feat : refactor to use autosave.ts for stygian

lib/editor/autosave.test.ts

@@ -53,13 +53,13 @@ describe("AutosaveCoordinator", () => {
     expect(saves).toEqual([{ value: "สอง", expectedVersion: 1 }]);
   });
 
-  it("serializes a new edit behind an in-flight save", async () => {
+  it("waits for the idle delay before saving an edit made during a request", async () => {
     vi.useFakeTimers();
     let resolveFirst: ((value: AutosaveResponse) => void) | undefined;
     const saves: string[] = [];
     const coordinator = new AutosaveCoordinator({
       initialVersion: 4,
-      debounceMs: 10,
+      debounceMs: 100,
       createPayload: (value: string, expectedVersion) => ({ value, expectedVersion }),
       save: async ({ value, expectedVersion }) => {
         saves.push(`${value}:${expectedVersion}`);
@@ -72,15 +72,52 @@ describe("AutosaveCoordinator", () => {
       },
     });
     coordinator.schedule("แรก");
-    await advance(10);
+    await advance(100);
     coordinator.schedule("ล่าสุด");
-    await advance(10);
+    await advance(50);
     expect(saves).toEqual(["แรก:4"]);
     resolveFirst?.({ status: "saved", version: 5 });
     await advance(0);
+    expect(saves).toEqual(["แรก:4"]);
+    await advance(49);
+    expect(saves).toEqual(["แรก:4"]);
+    await advance(1);
     expect(saves).toEqual(["แรก:4", "ล่าสุด:5"]);
   });
 
+  it("uses an externally updated version and drops invalid pending drafts", async () => {
+    vi.useFakeTimers();
+    const { coordinator, saves } = harness();
+    coordinator.updateVersion(8);
+    coordinator.schedule("invalid");
+    coordinator.cancelPending();
+    await advance(750);
+    expect(saves).toEqual([]);
+    coordinator.schedule("valid");
+    await advance(750);
+    expect(saves).toEqual([{ value: "valid", expectedVersion: 8 }]);
+  });
+
+  it("does not save the same draft twice when it is queued during a request", async () => {
+    vi.useFakeTimers();
+    let resolveFirst: ((value: AutosaveResponse) => void) | undefined;
+    const save = vi.fn(() => new Promise<AutosaveResponse>((resolve) => {
+      resolveFirst = resolve;
+    }));
+    const coordinator = new AutosaveCoordinator({
+      initialVersion: 1,
+      debounceMs: 100,
+      createPayload: (draft: string) => draft,
+      save,
+    });
+    coordinator.schedule("same");
+    await advance(100);
+    coordinator.schedule("same");
+    resolveFirst?.({ status: "saved", version: 2 });
+    await advance(100);
+    expect(save).toHaveBeenCalledTimes(1);
+  });
+
   it("retries only transient failures with capped exponential delays", async () => {
     vi.useFakeTimers();
     const { coordinator, save } = harness([