Add YtdlpClient: shared JSON invocation layer for yt-dlp

Every metadata call site previously built its own command list. The new
ytsage/core/ytsage_client.py centralizes binary resolution (managed,
verified binary only), cookie/proxy args from ConfigManager (with
session-state overrides), utf-8 output handling, process-group-safe
timeouts, and a short-TTL cache for flat/search results.

Provides fetch_video_info, fetch_flat_info, fetch_flat_entries (with
-I range pagination), search (ytsearchN:), and fetch_account_feed
(youtube.com/feed/subscriptions with cookies) plus a generic YtdlpWorker
QThread. AnalysisThread now delegates its subprocess execution to the
shared runner; its signal surface is unchanged.

Groundwork for the SageTube watch/search/browse/feed features.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ytsage/gui/ytsage_gui_analysis.py

@@ -1,16 +1,13 @@
 from typing import TYPE_CHECKING, Any, Dict, List, Optional, cast
 
 import json
-import os
-import signal
 import subprocess
-import sys
 from PySide6.QtCore import QMetaObject, Qt, Q_ARG, QThread, Signal, QTimer
 from PySide6.QtWidgets import QMessageBox
 
+from ..core.ytsage_client import run_ytdlp_capture
 from ..core.ytsage_utils import validate_video_url, parse_yt_dlp_error
 from ..core.ytsage_yt_dlp import get_yt_dlp_path
-from ..utils.ytsage_constants import SUBPROCESS_CREATIONFLAGS
 from ..utils.ytsage_localization import _
 from ..utils.ytsage_logger import logger
 
@@ -100,44 +97,8 @@ class AnalysisThread(QThread):
 
     @staticmethod
     def _run_ytdlp(cmd: list, timeout: int) -> subprocess.CompletedProcess:
-        """Run yt-dlp capturing output, killing the whole process group on timeout.
-
-        subprocess.run() only kills the direct child on TimeoutExpired, leaking
-        grandchildren (deno); it also loses any stderr produced before the
-        timeout. Use Popen with a new session so the entire group can be
-        reaped, and surface the partial stderr in the raised exception.
-        """
-        popen_kwargs: Dict[str, Any] = {
-            "stdout": subprocess.PIPE,
-            "stderr": subprocess.PIPE,
-            "text": True,
-            "encoding": "utf-8",
-            "errors": "replace",
-        }
-        if sys.platform == "win32":
-            popen_kwargs["creationflags"] = SUBPROCESS_CREATIONFLAGS
-        else:
-            popen_kwargs["start_new_session"] = True
-
-        proc = subprocess.Popen(cmd, **popen_kwargs)
-        try:
-            stdout, stderr = proc.communicate(timeout=timeout)
-        except subprocess.TimeoutExpired as exc:
-            if sys.platform == "win32":
-                subprocess.run(
-                    ["taskkill", "/F", "/T", "/PID", str(proc.pid)],
-                    stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL,
-                    creationflags=SUBPROCESS_CREATIONFLAGS,
-                )
-            else:
-                try:
-                    os.killpg(os.getpgid(proc.pid), signal.SIGKILL)
-                except (ProcessLookupError, PermissionError, OSError):
-                    pass
-            stdout, stderr = proc.communicate()
-            exc.stdout, exc.stderr = stdout, stderr
-            raise
-        return subprocess.CompletedProcess(cmd, proc.returncode, stdout, stderr)
+        """Run yt-dlp via the shared client runner (process-group-safe)."""
+        return run_ytdlp_capture(cmd, timeout=timeout)
 
     def _analyze_url_with_subprocess(self, url: str) -> None:
         """Analyze URL using yt-dlp executable."""