secondary) 70%, transparent);
+}
+
+.chat-text :where(.mermaid-block__render) {
+  overflow-x: auto;
+  padding: 12px;
+}
+
+.chat-text :where(.mermaid-block__render svg) {
+  display: block;
+  max-width: 100%;
+  height: auto;
+}
+
+.chat-text :where(.mermaid-block__source) {
+  border-top: 1px solid var(--border);
+}
+
+.chat-text :where(.mermaid-block__source > summary) {
+  cursor: pointer;
+  list-style: none;
+  user-select: none;
+  padding: 8px 12px;
+  font-size: 12px;
+  color: var(--muted);
+}
+
+.chat-text :where(.mermaid-block__source > summary::-webkit-details-marker) {
+  display: none;
+}

ui/src/ui/app-lifecycle.ts

@@ -17,6 +17,7 @@ import {
   syncThemeWithSettings,
 } from "./app-settings.ts";
 import { loadControlUiBootstrapConfig } from "./controllers/control-ui-bootstrap.ts";
+import { scheduleMermaidRender } from "./mermaid.ts";
 import type { Tab } from "./navigation.ts";
 
 type LifecycleHost = {
@@ -109,6 +110,7 @@ export function handleUpdated(host: LifecycleHost, changed: Map<PropertyKey, unk
       host as unknown as Parameters<typeof scheduleChatScroll>[0],
       forcedByTab || forcedByLoad || streamJustStarted || !host.chatHasAutoScrolled,
     );
+    scheduleMermaidRender();
   }
   if (
     host.tab === "logs" &&

ui/src/ui/markdown.test.ts

@@ -30,6 +30,16 @@ describe("toSanitizedMarkdownHtml", () => {
     expect(html).toContain("console.log(1)");
   });
 
+  it("renders mermaid fences into renderable mermaid blocks", () => {
+    const html = toSanitizedMarkdownHtml(
+      ["```mermaid", "flowchart TD", "A --> B", "```"].join("\n"),
+    );
+    expect(html).toContain('class="mermaid-block"');
+    expect(html).toContain('class="mermaid-block__render"');
+    expect(html).toContain('class="language-mermaid"');
+    expect(html).toContain("Mermaid source");
+  });
+
   it("flattens remote markdown images into alt text", () => {
     const html = toSanitizedMarkdownHtml("![Alt text](https://example.com/image.png)");
     expect(html).not.toContain("<img");

ui/src/ui/markdown.ts

@@ -48,6 +48,7 @@ const allowedAttrs = [
   "data-code",
   "type",
   "aria-label",
+  "role",
 ];
 const sanitizeOptions = {
   ALLOWED_TAGS: allowedTags,
@@ -184,6 +185,7 @@ htmlEscapeRenderer.code = ({
   lang?: string;
   escaped?: boolean;
 }) => {
+  const normalizedLang = lang?.trim().toLowerCase() ?? "";
   const langClass = lang ? ` class="language-${escapeHtml(lang)}"` : "";
   const safeText = escaped ? text : escapeHtml(text);
   const codeBlock = `<pre><code${langClass}>${safeText}</code></pre>`;
@@ -196,10 +198,14 @@ htmlEscapeRenderer.code = ({
   const copyBtn = `<button type="button" class="code-block-copy" data-code="${attrSafe}" aria-label="Copy code"><span class="code-block-copy__idle">Copy</span><span class="code-block-copy__done">Copied!</span></button>`;
   const header = `<div class="code-block-header">${langLabel}${copyBtn}</div>`;
 
+  if (normalizedLang === "mermaid") {
+    return `<div class="mermaid-block"><div class="mermaid-block__render" aria-label="Mermaid diagram" role="img"></div><details class="mermaid-block__source"><summary>Mermaid source</summary><div class="code-block-wrapper">${header}${codeBlock}</div></details></div>`;
+  }
+
   const trimmed = text.trim();
   const isJson =
-    lang === "json" ||
-    (!lang &&
+    normalizedLang === "json" ||
+    (!normalizedLang &&
       ((trimmed.startsWith("{") && trimmed.endsWith("}")) ||
         (trimmed.startsWith("[") && trimmed.endsWith("]"))));
 

ui/src/ui/mermaid.ts

@@ -0,0 +1,68 @@
+type MermaidApi = {
+  initialize: (config: Record<string, unknown>) => void;
+  render: (id: string, definition: string) => Promise<{ svg: string }>;
+};
+
+let mermaidApiPromise: Promise<MermaidApi> | null = null;
+let renderScheduled = false;
+let renderCounter = 0;
+
+async function loadMermaidApi(): Promise<MermaidApi> {
+  if (!mermaidApiPromise) {
+    mermaidApiPromise = import("mermaid").then((mod) => {
+      const api = (mod.default ?? mod) as MermaidApi;
+      api.initialize({
+        startOnLoad: false,
+        securityLevel: "strict",
+      });
+      return api;
+    });
+  }
+  return mermaidApiPromise;
+}
+
+export function scheduleMermaidRender(root: ParentNode = document): void {
+  if (renderScheduled) {
+    return;
+  }
+  renderScheduled = true;
+  queueMicrotask(() => {
+    requestAnimationFrame(() => {
+      renderScheduled = false;
+      void renderMermaidBlocks(root);
+    });
+  });
+}
+
+async function renderMermaidBlocks(root: ParentNode): Promise<void> {
+  const blocks = Array.from(
+    root.querySelectorAll<HTMLElement>(".mermaid-block:not([data-mermaid-status])"),
+  );
+  if (blocks.length === 0) {
+    return;
+  }
+
+  const api = await loadMermaidApi();
+
+  for (const block of blocks) {
+    const definition =
+      block.querySelector<HTMLElement>("code.language-mermaid")?.textContent?.trim() ?? "";
+    const renderTarget = block.querySelector<HTMLElement>(".mermaid-block__render");
+    if (!definition || !renderTarget) {
+      block.dataset.mermaidStatus = "error";
+      continue;
+    }
+
+    block.dataset.mermaidStatus = "rendering";
+    try {
+      const id = `openclaw-mermaid-${++renderCounter}`;
+      const { svg } = await api.render(id, definition);
+      renderTarget.innerHTML = svg;
+      block.dataset.mermaidStatus = "ready";
+    } catch (err) {
+      console.warn("[markdown] mermaid render failed", err);
+      renderTarget.textContent = "Mermaid render failed. Expand source to inspect diagram text.";
+      block.dataset.mermaidStatus = "error";
+    }
+  }
+}