fix(photos): убрать мигание предпросмотра и задержку сброса правок

- фото и photo.updated несут edit_pending: рендер сохранённых правок ещё идёт
- клиент держит предпросмотр, пока серверная версия не загружена и не
  декодирована, поэтому оригинал не мелькает при подмене
- сброс возвратом контролов в значения по умолчанию виден сразу, не через 10 с
- Viewer берёт URL из актуального объекта (SSE), fresh остаётся фолбэком
- попутно исправлен порядок чтения tags и album_title в ListTrash

frontend/src/lib/viewer-source.test.ts

@@ -0,0 +1,120 @@
+import { describe, expect, it } from 'vitest';
+import type { Photo } from './types';
+import { computeViewerSource, editPendingOf } from './viewer-source';
+
+const BASE = {
+	originalUrl: '/orig.jpg',
+	previewUrl: '/preview.jpg',
+	editUrl: '/edit.jpg',
+	editPreviewUrl: '/edit-preview.jpg'
+};
+
+describe('computeViewerSource', () => {
+	it('shows the server render when it matches the saved edits', () => {
+		const src = computeViewerSource({
+			zoomed: false,
+			dirty: false,
+			editPending: false,
+			localParamsEmpty: false,
+			...BASE
+		});
+		expect(src.useBase).toBe(false);
+		expect(src.serverSrc).toBe('/edit-preview.jpg');
+		expect(src.baseSrc).toBe('/preview.jpg');
+	});
+
+	it('uses the full-size variants in zoom', () => {
+		const src = computeViewerSource({
+			zoomed: true,
+			dirty: false,
+			editPending: false,
+			localParamsEmpty: false,
+			...BASE
+		});
+		expect(src.serverSrc).toBe('/edit.jpg');
+		expect(src.baseSrc).toBe('/orig.jpg');
+	});
+
+	it('keeps the client preview while local edits are unsaved', () => {
+		const src = computeViewerSource({
+			zoomed: true,
+			dirty: true,
+			editPending: false,
+			localParamsEmpty: false,
+			...BASE
+		});
+		expect(src.useBase).toBe(true);
+		expect(src.drawCanvas).toBe(true);
+		expect(src.baseSrc).toBe('/orig.jpg');
+	});
+
+	it('shows the base version immediately when the edits are reset to defaults', () => {
+		const src = computeViewerSource({
+			zoomed: true,
+			dirty: true,
+			editPending: false,
+			localParamsEmpty: true,
+			...BASE
+		});
+		expect(src.useBase).toBe(true);
+		expect(src.drawCanvas).toBe(false);
+		expect(src.baseSrc).toBe('/orig.jpg');
+	});
+
+	it('ignores a stale server render while the saved edits are still rendering', () => {
+		const src = computeViewerSource({
+			zoomed: false,
+			dirty: false,
+			editPending: true,
+			localParamsEmpty: false,
+			...BASE
+		});
+		expect(src.useBase).toBe(true);
+		expect(src.drawCanvas).toBe(true);
+	});
+
+	it('keeps the client preview when a second edit is pending over an old render', () => {
+		const src = computeViewerSource({
+			zoomed: true,
+			dirty: false,
+			editPending: true,
+			localParamsEmpty: false,
+			...BASE
+		});
+		expect(src.useBase).toBe(true);
+		expect(src.drawCanvas).toBe(true);
+		expect(src.baseSrc).toBe('/orig.jpg');
+	});
+
+	it('falls back to the base version when there is no edit render', () => {
+		const src = computeViewerSource({
+			zoomed: false,
+			dirty: false,
+			editPending: false,
+			localParamsEmpty: true,
+			originalUrl: '/orig.jpg',
+			previewUrl: '/preview.jpg'
+		});
+		expect(src.useBase).toBe(true);
+		expect(src.drawCanvas).toBe(false);
+		expect(src.serverSrc).toBe('/preview.jpg');
+	});
+
+	it('prefers the full-size base when zoomed without a preview', () => {
+		const src = computeViewerSource({
+			zoomed: true,
+			dirty: false,
+			editPending: false,
+			localParamsEmpty: true,
+			originalUrl: '/orig.jpg'
+		});
+		expect(src.baseSrc).toBe('/orig.jpg');
+		expect(src.serverSrc).toBe('/orig.jpg');
+	});
+
+	it('treats the old backend without edit_pending as a finished render', () => {
+		expect(editPendingOf(undefined)).toBe(false);
+		expect(editPendingOf({ id: 'p' } as Photo)).toBe(false);
+		expect(editPendingOf({ id: 'p', edit_pending: true } as Photo)).toBe(true);
+	});
+});