chore: upgrade rmcp to 3.3.0 and cover modern cancellation relay

Cargo.toml

@@ -24,7 +24,7 @@ repository = "https://github.com/contextforge-org/contextforge-data-plane"
 # Keep dependencies here only when at least two workspace members inherit them.
 contextforge-data-plane-cpex = { path = "./crates/contextforge-data-plane-cpex" }
 contextforge-data-plane-apis = { path = "./crates/contextforge-data-plane-apis"}
-rmcp = { version = "3.2.0", default-features = false, features = [
+rmcp = { version = "3.3.0", default-features = false, features = [
     "server",
     "client",
     "transport-streamable-http-server",

crates/contextforge-data-plane-lib/tests/gateway/plugins.rs

@@ -611,6 +611,51 @@ async fn post_hook_deny_drops_progress_notifications_without_failing_call() {
 }
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 1)]
+#[ignore = "2026-07-28 protocol transition"]
+async fn downstream_cancellation_is_relayed_to_backend() {
+    let gateway = start_gateway(TEST_USER_ID, true, Arc::new(CpexRuntimeRegistry::default())).await;
+    let service = gateway.connect(TEST_USER_ID).await;
+
+    let request = CallToolRequestParams::new("wait_for_cancellation");
+    let handle = service
+        .send_cancellable_request(
+            ClientRequest::CallToolRequest(Request::new(request)),
+            PeerRequestOptions::no_options(),
+        )
+        .await
+        .expect("wait_for_cancellation request is sent");
+    wait_for_event_count(&gateway.backend_state.calls, 1).await;
+
+    handle.cancel(Some("client gave up".to_owned())).await.expect("cancellation is sent");
+    wait_for_event_count(&gateway.backend_state.cancellations, 1).await;
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 1)]
+async fn modern_downstream_cancellation_is_relayed_to_backend() {
+    let gateway = start_gateway(TEST_USER_ID, true, Arc::new(CpexRuntimeRegistry::default())).await;
+    let service = crate::harness::connect_modern_client(
+        gateway.gateway_url(),
+        crate::harness::create_client(TEST_USER_ID),
+        crate::harness::modern_client_info(),
+    )
+    .await;
+
+    let request = CallToolRequestParams::new("wait_for_cancellation");
+    let handle = service
+        .send_cancellable_request(
+            ClientRequest::CallToolRequest(Request::new(request)),
+            PeerRequestOptions::no_options(),
+        )
+        .await
+        .expect("wait_for_cancellation request is sent");
+    wait_for_event_count(&gateway.backend_state.calls, 1).await;
+
+    handle.cancel(Some("client gave up".to_owned())).await.expect("cancellation is sent");
+    wait_for_event_count(&gateway.backend_state.cancellations, 1).await;
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 1)]
+
 async fn post_hook_can_return_raw_cmf_result_content() {
     let plugin = Arc::new(TestPlugin::new("post", vec![cmf_hook_names::TOOL_POST_INVOKE]).with_raw_post_rewrite());
     let runtime = runtime_with_post(plugin).await;