Accept base64-encoded YT_COOKIES and auto-add Netscape header

HF secret fields can convert the Netscape format's required TAB characters into spaces,
which makes yt-dlp reject the cookie file. _cookiefile now auto-detects and decodes a
base64-encoded cookies.txt (tab-safe), and prepends the Netscape header if missing.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app.py

@@ -6,6 +6,8 @@ startup stays fast.
 """
 from __future__ import annotations
 
+import base64
+import binascii
 import os
 import re
 import shutil
@@ -36,13 +38,50 @@ VLM_CHOICES = [
 ]
 
 
+def _looks_like_netscape(text: str) -> bool:
+    """True if ``text`` is already a tab-separated Netscape cookie file."""
+    head = text.lstrip()
+    return head.startswith("#") or "\tTRUE\t" in text or "\tFALSE\t" in text
+
+
+def _maybe_b64_decode(text: str) -> str | None:
+    """If ``text`` is base64 that decodes to a cookie file, return the decoded text.
+
+    HF secret fields can turn the required TAB characters into spaces, which breaks the
+    Netscape format. Pasting base64 of the file avoids that; we auto-detect and decode it.
+    """
+    compact = "".join(text.split())
+    if len(compact) < 16 or re.search(r"[^A-Za-z0-9+/=]", compact):
+        return None
+    try:
+        decoded = base64.b64decode(compact, validate=True).decode("utf-8", "replace")
+    except (binascii.Error, ValueError):
+        return None
+    return decoded if _looks_like_netscape(decoded) else None
+
+
 def _cookiefile(workdir: str) -> str | None:
-    """Materialize the YT_COOKIES secret (Netscape cookie file contents) to disk."""
+    """Materialize the YT_COOKIES secret to a Netscape cookie file on disk.
+
+    Accepts either the raw cookies.txt contents (tabs preserved) or a base64 encoding of
+    them. A missing header line is added so yt-dlp accepts the file.
+    """
     data = os.environ.get("YT_COOKIES")
-    if not data:
+    if not data or not data.strip():
         return None
+
+    if not _looks_like_netscape(data):
+        decoded = _maybe_b64_decode(data)
+        if decoded:
+            data = decoded
+
+    if not data.lstrip().startswith(("# Netscape", "# HTTP")):
+        data = "# Netscape HTTP Cookie File\n" + data.lstrip("\n")
+    if not data.endswith("\n"):
+        data += "\n"
+
     path = os.path.join(workdir, "cookies.txt")
-    with open(path, "w", encoding="utf-8") as fh:
+    with open(path, "w", encoding="utf-8", newline="\n") as fh:
         fh.write(data)
     return path