Write ffmpeg dir to user PATH via registry instead of setx

setx truncates values at 1024 characters, and the old code fed it the
merged process PATH (system + user), permanently duplicating every
system entry into the user hive and silently dropping anything past the
limit. Read and rewrite only the HKCU Environment Path value with
winreg, preserving REG_EXPAND_SZ, and broadcast WM_SETTINGCHANGE.

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

ytsage/core/ytsage_ffmpeg.py

@@ -337,29 +337,35 @@ def install_ffmpeg_windows(progress_callback=None) -> bool:
         if progress_callback:
             progress_callback("🔧 Configuring system paths...")
         
-        # Add to System Path
-        user_path = os.environ.get("PATH", "")
-        path_parts = user_path.split(os.pathsep)
-        
-        # Remove old FFmpeg paths and add new one
-        cleaned_paths = [p for p in path_parts if "ffmpeg" not in p.lower() or str(bin_dir) in p]
-        if str(bin_dir) not in cleaned_paths:
-            cleaned_paths.insert(0, str(bin_dir))
-        
-        new_path = os.pathsep.join(cleaned_paths)
-        
+        # Persist to the user PATH via the registry. setx must not be used here:
+        # it truncates values at 1024 characters, and os.environ["PATH"] is the
+        # merged system+user PATH, so writing it back would permanently duplicate
+        # every system entry into the user hive.
         try:
-            subprocess.run(
-                ["setx", "PATH", new_path],
-                creationflags=SUBPROCESS_CREATIONFLAGS,
-                timeout=30,
-                check=True,
-            )
-            os.environ["PATH"] = new_path
+            import winreg
+
+            with winreg.OpenKey(winreg.HKEY_CURRENT_USER, "Environment", 0, winreg.KEY_READ | winreg.KEY_WRITE) as key:
+                try:
+                    stored_path, value_type = winreg.QueryValueEx(key, "Path")
+                except FileNotFoundError:
+                    stored_path, value_type = "", winreg.REG_EXPAND_SZ
+                user_parts = [p for p in stored_path.split(os.pathsep) if p]
+                # Drop stale ffmpeg entries we previously added, then prepend the new one
+                user_parts = [p for p in user_parts if "ffmpeg" not in p.lower() or p == str(bin_dir)]
+                if str(bin_dir) not in user_parts:
+                    user_parts.insert(0, str(bin_dir))
+                winreg.SetValueEx(key, "Path", 0, value_type, os.pathsep.join(user_parts))
+
+            # Broadcast the change so new shells pick it up without relogin
+            import ctypes
+
+            ctypes.windll.user32.SendMessageTimeoutW(0xFFFF, 0x001A, 0, "Environment", 0x0002, 5000, None)
         except Exception as e:
             logger.warning(f"Failed to update PATH permanently: {e}")
-            # Still update for current session
-            os.environ["PATH"] = new_path
+
+        # Update for the current session regardless
+        if str(bin_dir) not in os.environ.get("PATH", "").split(os.pathsep):
+            os.environ["PATH"] = str(bin_dir) + os.pathsep + os.environ.get("PATH", "")
 
         # Verify installation
         if progress_callback: