diff --git a/scanslicer/entry.py b/scanslicer/entry.py
index c720416..997ecd7 100644
--- a/scanslicer/entry.py
+++ b/scanslicer/entry.py
@@ -36,3 +36,30 @@ def _detect_backend_from_qpa_env():
         if token in ("xcb", "x11"):
             return "x11"
     return None
+
+
+# resolve_runtime_backend: function definition for ScanSlicer behavior.
+def resolve_runtime_backend(backend):
+    if backend in ("wayland", "x11"):
+        return backend
+
+    env_backend = _detect_backend_from_qpa_env()
+    if env_backend is not None:
+        return env_backend
+
+    session_type = os.environ.get("XDG_SESSION_TYPE", "").strip().lower()
+    if session_type == "wayland":
+        return "wayland"
+    if session_type == "x11":
+        return "x11"
+
+    runtime_dir = os.environ.get("XDG_RUNTIME_DIR", "").strip()
+    wayland_display = os.environ.get("WAYLAND_DISPLAY", "").strip()
+    if runtime_dir and wayland_display and os.path.exists(os.path.join(runtime_dir, wayland_display)):
+        return "wayland"
+
+    if os.environ.get("DISPLAY", "").strip():
+        return "x11"
+
+    # Fall back to Wayland when auto-detection has no clear signal.
+    return "wayland"