fix(video): avoid a SQLite connection deadlock in the placeholder fallback

generateVideoPlaceholder() unconditionally called getThumbnailSettings(),
which queries the database directly (not through any active transaction).
videoProcessor.js's new placeholder fallback can run from inside
processUploadedPhotos' open per-file SQLite transaction (chunked video
upload) -- knex's default SQLite pool has exactly one connection, so
that second, un-transacted query deadlocks against the transaction
holding it, timing out after acquireConnectionTimeout (60s). Reproduced
directly against an isolated SQLite db.

generateVideoPlaceholder now skips the settings lookup entirely when
the caller supplies explicit width/height, and the video fallback
passes the same DEFAULT_THUMBNAIL_WIDTH/HEIGHT the settings lookup
would have fallen back to anyway (now exported for reuse).

Found by codex review.

backend/__tests__/services/videoPlaceholderNoDbLookup.test.js

@@ -0,0 +1,62 @@
+/**
+ * generateVideoPlaceholder() must not touch the database when the caller
+ * already supplies width/height (videoProcessor.js's thumbnail-generation
+ * fallback does exactly this).
+ *
+ * Why it matters: processUploadedPhotos() (chunked video upload) holds a
+ * per-file SQLite transaction open across thumbnail generation. SQLite's
+ * knex pool defaults to a single connection, so any second, un-transacted
+ * db() query made while that transaction is open blocks until
+ * acquireConnectionTimeout (60s in production) — verified directly against
+ * an isolated SQLite db (codex review of #1371/#1372). Passing explicit
+ * dimensions must skip getThumbnailSettings()'s db() call entirely, not
+ * just tolerate its failure.
+ */
+
+const path = require('path');
+const fs = require('fs').promises;
+const os = require('os');
+
+const mockDbSpy = jest.fn(() => {
+  throw new Error('db() must not be called when width/height are supplied');
+});
+jest.mock('../../src/database/db', () => ({ db: (...args) => mockDbSpy(...args) }));
+
+const storageModule = require('../../src/services/storage');
+const LocalFsStorage = require('../../src/services/storage/LocalFsStorage');
+
+describe('generateVideoPlaceholder skips the settings DB lookup given explicit dimensions', () => {
+  let storage;
+  let root;
+  let imageProcessor;
+
+  beforeAll(async () => {
+    root = await fs.mkdtemp(path.join(os.tmpdir(), 'picpeak-vidplaceholder-'));
+    storage = new LocalFsStorage({ root });
+    await storage.init();
+    storageModule.setStorageForTesting(storage);
+    imageProcessor = require('../../src/services/imageProcessor');
+  }, 30000);
+
+  afterAll(async () => {
+    storageModule.resetStorage();
+    await fs.rm(root, { recursive: true, force: true }).catch(() => {});
+  });
+
+  afterEach(() => mockDbSpy.mockClear());
+
+  it('never calls db() when width/height are provided', async () => {
+    const key = await imageProcessor.generateVideoPlaceholder('demo.mp4', { width: 300, height: 300 });
+
+    expect(key).toBe('thumbnails/thumb_demo.jpg');
+    expect(await storage.exists(key)).toBe(true);
+    expect(mockDbSpy).not.toHaveBeenCalled();
+  });
+
+  it('falls through to defaults (not a throw) when db() fails and no dimensions were given', async () => {
+    const key = await imageProcessor.generateVideoPlaceholder('demo2.mp4');
+
+    expect(key).toBe('thumbnails/thumb_demo2.jpg');
+    expect(mockDbSpy).toHaveBeenCalled();
+  });
+});

backend/src/services/__tests__/videoProcessor.test.js

@@ -4,7 +4,9 @@ jest.mock('../storage', () => ({
   getStorage: jest.fn()
 }));
 jest.mock('../imageProcessor', () => ({
-  generateVideoPlaceholder: jest.fn()
+  generateVideoPlaceholder: jest.fn(),
+  DEFAULT_THUMBNAIL_WIDTH: 300,
+  DEFAULT_THUMBNAIL_HEIGHT: 300
 }));
 
 const ffmpeg = require('fluent-ffmpeg');
@@ -98,7 +100,10 @@ describe('processUploadedVideo degrades gracefully instead of rejecting the whol
     expect(result.metadata).toEqual(expect.objectContaining({ duration: 5, videoCodec: 'h264' }));
     // thumbnailKey is always thumbnails/thumb_<name>.jpg — strip the prefix
     // back to a filename so generateVideoPlaceholder recomputes the same key.
-    expect(generateVideoPlaceholder).toHaveBeenCalledWith('wedding_001.jpg');
+    // Explicit width/height so generateVideoPlaceholder skips its DB-backed
+    // settings lookup — this can run inside an open per-file SQLite
+    // transaction (chunked video upload), where that lookup deadlocks.
+    expect(generateVideoPlaceholder).toHaveBeenCalledWith('wedding_001.jpg', { width: 300, height: 300 });
     expect(result.thumbnailKey).toBe('thumbnails/thumb_placeholder.jpg');
     expect(storage.putFromFile).not.toHaveBeenCalled();
   });

backend/src/services/imageProcessor.js

@@ -369,9 +369,15 @@ async function generateVideoPlaceholder(originalFilename, options = {}) {
   const thumbnailRelKey = path.posix.join('thumbnails', thumbnailFilename);
   const storage = getStorage();
 
-  const settings = await getThumbnailSettings();
-  const width = settings.width || DEFAULT_THUMBNAIL_WIDTH;
-  const height = settings.height || DEFAULT_THUMBNAIL_HEIGHT;
+  // Skip the settings lookup when the caller already supplies dimensions.
+  // This can run from inside an open per-file SQLite transaction (chunked
+  // video upload's fallback path in videoProcessor.js) — a second,
+  // un-transacted db() query for settings there deadlocks against SQLite's
+  // single-connection pool until acquireConnectionTimeout (60s), reproduced
+  // directly against an isolated SQLite db (codex review of #1371/#1372).
+  const settings = (options.width && options.height) ? {} : await getThumbnailSettings();
+  const width = options.width || settings.width || DEFAULT_THUMBNAIL_WIDTH;
+  const height = options.height || settings.height || DEFAULT_THUMBNAIL_HEIGHT;
 
   if (options.regenerate) {
     await storage.delete(thumbnailRelKey).catch(() => {});
@@ -864,4 +870,6 @@ module.exports = {
   ensurePreviewImage,
   extractCaptureDate,
   withLocalCopy,
+  DEFAULT_THUMBNAIL_WIDTH,
+  DEFAULT_THUMBNAIL_HEIGHT,
 };

backend/src/services/videoProcessor.js

@@ -190,9 +190,20 @@ async function processUploadedVideo(videoPath, thumbnailKey, options = {}) {
   // a filename so generateVideoPlaceholder recomputes this exact same key.
   if (!generatedThumbnailKey) {
     try {
-      const { generateVideoPlaceholder } = require('./imageProcessor');
+      const {
+        generateVideoPlaceholder,
+        DEFAULT_THUMBNAIL_WIDTH,
+        DEFAULT_THUMBNAIL_HEIGHT
+      } = require('./imageProcessor');
       const placeholderFilename = path.basename(thumbnailKey).replace(/^thumb_/, '');
-      const placeholderKey = await generateVideoPlaceholder(placeholderFilename);
+      // Explicit width/height make generateVideoPlaceholder skip its
+      // configured-thumbnail-size DB lookup (see its own comment) — this
+      // call can run from inside processUploadedPhotos' open per-file
+      // SQLite transaction, where that lookup would otherwise deadlock.
+      const placeholderKey = await generateVideoPlaceholder(placeholderFilename, {
+        width: DEFAULT_THUMBNAIL_WIDTH,
+        height: DEFAULT_THUMBNAIL_HEIGHT
+      });
       if (placeholderKey) {
         generatedThumbnailKey = placeholderKey;
       }