feat: add typed conditional API responses

crates/api-macros/tests/ui/duplicate_response_header.rs

@@ -0,0 +1,14 @@
+use api_macros::api;
+
+pub struct Body;
+
+#[api]
+pub trait DuplicateResponseHeaderApi {
+    #[get(
+        "/duplicate",
+        responses = [(status = 200, body = Body, headers = [("etag", String), ("ETag", String)])]
+    )]
+    async fn duplicate(&self) -> duplicate_response_header_api_responses::Duplicate;
+}
+
+fn main() {}