test(adapters): array-of-$ref resolution + style:simple/explode:true rejection (COV-12 review-002)

Array branch of resolve_refs_bounded expands items $refs (memo hit on
repeat resolution); simple+explode=true import fails naming OAI-06.

src/adapters/openapi_spec.rs

@@ -1335,6 +1335,38 @@ mod tests {
         }
     }
 
+    #[test]
+    fn array_of_ref_resolves_each_item() {
+        // The array branch of `resolve_refs_bounded` (the arm a coverage
+        // pass initially mis-flagged): `$ref`s inside `items` resolve to
+        // the component schema, not pass through verbatim.
+        let spec = schema_test_spec(json!({
+            "Tag": {"type": "string", "minLength": 1},
+            "Tags": {"type": "array", "items": {"$ref": "#/components/schemas/Tag"}}
+        }));
+        let schema = spec
+            .components
+            .as_ref()
+            .expect("test spec has schemas")
+            .schemas
+            .get("Tags")
+            .expect("test schema present")
+            .clone();
+        let resolved = spec
+            .resolve_refs_recursive(&schema)
+            .expect("array-of-$ref is acyclic and must resolve");
+        assert_eq!(resolved["type"], "array");
+        assert_eq!(
+            resolved["items"],
+            serde_json::json!({"type": "string", "minLength": 1}),
+            "the items $ref must expand to the Tag component schema"
+        );
+        let resolved_twice = spec
+            .resolve_refs_recursive(&schema)
+            .expect("second resolution hits the memo");
+        assert_eq!(resolved, resolved_twice);
+    }
+
     #[test]
     fn cycle_via_all_of_errors() {
         let spec = schema_test_spec(json!({
@@ -1570,6 +1602,39 @@ mod tests {
         }
     }
 
+    #[test]
+    fn simple_style_with_explode_true_is_rejected() {
+        let doc = r##"{
+            "openapi": "3.0.0",
+            "info": {"title": "T", "version": "1"},
+            "paths": {
+                "/f": {"get": {
+                    "operationId": "f",
+                    "parameters": [{
+                        "name": "X-Id",
+                        "in": "header",
+                        "style": "simple",
+                        "explode": true,
+                        "schema": {"type": "string"}
+                    }],
+                    "responses": {"200": {"content": {"application/json": {"schema": {}}}}}
+                }}
+            }
+        }"##;
+        match OpenAPISpec::from_json(doc) {
+            Err(AdapterError::SchemaParse { message }) => {
+                assert!(
+                    message.contains("simple") && message.contains("explode"),
+                    "the error must name the simple+explode conflict: {message}"
+                );
+                assert!(message.contains("X-Id"), "message was: {message}");
+                assert!(message.contains("OAI-06"), "message was: {message}");
+            }
+            Ok(_) => panic!("simple+explode=true has no wire meaning here; must fail loudly"),
+            other => panic!("expected SchemaParse, got {other:?}"),
+        }
+    }
+
     #[test]
     fn default_style_and_explode_forms_still_import() {
         let doc = r##"{