diff --git a/packages/super-editor/src/components/SuperEditor.test.js b/packages/super-editor/src/components/SuperEditor.test.js
index bb6f812fb7..c73e4a73e4 100644
--- a/packages/super-editor/src/components/SuperEditor.test.js
+++ b/packages/super-editor/src/components/SuperEditor.test.js
@@ -237,6 +237,119 @@ describe('SuperEditor.vue', () => {
     wrapper.unmount();
   });
 
+  it('waits for collaboration sync before loading a provided file source for an empty room', async () => {
+    vi.useFakeTimers();
+
+    EditorConstructor.loadXmlData.mockResolvedValueOnce([
+      '<docx />',
+      { media: true },
+      { files: true },
+      { fonts: true },
+    ]);
+
+    const metaMap = {
+      has: vi.fn(() => false),
+      get: vi.fn(() => undefined),
+    };
+    const partsMap = { size: 0 };
+    const fragment = { length: 0, observe: vi.fn(), unobserve: vi.fn() };
+    const ydoc = {
+      getMap: vi.fn((name) => (name === 'parts' ? partsMap : metaMap)),
+      getXmlFragment: vi.fn(() => fragment),
+    };
+
+    const provider = {
+      listeners: {},
+      on: vi.fn((event, handler) => {
+        provider.listeners[event] = handler;
+      }),
+      off: vi.fn(),
+    };
+
+    const fileSource = new Blob([], { type: DOCX_MIME });
+    const wrapper = mount(SuperEditor, {
+      props: {
+        documentId: 'doc-first-client-with-file',
+        fileSource,
+        options: {
+          ydoc,
+          collaborationProvider: provider,
+        },
+      },
+    });
+
+    await flushPromises();
+
+    expect(EditorConstructor.loadXmlData).not.toHaveBeenCalled();
+    expect(EditorConstructor).not.toHaveBeenCalled();
+
+    const syncedHandler = provider.on.mock.calls.find(([event]) => event === 'synced')[1];
+    syncedHandler();
+    await flushPromises();
+
+    vi.advanceTimersByTime(200);
+    await flushPromises();
+
+    expect(EditorConstructor.loadXmlData).toHaveBeenCalledWith(fileSource);
+    expect(EditorConstructor).toHaveBeenCalledTimes(1);
+    expect(EditorConstructor.mock.calls[0][0].isNewFile).toBe(true);
+
+    wrapper.unmount();
+    vi.useRealTimers();
+  });
+
+  it('ignores a provided file source when the collaboration room already has content', async () => {
+    vi.useFakeTimers();
+
+    const metaMap = {
+      has: vi.fn(() => false),
+      get: vi.fn(() => undefined),
+    };
+    const partsMap = { size: 1 };
+    const fragment = { length: 5 };
+    const ydoc = {
+      getMap: vi.fn((name) => (name === 'parts' ? partsMap : metaMap)),
+      getXmlFragment: vi.fn(() => fragment),
+    };
+
+    const provider = {
+      listeners: {},
+      on: vi.fn((event, handler) => {
+        provider.listeners[event] = handler;
+      }),
+      off: vi.fn(),
+    };
+
+    const fileSource = new Blob([], { type: DOCX_MIME });
+    const wrapper = mount(SuperEditor, {
+      props: {
+        documentId: 'doc-existing-room-with-file',
+        fileSource,
+        options: {
+          ydoc,
+          collaborationProvider: provider,
+        },
+      },
+    });
+
+    await flushPromises();
+
+    expect(EditorConstructor.loadXmlData).not.toHaveBeenCalled();
+    expect(EditorConstructor).not.toHaveBeenCalled();
+
+    const syncedHandler = provider.on.mock.calls.find(([event]) => event === 'synced')[1];
+    syncedHandler();
+    await flushPromises();
+
+    expect(EditorConstructor.loadXmlData).not.toHaveBeenCalled();
+    expect(EditorConstructor).toHaveBeenCalledTimes(1);
+    expect(EditorConstructor.mock.calls[0][0].fragment).toStrictEqual(fragment);
+    expect(EditorConstructor.mock.calls[0][0].isNewFile).toBe(false);
+
+    wrapper.unmount();
+    vi.useRealTimers();
+  });
+
   it('waits for fragment settling and passes the shared fragment to the editor for existing rooms', async () => {
     vi.useFakeTimers();
 
diff --git a/packages/super-editor/src/components/SuperEditor.vue b/packages/super-editor/src/components/SuperEditor.vue
index 5448af5540..ffd91dc8cc 100644
--- a/packages/super-editor/src/components/SuperEditor.vue
+++ b/packages/super-editor/src/components/SuperEditor.vue
@@ -816,21 +816,21 @@ const notifyFileLoadError = () => {
   console.warn(FILE_LOAD_ERROR_MESSAGE);
 };
 
-const initializeData = async () => {
-  // If we have the file, initialize immediately from file
-  if (props.fileSource) {
-    let fileData = await loadNewFileData();
-    if (!fileData) {
-      // TODO: show a visible error to the user (toast removed with naive-ui)
-      notifyFileLoadError();
-      await setDefaultBlankFile();
-      fileData = await loadNewFileData();
-    }
-    return initEditor(fileData);
+const initEditorFromFileSource = async () => {
+  let fileData = await loadNewFileData();
+  if (!fileData) {
+    notifyFileLoadError();
+    await setDefaultBlankFile();
+    fileData = await loadNewFileData();
   }
+  return initEditor(fileData);
+};
 
-  // If we are in collaboration mode, wait for sync then initialize
-  else if (props.options.ydoc && props.options.collaborationProvider) {
+const initializeData = async () => {
+  // Collaboration startup must own room classification before we initialize
+  // from a local file source. Otherwise the editor can render local content
+  // while the shared room remains blank until a later async seed.
+  if (props.options.ydoc && props.options.collaborationProvider) {
     delete props.options.content;
     const ydoc = props.options.ydoc;
     const provider = props.options.collaborationProvider;
@@ -885,13 +885,19 @@ const initializeData = async () => {
 
         initEditor({});
       } else {
-        // First client — load blank document
+        // First client — seed the room from the provided file source, or
+        // fall back to the blank template if no file is provided.
         props.options.isNewFile = true;
         delete props.options.fragment;
-        const fileData = await loadNewFileData();
-        if (fileData) initEditor(fileData);
+        await initEditorFromFileSource();
       }
     });
+    return;
+  }
+
+  // Non-collaborative mode: initialize immediately from the provided file.
+  if (props.fileSource) {
+    return initEditorFromFileSource();
   }
 };