fix: _lookup_bandwidth crashes on a truthy non-string gpu_name (#1641)

tests/test_hwfit_bandwidth_nonstring.py

@@ -0,0 +1,16 @@
+"""Regression: _lookup_bandwidth must tolerate a non-string gpu_name.
+
+It guarded only falsy values; a truthy non-string (e.g. a number from a
+malformed hardware probe) reached `gpu_name.lower()` and raised AttributeError.
+"""
+from services.hwfit.fit import _lookup_bandwidth
+
+
+def test_non_string_returns_none():
+    assert _lookup_bandwidth(123) is None
+    assert _lookup_bandwidth(["x"]) is None
+    assert _lookup_bandwidth(None) is None
+
+
+def test_known_gpu_resolves():
+    assert _lookup_bandwidth("NVIDIA GeForce RTX 4090") is not None