diff --git a/packages/desktop/package.json b/packages/desktop/package.json
index 35b982fd13..af7d1f7045 100644
--- a/packages/desktop/package.json
+++ b/packages/desktop/package.json
@@ -107,7 +107,8 @@
     "vega-embed": "^7.1.0",
     "vue-i18n": "^11.4.6",
     "vue-router": "^4.6.4",
-    "webfontloader": "^1.6.28"
+    "webfontloader": "^1.6.28",
+    "write-file-atomic": "^7.0.1"
   },
   "optionalDependencies": {
     "native-keymap": "^3.3.9"
@@ -126,6 +127,7 @@
     "@types/node": "^22.20.0",
     "@types/turndown": "^5.0.6",
     "@types/webfontloader": "^1.6.38",
+    "@types/write-file-atomic": "^4.0.3",
     "@vitejs/plugin-vue": "^6.0.7",
     "@vitest/coverage-v8": "^4.1.9",
     "cross-env": "^10.1.0",
diff --git a/packages/desktop/src/main/editorBufferStore/index.ts b/packages/desktop/src/main/editorBufferStore/index.ts
index e4f7a186b6..db24feb18d 100644
--- a/packages/desktop/src/main/editorBufferStore/index.ts
+++ b/packages/desktop/src/main/editorBufferStore/index.ts
@@ -1,5 +1,6 @@
 import fs from 'fs'
 import path from 'path'
+import writeFileAtomic from 'write-file-atomic'
 import { BrowserWindow, ipcMain, type IpcMainInvokeEvent } from 'electron'
 import { TypedEmitter } from '@shared/types/typedEmitter'
 import type BaseWindow from '../windows/base'
@@ -32,7 +33,6 @@ class EditorBufferStore extends TypedEmitter<EditorBufferStoreEvents> {
   bufferStores: Record<string, BufferStoreEntry> | null
   serviceName: string
   encryptKeys: string[]
-  writeSequence: number
 
   constructor(paths: EditorBufferStorePaths) {
     super()
@@ -45,7 +45,6 @@ class EditorBufferStore extends TypedEmitter<EditorBufferStoreEvents> {
     this.bufferStores = null
     this.serviceName = 'marktext'
     this.encryptKeys = []
-    this.writeSequence = 0
 
     this.init()
   }
@@ -177,26 +176,12 @@ class EditorBufferStore extends TypedEmitter<EditorBufferStoreEvents> {
   }
 
   writeBufferStoreFile(filePath: string, newState: unknown): void {
-    const tempPath = path.join(
-      path.dirname(filePath),
-      `.${path.basename(filePath)}.${process.pid}.${Date.now()}.${++this.writeSequence}.tmp`
-    )
-
-    try {
-      // Write temp file first, then rename to the final file for atomicity
-      // and reduced risk of data corruption.
-      fs.writeFileSync(tempPath, JSON.stringify(newState), 'utf8')
-      fs.renameSync(tempPath, filePath)
-    } catch (err) {
-      try {
-        if (fs.existsSync(tempPath)) {
-          fs.unlinkSync(tempPath)
-        }
-      } catch (cleanupErr) {
-        console.error('Failed to clean up temporary buffer store file', cleanupErr)
-      }
-      throw err
-    }
+    // Durable atomic write: write-file-atomic writes to a temp file, fsyncs it,
+    // then renames it over the target. The previous temp-file + rename here was
+    // namespace-atomic (crash-safe) but omitted the fsync, so a power loss could
+    // still leave this crash-recovery buffer — which holds unsaved tab content —
+    // truncated or zero-filled, the same gap the document save path had (#3786).
+    writeFileAtomic.sync(filePath, JSON.stringify(newState), 'utf8')
   }
 
   updateBufferState(e: IpcMainInvokeEvent, newState: unknown): boolean {
diff --git a/packages/desktop/src/main/filesystem/index.ts b/packages/desktop/src/main/filesystem/index.ts
index ccf848bf51..2180b3f819 100644
--- a/packages/desktop/src/main/filesystem/index.ts
+++ b/packages/desktop/src/main/filesystem/index.ts
@@ -1,5 +1,6 @@
-import { readlinkSync, outputFile, type WriteFileOptions } from 'fs-extra'
+import { readlinkSync, ensureDir } from 'fs-extra'
 import path from 'path'
+import writeFileAtomic from 'write-file-atomic'
 import { isDirectory, isFile, isSymbolicLink } from 'common/filesystem'
 
 /**
@@ -21,19 +22,28 @@ export const normalizeAndResolvePath = (pathname: string): string => {
   return path.resolve(pathname)
 }
 
-export const writeFile = (
+export const writeFile = async(
   pathname: string,
   content: string | Buffer,
   extension?: string,
-  options: WriteFileOptions | undefined = 'utf-8'
+  options: BufferEncoding | undefined = 'utf-8'
 ): Promise<void> => {
   if (!pathname) {
     return Promise.reject(new Error('[ERROR] Cannot save file without path.'))
   }
   pathname = !extension || pathname.endsWith(extension) ? pathname : `${pathname}${extension}`
 
-  // `outputFile` creates any missing parent directories before writing, so a
-  // save whose folder was moved/deleted recreates it and still succeeds —
-  // matching VS Code, and keeping (auto)save from ever silently failing (#3509).
-  return outputFile(pathname, content, options)
+  // write-file-atomic does not create parent directories; recreate a moved or
+  // deleted folder first so an (auto)save into it still succeeds (#3509).
+  await ensureDir(path.dirname(pathname))
+
+  // Durable atomic save: write to a temp file in the target's directory, fsync
+  // it, then rename it over the target. This survives an application crash AND
+  // a power loss / OS reboot — the fsync before the rename is what closes the
+  // power-loss window that otherwise leaves a full-length, zero-filled file
+  // (#3786, #3828); a bare rename is only namespace-atomic, not data-durable.
+  // write-file-atomic also preserves the target's mode/owner, writes through a
+  // symlink to its target, and uses a unique temp name — all of which a plain
+  // temp+rename dropped.
+  await writeFileAtomic(pathname, content, options)
 }
diff --git a/packages/desktop/src/main/filesystem/markdown.ts b/packages/desktop/src/main/filesystem/markdown.ts
index 52a4a8564c..e7f7069756 100644
--- a/packages/desktop/src/main/filesystem/markdown.ts
+++ b/packages/desktop/src/main/filesystem/markdown.ts
@@ -81,7 +81,6 @@ export const writeMarkdownFile = (
 
   const buffer = iconv.encode(content, encoding, { addBOM: isBom })
 
-  // TODO(@fxha): "safeSaveDocuments" using temporary file and rename syscall.
   return writeFile(pathname, buffer, extension, undefined)
 }
 
diff --git a/packages/desktop/src/main/utils/imagePathAutoComplement.ts b/packages/desktop/src/main/utils/imagePathAutoComplement.ts
index 96933bb53a..38dc1c470b 100644
--- a/packages/desktop/src/main/utils/imagePathAutoComplement.ts
+++ b/packages/desktop/src/main/utils/imagePathAutoComplement.ts
@@ -64,12 +64,28 @@ const rebuild = (directory: string): void => {
 
 const watchDirectory = (directory: string): void => {
   if (watchers.has(directory)) return // Do not duplicate watch the same directory
-  const watcher = fs.watch(directory, (eventType, _filename) => {
-    if (eventType === 'rename') {
-      rebuild(directory)
-    }
-  })
-  watchers.set(directory, watcher)
+  try {
+    const watcher = fs.watch(directory, (eventType, _filename) => {
+      if (eventType === 'rename') {
+        rebuild(directory)
+      }
+    })
+    // Some directories become unwatchable after construction (network mounts
+    // dropping, permission changes); swallow the error and stop watching
+    // rather than leaking an uncaught exception into the main process.
+    watcher.on('error', (err) => {
+      log.error('imagePathAutoComplement::watchDirectory:', err)
+      watcher.close()
+      watchers.delete(directory)
+    })
+    watchers.set(directory, watcher)
+  } catch (err) {
+    // `fs.watch` throws synchronously for directories the OS can't watch —
+    // e.g. UNC / \\wsl.localhost network paths on Windows (EISDIR). Image-path
+    // auto-complete must degrade to "not watching" instead of crashing the
+    // main process with an "Unexpected error" dialog (#3779).
+    log.error('imagePathAutoComplement::watchDirectory:', err)
+  }
 }
 
 export const searchFilesAndDir = (directory: string, key: string): Promise<DirOrImageEntry[]> => {
diff --git a/packages/desktop/test/unit/specs/buffer-store-durable.spec.ts b/packages/desktop/test/unit/specs/buffer-store-durable.spec.ts
new file mode 100644
index 0000000000..880763ec4c
--- /dev/null
+++ b/packages/desktop/test/unit/specs/buffer-store-durable.spec.ts
@@ -0,0 +1,52 @@
+import { mkdtempSync, readdirSync, readFileSync, rmSync } from 'fs'
+import { tmpdir } from 'os'
+import path from 'path'
+import { afterEach, describe, expect, it, vi } from 'vitest'
+
+// The store registers ipcMain handlers in its constructor; stub electron so the
+// module imports without a real main process. writeBufferStoreFile no longer
+// touches `this`, so we exercise it via the prototype without booting the store.
+vi.mock('electron', () => ({}))
+
+const { default: EditorBufferStore } = await import('main_renderer/editorBufferStore')
+
+// #4852 follow-up: the crash-recovery buffer holds unsaved tab content but used
+// a temp+rename with no fsync — the same power-loss zero-fill gap the document
+// save path had. writeBufferStoreFile now writes durably via write-file-atomic.
+const writeBufferStoreFile = EditorBufferStore.prototype.writeBufferStoreFile
+
+const dirs: string[] = []
+function tempDir(): string {
+  const d = mkdtempSync(path.join(tmpdir(), 'mt-buf-'))
+  dirs.push(d)
+  return d
+}
+
+afterEach(() => {
+  for (const d of dirs.splice(0)) rmSync(d, { recursive: true, force: true })
+})
+
+describe('EditorBufferStore.writeBufferStoreFile — durable atomic write (#4852 follow-up)', () => {
+  it('writes the state as JSON and leaves no temp file behind', () => {
+    const dir = tempDir()
+    const target = path.join(dir, 'buffer.json')
+    const state = { tabs: [{ id: '1', markdown: 'hello' }] }
+
+    writeBufferStoreFile(target, state)
+
+    expect(JSON.parse(readFileSync(target, 'utf8'))).toEqual(state)
+    // The temp file was renamed over the target — nothing left in the dir.
+    expect(readdirSync(dir)).toEqual(['buffer.json'])
+  })
+
+  it('overwrites an existing buffer file', () => {
+    const dir = tempDir()
+    const target = path.join(dir, 'buffer.json')
+
+    writeBufferStoreFile(target, { tabs: ['old'] })
+    writeBufferStoreFile(target, { tabs: ['new'] })
+
+    expect(JSON.parse(readFileSync(target, 'utf8'))).toEqual({ tabs: ['new'] })
+    expect(readdirSync(dir)).toEqual(['buffer.json'])
+  })
+})
diff --git a/packages/desktop/test/unit/specs/image-path-autocomplete.spec.ts b/packages/desktop/test/unit/specs/image-path-autocomplete.spec.ts
index de7a01f2be..423930fe8d 100644
--- a/packages/desktop/test/unit/specs/image-path-autocomplete.spec.ts
+++ b/packages/desktop/test/unit/specs/image-path-autocomplete.spec.ts
@@ -1,4 +1,4 @@
-import { describe, it, expect, beforeEach, afterEach } from 'vitest'
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest'
 import fs from 'fs'
 import os from 'os'
 import path from 'path'
@@ -103,4 +103,26 @@ describe('searchFilesAndDir', () => {
 
     await expect(searchFilesAndDir(missing, '')).rejects.toBeTruthy()
   })
+
+  it('still resolves when the directory cannot be watched (UNC/WSL paths, #3779)', async() => {
+    const dir = seedDir()
+    tmpDirs.push(dir)
+
+    // fs.watch throws synchronously for unwatchable dirs (e.g. \\wsl.localhost
+    // UNC paths on Windows -> EISDIR). This used to escape as an uncaught
+    // exception -> "Unexpected error in the main process" dialog.
+    const spy = vi.spyOn(fs, 'watch').mockImplementation(() => {
+      throw Object.assign(new Error('EISDIR: illegal operation on a directory, watch'), {
+        code: 'EISDIR'
+      })
+    })
+
+    const result = await searchFilesAndDir(dir, '')
+
+    expect(result.some((e) => e.file === 'a.png')).toBe(true)
+    // The unwatchable directory is simply not tracked.
+    expect(watchers.has(dir)).toBe(false)
+
+    spy.mockRestore()
+  })
 })
diff --git a/packages/desktop/test/unit/specs/write-file-atomic.spec.ts b/packages/desktop/test/unit/specs/write-file-atomic.spec.ts
new file mode 100644
index 0000000000..a712e7843a
--- /dev/null
+++ b/packages/desktop/test/unit/specs/write-file-atomic.spec.ts
@@ -0,0 +1,81 @@
+import {
+  chmodSync,
+  existsSync,
+  mkdtempSync,
+  readdirSync,
+  readFileSync,
+  rmSync,
+  statSync,
+  writeFileSync
+} from 'fs'
+import { tmpdir } from 'os'
+import path from 'path'
+import { afterEach, describe, expect, it } from 'vitest'
+import { writeFile } from 'main_renderer/filesystem'
+
+// #3786 / #3828: saves must survive an application crash AND a power loss.
+// writeFile writes to a temp file, fsyncs it, then renames it over the target
+// (via write-file-atomic), so an interrupted or unflushed write can never leave
+// the document truncated or zero-filled — and, unlike a plain temp+rename, the
+// target's permission mode is preserved across the save.
+
+const dirs: string[] = []
+function tempDir(): string {
+  const d = mkdtempSync(path.join(tmpdir(), 'mt-atomic-'))
+  dirs.push(d)
+  return d
+}
+
+afterEach(() => {
+  for (const d of dirs.splice(0)) rmSync(d, { recursive: true, force: true })
+})
+
+describe('writeFile — durable atomic save (#3786, #3828)', () => {
+  it('overwrites an existing file and leaves no temp file behind', async() => {
+    const dir = tempDir()
+    const target = path.join(dir, 'note.md')
+    writeFileSync(target, 'OLD')
+
+    await writeFile(target, 'NEW', undefined)
+
+    expect(readFileSync(target, 'utf-8')).toBe('NEW')
+    // The temp file was renamed over the target — nothing left in the dir.
+    expect(readdirSync(dir)).toEqual(['note.md'])
+  })
+
+  it('writes a Buffer payload (the markdown save path)', async() => {
+    const dir = tempDir()
+    const target = path.join(dir, 'note.md')
+
+    await writeFile(target, Buffer.from('buffered', 'utf-8'), undefined)
+
+    expect(readFileSync(target, 'utf-8')).toBe('buffered')
+  })
+
+  it('still recreates a missing parent directory (#3509)', async() => {
+    const base = tempDir()
+    const target = path.join(base, 'moved-away', 'note.md')
+
+    await writeFile(target, 'hello', undefined)
+
+    expect(existsSync(path.dirname(target))).toBe(true)
+    expect(readFileSync(target, 'utf-8')).toBe('hello')
+  })
+
+  it.skipIf(process.platform === 'win32')(
+    'preserves the target file\'s permission mode across a save',
+    async() => {
+      const dir = tempDir()
+      const target = path.join(dir, 'secret.md')
+      writeFileSync(target, 'v1')
+      chmodSync(target, 0o600)
+
+      await writeFile(target, 'v2', undefined)
+
+      expect(readFileSync(target, 'utf-8')).toBe('v2')
+      // A plain temp+rename would install a fresh 0o644 inode; write-file-atomic
+      // restores the original mode.
+      expect(statSync(target).mode & 0o777).toBe(0o600)
+    }
+  )
+})
diff --git a/packages/muya/src/block/commonMark/codeBlock/index.ts b/packages/muya/src/block/commonMark/codeBlock/index.ts
index f647508435..3c130750f2 100644
--- a/packages/muya/src/block/commonMark/codeBlock/index.ts
+++ b/packages/muya/src/block/commonMark/codeBlock/index.ts
@@ -2,7 +2,7 @@ import type { Muya } from '../../../muya';
 import type { ICodeBlockState } from '../../../state/types';
 import type { TBlockPath } from '../../types';
 import diff from 'fast-diff';
-import { diffToTextOp } from '../../../utils';
+import { diffToTextOp, firstWordOfInfo } from '../../../utils';
 import { operateClassName } from '../../../utils/dom';
 import logger from '../../../utils/logger';
 import { loadLanguage } from '../../../utils/prism';
@@ -72,8 +72,10 @@ class CodeBlock extends Parent {
             operateClassName(this.domNode!, 'add', 'mu-fenced-code');
         }
 
-        !!value
-        && loadLanguage(value)
+        // `value` is the full info string; load Prism for its first word only.
+        const language = firstWordOfInfo(value);
+        !!language
+        && loadLanguage(language)
             .then((infoList) => {
                 if (!Array.isArray(infoList))
                     return;
diff --git a/packages/muya/src/block/content/codeBlockContent/__tests__/infoStringHighlight.spec.ts b/packages/muya/src/block/content/codeBlockContent/__tests__/infoStringHighlight.spec.ts
new file mode 100644
index 0000000000..6aa947c227
--- /dev/null
+++ b/packages/muya/src/block/content/codeBlockContent/__tests__/infoStringHighlight.spec.ts
@@ -0,0 +1,40 @@
+// @vitest-environment happy-dom
+import { describe, expect, it } from 'vitest';
+import { Muya } from '../../../../muya';
+
+// The `meta.lang` field now holds the whole fenced info string; the language
+// used for the `language-*` class / Prism is derived as its first word
+// (`firstWordOfInfo`). A multi-word info string must therefore neither crash
+// the renderer (a space in `classList.add(`language-${lang}`)` would throw) nor
+// leak the attributes into the class. The async Prism highlight itself is
+// rAF-driven and does not run under happy-dom, so the highlighted class is
+// checked in the real app (see the plan's manual verification); here we lock
+// the crash-safety and the live-block round-trip.
+
+function boot(markdown: string): Muya {
+    const host = document.createElement('div');
+    document.body.appendChild(host);
+    const muya = new Muya(host, { markdown } as ConstructorParameters<typeof Muya>[1]);
+    muya.init();
+    return muya;
+}
+
+describe('code fence info string through the live block', () => {
+    it('does not crash on a language + attributes info string', () => {
+        expect(() => boot('```js title="app.js"\nconst a = 1\n```\n')).not.toThrow();
+    });
+
+    it('does not crash on a Pandoc attribute info string', () => {
+        expect(() => boot('```{example, listing1-name}\nx\n```\n')).not.toThrow();
+    });
+
+    it('never builds a language class token containing a space', () => {
+        const muya = boot('```js title="app.js"\nconst a = 1\n```\n');
+        expect(muya.domNode!.innerHTML).not.toContain('language-js title');
+    });
+
+    it('round-trips the full info string through the live block', () => {
+        const muya = boot('```js title="app.js"\nconst a = 1\n```\n');
+        expect(muya.getMarkdown()).toContain('```js title="app.js"');
+    });
+});
diff --git a/packages/muya/src/block/content/codeBlockContent/index.ts b/packages/muya/src/block/content/codeBlockContent/index.ts
index 6c57fc4200..a789f71fab 100644
--- a/packages/muya/src/block/content/codeBlockContent/index.ts
+++ b/packages/muya/src/block/content/codeBlockContent/index.ts
@@ -9,7 +9,7 @@ import type {
 import type Code from '../../commonMark/codeBlock/code';
 import type HTMLPreview from '../../commonMark/html/htmlPreview';
 import { HTML_TAGS, VOID_HTML_TAGS } from '../../../config';
-import { adjustOffset, escapeHTML } from '../../../utils';
+import { adjustOffset, escapeHTML, firstWordOfInfo } from '../../../utils';
 import { computeLineCount, repositionLineNumberSpans, syncLineNumbersSpans } from '../../../utils/codeBlockLineNumbers';
 import { getHighlightHtml, MARKER_HASH } from '../../../utils/highlightHTML';
 import prism, { loadedLanguages, transformAliasToOrigin, walkTokens } from '../../../utils/prism/index';
@@ -97,10 +97,15 @@ class CodeBlockContent extends Content {
         return content;
     }
 
+    // The language word for highlighting / tokenizing — the first word of the
+    // code container's info string (which may carry attributes, e.g.
+    // `js title="x"`). Every consumer of `_lang` wants the language, never the
+    // full info string (that is read from `meta.lang` directly by the language
+    // input), so derive it once here.
     private get _lang() {
         const { _codeContainer: codeContainer } = this;
 
-        return codeContainer ? codeContainer.lang : this._initialLang;
+        return firstWordOfInfo(codeContainer ? codeContainer.lang : this._initialLang);
     }
 
     /**
diff --git a/packages/muya/src/block/content/langInputContent/__tests__/editInfoString.spec.ts b/packages/muya/src/block/content/langInputContent/__tests__/editInfoString.spec.ts
new file mode 100644
index 0000000000..5644c0a84f
--- /dev/null
+++ b/packages/muya/src/block/content/langInputContent/__tests__/editInfoString.spec.ts
@@ -0,0 +1,43 @@
+// @vitest-environment happy-dom
+import { describe, expect, it } from 'vitest';
+import { Muya } from '../../../../muya';
+
+function boot(markdown: string): Muya {
+    const host = document.createElement('div');
+    document.body.appendChild(host);
+    const muya = new Muya(host, { markdown } as ConstructorParameters<typeof Muya>[1]);
+    muya.init();
+    return muya;
+}
+
+interface ILangInput {
+    domNode: HTMLElement;
+    inputHandler: () => void;
+}
+
+function firstLangInput(muya: Muya): ILangInput {
+    const codeBlock = muya.editor.scrollPage!.firstChild as unknown as {
+        firstContentInDescendant: () => ILangInput;
+    };
+    return codeBlock.firstContentInDescendant();
+}
+
+describe('language input edits the whole info string (#4770 follow-up)', () => {
+    it('keeps a typed multi-word info string instead of truncating it', () => {
+        const muya = boot('```js\nx\n```\n');
+        const li = firstLangInput(muya);
+        // Emulate typing the full info string into the language input, with the
+        // caret inside it (inputHandler reads the live selection).
+        li.domNode.textContent = 'js title="app.js"';
+        const range = document.createRange();
+        range.selectNodeContents(li.domNode);
+        range.collapse(false);
+        const selection = window.getSelection()!;
+        selection.removeAllRanges();
+        selection.addRange(range);
+
+        li.inputHandler();
+        muya.editor.jsonState.flush();
+        expect(muya.getMarkdown().split('\n')[0]).toBe('```js title="app.js"');
+    });
+});
diff --git a/packages/muya/src/block/content/langInputContent/index.ts b/packages/muya/src/block/content/langInputContent/index.ts
index 821da3cdb3..25ac1e0fd0 100644
--- a/packages/muya/src/block/content/langInputContent/index.ts
+++ b/packages/muya/src/block/content/langInputContent/index.ts
@@ -55,8 +55,10 @@ class LangInputContent extends Content {
 
     override inputHandler() {
         const textContent = this.domNode!.textContent ?? '';
-        const lang = textContent.split(/\s+/)[0];
-        this._updateLanguage(lang);
+        // Store the whole info string; the language is derived as its first word
+        // elsewhere (`firstWordOfInfo`). Previously this truncated at the first
+        // whitespace, which dropped `title="x"` / Pandoc attributes on edit.
+        this._updateLanguage(textContent);
     }
 
     override enterHandler(event: Event) {
diff --git a/packages/muya/src/locales/de.ts b/packages/muya/src/locales/de.ts
index 1fc782910c..49caad7d1f 100644
--- a/packages/muya/src/locales/de.ts
+++ b/packages/muya/src/locales/de.ts
@@ -16,12 +16,12 @@ export const de = {
         'Paragraph': 'Absatz',
         'Horizontal Line': 'Horizontale Linie',
         'Front Matter': 'Front Matter',
-        'Header 1': 'Überschrift 1',
-        'Header 2': 'Überschrift 2',
-        'Header 3': 'Überschrift 3',
-        'Header 4': 'Überschrift 4',
-        'Header 5': 'Überschrift 5',
-        'Header 6': 'Überschrift 6',
+        'Heading 1': 'Überschrift 1',
+        'Heading 2': 'Überschrift 2',
+        'Heading 3': 'Überschrift 3',
+        'Heading 4': 'Überschrift 4',
+        'Heading 5': 'Überschrift 5',
+        'Heading 6': 'Überschrift 6',
         'Table Block': 'Tabelle',
         'Display Math': 'Mathematische Formel',
         'HTML Block': 'HTML-Block',
@@ -34,7 +34,7 @@ export const de = {
         'Mermaid': 'Mermaid',
         'Plantuml': 'Plantuml',
         'basic blocks': 'Grundblöcke',
-        'headers': 'Überschriften',
+        'headings': 'Überschriften',
         'advanced blocks': 'Erweiterte Blöcke',
         'list blocks': 'Listen',
         'diagrams': 'Diagramme',
diff --git a/packages/muya/src/locales/en.ts b/packages/muya/src/locales/en.ts
index ed911ee141..da15c707dd 100644
--- a/packages/muya/src/locales/en.ts
+++ b/packages/muya/src/locales/en.ts
@@ -16,12 +16,12 @@ export const en = {
         'Paragraph': 'Paragraph',
         'Horizontal Line': 'Horizontal Line',
         'Front Matter': 'Front Matter',
-        'Header 1': 'Header 1',
-        'Header 2': 'Header 2',
-        'Header 3': 'Header 3',
-        'Header 4': 'Header 4',
-        'Header 5': 'Header 5',
-        'Header 6': 'Header 6',
+        'Heading 1': 'Heading 1',
+        'Heading 2': 'Heading 2',
+        'Heading 3': 'Heading 3',
+        'Heading 4': 'Heading 4',
+        'Heading 5': 'Heading 5',
+        'Heading 6': 'Heading 6',
         'Table Block': 'Table Block',
         'Display Math': 'Display Math',
         'HTML Block': 'HTML Block',
@@ -34,7 +34,7 @@ export const en = {
         'Mermaid': 'Mermaid',
         'Plantuml': 'Plantuml',
         'basic blocks': 'basic blocks',
-        'headers': 'headers',
+        'headings': 'headings',
         'advanced blocks': 'advanced blocks',
         'list blocks': 'list blocks',
         'diagrams': 'diagrams',
diff --git a/packages/muya/src/locales/es.ts b/packages/muya/src/locales/es.ts
index ea83bfcd95..1d1dd251a1 100644
--- a/packages/muya/src/locales/es.ts
+++ b/packages/muya/src/locales/es.ts
@@ -16,12 +16,12 @@ export const es = {
         'Paragraph': 'Párrafo',
         'Horizontal Line': 'Línea horizontal',
         'Front Matter': 'Front Matter',
-        'Header 1': 'Encabezado 1',
-        'Header 2': 'Encabezado 2',
-        'Header 3': 'Encabezado 3',
-        'Header 4': 'Encabezado 4',
-        'Header 5': 'Encabezado 5',
-        'Header 6': 'Encabezado 6',
+        'Heading 1': 'Encabezado 1',
+        'Heading 2': 'Encabezado 2',
+        'Heading 3': 'Encabezado 3',
+        'Heading 4': 'Encabezado 4',
+        'Heading 5': 'Encabezado 5',
+        'Heading 6': 'Encabezado 6',
         'Table Block': 'Tabla',
         'Display Math': 'Fórmula matemática',
         'HTML Block': 'Bloque HTML',
@@ -34,7 +34,7 @@ export const es = {
         'Mermaid': 'Mermaid',
         'Plantuml': 'Plantuml',
         'basic blocks': 'bloques básicos',
-        'headers': 'encabezados',
+        'headings': 'encabezados',
         'advanced blocks': 'bloques avanzados',
         'list blocks': 'listas',
         'diagrams': 'diagramas',
diff --git a/packages/muya/src/locales/fr.ts b/packages/muya/src/locales/fr.ts
index ae217566c3..622b4cd20e 100644
--- a/packages/muya/src/locales/fr.ts
+++ b/packages/muya/src/locales/fr.ts
@@ -16,12 +16,12 @@ export const fr = {
         'Paragraph': 'Paragraphe',
         'Horizontal Line': 'Ligne horizontale',
         'Front Matter': 'Front Matter',
-        'Header 1': 'Titre 1',
-        'Header 2': 'Titre 2',
-        'Header 3': 'Titre 3',
-        'Header 4': 'Titre 4',
-        'Header 5': 'Titre 5',
-        'Header 6': 'Titre 6',
+        'Heading 1': 'Titre 1',
+        'Heading 2': 'Titre 2',
+        'Heading 3': 'Titre 3',
+        'Heading 4': 'Titre 4',
+        'Heading 5': 'Titre 5',
+        'Heading 6': 'Titre 6',
         'Table Block': 'Tableau',
         'Display Math': 'Formule mathématique',
         'HTML Block': 'Bloc HTML',
@@ -34,7 +34,7 @@ export const fr = {
         'Mermaid': 'Mermaid',
         'Plantuml': 'Plantuml',
         'basic blocks': 'blocs de base',
-        'headers': 'titres',
+        'headings': 'titres',
         'advanced blocks': 'blocs avancés',
         'list blocks': 'listes',
         'diagrams': 'diagrammes',
diff --git a/packages/muya/src/locales/ja.ts b/packages/muya/src/locales/ja.ts
index b54a05e2eb..3ece39198e 100644
--- a/packages/muya/src/locales/ja.ts
+++ b/packages/muya/src/locales/ja.ts
@@ -16,12 +16,12 @@ export const ja = {
         'Paragraph': '一般段落',
         'Horizontal Line': '水平分割線',
         'Front Matter': '上部情報ブロック',
-        'Header 1': 'タイトル 1',
-        'Header 2': 'タイトル 2',
-        'Header 3': 'タイトル 3',
-        'Header 4': 'タイトル 4',
-        'Header 5': 'タイトル 5',
-        'Header 6': 'タイトル 6',
+        'Heading 1': 'タイトル 1',
+        'Heading 2': 'タイトル 2',
+        'Heading 3': 'タイトル 3',
+        'Heading 4': 'タイトル 4',
+        'Heading 5': 'タイトル 5',
+        'Heading 6': 'タイトル 6',
         'Table Block': '表',
         'Display Math': '数式',
         'HTML Block': 'HTMLブロック',
@@ -34,7 +34,7 @@ export const ja = {
         'Mermaid': 'Mermaid',
         'Plantuml': 'Plantuml',
         'basic blocks': '基礎ブロック',
-        'headers': 'タイトル',
+        'headings': 'タイトル',
         'advanced blocks': '高級ブロック',
         'list blocks': 'リスト',
         'diagrams': '図表',
diff --git a/packages/muya/src/locales/ko.ts b/packages/muya/src/locales/ko.ts
index 1d001234e3..51125fdc25 100644
--- a/packages/muya/src/locales/ko.ts
+++ b/packages/muya/src/locales/ko.ts
@@ -16,12 +16,12 @@ export const ko = {
         'Paragraph': '단락',
         'Horizontal Line': '수평선',
         'Front Matter': '머리말 블록',
-        'Header 1': '제목 1',
-        'Header 2': '제목 2',
-        'Header 3': '제목 3',
-        'Header 4': '제목 4',
-        'Header 5': '제목 5',
-        'Header 6': '제목 6',
+        'Heading 1': '제목 1',
+        'Heading 2': '제목 2',
+        'Heading 3': '제목 3',
+        'Heading 4': '제목 4',
+        'Heading 5': '제목 5',
+        'Heading 6': '제목 6',
         'Table Block': '표',
         'Display Math': '수식',
         'HTML Block': 'HTML 블록',
@@ -34,7 +34,7 @@ export const ko = {
         'Mermaid': 'Mermaid',
         'Plantuml': 'Plantuml',
         'basic blocks': '기본 블록',
-        'headers': '제목',
+        'headings': '제목',
         'advanced blocks': '고급 블록',
         'list blocks': '목록',
         'diagrams': '다이어그램',
diff --git a/packages/muya/src/locales/pt.ts b/packages/muya/src/locales/pt.ts
index 9c2728bdab..bd54634d90 100644
--- a/packages/muya/src/locales/pt.ts
+++ b/packages/muya/src/locales/pt.ts
@@ -16,12 +16,12 @@ export const pt = {
         'Paragraph': 'Parágrafo',
         'Horizontal Line': 'Linha horizontal',
         'Front Matter': 'Front Matter',
-        'Header 1': 'Título 1',
-        'Header 2': 'Título 2',
-        'Header 3': 'Título 3',
-        'Header 4': 'Título 4',
-        'Header 5': 'Título 5',
-        'Header 6': 'Título 6',
+        'Heading 1': 'Título 1',
+        'Heading 2': 'Título 2',
+        'Heading 3': 'Título 3',
+        'Heading 4': 'Título 4',
+        'Heading 5': 'Título 5',
+        'Heading 6': 'Título 6',
         'Table Block': 'Tabela',
         'Display Math': 'Fórmula matemática',
         'HTML Block': 'Bloco HTML',
@@ -34,7 +34,7 @@ export const pt = {
         'Mermaid': 'Mermaid',
         'Plantuml': 'Plantuml',
         'basic blocks': 'blocos básicos',
-        'headers': 'títulos',
+        'headings': 'títulos',
         'advanced blocks': 'blocos avançados',
         'list blocks': 'listas',
         'diagrams': 'diagramas',
diff --git a/packages/muya/src/locales/tr.ts b/packages/muya/src/locales/tr.ts
index 75ef60bd51..2772e6d9c3 100644
--- a/packages/muya/src/locales/tr.ts
+++ b/packages/muya/src/locales/tr.ts
@@ -16,12 +16,12 @@ export const tr = {
         'Paragraph': 'Paragraf',
         'Horizontal Line': 'Yatay Çizgi',
         'Front Matter': 'Ön Bilgi',
-        'Header 1': 'Başlık 1',
-        'Header 2': 'Başlık 2',
-        'Header 3': 'Başlık 3',
-        'Header 4': 'Başlık 4',
-        'Header 5': 'Başlık 5',
-        'Header 6': 'Başlık 6',
+        'Heading 1': 'Başlık 1',
+        'Heading 2': 'Başlık 2',
+        'Heading 3': 'Başlık 3',
+        'Heading 4': 'Başlık 4',
+        'Heading 5': 'Başlık 5',
+        'Heading 6': 'Başlık 6',
         'Table Block': 'Tablo Bloğu',
         'Display Math': 'Matematik Bloğu',
         'HTML Block': 'HTML Bloğu',
@@ -34,7 +34,7 @@ export const tr = {
         'Mermaid': 'Mermaid',
         'Plantuml': 'Plantuml',
         'basic blocks': 'temel bloklar',
-        'headers': 'başlıklar',
+        'headings': 'başlıklar',
         'advanced blocks': 'gelişmiş bloklar',
         'list blocks': 'liste blokları',
         'diagrams': 'diyagramlar',
diff --git a/packages/muya/src/locales/zh-CN.ts b/packages/muya/src/locales/zh-CN.ts
index d05b0fd135..01115928bf 100644
--- a/packages/muya/src/locales/zh-CN.ts
+++ b/packages/muya/src/locales/zh-CN.ts
@@ -16,12 +16,12 @@ export const zhCN = {
         'Paragraph': '普通段落',
         'Horizontal Line': '水平分割线',
         'Front Matter': '顶部信息块',
-        'Header 1': '标题 1',
-        'Header 2': '标题 2',
-        'Header 3': '标题 3',
-        'Header 4': '标题 4',
-        'Header 5': '标题 5',
-        'Header 6': '标题 6',
+        'Heading 1': '标题 1',
+        'Heading 2': '标题 2',
+        'Heading 3': '标题 3',
+        'Heading 4': '标题 4',
+        'Heading 5': '标题 5',
+        'Heading 6': '标题 6',
         'Table Block': '表格',
         'Display Math': '数学公式',
         'HTML Block': 'HTML块',
@@ -34,7 +34,7 @@ export const zhCN = {
         'Mermaid': 'Mermaid',
         'Plantuml': 'Plantuml',
         'basic blocks': '基础块',
-        'headers': '标题',
+        'headings': '标题',
         'advanced blocks': '高级块',
         'list blocks': '列表',
         'diagrams': '图表',
diff --git a/packages/muya/src/locales/zh-TW.ts b/packages/muya/src/locales/zh-TW.ts
index a2d5260cca..ea07c45e7c 100644
--- a/packages/muya/src/locales/zh-TW.ts
+++ b/packages/muya/src/locales/zh-TW.ts
@@ -16,12 +16,12 @@ export const zhTW = {
         'Paragraph': '一般段落',
         'Horizontal Line': '水平分隔線',
         'Front Matter': '頂部資訊區塊',
-        'Header 1': '標題 1',
-        'Header 2': '標題 2',
-        'Header 3': '標題 3',
-        'Header 4': '標題 4',
-        'Header 5': '標題 5',
-        'Header 6': '標題 6',
+        'Heading 1': '標題 1',
+        'Heading 2': '標題 2',
+        'Heading 3': '標題 3',
+        'Heading 4': '標題 4',
+        'Heading 5': '標題 5',
+        'Heading 6': '標題 6',
         'Table Block': '表格',
         'Display Math': '數學公式',
         'HTML Block': 'HTML 區塊',
@@ -34,7 +34,7 @@ export const zhTW = {
         'Mermaid': 'Mermaid',
         'Plantuml': 'Plantuml',
         'basic blocks': '基礎區塊',
-        'headers': '標題',
+        'headings': '標題',
         'advanced blocks': '進階區塊',
         'list blocks': '清單',
         'diagrams': '圖表',
diff --git a/packages/muya/src/state/__tests__/codeFenceInfoString.spec.ts b/packages/muya/src/state/__tests__/codeFenceInfoString.spec.ts
index b27a950e59..f32d7be57e 100644
--- a/packages/muya/src/state/__tests__/codeFenceInfoString.spec.ts
+++ b/packages/muya/src/state/__tests__/codeFenceInfoString.spec.ts
@@ -34,20 +34,4 @@ describe('#4770: fenced code block info string round-trip', () => {
         expect(out).toContain('```\n');
         expect(out).not.toContain('```undefined');
     });
-
-    it('uses the edited language when a stored info string is now stale', () => {
-    // Emulates the user opening ```{example, listing1-name} then changing the
-    // language to `python` via the language input: `lang` no longer matches the
-    // stored info's first word, so serialization must emit the edited language.
-        const states = [
-            {
-                name: 'code-block' as const,
-                meta: { type: 'fenced', lang: 'python', info: '{example, listing1-name}' },
-                text: 'x',
-            },
-        ];
-        const out = new ExportMarkdown({ listIndentation: 1 }).generate(states);
-        expect(out).toContain('```python\n');
-        expect(out).not.toContain('example');
-    });
 });
diff --git a/packages/muya/src/state/__tests__/infoStringModel.spec.ts b/packages/muya/src/state/__tests__/infoStringModel.spec.ts
new file mode 100644
index 0000000000..e907ee2068
--- /dev/null
+++ b/packages/muya/src/state/__tests__/infoStringModel.spec.ts
@@ -0,0 +1,25 @@
+import { describe, expect, it } from 'vitest';
+import { MarkdownToState } from '../markdownToState';
+
+function codeMeta(md: string): { type: string; lang: string } {
+    const states = new MarkdownToState().generate(md) as Array<{
+        name: string;
+        meta?: { type: string; lang: string };
+    }>;
+    const block = states.find(s => s.name === 'code-block')!;
+    return block.meta!;
+}
+
+describe('info string is stored whole on meta.lang', () => {
+    it('keeps a language + attributes verbatim', () => {
+        expect(codeMeta('```js title="app.js"\nx\n```\n').lang).toBe('js title="app.js"');
+    });
+
+    it('keeps a Pandoc attribute block verbatim', () => {
+        expect(codeMeta('```{example, listing1-name}\nx\n```\n').lang).toBe('{example, listing1-name}');
+    });
+
+    it('stores a plain language as-is', () => {
+        expect(codeMeta('```js\nx\n```\n').lang).toBe('js');
+    });
+});
diff --git a/packages/muya/src/state/markdownToState.ts b/packages/muya/src/state/markdownToState.ts
index facfeca41a..1c44532f7d 100644
--- a/packages/muya/src/state/markdownToState.ts
+++ b/packages/muya/src/state/markdownToState.ts
@@ -10,6 +10,7 @@ import type {
     ITaskListState,
     TState,
 } from './types';
+import { firstWordOfInfo } from '../utils';
 import logger from '../utils/logger';
 import { lexBlock } from '../utils/marked';
 
@@ -415,10 +416,10 @@ export class MarkdownToState {
         trimUnnecessaryCodeBlockEmptyLines: boolean,
         fenceLength?: number,
     ): TState {
-        // GH#697, markedjs#1387 — strip everything past the first
-        // whitespace; `\S*` matches the empty string so this is
-        // always non-null even for `infoString === ''`.
-        const lang = (infoString || '').match(/\S*/)?.[0] ?? '';
+        // Keep the whole info string; the language for highlighting / diagram
+        // detection is its first word (CommonMark §4.5).
+        const info = (infoString || '').trim();
+        const lang = firstWordOfInfo(info);
 
         let value = text;
         // Fix: #1265.
@@ -449,17 +450,14 @@ export class MarkdownToState {
         // but `'fenced'` reaches us at runtime via the
         // walkTokens assignment — hence the cast.
         const isFenced = (codeBlockStyle as 'indented' | 'fenced' | undefined) === 'fenced';
-        // Preserve the full info string when it carries more than the language
-        // word (attributes like `title="x"`, or a Pandoc/RMarkdown `{…}` block),
-        // so the fence round-trips instead of collapsing to its first word (#4770).
-        const info = infoString || '';
         return {
             name: 'code-block' as const,
             meta: {
                 type: isFenced ? 'fenced' : 'indented',
-                lang,
+                // The full info string verbatim (empty for indented blocks); the
+                // language is its first word — see `firstWordOfInfo`.
+                lang: info,
                 ...(isFenced && fenceLength && fenceLength > 3 ? { fenceLength } : {}),
-                ...(isFenced && info !== lang ? { info } : {}),
             },
             text: value,
         };
diff --git a/packages/muya/src/state/stateToMarkdown.ts b/packages/muya/src/state/stateToMarkdown.ts
index 4064479bc4..bb05294123 100644
--- a/packages/muya/src/state/stateToMarkdown.ts
+++ b/packages/muya/src/state/stateToMarkdown.ts
@@ -353,17 +353,12 @@ export default class ExportMarkdown {
         const result = [];
         const { text, meta } = state;
         const textList = text.split('\n');
+        // `meta.lang` holds the full info string verbatim, so emit it as-is.
         const { type, lang } = meta;
-        // Emit the preserved full info string (`js title="x"`, Pandoc `{…}`
-        // attributes), but only while `lang` is still its first word: once the
-        // language is edited the stored info is stale, so the edited language
-        // wins (#4770).
-        const info
-            = meta.info && meta.info.match(/\S*/)?.[0] === lang ? meta.info : lang;
 
         if (type === 'fenced') {
             const fence = '`'.repeat(this._codeFenceLength(text, meta.fenceLength));
-            result.push(`${indent}${info ? `${fence}${info}\n` : `${fence}\n`}`);
+            result.push(`${indent}${lang ? `${fence}${lang}\n` : `${fence}\n`}`);
             textList.forEach((text) => {
                 result.push(`${indent}${text}\n`);
             });
diff --git a/packages/muya/src/state/types.ts b/packages/muya/src/state/types.ts
index 3500d3fa76..8f9f03a2bc 100644
--- a/packages/muya/src/state/types.ts
+++ b/packages/muya/src/state/types.ts
@@ -29,13 +29,11 @@ export interface ICodeBlockState {
     name: 'code-block';
     meta: {
         type: string; // "indented" | "fenced";
+        // The full fenced info string, verbatim (e.g. `js`, `js title="x"`, or a
+        // Pandoc/RMarkdown `{…}` block). The language for highlighting is its
+        // first word — derive via `firstWordOfInfo()`, never assume a single word.
         lang: string;
         fenceLength?: number;
-        // Full fenced info string when it carries more than the language word
-        // (e.g. `js title="x"` or a Pandoc/RMarkdown `{…}` attribute block).
-        // `lang` keeps just the first word for highlighting; `info` preserves
-        // the whole string so the fence round-trips losslessly (#4770).
-        info?: string;
     };
     text: string;
 }
diff --git a/packages/muya/src/ui/paragraphQuickInsertMenu/__tests__/search.spec.ts b/packages/muya/src/ui/paragraphQuickInsertMenu/__tests__/search.spec.ts
index 7b5c25840c..fcd73884cf 100644
--- a/packages/muya/src/ui/paragraphQuickInsertMenu/__tests__/search.spec.ts
+++ b/packages/muya/src/ui/paragraphQuickInsertMenu/__tests__/search.spec.ts
@@ -85,7 +85,7 @@ describe('paragraphQuickInsertMenu search() — zh-CN localized matching', () =>
         const sectionNames = menu.renderData.map(d => d.name);
         expect(sectionNames).toEqual([
             'basic blocks',
-            'headers',
+            'headings',
             'advanced blocks',
             'list blocks',
             'diagrams',
@@ -99,6 +99,17 @@ describe('paragraphQuickInsertMenu search() — zh-CN localized matching', () =>
             'thematic-break',
             'frontmatter',
         ]);
+
+        // h1-h6 are "headings" in CommonMark, not "headers" (#3811).
+        const headings = menu.renderData.find(d => d.name === 'headings')!;
+        expect(headings.children.map(c => c.title)).toEqual([
+            'Heading 1',
+            'Heading 2',
+            'Heading 3',
+            'Heading 4',
+            'Heading 5',
+            'Heading 6',
+        ]);
     });
 
     it('search(localized fragment) keeps only sections whose i18nTitle matched', () => {
diff --git a/packages/muya/src/ui/paragraphQuickInsertMenu/config.ts b/packages/muya/src/ui/paragraphQuickInsertMenu/config.ts
index 41751f435a..7d4d20234e 100644
--- a/packages/muya/src/ui/paragraphQuickInsertMenu/config.ts
+++ b/packages/muya/src/ui/paragraphQuickInsertMenu/config.ts
@@ -100,10 +100,10 @@ export const MENU_CONFIG: IQuickInsertMenuItem[] = [
         ],
     },
     {
-        name: 'headers',
+        name: 'headings',
         children: [
             {
-                title: 'Header 1',
+                title: 'Heading 1',
                 subTitle: '# Lorem Ipsum...',
                 label: 'atx-heading 1',
                 shortCut: `${COMMAND_KEY}+1`,
@@ -116,7 +116,7 @@ export const MENU_CONFIG: IQuickInsertMenuItem[] = [
                 icon: header1Icon,
             },
             {
-                title: 'Header 2',
+                title: 'Heading 2',
                 subTitle: '## Lorem Ipsum...',
                 label: 'atx-heading 2',
                 shortCut: `${COMMAND_KEY}+2`,
@@ -129,7 +129,7 @@ export const MENU_CONFIG: IQuickInsertMenuItem[] = [
                 icon: header2Icon,
             },
             {
-                title: 'Header 3',
+                title: 'Heading 3',
                 subTitle: '### Lorem Ipsum...',
                 label: 'atx-heading 3',
                 shortCut: `${COMMAND_KEY}+3`,
@@ -142,7 +142,7 @@ export const MENU_CONFIG: IQuickInsertMenuItem[] = [
                 icon: header3Icon,
             },
             {
-                title: 'Header 4',
+                title: 'Heading 4',
                 subTitle: '#### Lorem Ipsum...',
                 label: 'atx-heading 4',
                 shortCut: `${COMMAND_KEY}+4`,
@@ -155,7 +155,7 @@ export const MENU_CONFIG: IQuickInsertMenuItem[] = [
                 icon: header4Icon,
             },
             {
-                title: 'Header 5',
+                title: 'Heading 5',
                 subTitle: '##### Lorem Ipsum...',
                 label: 'atx-heading 5',
                 shortCut: `${COMMAND_KEY}+5`,
@@ -168,7 +168,7 @@ export const MENU_CONFIG: IQuickInsertMenuItem[] = [
                 icon: header5Icon,
             },
             {
-                title: 'Header 6',
+                title: 'Heading 6',
                 subTitle: '###### Lorem Ipsum...',
                 label: 'atx-heading 6',
                 shortCut: `${COMMAND_KEY}+6`,
diff --git a/packages/muya/src/utils/__tests__/firstWordOfInfo.spec.ts b/packages/muya/src/utils/__tests__/firstWordOfInfo.spec.ts
new file mode 100644
index 0000000000..fc46906940
--- /dev/null
+++ b/packages/muya/src/utils/__tests__/firstWordOfInfo.spec.ts
@@ -0,0 +1,21 @@
+import { describe, expect, it } from 'vitest';
+import { firstWordOfInfo } from '../index';
+
+describe('firstWordOfInfo', () => {
+    it('returns the whole word for a plain language', () => {
+        expect(firstWordOfInfo('js')).toBe('js');
+    });
+
+    it('returns the first word for a language + attributes', () => {
+        expect(firstWordOfInfo('js title="app.js"')).toBe('js');
+    });
+
+    it('returns the first token for a Pandoc-style attribute block', () => {
+        expect(firstWordOfInfo('{example, listing1-name}')).toBe('{example,');
+    });
+
+    it('returns empty string for empty / whitespace info', () => {
+        expect(firstWordOfInfo('')).toBe('');
+        expect(firstWordOfInfo('   ')).toBe('');
+    });
+});
diff --git a/packages/muya/src/utils/index.ts b/packages/muya/src/utils/index.ts
index 7d49fbb368..71c578c790 100644
--- a/packages/muya/src/utils/index.ts
+++ b/packages/muya/src/utils/index.ts
@@ -50,6 +50,14 @@ export const isLengthEven = (str = '') => str.length % 2 === 0;
 export function snakeToCamel(name: string) {
     return name.replace(/_([a-z])/g, (_p0, p1) => p1.toUpperCase());
 }
+
+// The fenced code block info string's first non-whitespace run is the
+// "language" used for syntax highlighting and the `language-*` class
+// (CommonMark §4.5). The rest of the info string is preserved as-is on the
+// block so the fence round-trips.
+export function firstWordOfInfo(info: string): string {
+    return info.match(/\S*/)?.[0] ?? '';
+}
 /**
  *  Are two arrays have intersection
  */
diff --git a/packages/muya/src/utils/prism/__tests__/loadLanguageDependencyOrder.spec.ts b/packages/muya/src/utils/prism/__tests__/loadLanguageDependencyOrder.spec.ts
new file mode 100644
index 0000000000..4e5016b86b
--- /dev/null
+++ b/packages/muya/src/utils/prism/__tests__/loadLanguageDependencyOrder.spec.ts
@@ -0,0 +1,49 @@
+// @vitest-environment happy-dom
+
+// Regression for the flaky `c++`/`cpp` load: Prism components load their
+// dependencies via `getLoader().load()`. Without a Promise `chainer`, the
+// loader fires a dependent component's import without awaiting its dependency,
+// so `cpp` (whose grammar `extend`s `c`) could evaluate before `c` was
+// registered — `Prism.languages.extend('c', …)` then ran on `undefined` and
+// threw "Cannot set properties of undefined (setting 'class-name')", which also
+// left the load promise unresolved (a hang, surfacing as a CI test timeout).
+// The fix loads in dependency order; this pins that contract.
+
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import prism, { loadLanguage } from '../index';
+import { loadedLanguages } from '../loadLanguage';
+
+function resetCppState() {
+    for (const lang of ['c', 'cpp']) {
+        delete (prism.languages as Record<string, unknown>)[lang];
+        loadedLanguages.delete(lang);
+    }
+}
+
+afterEach(() => {
+    vi.restoreAllMocks();
+});
+
+describe('loadLanguage — dependency load order (flaky c++ fix)', () => {
+    it('loads a dependency (`c`) before the dependent (`cpp`) that extends it', async () => {
+        resetCppState();
+
+        const addOrder: string[] = [];
+        const realAdd = loadedLanguages.add.bind(loadedLanguages);
+        vi.spyOn(loadedLanguages, 'add').mockImplementation((lang: string) => {
+            addOrder.push(lang);
+            return realAdd(lang);
+        });
+
+        await expect(loadLanguage('c++')).resolves.toBeDefined();
+
+        // `cpp` requires `c`; the fix guarantees `c` is registered first.
+        expect(addOrder).toContain('c');
+        expect(addOrder).toContain('cpp');
+        expect(addOrder.indexOf('c')).toBeLessThan(addOrder.indexOf('cpp'));
+
+        // And the resulting grammar is the valid extend-of-c, not `undefined`.
+        expect(prism.languages.cpp).toBeTruthy();
+        expect(() => prism.tokenize('int main(){}', prism.languages.cpp)).not.toThrow();
+    });
+});
diff --git a/packages/muya/src/utils/prism/loadLanguage.ts b/packages/muya/src/utils/prism/loadLanguage.ts
index 77d6dbc531..488a46d96d 100644
--- a/packages/muya/src/utils/prism/loadLanguage.ts
+++ b/packages/muya/src/utils/prism/loadLanguage.ts
@@ -1,6 +1,5 @@
 import components from 'prismjs/components.js';
 import getLoader from 'prismjs/dependencies';
-import { getDefer } from '../index';
 
 interface ILangLoadStatus {
     lang: string;
@@ -77,39 +76,43 @@ function initLoadLanguage(Prism: IPrismLike) {
         if (!Array.isArray(langs))
             langs = [langs];
 
-        const promises: Promise<ILangLoadStatus>[] = [];
+        const statuses: ILangLoadStatus[] = [];
         // The user might have loaded languages via some other way or used `prism.js` which already includes some
         // We don't need to validate the ids because `getLoader` will ignore invalid ones
         const loaded = [...loadedLanguages, ...Object.keys(Prism.languages)];
-        getLoader(components, langs, loaded).load(async (lang: string) => {
-            const defer = getDefer<ILangLoadStatus>();
-            promises.push(defer.promise);
+
+        const loadComponent = async (lang: string): Promise<void> => {
             if (!(lang in components.languages)) {
-                defer.resolve({
-                    lang,
-                    status: 'noexist',
-                });
-            }
-            else if (loadedLanguages.has(lang)) {
-                defer.resolve({
-                    lang,
-                    status: 'cached',
-                });
+                statuses.push({ lang, status: 'noexist' });
+                return;
             }
-            else {
-                delete Prism.languages[lang];
-                await import(
-                    `../../../node_modules/prismjs/components/prism-${lang}.js`,
-                );
-                defer.resolve({
-                    lang,
-                    status: 'loaded',
-                });
-                loadedLanguages.add(lang);
+            if (loadedLanguages.has(lang)) {
+                statuses.push({ lang, status: 'cached' });
+                return;
             }
+            delete Prism.languages[lang];
+            await import(
+                `../../../node_modules/prismjs/components/prism-${lang}.js`,
+            );
+            loadedLanguages.add(lang);
+            statuses.push({ lang, status: 'loaded' });
+        };
+
+        // Load in dependency order: a component whose grammar `extend`s another
+        // (e.g. `cpp` extends `c`) must be imported only AFTER its dependency has
+        // registered. The `chainer`'s `series`/`parallel` are Prism's async hooks
+        // (`Promise#then` / `Promise.all`); without it the loader fires the
+        // dependent's import without awaiting the dependency, racing them — if the
+        // dependent evaluates first, `Prism.languages.extend('c', …)` runs on
+        // `undefined` and throws "Cannot set properties of undefined (setting
+        // 'class-name')", which also left the load promise unresolved (a hang).
+        await getLoader(components, langs, loaded).load(loadComponent, {
+            series: (before: Promise<void>, after: () => Promise<void>) =>
+                before.then(after),
+            parallel: (values: Promise<void>[]) => Promise.all(values),
         });
 
-        return Promise.all(promises);
+        return statuses;
     };
 }
 
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 51b617fcde..61d01598eb 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -219,6 +219,9 @@ importers:
       webfontloader:
         specifier: ^1.6.28
         version: 1.6.28
+      write-file-atomic:
+        specifier: ^7.0.1
+        version: 7.0.1
     devDependencies:
       '@electron/rebuild':
         specifier: ^4.0.4
@@ -259,6 +262,9 @@ importers:
       '@types/webfontloader':
         specifier: ^1.6.38
         version: 1.6.38
+      '@types/write-file-atomic':
+        specifier: ^4.0.3
+        version: 4.0.3
       '@vitejs/plugin-vue':
         specifier: ^6.0.7
         version: 6.0.7(vite@7.3.5(@types/node@22.20.0)(jiti@2.7.0)(lightningcss@1.32.0)(terser@5.16.9)(tsx@4.22.4)(yaml@2.9.0))(vue@3.5.38(typescript@6.0.3))
@@ -3561,6 +3567,9 @@ packages:
   '@types/whatwg-mimetype@3.0.2':
     resolution: {integrity: sha512-c2AKvDT8ToxLIOUlN51gTiHXflsfIFisS4pO7pDPoKouJCESkhZnEy623gwP9laCy5lnLDAw1vAzu2vM2YLOrA==}
 
+  '@types/write-file-atomic@4.0.3':
+    resolution: {integrity: sha512-qdo+vZRchyJIHNeuI1nrpsLw+hnkgqP/8mlaN6Wle/NKhydHmUN9l4p3ZE8yP90AJNJW4uB8HQhedb4f1vNayQ==}
+
   '@types/ws@8.18.1':
     resolution: {integrity: sha512-ThVF6DCVhA8kUGy+aazFQ4kXQ7E1Ty7A3ypFOe0IcJV8O/M511G99AW24irKrW56Wt44yG9+ij8FaqoBGkuBXg==}
 
@@ -12504,6 +12513,10 @@ snapshots:
 
   '@types/whatwg-mimetype@3.0.2': {}
 
+  '@types/write-file-atomic@4.0.3':
+    dependencies:
+      '@types/node': 22.20.0
+
   '@types/ws@8.18.1':
     dependencies:
       '@types/node': 26.0.0
@@ -12906,7 +12919,7 @@ snapshots:
       magicast: 0.5.3
       obug: 2.1.3
       tinyrainbow: 3.1.0
-      vitest: 4.1.9(@opentelemetry/api@1.9.0)(@types/node@22.20.0)(@vitest/coverage-istanbul@4.1.9)(@vitest/coverage-v8@4.1.9)(happy-dom@20.10.6)(jsdom@29.1.1(@noble/hashes@2.2.0))(vite@7.3.5(@types/node@22.20.0)(jiti@2.7.0)(lightningcss@1.32.0)(terser@5.16.9)(tsx@4.22.4)(yaml@2.9.0))
+      vitest: 4.1.9(@opentelemetry/api@1.9.0)(@types/node@26.0.0)(@vitest/coverage-istanbul@4.1.9)(@vitest/coverage-v8@4.1.9)(happy-dom@20.10.6)(jsdom@29.1.1(@noble/hashes@2.2.0))(vite@8.0.16(@types/node@26.0.0)(esbuild@0.28.1)(jiti@2.7.0)(terser@5.16.9)(tsx@4.22.4)(yaml@2.9.0))
     transitivePeerDependencies:
       - supports-color
 
@@ -12922,7 +12935,7 @@ snapshots:
       obug: 2.1.3
       std-env: 4.1.0
       tinyrainbow: 3.1.0
-      vitest: 4.1.9(@opentelemetry/api@1.9.0)(@types/node@22.20.0)(@vitest/coverage-istanbul@4.1.9)(@vitest/coverage-v8@4.1.9)(happy-dom@20.10.6)(jsdom@29.1.1(@noble/hashes@2.2.0))(vite@7.3.5(@types/node@22.20.0)(jiti@2.7.0)(lightningcss@1.32.0)(terser@5.16.9)(tsx@4.22.4)(yaml@2.9.0))
+      vitest: 4.1.9(@opentelemetry/api@1.9.0)(@types/node@26.0.0)(@vitest/coverage-istanbul@4.1.9)(@vitest/coverage-v8@4.1.9)(happy-dom@20.10.6)(jsdom@29.1.1(@noble/hashes@2.2.0))(vite@8.0.16(@types/node@26.0.0)(esbuild@0.28.1)(jiti@2.7.0)(terser@5.16.9)(tsx@4.22.4)(yaml@2.9.0))
 
   '@vitest/eslint-plugin@1.6.20(@typescript-eslint/eslint-plugin@8.61.1(@typescript-eslint/parser@8.61.1(eslint@10.5.0(jiti@2.7.0))(typescript@6.0.3))(eslint@10.5.0(jiti@2.7.0))(typescript@6.0.3))(eslint@10.5.0(jiti@2.7.0))(typescript@6.0.3)(vitest@4.1.9)':
     dependencies: