feat(http/adapters/from-openapi-sse-streaming): branch from_openapi forwarding on op_type; Subscription → StreamingHandler (SSE → BoxStream<ResponseEnvelope>)

build_registration now branches on op_type: Subscription ops register a
StreamingHandler (HandlerKind::Stream) via make_streaming_handler that
streams SSE response chunks as ResponseEnvelope::ok() items (one per
data: frame); Query/Mutation ops keep the existing Handler
(HandlerKind::Once) via forward(). Closes the gap where a from_openapi-
imported Subscription returned only the last SSE event.

- forward_stream(): non-async fn returning ResponseStream; sends the
  request with Accept: text/event-stream, then streams SSE chunks via
  stream::unfold over response.bytes_stream(), reusing parse_sse_frames
  (multi-event, partial trailing, comments, multi-line data, BOM).
  HTTP error (non-2xx) → single ResponseEnvelope::error(), stream ends;
  SSE stream end → ResponseStream ends (→ call.completed on wire).
- Removed stream_subscription() (the collect-all placeholder that
  truncated to the last event). parse_sse_frames stays (reused).
- Query/Mutation forwarding unchanged (existing forward() path).
- Tests: Subscription registration is HandlerKind::Stream; Query
  registration is HandlerKind::Once; SSE subscription streams multiple
  ResponseEnvelope::ok() (one per data: frame); HTTP error → single
  error envelope; Query forwarding unchanged (single response).

crates/alknet-http/src/adapters/from_openapi.rs

@@ -18,13 +18,15 @@ use alknet_call::client::{AdapterError, OperationAdapter};
 use alknet_call::protocol::wire::{CallError, ResponseEnvelope};
 use alknet_call::registry::context::OperationContext;
 use alknet_call::registry::registration::{
-    make_handler, HandlerKind, HandlerRegistration, OperationProvenance,
+    make_handler, make_streaming_handler, HandlerKind, HandlerRegistration, OperationProvenance,
+    ResponseStream,
 };
 use alknet_call::registry::spec::{
     AccessControl, ErrorDefinition, OperationSpec, OperationType, Visibility,
 };
 use alknet_core::types::Capabilities;
 use async_trait::async_trait;
+use futures::stream;
 use futures::StreamExt;
 use reqwest::header::{HeaderMap, HeaderName, HeaderValue, ACCEPT, AUTHORIZATION, CONTENT_TYPE};
 use reqwest::Method;
@@ -440,7 +442,33 @@ impl FromOpenAPI {
             .map(|e| (e.http_status.unwrap_or(0), e.code.clone()))
             .collect();
 
-        let handler = make_handler(move |input: Value, context: OperationContext| {
+        let handler = if op_type == OperationType::Subscription {
+            let stream_handler =
+                make_streaming_handler(move |input: Value, context: OperationContext| {
+                    let path_template = path_template.clone();
+                    let method_upper = method_upper.clone();
+                    let auth_scheme = auth_scheme.clone();
+                    let default_headers = default_headers.clone();
+                    let base_url = base_url.clone();
+                    let namespace = namespace.clone();
+                    let http_client = Arc::clone(&http_client);
+                    let error_status_codes = error_status_codes.clone();
+                    forward_stream(
+                        &http_client,
+                        &base_url,
+                        &path_template,
+                        &method_upper,
+                        &auth_scheme,
+                        &default_headers,
+                        &namespace,
+                        &error_status_codes,
+                        input,
+                        context,
+                    )
+                });
+            HandlerKind::Stream(stream_handler)
+        } else {
+            let once_handler = make_handler(move |input: Value, context: OperationContext| {
                 let path_template = path_template.clone();
                 let method_upper = method_upper.clone();
                 let auth_scheme = auth_scheme.clone();
@@ -467,11 +495,13 @@ impl FromOpenAPI {
                     .await
                 }
             });
+            HandlerKind::Once(once_handler)
+        };
 
         let capabilities = Capabilities::new();
         Ok(HandlerRegistration::new(
             spec,
-            HandlerKind::Once(handler),
+            handler,
             OperationProvenance::FromOpenAPI,
             None,
             None,
@@ -666,10 +696,6 @@ async fn forward(
 
     let status = response.status();
 
-    if op_type == OperationType::Subscription && status.is_success() {
-        return stream_subscription(request_id, response).await;
-    }
-
     if !status.is_success() {
         let code = error_status_codes
             .iter()
@@ -721,35 +747,136 @@ async fn forward(
     }
 }
 
-async fn stream_subscription(request_id: String, response: reqwest::Response) -> ResponseEnvelope {
+#[allow(clippy::too_many_arguments)]
-    let mut stream = response.bytes_stream();
+fn forward_stream(
-    let mut buffer = String::new();
+    http_client: &Arc<SharedHttpClient>,
-    let mut last_event: Option<Value> = None;
+    base_url: &str,
-    while let Some(chunk_result) = stream.next().await {
+    path_template: &str,
-        match chunk_result {
+    method: &str,
-            Ok(chunk) => {
+    auth_scheme: &Option<HttpAuthScheme>,
+    default_headers: &HashMap<String, String>,
+    namespace: &str,
+    error_status_codes: &[(u16, String)],
+    input: Value,
+    context: OperationContext,
+) -> ResponseStream {
+    let request_id = context.request_id.clone();
+
+    let (http_method, url, body, headers) = match build_request(
+        base_url,
+        path_template,
+        method,
+        auth_scheme,
+        default_headers,
+        namespace,
+        &input,
+        &context,
+    ) {
+        Ok(parts) => parts,
+        Err(err) => {
+            return Box::pin(stream::once(async move {
+                ResponseEnvelope::error(request_id, err)
+            }));
+        }
+    };
+
+    let http_client = Arc::clone(http_client);
+    let error_status_codes = error_status_codes.to_vec();
+
+    let request_id_stream = request_id.clone();
+    let error_status_codes_stream = error_status_codes.clone();
+
+    let init = async move {
+        let request_builder = http_client
+            .client()
+            .request(http_method, url.as_str())
+            .headers(headers)
+            .header(ACCEPT, "text/event-stream");
+        let request_builder = match body.as_ref() {
+            Some(b) => {
+                let serialized = serde_json::to_string(b).unwrap_or_else(|_| String::from("null"));
+                request_builder.body(serialized)
+            }
+            None => request_builder,
+        };
+        request_builder.send().await
+    };
+
+    let sse = stream::once(init).flat_map(move |result| {
+        let request_id = request_id_stream.clone();
+        let error_status_codes = error_status_codes_stream.clone();
+        match result {
+            Err(err) => Box::pin(stream::once(async move {
+                ResponseEnvelope::error(
+                    request_id,
+                    CallError::internal(format!("HTTP request failed: {err}")),
+                )
+            })) as ResponseStream,
+            Ok(response) => {
+                let status = response.status();
+                if !status.is_success() {
+                    let code = error_status_codes
+                        .iter()
+                        .find(|(s, _)| *s == status.as_u16())
+                        .map(|(_, c)| c.clone())
+                        .unwrap_or_else(|| format!("HTTP_{}", status.as_u16()));
+                    let message = format!(
+                        "HTTP {}: {}",
+                        status.as_u16(),
+                        status.canonical_reason().unwrap_or("")
+                    );
+                    Box::pin(stream::once(async move {
+                        ResponseEnvelope::error(request_id, CallError::new(code, message, false))
+                    })) as ResponseStream
+                } else {
+                    let request_id_inner = request_id.clone();
+                    Box::pin(
+                        stream::unfold(
+                            (response.bytes_stream(), String::new()),
+                            move |(mut bytes, mut buffer)| {
+                                let request_id = request_id_inner.clone();
+                                async move {
+                                    match bytes.next().await {
+                                        Some(Ok(chunk)) => {
                                             buffer.push_str(&String::from_utf8_lossy(&chunk));
                                             let (events, remaining) = parse_sse_frames(&buffer);
-                buffer = remaining;
+                                            let envelopes: Vec<ResponseEnvelope> = events
-                for event in events {
+                                                .into_iter()
-                    let parsed = if event.data.trim().is_empty() {
+                                                .map(|e| {
+                                                    let parsed = if e.data.trim().is_empty() {
                                                         Value::Null
                                                     } else {
-                        serde_json::from_str(&event.data)
+                                                        serde_json::from_str(&e.data).unwrap_or(
-                            .unwrap_or(Value::String(event.data.clone()))
+                                                            Value::String(e.data.clone()),
+                                                        )
                                                     };
-                    last_event = Some(parsed.clone());
+                                                    ResponseEnvelope::ok(&request_id, parsed)
+                                                })
+                                                .collect();
+                                            Some((envelopes, (bytes, remaining)))
+                                        }
+                                        Some(Err(err)) => {
+                                            let error = CallError::internal(format!(
+                                                "SSE stream error: {err}"
+                                            ));
+                                            Some((
+                                                vec![ResponseEnvelope::error(request_id, error)],
+                                                (bytes, buffer),
+                                            ))
+                                        }
+                                        None => None,
                                     }
                                 }
-            Err(err) => {
+                            },
-                return ResponseEnvelope::error(
+                        )
-                    request_id,
+                        .flat_map(stream::iter),
-                    CallError::internal(format!("SSE stream error: {err}")),
+                    ) as ResponseStream
-                );
                 }
             }
         }
-    ResponseEnvelope::ok(request_id, last_event.unwrap_or(Value::Null))
+    });
+
+    Box::pin(sse)
 }
 
 struct SseEvent {
@@ -1194,6 +1321,34 @@ mod tests {
         }
     }
 
+    #[tokio::test]
+    async fn subscription_op_registration_is_handler_kind_stream() {
+        let spec = OpenAPISpec::from_json(
+            r##"{"openapi":"3.0.0","info":{"title":"T","version":"1"},
+            "paths":{"/stream":{"post":{"operationId":"stream","responses":{"200":{"content":{"text/event-stream":{"schema":{}}}}}}}}}"##,
+        )
+        .unwrap();
+        let bundles = adapter(spec, config("svc", "https://x", None))
+            .import()
+            .await
+            .unwrap();
+        assert!(matches!(bundles[0].handler, HandlerKind::Stream(_)));
+    }
+
+    #[tokio::test]
+    async fn query_op_registration_is_handler_kind_once() {
+        let spec = OpenAPISpec::from_json(
+            r#"{"openapi":"3.0.0","info":{"title":"T","version":"1"},
+            "paths":{"/data":{"get":{"operationId":"data","responses":{"200":{"content":{"application/json":{"schema":{}}}}}}}}}"#,
+        )
+        .unwrap();
+        let bundles = adapter(spec, config("svc", "https://x", None))
+            .import()
+            .await
+            .unwrap();
+        assert!(matches!(bundles[0].handler, HandlerKind::Once(_)));
+    }
+
     #[tokio::test]
     async fn integration_sse_subscription_streams_responded_events() {
         let sse_body = "data: {\"n\":1}\n\ndata: {\"n\":2}\n\n";
@@ -1209,13 +1364,67 @@ mod tests {
             .unwrap();
         let registration = &bundles[0];
         let ctx = noop_context("req-12", Capabilities::new());
+        let stream = match &registration.handler {
+            HandlerKind::Stream(h) => h(serde_json::json!({}), ctx),
+            _ => panic!("expected Stream handler"),
+        };
+        let collected: Vec<ResponseEnvelope> = stream.collect().await;
+        assert_eq!(collected.len(), 2);
+        assert_eq!(collected[0].result, Ok(serde_json::json!({"n":1})));
+        assert_eq!(collected[1].result, Ok(serde_json::json!({"n":2})));
+        assert_eq!(collected[0].request_id, "req-12");
+        assert_eq!(collected[1].request_id, "req-12");
+    }
+
+    #[tokio::test]
+    async fn integration_sse_subscription_http_error_returns_single_error_envelope() {
+        let base = spawn_echo_server(404, r#"{"error":"missing"}"#, "application/json").await;
+        let spec = OpenAPISpec::from_json(
+            r##"{"openapi":"3.0.0","info":{"title":"T","version":"1"},
+            "paths":{"/stream":{"post":{"operationId":"stream","responses":{
+                "200":{"content":{"text/event-stream":{"schema":{}}}},
+                "404":{"content":{"application/json":{"schema":{"type":"object"}}}}
+            }}}}}"##,
+        )
+        .unwrap();
+        let bundles = adapter(spec, config("svc", &base, None))
+            .import()
+            .await
+            .unwrap();
+        let registration = &bundles[0];
+        let ctx = noop_context("req-err", Capabilities::new());
+        let stream = match &registration.handler {
+            HandlerKind::Stream(h) => h(serde_json::json!({}), ctx),
+            _ => panic!("expected Stream handler"),
+        };
+        let collected: Vec<ResponseEnvelope> = stream.collect().await;
+        assert_eq!(collected.len(), 1);
+        match &collected[0].result {
+            Err(e) => assert_eq!(e.code, "HTTP_404"),
+            other => panic!("expected HTTP_404 error, got {other:?}"),
+        }
+    }
+
+    #[tokio::test]
+    async fn integration_query_forwarding_unchanged_single_response() {
+        let base = spawn_echo_server(200, r#"{"ok":true}"#, "application/json").await;
+        let spec = OpenAPISpec::from_json(
+            r#"{"openapi":"3.0.0","info":{"title":"T","version":"1"},
+            "paths":{"/data":{"get":{"operationId":"data","responses":{"200":{"content":{"application/json":{"schema":{}}}}}}}}}"#,
+        )
+        .unwrap();
+        let bundles = adapter(spec, config("svc", &base, None))
+            .import()
+            .await
+            .unwrap();
+        let registration = &bundles[0];
+        let ctx = noop_context("req-q", Capabilities::new());
         let response = match &registration.handler {
             HandlerKind::Once(h) => h(serde_json::json!({}), ctx).await,
             _ => panic!("expected Once handler"),
         };
-        assert!(response.result.is_ok());
+        assert_eq!(response.request_id, "req-q");
-        let last = response.result.unwrap();
+        assert_eq!(response.result, Ok(serde_json::json!({"ok":true})));
-        assert_eq!(last, serde_json::json!({"n":2}));
     }
 
     #[test]