ScalingSettings::MinPartiality: validate the argument, not the value it replaces

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015CeEGgpKdfkCTJb3YNMJcu
(cherry picked from commit df5f2ae22f979a5569f4d569fe2a8cdd5999d242)

tests/MergeScaleTest.cpp

@@ -1143,3 +1143,12 @@ TEST_CASE("MergeOnTheFly_CaptureTermDownweightsPartials") {
     CHECK(with < without);
     CHECK(with < 1.08f);
 }
+
+// The setter checks the value it is given, not the one it replaces.
+TEST_CASE("ScalingSettings_MinPartialityRange") {
+    ScalingSettings s;
+    CHECK_THROWS(s.MinPartiality(1.5));
+    CHECK_THROWS(s.MinPartiality(-0.1));
+    CHECK_NOTHROW(s.MinPartiality(0.5));
+    CHECK(s.GetMinPartiality() == 0.5);
+}