Fix extra empty paragraph in a fresh draft after reload

app/src/lib/local_project.test.ts

@@ -0,0 +1,24 @@
+import { describe, expect, it } from "vitest";
+import { defaultConfig } from "./config";
+import { loadIdentity } from "./identity";
+import { LocalProject } from "./project";
+
+describe("LocalProject.open", () => {
+  it("creates a single blank document when an empty project is opened twice concurrently", async () => {
+    const identity = await loadIdentity(defaultConfig);
+    const projectId = `concurrent-open-${crypto.randomUUID()}`;
+
+    const opened = await Promise.all([
+      LocalProject.open(identity, defaultConfig, projectId),
+      LocalProject.open(identity, defaultConfig, projectId),
+    ]);
+    for (const project of opened) project.destroy();
+
+    const reopened = await LocalProject.open(identity, defaultConfig, projectId);
+    try {
+      expect(reopened.snapshot().paragraphs).toHaveLength(1);
+    } finally {
+      reopened.destroy();
+    }
+  });
+});

app/src/lib/project.ts

@@ -223,6 +223,8 @@ const mapParagraph = (paragraph: ScreenplayParagraph) => {
   return map;
 };
 
+const openingProjects = new Map<string, Promise<LocalProject>>();
+
 export class LocalProject {
   readonly doc = new Y.Doc();
   readonly persistence: IndexeddbPersistence;
@@ -267,13 +269,24 @@ export class LocalProject {
     projectId = "local-draft",
     initialTitle = "Untitled screenplay",
   ) {
-    const project = new LocalProject(identity, projectId, config);
-    await project.persistence.whenSynced;
-    project.migrateParagraphText();
-    if (project.paragraphStore.length === 0) {
-      await project.createDocument(initialTitle);
+    // Opening the same empty project twice (e.g. a StrictMode double effect) would create two
+    // blank documents that merge in IndexedDB, so each open waits for the previous one to finish.
+    const previous = openingProjects.get(projectId);
+    const opening = (previous?.catch(() => undefined) ?? Promise.resolve()).then(async () => {
+      const project = new LocalProject(identity, projectId, config);
+      await project.persistence.whenSynced;
+      project.migrateParagraphText();
+      if (project.paragraphStore.length === 0) {
+        project.createDocument(initialTitle);
+      }
+      return project;
+    });
+    openingProjects.set(projectId, opening);
+    try {
+      return await opening;
+    } finally {
+      if (openingProjects.get(projectId) === opening) openingProjects.delete(projectId);
     }
-    return project;
   }
 
   subscribe = (listener: () => void) => {