fix(sof): honor Accept header on export status polls (406 for fhir+xml)

Per SoF PR HL7/sql-on-fhir#365 (Common Operation Behavior — Asynchronous
Delivery), each status poll's headers govern that poll's response,
including the 200 OK completion manifest. The status handler now rejects
Accept: application/fhir+xml (without fhir+json) with 406 Not Acceptable
+ OperationOutcome, matching the run operations' behavior, instead of
silently returning JSON.

Author: smunini

crates/rest/src/handlers/sof/export.rs

@@ -47,6 +47,7 @@ use helios_persistence::tenant::TenantContext;
 use helios_persistence::types::{
     SearchParamType, SearchParameter, SearchPrefix, SearchQuery, SearchValue,
 };
+use helios_sof::fhir_format::accept_requires_unsupported_fhir_xml;
 use serde::Deserialize;
 use serde_json::{Value, json};
 
@@ -1018,10 +1019,24 @@ pub async fn get_export_status_handler<S>(
     State(state): State<AppState<S>>,
     tenant: TenantExtractor,
     Path(job_id): Path<String>,
+    headers: HeaderMap,
 ) -> Result<Response, RestError>
 where
     S: ResourceStorage + Send + Sync + 'static,
 {
+    // Spec Common Operation Behavior — Asynchronous Delivery: the `Accept`
+    // header on each poll governs that poll's response, including the
+    // completion manifest. The FHIR XML representation is not supported →
+    // 406, same as the run operations.
+    let accept = headers.get(header::ACCEPT).and_then(|v| v.to_str().ok());
+    if accept_requires_unsupported_fhir_xml(accept) {
+        return Err(RestError::NotAcceptable {
+            message: "the application/fhir+xml representation is not supported; \
+                      use application/fhir+json"
+                .to_string(),
+        });
+    }
+
     let controller = match state.export_controller() {
         Some(c) => c,
         None => {

crates/rest/tests/sof_export.rs

@@ -177,6 +177,46 @@ mod sof_export_tests {
         );
     }
 
+    /// `Accept: application/fhir+xml` (without fhir+json) on a status poll is
+    /// not supported → `406 Not Acceptable` + OperationOutcome, same as the
+    /// run operations. The poll's `Accept` header governs the manifest
+    /// representation per Common Operation Behavior — Asynchronous Delivery.
+    #[tokio::test]
+    async fn test_export_status_poll_accept_fhir_xml_returns_406() {
+        let (server, backend) = create_test_server_with_export().await;
+        seed_patients(&backend).await;
+
+        let submit_resp = server
+            .post("/ViewDefinition/$viewdefinition-export")
+            .add_header(PREFER, "respond-async")
+            .add_header(X_TENANT_ID, "test-tenant")
+            .json(&patient_view())
+            .await;
+        assert_eq!(submit_resp.status_code(), StatusCode::ACCEPTED);
+
+        let location = submit_resp
+            .headers()
+            .get("content-location")
+            .unwrap()
+            .to_str()
+            .unwrap()
+            .to_string();
+
+        let poll = server
+            .get(&location)
+            .add_header(X_TENANT_ID, "test-tenant")
+            .add_header(HeaderName::from_static("accept"), "application/fhir+xml")
+            .await;
+        assert_eq!(
+            poll.status_code(),
+            StatusCode::NOT_ACCEPTABLE,
+            "{}",
+            poll.text()
+        );
+        let body: Value = poll.json();
+        assert_eq!(body["resourceType"], json!("OperationOutcome"));
+    }
+
     // =========================================================================
     // 3. Cancel → 202 Accepted, then poll → 404
     // =========================================================================