src/vs/workbench/browser/layout.ts/Layout/getInitialFilesToOpen
class Layout:	private getInitialFilesToOpen(): { filesToOpenOrCreate?: IPath[], filesToDiff?: IPath[]; } | undefined {

		// Check for editors from `defaultLayout` options first
		const defaultLayout = this.environmentService.options?.defaultLayout;
		if (defaultLayout?.editors?.length && (defaultLayout.force || this.storageService.isNew(StorageScope.WORKSPACE))) {
			this._openedDefaultEditors = true;

			return {
				filesToOpenOrCreate: defaultLayout.editors.map<IPath>(file => {
					return { fileUri: URI.revive(file.uri), openOnlyIfExists: file.openOnlyIfExists, editorOverrideId: file.openWith };
				})
			};
		}

		// Then check for files to open, create or diff from main side
		const { filesToOpenOrCreate, filesToDiff } = this.environmentService.configuration;
		if (filesToOpenOrCreate || filesToDiff) {
			return { filesToOpenOrCreate, filesToDiff };
		}

		return undefined;
	}