src/vs/workbench/electron-sandbox/shared.desktop.main.ts/SharedDesktopMain/resolveWorkspaceInitializationPayload
class SharedDesktopMain:	private resolveWorkspaceInitializationPayload(environmentService: INativeWorkbenchEnvironmentService): IWorkspaceInitializationPayload {
		let workspaceInitializationPayload: IWorkspaceInitializationPayload | undefined = this.configuration.workspace;

		// Fallback to empty workspace if we have no payload yet.
		if (!workspaceInitializationPayload) {
			let id: string;
			if (this.configuration.backupPath) {
				id = basename(this.configuration.backupPath); // we know the backupPath must be a unique path so we leverage its name as workspace ID
			} else if (environmentService.isExtensionDevelopment) {
				id = 'ext-dev'; // extension development window never stores backups and is a singleton
			} else {
				throw new Error('Unexpected window configuration without backupPath');
			}

			workspaceInitializationPayload = { id };
		}

		return workspaceInitializationPayload;
	}