diff --git a/scanslicer/entry.py b/scanslicer/entry.py
index 2e0e858..a33f1b9 100644
--- a/scanslicer/entry.py
+++ b/scanslicer/entry.py
@@ -123,3 +123,39 @@ def validate_x11_environment():
         raise RuntimeError(
             "Missing X11 runtime environment. Set DISPLAY or use --backend wayland."
         )
+
+
+# main: function definition for ScanSlicer behavior.
+def main(argv=None):
+    args = parse_args(sys.argv[1:] if argv is None else argv)
+    runtime_backend = None
+
+    try:
+        runtime_backend = resolve_runtime_backend(args.backend)
+        configure_qt_backend(runtime_backend)
+        if runtime_backend == "wayland":
+            validate_wayland_environment()
+        elif runtime_backend == "x11":
+            validate_x11_environment()
+
+        from .main import run_app
+
+        return run_app(args.path)
+    except Exception as exc:
+        selected = os.environ.get("QT_QPA_PLATFORM", "<unset>")
+        print(
+            f"Failed to start ScanSlicer Qt UI (backend={runtime_backend or args.backend}, QT_QPA_PLATFORM={selected}).",
+            file=sys.stderr,
+        )
+        print(str(exc), file=sys.stderr)
+        if runtime_backend == "x11":
+            print(
+                "X11 hint: ensure DISPLAY is set and an X server is available.",
+                file=sys.stderr,
+            )
+        else:
+            print(
+                "Wayland hint: ensure XDG_RUNTIME_DIR and WAYLAND_DISPLAY are set and the Wayland socket is mounted.",
+                file=sys.stderr,
+            )
+        return 1