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-macros/src/lib.rs

@@ -112,6 +112,36 @@ fn expand_interface(attribute: TokenStream2, item: ItemTrait) -> syn::Result<Tok
         operations.push(operation);
     }
 
+    // PascalCase normalization is convenient for the public generated item,
+    // but distinct Rust names such as `item` and `item_` normalize identically.
+    // Add a stable source-name suffix to every member of a colliding group so
+    // otherwise-valid operations always produce distinct public Rust items.
+    let mut seen_argument_items = HashSet::new();
+    let mut colliding_argument_items = HashSet::new();
+    for operation in &operations {
+        let name = operation.arguments_ident.to_string();
+        if !seen_argument_items.insert(name.clone()) {
+            colliding_argument_items.insert(name);
+        }
+    }
+    for operation in &mut operations {
+        if colliding_argument_items.contains(&operation.arguments_ident.to_string()) {
+            let suffix = operation
+                .name
+                .as_bytes()
+                .iter()
+                .map(|byte| format!("{byte:02x}"))
+                .collect::<String>();
+            operation.arguments_ident = format_ident!(
+                "{}{}ArgumentsN{}",
+                trait_ident,
+                pascal_case(&operation.name),
+                suffix,
+                span = operation.ident.span()
+            );
+        }
+    }
+
     let argument_items = operations.iter().map(argument_item);
     let operation_declarations = operations.iter().map(operation_declaration);
     let declaration_collectors = operations.iter().flat_map(operation_collectors);