diff --git a/crates/core/src/route_handler.rs b/crates/core/src/route_handler.rs
index db6c91b..e079bb7 100644
--- a/crates/core/src/route_handler.rs
+++ b/crates/core/src/route_handler.rs
@@ -56,6 +56,20 @@ pub enum HandlerAction {
     NeedsBody(PendingRequest),
 }
 
+impl HandlerAction {
+    /// Returns a mutable reference to the response headers, if available.
+    ///
+    /// Returns `Some(&mut HeaderMap)` for `Response` and `Forward` variants,
+    /// `None` for `NeedsBody` (which has no response yet).
+    pub fn response_headers_mut(&mut self) -> Option<&mut HeaderMap> {
+        match self {
+            HandlerAction::Response(result) => Some(&mut result.headers),
+            HandlerAction::Forward(fwd) => Some(&mut fwd.headers),
+            HandlerAction::NeedsBody(_) => None,
+        }
+    }
+}
+
 /// A presigned URL request for the runtime to execute.
 pub struct ForwardRequest {
     /// HTTP method for the backend request.
@@ -271,6 +285,53 @@ pub trait RouteHandler: MaybeSend + MaybeSync {
 mod tests {
     use super::*;
 
+    #[test]
+    fn test_response_headers_mut_on_response() {
+        let mut action = HandlerAction::Response(ProxyResult {
+            status: 200,
+            headers: HeaderMap::new(),
+            body: ProxyResponseBody::Empty,
+        });
+        let headers = action.response_headers_mut().unwrap();
+        headers.insert("x-custom", "value".parse().unwrap());
+        if let HandlerAction::Response(result) = &action {
+            assert_eq!(result.headers.get("x-custom").unwrap(), "value");
+        }
+    }
+
+    #[test]
+    fn test_response_headers_mut_on_forward() {
+        let mut action = HandlerAction::Forward(ForwardRequest {
+            method: Method::GET,
+            url: "https://example.com".parse().unwrap(),
+            headers: HeaderMap::new(),
+            request_id: String::new(),
+        });
+        assert!(action.response_headers_mut().is_some());
+    }
+
+    #[test]
+    fn test_response_headers_mut_on_needs_body() {
+        use crate::types::{BucketConfig, S3Operation};
+        let mut action = HandlerAction::NeedsBody(PendingRequest {
+            operation: S3Operation::CreateMultipartUpload {
+                bucket: "b".into(),
+                key: "k".into(),
+            },
+            bucket_config: BucketConfig {
+                name: String::new(),
+                backend_type: "s3".into(),
+                backend_prefix: None,
+                anonymous_access: false,
+                backend_options: Default::default(),
+                allowed_roles: Vec::new(),
+            },
+            original_headers: HeaderMap::new(),
+            request_id: String::new(),
+        });
+        assert!(action.response_headers_mut().is_none());
+    }
+
     #[test]
     fn test_blocks_hop_by_hop_headers() {
         let mut headers = http::HeaderMap::new();