Add cookies file support for Docker; auto-detect /data/cookies.txt

backend/services/ytdlp.py

@@ -401,8 +401,11 @@ def predicted_file_path(video_id: str) -> Path:
 _SEMAPHORE = threading.Semaphore(3)
 _semaphore_lock = threading.Lock()
 _cookies_browser: str = ""
+_cookies_file: str = ""
 _cookies_lock = threading.Lock()
 
+_AUTO_COOKIES_PATHS = ["/data/cookies.txt"]
+
 
 def set_max_concurrent(n: int) -> None:
     global _SEMAPHORE
@@ -416,10 +419,27 @@ def set_cookies_browser(browser: str) -> None:
         _cookies_browser = browser.strip().lower()
 
 
+def set_cookies_file(path: str) -> None:
+    global _cookies_file
+    with _cookies_lock:
+        _cookies_file = path.strip()
+
+
 def _cookie_args() -> list[str]:
     with _cookies_lock:
+        cf = _cookies_file
         b = _cookies_browser
-    return ["--cookies-from-browser", b] if b else []
+    # Prefer explicit cookies file
+    if cf and Path(cf).exists():
+        return ["--cookies", cf]
+    # Auto-detect cookies.txt in well-known Docker locations
+    for candidate in _AUTO_COOKIES_PATHS:
+        if Path(candidate).exists():
+            return ["--cookies", candidate]
+    # Fall back to browser (works in local dev, not in Docker)
+    if b:
+        return ["--cookies-from-browser", b]
+    return []
 
 
 def start_download(