fix(interface): preserve operation item uniqueness

Disambiguate generated argument types when distinct operation names normalize to the same PascalCase form, and add the requested Number round-trip and collision regression coverage.

crates/wip-interface/tests/interface.rs

@@ -216,3 +216,41 @@ fn typed_dispatch_validates_decodes_invokes_encodes_and_validates() {
     let unknown = CatalogDefinition::dispatch(&AcceptingCatalog, "missing", vec![]).unwrap_err();
     assert!(matches!(unknown, DispatchError::UnknownOperation(name) if name == "missing"));
 }
+
+/// Operations whose distinct source names normalize to the same PascalCase.
+#[interface]
+pub trait DistinctOperations {
+    /// Returns the first item marker.
+    fn item(&self) -> OperationResult<String>;
+
+    /// Returns the underscored item marker.
+    fn item_(&self) -> OperationResult<String>;
+}
+
+struct DistinctImplementation;
+
+impl DistinctOperations for DistinctImplementation {
+    fn item(&self) -> OperationResult<String> {
+        Ok("item".into())
+    }
+
+    fn item_(&self) -> OperationResult<String> {
+        Ok("item_".into())
+    }
+}
+
+#[test]
+fn distinct_operation_names_always_generate_distinct_public_items() {
+    let descriptor = DistinctOperationsDefinition::descriptor();
+    assert_eq!(descriptor.operations[0].name, "item");
+    assert_eq!(descriptor.operations[1].name, "item_");
+
+    let first = DistinctOperationsDefinition::dispatch(&DistinctImplementation, "item", vec![])
+        .unwrap()
+        .unwrap();
+    let second = DistinctOperationsDefinition::dispatch(&DistinctImplementation, "item_", vec![])
+        .unwrap()
+        .unwrap();
+    assert_eq!(first, Value::String("item".into()));
+    assert_eq!(second, Value::String("item_".into()));
+}