diff --git a/tests/unit/editor-autosave.test.ts b/tests/unit/editor-autosave.test.ts
new file mode 100644
index 00000000..6d99af52
--- /dev/null
+++ b/tests/unit/editor-autosave.test.ts
@@ -0,0 +1,130 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+import { EditorAutosaveController } from "../../src/serialization/editor-autosave";
+
+function createSavedResult(message = "Autosave updated.") {
+  return {
+    status: "saved" as const,
+    message
+  };
+}
+
+describe("EditorAutosaveController", () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it("debounces repeated autosave schedules into one async save", async () => {
+    const saveDraft = vi.fn(async () => createSavedResult());
+    const autosave = new EditorAutosaveController({
+      debounceMs: 200,
+      saveDraft
+    });
+
+    autosave.schedule("document");
+    autosave.schedule("document");
+    autosave.schedule("document");
+
+    await vi.advanceTimersByTimeAsync(199);
+    expect(saveDraft).not.toHaveBeenCalled();
+
+    await vi.advanceTimersByTimeAsync(1);
+    expect(saveDraft).toHaveBeenCalledTimes(1);
+    expect(saveDraft).toHaveBeenCalledWith({
+      document: true,
+      viewportLayout: false
+    });
+  });
+
+  it("flushes a pending autosave immediately", async () => {
+    const saveDraft = vi.fn(async () => createSavedResult());
+    const autosave = new EditorAutosaveController({
+      debounceMs: 200,
+      saveDraft
+    });
+
+    autosave.schedule("viewport");
+    const flushResult = await autosave.flush();
+
+    expect(flushResult).toEqual({
+      status: "saved",
+      message: "Autosave updated."
+    });
+    expect(saveDraft).toHaveBeenCalledTimes(1);
+    expect(saveDraft).toHaveBeenCalledWith({
+      document: false,
+      viewportLayout: true
+    });
+
+    await vi.advanceTimersByTimeAsync(200);
+    expect(saveDraft).toHaveBeenCalledTimes(1);
+  });
+
+  it("reports autosave failures through the completion callback", async () => {
+    const onComplete = vi.fn();
+    const autosave = new EditorAutosaveController({
+      debounceMs: 100,
+      onComplete,
+      saveDraft: async () => ({
+        status: "error" as const,
+        message: "Autosave could not be saved. quota exceeded"
+      })
+    });
+
+    autosave.schedule("document");
+    await vi.advanceTimersByTimeAsync(100);
+
+    expect(onComplete).toHaveBeenCalledWith({
+      status: "error",
+      message: "Autosave could not be saved. quota exceeded"
+    });
+  });
+
+  it("coalesces in-flight autosaves into one latest follow-up save", async () => {
+    const resolvers: Array<(result: ReturnType<typeof createSavedResult>) => void> =
+      [];
+    const saveDraft = vi.fn(
+      () =>
+        new Promise<ReturnType<typeof createSavedResult>>((resolve) => {
+          resolvers.push(resolve);
+        })
+    );
+    const autosave = new EditorAutosaveController({
+      debounceMs: 10,
+      saveDraft
+    });
+
+    autosave.schedule("document");
+    await vi.advanceTimersByTimeAsync(10);
+
+    expect(saveDraft).toHaveBeenCalledTimes(1);
+    expect(saveDraft).toHaveBeenLastCalledWith({
+      document: true,
+      viewportLayout: false
+    });
+
+    autosave.schedule("viewport");
+    autosave.schedule("document");
+    await vi.advanceTimersByTimeAsync(10);
+
+    expect(saveDraft).toHaveBeenCalledTimes(1);
+
+    resolvers[0]!(createSavedResult("first"));
+    await vi.runAllTimersAsync();
+
+    expect(saveDraft).toHaveBeenCalledTimes(2);
+    expect(saveDraft).toHaveBeenLastCalledWith({
+      document: true,
+      viewportLayout: true
+    });
+
+    resolvers[1]!(createSavedResult("second"));
+    await vi.runAllTimersAsync();
+
+    expect(saveDraft).toHaveBeenCalledTimes(2);
+  });
+});