Respect OpenAPI parameter serialization rules (#588)

crates/yaak-models/src/queries/mod.rs

@@ -28,21 +28,59 @@ pub(crate) use duplicate_name::conflict_free_name;
 const MAX_HISTORY_ITEMS: usize = 20;
 
 use crate::models::HttpRequestHeader;
-use std::collections::HashMap;
+use std::collections::HashSet;
 
-/// Deduplicate headers by name (case-insensitive), keeping the latest (most specific) value.
-/// Preserves the order of first occurrence for each header name.
-pub(crate) fn dedupe_headers(headers: Vec<HttpRequestHeader>) -> Vec<HttpRequestHeader> {
-    let mut index_by_name: HashMap<String, usize> = HashMap::new();
-    let mut deduped: Vec<HttpRequestHeader> = Vec::new();
-    for header in headers {
-        let key = header.name.to_lowercase();
-        if let Some(&idx) = index_by_name.get(&key) {
-            deduped[idx] = header;
-        } else {
-            index_by_name.insert(key, deduped.len());
-            deduped.push(header);
-        }
-    }
-    deduped
+/// Merge a more-specific header layer over its parent. Names in the child replace
+/// inherited values case-insensitively, while duplicates declared together in
+/// either layer remain independent entries.
+pub(crate) fn merge_headers(
+    mut parent: Vec<HttpRequestHeader>,
+    child: Vec<HttpRequestHeader>,
+) -> Vec<HttpRequestHeader> {
+    let child_names = child.iter().map(|header| header.name.to_lowercase()).collect::<HashSet<_>>();
+    parent.retain(|header| !child_names.contains(&header.name.to_lowercase()));
+    parent.extend(child);
+    parent
+}
+
+#[cfg(test)]
+mod tests {
+    use super::merge_headers;
+    use crate::models::HttpRequestHeader;
+
+    fn header(name: &str, value: &str) -> HttpRequestHeader {
+        HttpRequestHeader { name: name.to_string(), value: value.to_string(), ..Default::default() }
+    }
+
+    #[test]
+    fn preserves_duplicate_headers_declared_in_one_layer() {
+        let merged = merge_headers(
+            vec![header("Cookie", "inherited=1")],
+            vec![
+                header("Cookie", "required=1"),
+                header("cookie", "optional=1"),
+            ],
+        );
+
+        assert_eq!(
+            merged.iter().map(|header| header.value.as_str()).collect::<Vec<_>>(),
+            vec!["required=1", "optional=1"],
+        );
+    }
+
+    #[test]
+    fn child_names_override_parent_names_without_affecting_other_headers() {
+        let merged = merge_headers(
+            vec![header("Accept", "*/*"), header("X-Parent", "kept")],
+            vec![header("accept", "application/json")],
+        );
+
+        assert_eq!(
+            merged
+                .iter()
+                .map(|header| (header.name.as_str(), header.value.as_str()))
+                .collect::<Vec<_>>(),
+            vec![("X-Parent", "kept"), ("accept", "application/json")],
+        );
+    }
 }