diff --git a/apps/server/src/app.ts b/apps/server/src/app.ts
index ea1756d..0032303 100644
--- a/apps/server/src/app.ts
+++ b/apps/server/src/app.ts
@@ -8,7 +8,11 @@ import {
   exportConfigSchema,
   supportedPaperFormats
 } from "@md-to-pdf/core";
-import { RENDERER_VERSION, renderMarkdown } from "@md-to-pdf/renderer";
+import {
+  MarkdownDocumentParseError,
+  RENDERER_VERSION,
+  renderMarkdown
+} from "@md-to-pdf/renderer";
 import {
   createPdfGenerator,
   PdfEngineClosedError,
@@ -66,6 +70,29 @@ function validateMarkdownRequest(
   };
 }
 
+function renderMarkdownRequest(
+  markdown: string,
+  language: string | undefined
+) {
+  try {
+    return {
+      success: true as const,
+      document: renderMarkdown(markdown, {
+        ...(language ? { language } : {})
+      })
+    };
+  } catch (error) {
+    if (error instanceof MarkdownDocumentParseError) {
+      return {
+        success: false as const,
+        error: error.code,
+        message: error.message
+      };
+    }
+    throw error;
+  }
+}
+
 function encodeRfc5987(value: string) {
   return encodeURIComponent(value).replace(
     /[!'()*]/g,
@@ -142,7 +169,8 @@ export function buildApp(options: BuildAppOptions = {}) {
   const themes = createThemeRegistry({
     bundledRoot: resolve(projectRoot, "themes"),
     localRoot:
-      options.localThemeRoot ?? resolve(projectRoot, ".local", "themes")
+      options.localThemeRoot ?? resolve(projectRoot, ".local", "themes"),
+    onWarning: (message) => app.log.warn(message)
   });
   const pdfGenerator =
     options.pdfGenerator ?? createPdfGenerator();
@@ -254,9 +282,17 @@ export function buildApp(options: BuildAppOptions = {}) {
         });
       }
 
-      return renderMarkdown(validated.markdown, {
-        ...(validated.language ? { language: validated.language } : {})
-      });
+      const rendered = renderMarkdownRequest(
+        validated.markdown,
+        validated.language
+      );
+      if (!rendered.success) {
+        return reply.code(400).send({
+          error: rendered.error,
+          message: rendered.message
+        });
+      }
+      return rendered.document;
     }
   );
 
@@ -304,10 +340,18 @@ export function buildApp(options: BuildAppOptions = {}) {
       }
 
       const markdownStartedAt = performance.now();
-      const rendered = renderMarkdown(validated.markdown, {
-        ...(validated.language ? { language: validated.language } : {})
-      });
+      const renderedResult = renderMarkdownRequest(
+        validated.markdown,
+        validated.language
+      );
       const markdownMs = performance.now() - markdownStartedAt;
+      if (!renderedResult.success) {
+        return reply.code(400).send({
+          error: renderedResult.error,
+          message: renderedResult.message
+        });
+      }
+      const rendered = renderedResult.document;
 
       try {
         const generated = await pdfGenerator.generate({
diff --git a/apps/server/src/pdf-engine.ts b/apps/server/src/pdf-engine.ts
index 35871c8..1cc1eee 100644
--- a/apps/server/src/pdf-engine.ts
+++ b/apps/server/src/pdf-engine.ts
@@ -232,6 +232,46 @@ export function isAllowedPdfRequestUrl(
   return url.origin === renderOrigin;
 }
 
+async function waitWithPdfTimeout<T>(
+  operation: Promise<T>,
+  timeoutMs: number
+) {
+  let timeout: NodeJS.Timeout | undefined;
+  try {
+    return await Promise.race([
+      operation,
+      new Promise<never>((_, reject) => {
+        timeout = setTimeout(() => {
+          reject(new PdfRenderTimeoutError(timeoutMs));
+        }, timeoutMs);
+      })
+    ]);
+  } finally {
+    if (timeout) {
+      clearTimeout(timeout);
+    }
+  }
+}
+
+async function closeContextWithin(
+  context: Awaited<ReturnType<Browser["newContext"]>>,
+  timeoutMs: number
+) {
+  let timeout: NodeJS.Timeout | undefined;
+  try {
+    await Promise.race([
+      context.close().catch(() => undefined),
+      new Promise<void>((resolve) => {
+        timeout = setTimeout(resolve, Math.min(timeoutMs, 5_000));
+      })
+    ]);
+  } finally {
+    if (timeout) {
+      clearTimeout(timeout);
+    }
+  }
+}
+
 export class PlaywrightPdfGenerator implements PdfGenerator {
   private readonly renderOrigin: string;
   private readonly renderUrl: string;
@@ -284,7 +324,7 @@ export class PlaywrightPdfGenerator implements PdfGenerator {
     if (this.closed) {
       throw new PdfEngineClosedError();
     }
-    await this.getBrowser();
+    await waitWithPdfTimeout(this.getBrowser(), this.timeoutMs);
   }
 
   async close() {
@@ -330,57 +370,67 @@ export class PlaywrightPdfGenerator implements PdfGenerator {
     queuedAt: number,
     queueMs: number
   ): Promise<PdfGenerationResult> {
-    const browserStartedAt = performance.now();
-    const browser = await this.getBrowser();
-    const browserMs = performance.now() - browserStartedAt;
-    const contextStartedAt = performance.now();
-    const context = await browser.newContext({
-      locale: payload.metadata.language || "zh-CN",
-      serviceWorkers: "block"
-    });
-    const contextMs = performance.now() - contextStartedAt;
-    let timeout: NodeJS.Timeout | undefined;
+    let context:
+      | Awaited<ReturnType<Browser["newContext"]>>
+      | undefined;
+    let expired = false;
 
     try {
-      await context.route("**/*", async (route) => {
-        if (
-          isAllowedPdfRequestUrl(
-            route.request().url(),
-            this.renderOrigin
-          )
-        ) {
-          await route.continue();
-          return;
+      const operation = (async (): Promise<PdfGenerationResult> => {
+        const browserStartedAt = performance.now();
+        const browser = await this.getBrowser();
+        const browserMs = performance.now() - browserStartedAt;
+        if (expired) {
+          throw new PdfRenderTimeoutError(this.timeoutMs);
         }
-        await route.abort("blockedbyclient");
-      });
 
-      const operation = this.renderWithContext(context, payload);
-      const timeoutPromise = new Promise<never>((_, reject) => {
-        timeout = setTimeout(() => {
-          reject(new PdfRenderTimeoutError(this.timeoutMs));
-        }, this.timeoutMs);
-      });
-
-      const generated = await Promise.race([
-        operation,
-        timeoutPromise
-      ]);
-      return {
-        ...generated,
-        timings: {
-          queueMs,
-          browserMs,
-          contextMs,
-          ...generated.timings,
-          totalMs: performance.now() - queuedAt
+        const contextStartedAt = performance.now();
+        const createdContext = await browser.newContext({
+          locale: payload.metadata.language || "zh-CN",
+          serviceWorkers: "block"
+        });
+        context = createdContext;
+        const contextMs = performance.now() - contextStartedAt;
+        if (expired) {
+          await closeContextWithin(createdContext, this.timeoutMs);
+          throw new PdfRenderTimeoutError(this.timeoutMs);
         }
-      };
+
+        await createdContext.route("**/*", async (route) => {
+          if (
+            isAllowedPdfRequestUrl(
+              route.request().url(),
+              this.renderOrigin
+            )
+          ) {
+            await route.continue();
+            return;
+          }
+          await route.abort("blockedbyclient");
+        });
+
+        const generated = await this.renderWithContext(
+          createdContext,
+          payload
+        );
+        return {
+          ...generated,
+          timings: {
+            queueMs,
+            browserMs,
+            contextMs,
+            ...generated.timings,
+            totalMs: performance.now() - queuedAt
+          }
+        };
+      })();
+
+      return await waitWithPdfTimeout(operation, this.timeoutMs);
     } finally {
-      if (timeout) {
-        clearTimeout(timeout);
+      expired = true;
+      if (context) {
+        await closeContextWithin(context, this.timeoutMs);
       }
-      await context.close().catch(() => undefined);
     }
   }
 
diff --git a/apps/server/src/theme-registry.ts b/apps/server/src/theme-registry.ts
index 2394f5f..6ebb5ff 100644
--- a/apps/server/src/theme-registry.ts
+++ b/apps/server/src/theme-registry.ts
@@ -26,6 +26,7 @@ export interface ThemeRecord {
 export interface ThemeRegistryOptions {
   bundledRoot: string;
   localRoot: string;
+  onWarning?: (message: string) => void;
 }
 
 const assetContentTypes: Record<string, string> = {
@@ -92,7 +93,8 @@ async function resolveThemeFile(directory: string, relativePath: string) {
 
 async function readThemeRoot(
   root: string,
-  source: ThemeRecord["source"]
+  source: ThemeRecord["source"],
+  onWarning?: (message: string) => void
 ): Promise<ThemeRecord[]> {
   let entries;
   try {
@@ -139,6 +141,10 @@ async function readThemeRoot(
       });
     } catch (error) {
       const message = error instanceof Error ? error.message : String(error);
+      if (source === "local") {
+        onWarning?.(`已忽略无效本地主题 ${entry.name}：${message}`);
+        continue;
+      }
       throw new Error(`主题 ${entry.name} 无效：${message}`);
     }
   }
@@ -272,7 +278,7 @@ export function createThemeRegistry(options: ThemeRegistryOptions) {
   async function list() {
     const [bundledThemes, localThemes] = await Promise.all([
       readThemeRoot(options.bundledRoot, "bundled"),
-      readThemeRoot(options.localRoot, "local")
+      readThemeRoot(options.localRoot, "local", options.onWarning)
     ]);
 
     const themes = [...bundledThemes, ...localThemes];
diff --git a/apps/server/tests/app.test.ts b/apps/server/tests/app.test.ts
index 5461e2d..08d17af 100644
--- a/apps/server/tests/app.test.ts
+++ b/apps/server/tests/app.test.ts
@@ -110,6 +110,20 @@ describe("预览 API", () => {
     expect(response.json().error).toBe("INVALID_MARKDOWN");
   });
 
+  it("将无效 Front Matter 映射为文档请求错误", async () => {
+    app = buildApp({ logger: false });
+    const response = await app.inject({
+      method: "POST",
+      url: "/api/render",
+      payload: {
+        markdown: "---\ntitle: [未闭合\n---\n\n# 文档"
+      }
+    });
+
+    expect(response.statusCode).toBe(400);
+    expect(response.json().error).toBe("INVALID_FRONT_MATTER");
+  });
+
   it("返回内置主题 CSS", async () => {
     app = buildApp();
     const response = await app.inject({
@@ -237,6 +251,42 @@ describe("预览 API", () => {
     );
   });
 
+  it("忽略无效本地主题而不影响其他主题", async () => {
+    temporaryDirectory = await mkdtemp(join(tmpdir(), "md-to-pdf-theme-"));
+    const bundledRoot = join(temporaryDirectory, "bundled");
+    const localRoot = join(temporaryDirectory, "local");
+    const validThemeRoot = join(localRoot, "valid-theme");
+    const invalidThemeRoot = join(localRoot, "invalid-theme");
+    await mkdir(bundledRoot, { recursive: true });
+    await mkdir(validThemeRoot, { recursive: true });
+    await mkdir(invalidThemeRoot, { recursive: true });
+    await writeFile(
+      join(validThemeRoot, "theme.json"),
+      JSON.stringify(localThemeManifest("valid-theme")),
+      "utf8"
+    );
+    await writeFile(
+      join(validThemeRoot, "theme.css"),
+      "#write { color: #333; }",
+      "utf8"
+    );
+    const onWarning = vi.fn();
+    const registry = createThemeRegistry({
+      bundledRoot,
+      localRoot,
+      onWarning
+    });
+
+    await expect(registry.list()).resolves.toEqual([
+      expect.objectContaining({
+        manifest: expect.objectContaining({ id: "valid-theme" })
+      })
+    ]);
+    expect(onWarning).toHaveBeenCalledWith(
+      expect.stringContaining("invalid-theme")
+    );
+  });
+
   it("拒绝主题 CSS 导入外部地址", async () => {
     temporaryDirectory = await mkdtemp(join(tmpdir(), "md-to-pdf-theme-"));
     const bundledRoot = join(temporaryDirectory, "bundled");
@@ -357,6 +407,29 @@ describe("PDF API", () => {
     expect(response.json().error).toBe("INVALID_EXPORT_CONFIG");
   });
 
+  it("在 PDF 生成前拒绝无效 Front Matter", async () => {
+    const generate = vi.fn();
+    app = buildApp({
+      logger: false,
+      pdfGenerator: {
+        generate,
+        close: vi.fn(async () => undefined)
+      }
+    });
+    const response = await app.inject({
+      method: "POST",
+      url: "/api/pdf",
+      payload: {
+        markdown: "---\ntitle: [未闭合\n---\n",
+        exportConfig: defaultExportConfig
+      }
+    });
+
+    expect(response.statusCode).toBe(400);
+    expect(response.json().error).toBe("INVALID_FRONT_MATTER");
+    expect(generate).not.toHaveBeenCalled();
+  });
+
   it("映射 PDF 队列已满错误", async () => {
     app = buildApp({
       logger: false,
diff --git a/apps/server/tests/pdf-engine.test.ts b/apps/server/tests/pdf-engine.test.ts
index c80235b..a9a5f2e 100644
--- a/apps/server/tests/pdf-engine.test.ts
+++ b/apps/server/tests/pdf-engine.test.ts
@@ -29,7 +29,10 @@ function payload(): PdfRenderPayload {
   };
 }
 
-function fakeBrowser(options: { hangOnGoto?: boolean } = {}) {
+function fakeBrowser(
+  options: { hangOnGoto?: boolean; hangOnNewContext?: boolean } = {}
+) {
+  let releaseNewContext: (() => void) | undefined;
   const route = vi.fn();
   const closeContext = vi.fn(async () => undefined);
   const closeBrowser = vi.fn(async () => undefined);
@@ -65,7 +68,14 @@ function fakeBrowser(options: { hangOnGoto?: boolean } = {}) {
     close: closeContext
   };
   const browser = {
-    newContext: vi.fn(async () => context),
+    newContext: options.hangOnNewContext
+      ? vi.fn(
+          () =>
+            new Promise<typeof context>((resolve) => {
+              releaseNewContext = () => resolve(context);
+            })
+        )
+      : vi.fn(async () => context),
     close: closeBrowser,
     on: vi.fn()
   } as unknown as Browser;
@@ -77,6 +87,9 @@ function fakeBrowser(options: { hangOnGoto?: boolean } = {}) {
     context,
     page,
     pdfBuffer,
+    releaseNewContext() {
+      releaseNewContext?.();
+    },
     route
   };
 }
@@ -240,4 +253,39 @@ describe("Playwright PDF 生成器", () => {
     expect(fake.closeContext).toHaveBeenCalledTimes(1);
     await generator.close();
   });
+
+  it("浏览器启动阶段也受生成超时限制", async () => {
+    const fake = fakeBrowser();
+    let releaseBrowser: (() => void) | undefined;
+    const generator = new PlaywrightPdfGenerator({
+      launchBrowser: () =>
+        new Promise<Browser>((resolve) => {
+          releaseBrowser = () => resolve(fake.browser);
+        }),
+      timeoutMs: 10
+    });
+
+    await expect(generator.generate(payload())).rejects.toBeInstanceOf(
+      PdfRenderTimeoutError
+    );
+    releaseBrowser?.();
+    await new Promise((resolve) => setTimeout(resolve, 0));
+    await generator.close();
+  });
+
+  it("上下文创建阶段也受生成超时限制并清理迟到上下文", async () => {
+    const fake = fakeBrowser({ hangOnNewContext: true });
+    const generator = new PlaywrightPdfGenerator({
+      launchBrowser: async () => fake.browser,
+      timeoutMs: 10
+    });
+
+    await expect(generator.generate(payload())).rejects.toBeInstanceOf(
+      PdfRenderTimeoutError
+    );
+    fake.releaseNewContext();
+    await new Promise((resolve) => setTimeout(resolve, 0));
+    expect(fake.closeContext).toHaveBeenCalledTimes(1);
+    await generator.close();
+  });
 });
diff --git a/apps/web/src/App.tsx b/apps/web/src/App.tsx
index cceccdb..f203727 100644
--- a/apps/web/src/App.tsx
+++ b/apps/web/src/App.tsx
@@ -608,6 +608,9 @@ export function App() {
   }
 
   function handlePreviewModeChange(mode: PreviewMode) {
+    if (mode === previewMode) {
+      return;
+    }
     setPreviewMode(mode);
     setPreviewFrameReady(false);
     setPreviewPagination({ current: 0, total: 0 });
diff --git a/apps/web/src/ExportSettingsDrawer.tsx b/apps/web/src/ExportSettingsDrawer.tsx
index cda91da..11e9a0e 100644
--- a/apps/web/src/ExportSettingsDrawer.tsx
+++ b/apps/web/src/ExportSettingsDrawer.tsx
@@ -1,5 +1,6 @@
 import {
   getPaperDimensionsMm,
+  lengthToMillimeters,
   paperFormatLabels,
   supportedMermaidLayouts,
   supportedMermaidLooks,
@@ -76,10 +77,6 @@ const mermaidFontFamilies = [
   "Consolas, Microsoft YaHei, monospace"
 ] as const;
 
-function millimeters(value: string) {
-  return Number.parseFloat(value.replace(/mm$/i, ""));
-}
-
 function fitMarginPair(
   first: number,
   second: number,
@@ -103,16 +100,18 @@ function LengthInput({
   maximum,
   onChange
 }: LengthInputProps) {
-  const [draft, setDraft] = useState(String(millimeters(value)));
+  const [draft, setDraft] = useState(
+    String(lengthToMillimeters(value))
+  );
 
   useEffect(() => {
-    setDraft(String(millimeters(value)));
+    setDraft(String(lengthToMillimeters(value)));
   }, [value]);
 
   function commit() {
     const number = Number.parseFloat(draft);
     if (!Number.isFinite(number)) {
-      setDraft(String(millimeters(value)));
+      setDraft(String(lengthToMillimeters(value)));
       return;
     }
     const normalized = Math.min(Math.max(number, 0), maximum);
@@ -231,13 +230,13 @@ export function ExportSettingsDrawer({
       nextPaper.orientation
     );
     const [left, right] = fitMarginPair(
-      millimeters(nextPaper.margins.left),
-      millimeters(nextPaper.margins.right),
+      lengthToMillimeters(nextPaper.margins.left),
+      lengthToMillimeters(nextPaper.margins.right),
       nextDimensions.width - 1
     );
     const [top, bottom] = fitMarginPair(
-      millimeters(nextPaper.margins.top),
-      millimeters(nextPaper.margins.bottom),
+      lengthToMillimeters(nextPaper.margins.top),
+      lengthToMillimeters(nextPaper.margins.bottom),
       nextDimensions.height - 1
     );
 
@@ -380,7 +379,9 @@ export function ExportSettingsDrawer({
                 label="上"
                 value={margins.top}
                 maximum={
-                  dimensions.height - millimeters(margins.bottom) - verticalGap
+                  dimensions.height -
+                  lengthToMillimeters(margins.bottom) -
+                  verticalGap
                 }
                 onChange={(value) => updateMargin("top", value)}
               />
@@ -388,7 +389,9 @@ export function ExportSettingsDrawer({
                 label="右"
                 value={margins.right}
                 maximum={
-                  dimensions.width - millimeters(margins.left) - horizontalGap
+                  dimensions.width -
+                  lengthToMillimeters(margins.left) -
+                  horizontalGap
                 }
                 onChange={(value) => updateMargin("right", value)}
               />
@@ -396,7 +399,9 @@ export function ExportSettingsDrawer({
                 label="下"
                 value={margins.bottom}
                 maximum={
-                  dimensions.height - millimeters(margins.top) - verticalGap
+                  dimensions.height -
+                  lengthToMillimeters(margins.top) -
+                  verticalGap
                 }
                 onChange={(value) => updateMargin("bottom", value)}
               />
@@ -404,7 +409,9 @@ export function ExportSettingsDrawer({
                 label="左"
                 value={margins.left}
                 maximum={
-                  dimensions.width - millimeters(margins.right) - horizontalGap
+                  dimensions.width -
+                  lengthToMillimeters(margins.right) -
+                  horizontalGap
                 }
                 onChange={(value) => updateMargin("left", value)}
               />
diff --git a/apps/web/src/paged-document-runtime.ts b/apps/web/src/paged-document-runtime.ts
index 8e7c470..71ec3f1 100644
--- a/apps/web/src/paged-document-runtime.ts
+++ b/apps/web/src/paged-document-runtime.ts
@@ -2,10 +2,14 @@ import highlightCss from "highlight.js/styles/github.css?inline";
 import katexCss from "katex/dist/katex.min.css?inline";
 import { Previewer } from "pagedjs";
 import { createMermaidSiteConfig } from "./mermaid-config";
-import { fitOversizedMermaidToPage } from "./mermaid-page-fit";
+import {
+  fitOversizedMermaidToPage,
+  getPageContentDimensions
+} from "./mermaid-page-fit";
 import { renderMermaidDefinitions } from "./mermaid-renderer";
 import { replaceMermaidSvgWithImages } from "./mermaid-static-image";
 import type { MermaidOutputMode } from "./mermaid-static-image";
+import { enablePrintMediaForPreview } from "./preview-styles";
 import "./paged-table-handler";
 import {
   buildPagedMediaCss,
@@ -70,6 +74,54 @@ function stylesheet(
   };
 }
 
+function mountMeasurementContainer(
+  documentRef: Document,
+  content: DocumentFragment,
+  payload: PagedPreviewPayload,
+  target: PagedRenderTarget
+) {
+  const pageContent = getPageContentDimensions(payload.exportConfig);
+  const style = documentRef.createElement("style");
+  const themeCss =
+    target === "preview"
+      ? enablePrintMediaForPreview(payload.themeCss)
+      : payload.themeCss;
+  style.dataset.pagedMeasurementStyle = "true";
+  style.textContent = [
+    documentBaseCss,
+    highlightCss,
+    katexCss,
+    themeCss,
+    documentGeometryCss
+  ].join("\n");
+
+  const host = documentRef.createElement("div");
+  host.dataset.pagedMeasurementHost = "true";
+  host.style.cssText = [
+    "position: fixed",
+    "left: -100000px",
+    "top: 0",
+    `width: ${pageContent.width}px`,
+    "height: auto",
+    "opacity: 0",
+    "pointer-events: none",
+    "contain: layout style paint"
+  ].join(";");
+
+  documentRef.head.append(style);
+  host.append(content);
+  documentRef.body.append(host);
+
+  return {
+    host,
+    restore() {
+      content.append(...Array.from(host.childNodes));
+      host.remove();
+      style.remove();
+    }
+  };
+}
+
 function applyPageNumbers(
   container: ParentNode,
   payload: PagedPreviewPayload,
@@ -233,16 +285,37 @@ export class PagedDocumentRuntime {
     const mermaidErrors = await this.renderMermaid(content, payload);
     const mermaidMs = performance.now() - mermaidStartedAt;
 
-    const mermaidFitStartedAt = performance.now();
-    fitOversizedMermaidToPage(content, payload.exportConfig);
-    const mermaidFitMs = performance.now() - mermaidFitStartedAt;
+    let mermaidFitMs = 0;
+    let mermaidConversionMs = 0;
+    if (content.querySelector(".mermaid svg")) {
+      const measurement = mountMeasurementContainer(
+        documentRef,
+        content,
+        payload,
+        options.target
+      );
+      try {
+        await documentRef.fonts.ready;
+        await waitForImages(measurement.host);
 
-    const mermaidConversionStartedAt = performance.now();
-    if (options.mermaidOutput === "svg-image") {
-      replaceMermaidSvgWithImages(content);
+        const mermaidFitStartedAt = performance.now();
+        fitOversizedMermaidToPage(
+          measurement.host,
+          payload.exportConfig
+        );
+        mermaidFitMs = performance.now() - mermaidFitStartedAt;
+
+        const mermaidConversionStartedAt = performance.now();
+        if (options.mermaidOutput === "svg-image") {
+          replaceMermaidSvgWithImages(measurement.host);
+          await waitForImages(measurement.host);
+        }
+        mermaidConversionMs =
+          performance.now() - mermaidConversionStartedAt;
+      } finally {
+        measurement.restore();
+      }
     }
-    const mermaidConversionMs =
-      performance.now() - mermaidConversionStartedAt;
 
     if (!shouldContinue()) {
       return undefined;
diff --git a/packages/renderer/src/render-markdown.ts b/packages/renderer/src/render-markdown.ts
index a0bbbe4..53a6b55 100644
--- a/packages/renderer/src/render-markdown.ts
+++ b/packages/renderer/src/render-markdown.ts
@@ -13,6 +13,15 @@ import sanitizeHtml from "sanitize-html";
 
 export const RENDERER_VERSION = 1;
 
+export class MarkdownDocumentParseError extends Error {
+  readonly code = "INVALID_FRONT_MATTER";
+
+  constructor(message: string, options?: ErrorOptions) {
+    super(message, options);
+    this.name = "MarkdownDocumentParseError";
+  }
+}
+
 export interface MarkdownDocumentMetadata {
   title: string;
   author: string;
@@ -198,9 +207,10 @@ function parseFrontMatter(source: string) {
     return matter(source);
   } catch (error) {
     const message = error instanceof Error ? error.message : "未知错误";
-    throw new Error(`无法解析 Markdown Front Matter：${message}`, {
-      cause: error
-    });
+    throw new MarkdownDocumentParseError(
+      `无法解析 Markdown Front Matter：${message}`,
+      { cause: error }
+    );
   }
 }
 
diff --git a/packages/renderer/tests/render-markdown.test.ts b/packages/renderer/tests/render-markdown.test.ts
index 6cd15b1..a131062 100644
--- a/packages/renderer/tests/render-markdown.test.ts
+++ b/packages/renderer/tests/render-markdown.test.ts
@@ -1,5 +1,8 @@
 import { describe, expect, it } from "vitest";
-import { renderMarkdown } from "../src/render-markdown.js";
+import {
+  MarkdownDocumentParseError,
+  renderMarkdown
+} from "../src/render-markdown.js";
 
 describe("renderMarkdown", () => {
   it("渲染常用 Markdown 扩展并识别能力", () => {
@@ -71,6 +74,17 @@ lang: zh-CN
     });
   });
 
+  it("使用稳定错误类型报告无效 Front Matter", () => {
+    expect(() =>
+      renderMarkdown(`---
+title: [未闭合
+---
+
+# 文档
+`)
+    ).toThrow(MarkdownDocumentParseError);
+  });
+
   it("服务端渲染公式并保留 Mermaid 安全占位", () => {
     const result = renderMarkdown(`
 内联公式 $E=mc^2$。