fix(autosave) : retry constellation version conflicts

lib/editor/autosave.test.ts

@@ -2,6 +2,7 @@ import { afterEach, describe, expect, it, vi } from "vitest";
 
 import {
   AutosaveCoordinator,
+  saveWithConflictRetry,
   type AutosaveResponse,
   type AutosaveStatus,
 } from "./autosave";
@@ -114,3 +115,24 @@ describe("AutosaveCoordinator", () => {
     expect(invalid.statuses.at(-1)).toMatchObject({ state: "error", issues: ["title"] });
   });
 });
+
+describe("saveWithConflictRetry", () => {
+  it("retries one version conflict against the current server version", async () => {
+    const calls: number[] = [];
+    const save = vi.fn(async (_value: string, expectedVersion: number) => {
+      calls.push(expectedVersion);
+      if (calls.length === 1) return { status: "conflict" as const, currentVersion: 8 };
+      return { status: "saved" as const, version: 9 };
+    });
+    const result = await saveWithConflictRetry(save, "constellation draft", 7);
+    expect(calls).toEqual([7, 8]);
+    expect(result).toEqual({ response: { status: "saved", version: 9 }, version: 8, retried: true });
+  });
+
+  it("stops after one retry when another concurrent save wins", async () => {
+    const save = vi.fn(async (_value: string, expectedVersion: number) => ({ status: "conflict" as const, currentVersion: expectedVersion + 1 }));
+    const result = await saveWithConflictRetry(save, "constellation draft", 3);
+    expect(save).toHaveBeenCalledTimes(2);
+    expect(result.response).toEqual({ status: "conflict", currentVersion: 5 });
+  });
+});

lib/editor/autosave.ts

@@ -12,6 +12,22 @@ export type AutosaveStatus =
   | { state: "conflict"; currentVersion: number }
   | { state: "error"; message: string; issues?: string[] };
 
+export async function saveWithConflictRetry<Value, Response extends { status: string; currentVersion?: number }>(
+  save: (value: Value, expectedVersion: number) => Promise<Response>,
+  value: Value,
+  expectedVersion: number,
+): Promise<{ response: Response; version: number; retried: boolean }> {
+  const first = await save(value, expectedVersion);
+  if (first.status !== "conflict" || !first.currentVersion || first.currentVersion === expectedVersion) {
+    return { response: first, version: expectedVersion, retried: false };
+  }
+  return {
+    response: await save(value, first.currentVersion),
+    version: first.currentVersion,
+    retried: true,
+  };
+}
+
 interface AutosaveCoordinatorOptions<Draft, Payload, Snapshot> {
   initialVersion: number;
   createPayload: (draft: Draft, expectedVersion: number) => Payload;