feat(http/server/subscribe-sse-streaming): wire /subscribe to invoke_streaming and pipe BoxStream to SSE

Replace the one-event placeholder (subscribe_stream_from_envelope +
envelope_to_sse_stream, which called invoke() and wrapped the single
ResponseEnvelope) with the real streaming path: subscribe_handler now
calls GatewayDispatch::invoke_streaming() and pipes the
BoxStream<ResponseEnvelope> to SSE via subscribe_stream_from_envelope_stream
(futures::StreamExt::map). Each Ok(output) becomes a data: frame; each
Err becomes an event:error frame (terminal — stream ends after it);
natural stream end closes the SSE. Internal ops still return a single
NOT_FOUND error event via subscribe_stream_internal_error (kept). Client
disconnect drops the stream via Rust's Drop (abort cascade per ADR-016).

crates/alknet-http/src/server/gateway_routes.rs

@@ -17,7 +17,8 @@ use axum::response::sse::Event;
 use axum::response::{IntoResponse, Json, Response, Sse};
 use axum::routing::{get, post};
 use axum::Router;
-use futures::stream::{self, BoxStream, Stream};
+use futures::stream::{self, BoxStream};
+use futures::StreamExt;
 use serde::Deserialize;
 use serde_json::{json, Value};
 
@@ -163,18 +164,29 @@ pub(crate) async fn subscribe_handler(
         subscribe_stream_internal_error(request.operation)
     } else {
         let dispatch = state.dispatch();
-        let envelope = dispatch
-            .invoke(identity, &request.operation, request.input)
-            .await;
-        subscribe_stream_from_envelope(envelope)
+        let envelope_stream =
+            dispatch.invoke_streaming(identity, &request.operation, request.input);
+        subscribe_stream_from_envelope_stream(envelope_stream)
     };
     Sse::new(stream)
 }
 
 pub type SubscribeStream = BoxStream<'static, Result<Event, Infallible>>;
 
-fn subscribe_stream_from_envelope(envelope: ResponseEnvelope) -> SubscribeStream {
-    Box::pin(envelope_to_sse_stream(envelope))
+fn subscribe_stream_from_envelope_stream(
+    stream: BoxStream<'static, ResponseEnvelope>,
+) -> SubscribeStream {
+    Box::pin(stream.map(|envelope| match envelope.result {
+        Ok(output) => {
+            let data = serde_json::to_string(&output).unwrap_or_else(|_| "null".to_string());
+            Ok(Event::default().data(data))
+        }
+        Err(error) => {
+            let payload = serde_json::to_value(&error).unwrap_or(Value::Null);
+            let data = serde_json::to_string(&payload).unwrap_or_else(|_| "null".to_string());
+            Ok(Event::default().event("error").data(data))
+        }
+    }))
 }
 
 fn subscribe_stream_internal_error(operation: String) -> SubscribeStream {
@@ -263,24 +275,6 @@ fn is_internal_op(registry: &OperationRegistry, operation: &str) -> bool {
     }
 }
 
-fn envelope_to_sse_stream(
-    envelope: ResponseEnvelope,
-) -> impl Stream<Item = Result<Event, Infallible>> {
-    stream::once(async move {
-        match envelope.result {
-            Ok(output) => {
-                let data = serde_json::to_string(&output).unwrap_or_else(|_| "null".to_string());
-                Ok(Event::default().data(data))
-            }
-            Err(error) => {
-                let payload = serde_json::to_value(&error).unwrap_or(Value::Null);
-                let data = serde_json::to_string(&payload).unwrap_or_else(|_| "null".to_string());
-                Ok(Event::default().event("error").data(data))
-            }
-        }
-    })
-}
-
 fn error_event(operation: &str) -> Result<Event, Infallible> {
     let error = CallError::not_found(operation);
     let payload = serde_json::to_value(&error).unwrap_or(Value::Null);
@@ -295,7 +289,7 @@ mod tests {
         services_list_handler, services_list_spec, services_schema_handler, services_schema_spec,
     };
     use alknet_call::registry::registration::{
-        make_handler, HandlerKind, HandlerRegistration, OperationProvenance,
+        make_handler, make_streaming_handler, HandlerKind, HandlerRegistration, OperationProvenance,
     };
     use alknet_call::registry::spec::{AccessControl, OperationSpec, OperationType};
     use alknet_core::auth::{AuthToken, Identity};
@@ -425,6 +419,73 @@ mod tests {
         Arc::new(registry)
     }
 
+    fn subscription_spec(name: &str, visibility: Visibility, acl: AccessControl) -> OperationSpec {
+        OperationSpec::new(
+            name,
+            OperationType::Subscription,
+            visibility,
+            json!({}),
+            json!({}),
+            vec![],
+            acl,
+        )
+    }
+
+    fn multi_event_streaming_handler(
+        outputs: Vec<Value>,
+    ) -> alknet_call::registry::registration::StreamingHandler {
+        make_streaming_handler(move |_input, ctx| {
+            let request_id = ctx.request_id.clone();
+            let outputs = outputs.clone();
+            futures::stream::iter(
+                outputs
+                    .into_iter()
+                    .map(move |o| ResponseEnvelope::ok(request_id.clone(), o)),
+            )
+        })
+    }
+
+    fn error_streaming_handler(error: CallError) -> HandlerKind {
+        HandlerKind::Stream(make_streaming_handler(move |_input, ctx| {
+            let request_id = ctx.request_id.clone();
+            let error = error.clone();
+            futures::stream::iter(vec![ResponseEnvelope::error(request_id, error)])
+        }))
+    }
+
+    fn registry_with_subscription_stream(
+        name: &str,
+        outputs: Vec<Value>,
+    ) -> Arc<OperationRegistry> {
+        let mut registry = OperationRegistry::new();
+        registry
+            .register(HandlerRegistration::new(
+                subscription_spec(name, Visibility::External, AccessControl::default()),
+                HandlerKind::Stream(multi_event_streaming_handler(outputs)),
+                OperationProvenance::Local,
+                None,
+                None,
+                Capabilities::new(),
+            ))
+            .unwrap();
+        Arc::new(registry)
+    }
+
+    fn registry_with_subscription_error(name: &str, error: CallError) -> Arc<OperationRegistry> {
+        let mut registry = OperationRegistry::new();
+        registry
+            .register(HandlerRegistration::new(
+                subscription_spec(name, Visibility::External, AccessControl::default()),
+                error_streaming_handler(error),
+                OperationProvenance::Local,
+                None,
+                None,
+                Capabilities::new(),
+            ))
+            .unwrap();
+        Arc::new(registry)
+    }
+
     fn registry_with_discovery_and_ops(
         inner_ops: Vec<HandlerRegistration>,
     ) -> Arc<OperationRegistry> {
@@ -771,15 +832,20 @@ mod tests {
     }
 
     #[tokio::test]
-    async fn subscribe_streams_sse_data_event_until_completed() {
-        let router = build_router(registry_with_echo(), unused_provider());
+    async fn subscribe_on_subscription_streams_multiple_data_frames() {
+        let router = build_router(
+            registry_with_subscription_stream(
+                "events/stream",
+                vec![json!({ "n": 1 }), json!({ "n": 2 }), json!({ "n": 3 })],
+            ),
+            unused_provider(),
+        );
         let req = Request::builder()
             .method("POST")
             .uri("/subscribe")
             .header("content-type", "application/json")
             .body(Body::from(
-                serde_json::to_vec(&json!({ "operation": "echo/run", "input": { "v": 9 } }))
-                    .unwrap(),
+                serde_json::to_vec(&json!({ "operation": "events/stream", "input": {} })).unwrap(),
             ))
             .unwrap();
         let resp = router.oneshot(req).await.unwrap();
@@ -797,10 +863,73 @@ mod tests {
         );
         let bytes = resp.into_body().collect().await.unwrap().to_bytes();
         let body = String::from_utf8_lossy(&bytes);
-        assert!(body.contains("data:"), "expected a data frame, got: {body}");
+        let data_frames = body.matches("data:").count();
+        assert_eq!(data_frames, 3, "expected 3 data frames, got: {body}");
+        assert!(body.contains("\"n\":1"), "expected n=1, got: {body}");
+        assert!(body.contains("\"n\":2"), "expected n=2, got: {body}");
+        assert!(body.contains("\"n\":3"), "expected n=3, got: {body}");
+    }
+
+    #[tokio::test]
+    async fn subscribe_on_subscription_that_yields_error_emits_error_event_then_closes() {
+        let router = build_router(
+            registry_with_subscription_error("events/fail", CallError::internal("handler blew up")),
+            unused_provider(),
+        );
+        let req = Request::builder()
+            .method("POST")
+            .uri("/subscribe")
+            .header("content-type", "application/json")
+            .body(Body::from(
+                serde_json::to_vec(&json!({ "operation": "events/fail", "input": {} })).unwrap(),
+            ))
+            .unwrap();
+        let resp = router.oneshot(req).await.unwrap();
+        assert_eq!(resp.status(), StatusCode::OK);
+        let bytes = resp.into_body().collect().await.unwrap().to_bytes();
+        let body = String::from_utf8_lossy(&bytes);
         assert!(
-            body.contains("\"v\":9"),
-            "expected output payload, got: {body}"
+            body.contains("event:error") || body.contains("event: error"),
+            "expected error event, got: {body}"
+        );
+        assert!(
+            body.contains("INTERNAL"),
+            "expected INTERNAL code, got: {body}"
+        );
+        assert!(
+            body.contains("handler blew up"),
+            "expected error message, got: {body}"
+        );
+        let data_frames = body.matches("data:").count();
+        assert_eq!(
+            data_frames, 1,
+            "expected exactly one data frame (the error payload), got: {body}"
+        );
+    }
+
+    #[tokio::test]
+    async fn subscribe_response_content_type_is_text_event_stream() {
+        let router = build_router(
+            registry_with_subscription_stream("events/stream", vec![json!({ "ok": true })]),
+            unused_provider(),
+        );
+        let req = Request::builder()
+            .method("POST")
+            .uri("/subscribe")
+            .header("content-type", "application/json")
+            .body(Body::from(
+                serde_json::to_vec(&json!({ "operation": "events/stream", "input": {} })).unwrap(),
+            ))
+            .unwrap();
+        let resp = router.oneshot(req).await.unwrap();
+        let ctype = resp
+            .headers()
+            .get(axum::http::header::CONTENT_TYPE)
+            .map(|v| v.to_str().unwrap().to_string());
+        assert_eq!(
+            ctype.as_deref(),
+            Some("text/event-stream"),
+            "expected text/event-stream, got {ctype:?}"
         );
     }
 
@@ -829,6 +958,59 @@ mod tests {
         );
     }
 
+    #[tokio::test]
+    async fn subscribe_unknown_op_emits_not_found_error_event() {
+        let router = build_router(
+            registry_with_subscription_stream("events/stream", vec![json!({})]),
+            unused_provider(),
+        );
+        let req = Request::builder()
+            .method("POST")
+            .uri("/subscribe")
+            .header("content-type", "application/json")
+            .body(Body::from(
+                serde_json::to_vec(&json!({ "operation": "no/such", "input": {} })).unwrap(),
+            ))
+            .unwrap();
+        let resp = router.oneshot(req).await.unwrap();
+        assert_eq!(resp.status(), StatusCode::OK);
+        let bytes = resp.into_body().collect().await.unwrap().to_bytes();
+        let body = String::from_utf8_lossy(&bytes);
+        assert!(
+            body.contains("event:error") || body.contains("event: error"),
+            "expected error event, got: {body}"
+        );
+        assert!(
+            body.contains("NOT_FOUND"),
+            "expected NOT_FOUND, got: {body}"
+        );
+    }
+
+    #[tokio::test]
+    async fn subscribe_on_query_op_emits_invalid_operation_type_error_event() {
+        let router = build_router(registry_with_echo(), unused_provider());
+        let req = Request::builder()
+            .method("POST")
+            .uri("/subscribe")
+            .header("content-type", "application/json")
+            .body(Body::from(
+                serde_json::to_vec(&json!({ "operation": "echo/run", "input": {} })).unwrap(),
+            ))
+            .unwrap();
+        let resp = router.oneshot(req).await.unwrap();
+        assert_eq!(resp.status(), StatusCode::OK);
+        let bytes = resp.into_body().collect().await.unwrap().to_bytes();
+        let body = String::from_utf8_lossy(&bytes);
+        assert!(
+            body.contains("event:error") || body.contains("event: error"),
+            "expected error event, got: {body}"
+        );
+        assert!(
+            body.contains("INVALID_OPERATION_TYPE"),
+            "expected INVALID_OPERATION_TYPE, got: {body}"
+        );
+    }
+
     #[test]
     fn is_internal_op_returns_false_for_unknown() {
         let registry = OperationRegistry::new();