fix: Implement drag-and-drop functionality with QWebChannel integration

src/webdrop_bridge/ui/main_window.py

@@ -5,7 +5,9 @@ import logging
 from pathlib import Path
 from typing import Optional
 
-from PySide6.QtCore import QObject, QSize, Qt, QThread, QUrl, Signal
+from PySide6.QtCore import QObject, QPoint, QSize, Qt, QThread, QTimer, QUrl, Signal, Slot
+from PySide6.QtWebChannel import QWebChannel
+from PySide6.QtWebEngineCore import QWebEngineScript
 from PySide6.QtWidgets import QLabel, QMainWindow, QStatusBar, QToolBar, QVBoxLayout, QWidget
 
 from webdrop_bridge.config import Config
@@ -170,6 +172,39 @@ DEFAULT_WELCOME_PAGE = """
 """
 
 
+class _DragBridge(QObject):
+    """JavaScript bridge for drag operations via QWebChannel.
+    
+    Exposed to JavaScript as 'bridge' object.
+    """
+    
+    def __init__(self, window: 'MainWindow', parent: Optional[QObject] = None):
+        """Initialize the drag bridge.
+        
+        Args:
+            window: MainWindow instance
+            parent: Parent QObject
+        """
+        super().__init__(parent)
+        self.window = window
+    
+    @Slot(str)
+    def start_file_drag(self, path_text: str) -> None:
+        """Start a native file drag for the given path.
+        
+        Called from JavaScript when user drags a Z:\ path item.
+        Defers execution to avoid Qt drag manager state issues.
+        
+        Args:
+            path_text: File path string to drag
+        """
+        logger.debug(f"Bridge: start_file_drag called for {path_text}")
+        
+        # Defer to avoid drag manager state issues
+        # initiate_drag() handles validation internally
+        QTimer.singleShot(0, lambda: self.window.drag_interceptor.initiate_drag([path_text]))
+
+
 class MainWindow(QMainWindow):
     """Main application window for WebDrop Bridge.
 
@@ -221,7 +256,6 @@ class MainWindow(QMainWindow):
 
         # Create drag interceptor
         self.drag_interceptor = DragInterceptor()
-
         # Set up path validator
         validator = PathValidator(config.allowed_roots)
         self.drag_interceptor.set_validator(validator)
@@ -230,6 +264,15 @@ class MainWindow(QMainWindow):
         self.drag_interceptor.drag_started.connect(self._on_drag_started)
         self.drag_interceptor.drag_failed.connect(self._on_drag_failed)
 
+        # Set up JavaScript bridge with QWebChannel
+        self._drag_bridge = _DragBridge(self)
+        web_channel = QWebChannel(self)
+        web_channel.registerObject("bridge", self._drag_bridge)
+        self.web_view.page().setWebChannel(web_channel)
+        
+        # Install the drag bridge script
+        self._install_bridge_script()
+
         # Set up central widget with layout
         central_widget = QWidget()
         layout = QVBoxLayout()
@@ -248,6 +291,7 @@ class MainWindow(QMainWindow):
         """Load the web application.
 
         Loads HTML from the configured webapp URL or from local file.
+        Injects the WebChannel bridge JavaScript for drag-and-drop.
         Supports both bundled apps (PyInstaller) and development mode.
         Falls back to default welcome page if webapp not found.
         """
@@ -282,15 +326,55 @@ class MainWindow(QMainWindow):
                     self.web_view.setHtml(welcome_html)
                     return
 
-                # Load local file as file:// URL
-                file_url = file_path.as_uri()
-                self.web_view.load(QUrl(file_url))
+                # Load local file
+                html_content = file_path.read_text(encoding='utf-8')
+                
+                # Inject WebChannel bridge JavaScript
+                injected_html = self._inject_drag_bridge(html_content)
+                
+                # Load the modified HTML
+                self.web_view.setHtml(injected_html, QUrl.fromLocalFile(file_path.parent))
 
             except (OSError, ValueError) as e:
                 # Show welcome page on error
                 welcome_html = DEFAULT_WELCOME_PAGE.format(version=self.config.app_version)
                 self.web_view.setHtml(welcome_html)
 
+    def _install_bridge_script(self) -> None:
+        """Install the drag bridge JavaScript via QWebEngineScript.
+        
+        Follows the POC pattern for proper script injection and QWebChannel setup.
+        """
+        script = QWebEngineScript()
+        script.setName("webdrop-bridge")
+        script.setInjectionPoint(QWebEngineScript.InjectionPoint.DocumentReady)
+        script.setWorldId(QWebEngineScript.ScriptWorldId.MainWorld)
+        script.setRunsOnSubFrames(False)
+        
+        # Load bridge script from file
+        script_path = Path(__file__).parent / "bridge_script.js"
+        try:
+            with open(script_path, 'r', encoding='utf-8') as f:
+                script.setSourceCode(f.read())
+            self.web_view.page().scripts().insert(script)
+            logger.debug(f"Installed bridge script from {script_path}")
+        except (OSError, IOError) as e:
+            logger.warning(f"Failed to load bridge script: {e}")
+    
+    def _inject_drag_bridge(self, html_content: str) -> str:
+        """Return HTML content unmodified.
+        
+        The drag bridge script is now injected via QWebEngineScript in _install_bridge_script().
+        This method is kept for compatibility but does nothing.
+        
+        Args:
+            html_content: Original HTML content
+            
+        Returns:
+            HTML unchanged
+        """
+        return html_content
+
     def _apply_stylesheet(self) -> None:
         """Apply application stylesheet if available."""
         stylesheet_path = Path(__file__).parent.parent.parent.parent / \