fix(workers): yt-dlp argv injection — scheme check + -- separator

The url passed to yt-dlp is user-controllable (via /api/capture). Any
string starting with '-' would be parsed as a flag (e.g.
--config-location=/etc/passwd). Mitigations:
1. Validate scheme is http(s) and hostname is present before subprocess.
2. Pass `--` to yt-dlp so it stops flag parsing before the positional
   URL.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

workers/void_workers/handlers/video.py

@@ -3,17 +3,34 @@ import json
 import os
 import subprocess
 import tempfile
+from urllib.parse import urlparse
 from .. import repo
 from ..model import whisper_transcribe
 
 NAME = "ingest.video"
 
 
+def _validate_url(url):
+    """yt-dlp accepts URLs as positional args; require http(s) scheme so a
+    crafted '--config-location=...' string can't smuggle a flag. We pass
+    `--` to yt-dlp too as belt + suspenders."""
+    try:
+        p = urlparse(url)
+    except Exception as e:
+        raise ValueError(f"invalid url: {e}")
+    if p.scheme not in ("http", "https"):
+        raise ValueError(f"unsupported scheme: {p.scheme}")
+    if not p.hostname:
+        raise ValueError("missing hostname")
+    return url
+
+
 def _yt_dlp_info(url):
     """Returns dict of metadata, or None if yt-dlp could not extract."""
+    safe = _validate_url(url)
     try:
         out = subprocess.check_output(
-            ["yt-dlp", "-J", "--no-warnings", "--no-playlist", url],
+            ["yt-dlp", "-J", "--no-warnings", "--no-playlist", "--", safe],
             timeout=60
         )
         return json.loads(out)
@@ -23,11 +40,12 @@ def _yt_dlp_info(url):
 
 def _yt_dlp_audio(url):
     """Downloads bestaudio to a temp .opus and returns the path."""
+    safe = _validate_url(url)
     tmp_dir = tempfile.mkdtemp(prefix="void-yt-")
     out_template = os.path.join(tmp_dir, "audio.%(ext)s")
     subprocess.run(
         ["yt-dlp", "-x", "--audio-format", "opus", "-o", out_template,
-         "--no-warnings", "--no-playlist", url],
+         "--no-warnings", "--no-playlist", "--", safe],
         check=True, timeout=600
     )
     for f in os.listdir(tmp_dir):