Add .labui file association — open by double-click, cross-platform

Windows/Linux self-register via core/file_association.py (winreg /
XDG .desktop+mime), triggered from a new Settings button since there's
no installer to do it at install time. macOS gets it at build time via
labui.spec's new BUNDLE() step (CFBundleDocumentTypes in Info.plist) —
that step also makes mac builds a real .app bundle for the first time,
not just a bare onedir folder. main.py gains a LabUIApplication
subclass to catch the macOS QFileOpenEvent (buffered if it arrives
before MainWindow exists) plus argv[1] handling for Windows/Linux.
ProfileButton.load_path() extracted so both paths share the same
load-and-apply logic as the existing file-dialog flow.

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

3 files changed, 44 insertions, 0 deletions

diff --git a/ui/main_window.py b/ui/main_window.py
index 012d6f5..b632535 100644
--- a/ui/main_window.py
+++ b/ui/main_window.py
@@ -601,6 +601,11 @@ class MainWindow(QMainWindow):
 
     # ── Profile callbacks ─────────────────────────────────────────────────
 
+    def load_profile_path(self, path: str) -> bool:
+        """Load a .labui file from an explicit path — used when one is
+        opened from the OS (double-click / CLI argv), see main.py."""
+        return self._file_btn.load_path(path)
+
     def _profile_new(self):
         """Reset to a blank slate."""
         # Clear devices
diff --git a/ui/profile_manager_ui.py b/ui/profile_manager_ui.py
index 446e867..79f333e 100644
--- a/ui/profile_manager_ui.py
+++ b/ui/profile_manager_ui.py
@@ -85,13 +85,21 @@ class ProfileButton(QPushButton):
         )
         if not path:
             return
+        self.load_path(path)
+
+    def load_path(self, path: str) -> bool:
+        """Load a profile from an explicit path — shared by the file dialog
+        above and by opening a .labui file from the OS (double-click / CLI
+        argv), see main.py."""
         try:
             profile = Profile.load(path)
             self._apply_profile(profile)
             self._current_path = path
             self._update_title(profile.name)
+            return True
         except Exception as e:
             QMessageBox.critical(self, "Load Failed", str(e))
+            return False
 
     def _do_save(self):
         if not self._current_path:
diff --git a/ui/windows/settings_window.py b/ui/windows/settings_window.py
index cea7e5c..ae44c31 100644
--- a/ui/windows/settings_window.py
+++ b/ui/windows/settings_window.py
@@ -137,6 +137,24 @@ class SettingsWindow(QWidget):
         self._update_status_lbl.setWordWrap(True)
         lay.addRow("", self._update_status_lbl)
 
+        import sys as _sys
+        if _sys.platform.startswith(("win", "linux")):
+            assoc_row = QHBoxLayout()
+            self._assoc_btn = QPushButton("Register .labui Files")
+            self._assoc_btn.setObjectName("configButton")
+            self._assoc_btn.setToolTip(
+                "Associates .labui files with LabUI so double-clicking one\n"
+                "in the OS file browser opens it here."
+            )
+            self._assoc_btn.clicked.connect(self._register_file_association)
+            assoc_row.addWidget(self._assoc_btn)
+            assoc_row.addStretch()
+            lay.addRow("File Associations:", assoc_row)
+            self._assoc_status_lbl = QLabel("")
+            self._assoc_status_lbl.setObjectName("traceSource")
+            self._assoc_status_lbl.setWordWrap(True)
+            lay.addRow("", self._assoc_status_lbl)
+
         rst = QPushButton("Reset to Defaults"); rst.setObjectName("configButton")
         rst.clicked.connect(self._reset_to_defaults)
         lay.addRow("", rst)
@@ -390,6 +408,19 @@ class SettingsWindow(QWidget):
             except Exception as e:
                 QMessageBox.critical(self, "Update Failed", str(e))
 
+    def _register_file_association(self):
+        from core.updater import is_frozen
+        if not is_frozen():
+            self._assoc_status_lbl.setText("Not available outside the packaged app (dev mode).")
+            return
+
+        from core.file_association import register
+        err = register()
+        if err:
+            self._assoc_status_lbl.setText(f"Failed: {err}")
+        else:
+            self._assoc_status_lbl.setText("✓ .labui files now open with LabUI.")
+
     def _reset_to_defaults(self):
         reply = QMessageBox.question(
             self, "Reset Settings",