feat: Start on new session restore, b=no-bug, c=no-component

prefs/browser.yaml

@@ -3,7 +3,8 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 - name: browser.startup.page
-  value: 3
+  value: 0
+  locked: true
 
 - name: browser.sessionstore.restore_pinned_tabs_on_demand
   value: true

src/zen/sessionstore/ZenSessionFile.sys.mjs

@@ -0,0 +1,27 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+const FILE_NAME = 'zen-sessions.jsonlz4';
+
+export class nsZenSessionFile {
+  #path;
+
+  #windows;
+
+  constructor() {
+    this.#path = PathUtils.join(profileDir, FILE_NAME);
+  }
+
+  async read() {
+    try {
+      return await IOUtils.readJSON(this.#path, { compress: true });
+    } catch (e) {
+      return {};
+    }
+  }
+
+  async write(data) {
+    await IOUtils.writeJSON(this.#path, data, { compress: true });
+  }
+}

src/zen/sessionstore/ZenSessionManager.sys.mjs

@@ -0,0 +1,50 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+import {
+  cancelIdleCallback,
+  clearTimeout,
+  requestIdleCallback,
+  setTimeout,
+} from 'resource://gre/modules/Timer.sys.mjs';
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  ZenSessionFile: 'resource://gre/modules/ZenSessionFile.sys.mjs',
+  PrivateBrowsingUtils: 'resource://gre/modules/PrivateBrowsingUtils.sys.mjs',
+  RunState: 'resource:///modules/sessionstore/RunState.sys.mjs',
+});
+
+class nsZenSessionManager {
+  #file;
+
+  constructor() {
+    this.#file = null;
+  }
+
+  get file() {
+    if (!this.#file) {
+      this.#file = lazy.ZenSessionFile;
+    }
+    return this.#file;
+  }
+
+  /**
+   * Saves the current session state. Collects data and writes to disk.
+   *
+   * @param forceUpdateAllWindows (optional)
+   *        Forces us to recollect data for all windows and will bypass and
+   *        update the corresponding caches.
+   */
+  saveState(forceUpdateAllWindows = false) {
+    if (lazy.PrivateBrowsingUtils.permanentPrivateBrowsing) {
+      // Don't save (or even collect) anything in permanent private
+      // browsing mode
+      return Promise.resolve();
+    }
+  }
+}
+
+export const ZenSessionStore = new nsZenSessionManager();

src/zen/sessionstore/ZenSessionWindow.sys.mjs

@@ -0,0 +1,35 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+export class ZenSessionWindow {
+  #id;
+  #selectedWorkspace;
+  #selectedTab;
+
+  constructor(id) {
+    this.#id = id;
+    this.#selectedWorkspace = null;
+    this.#selectedTab = null;
+  }
+
+  get id() {
+    return this.#id;
+  }
+
+  get selectedWorkspace() {
+    return this.#selectedWorkspace;
+  }
+
+  set selectedWorkspace(workspace) {
+    this.#selectedWorkspace = workspace;
+  }
+
+  get selectedTab() {
+    return this.#selectedTab;
+  }
+
+  set selectedTab(tab) {
+    this.#selectedTab = tab;
+  }
+}