clients/rust: SDK methods for AcknowledgeAlarm + QueryActiveAlarms (PR E.6)

Eleventh PR of the alarms-over-gateway epic
(docs/plans/alarms-over-gateway.md). Mirrors PR E.2's .NET surface
on the Rust async SDK. Depends on PR E.1 (regen, merged).

- GatewayClient::acknowledge_alarm — async unary call. Uses the
  existing unary_request helper (call timeout) and routes failures
  through Error mapping; non-OK protocol status promotes to
  Error::ProtocolStatus via ensure_protocol_success.
- GatewayClient::query_active_alarms — async server-streaming call
  returning a new ActiveAlarmStream type alias (parallel to
  EventStream). Errors are pre-mapped from tonic::Status; dropping
  the stream cancels the call cooperatively.
- GATEWAY_PROTOCOL_VERSION bumped 2 → 3 to match the .NET contract.
- FakeGateway test impl extends to satisfy the new trait methods so
  client_behavior.rs builds. Two new integration tests cover the
  new SDK methods.

Tests:
- 12 unit + 10 client_behavior + 4 proto_fixtures = 26 tests, all
  pass under cargo test (Rust 1.x via existing toolchain).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

clients/rust/tests/client_behavior.rs

@@ -14,10 +14,11 @@ use mxgateway_client::generated::mxaccess_gateway::v1::mx_access_gateway_server:
 use mxgateway_client::generated::mxaccess_gateway::v1::mx_command_reply;
 use mxgateway_client::generated::mxaccess_gateway::v1::mx_value::Kind;
 use mxgateway_client::generated::mxaccess_gateway::v1::{
-    AddItemReply, BulkSubscribeReply, CloseSessionReply, CloseSessionRequest, MxCommandKind,
-    MxCommandReply, MxDataType, MxEvent, MxEventFamily, MxStatusCategory, MxStatusProxy,
-    MxStatusSource, MxValue, OpenSessionReply, OpenSessionRequest, ProtocolStatus,
-    ProtocolStatusCode, SessionState, StreamEventsRequest, SubscribeResult,
+    AcknowledgeAlarmReply, AcknowledgeAlarmRequest, ActiveAlarmSnapshot, AddItemReply,
+    BulkSubscribeReply, CloseSessionReply, CloseSessionRequest, MxCommandKind, MxCommandReply,
+    MxDataType, MxEvent, MxEventFamily, MxStatusCategory, MxStatusProxy, MxStatusSource, MxValue,
+    OpenSessionReply, OpenSessionRequest, ProtocolStatus, ProtocolStatusCode,
+    QueryActiveAlarmsRequest, SessionState, StreamEventsRequest, SubscribeResult,
 };
 use mxgateway_client::{
     ApiKey, ClientOptions, CommandError, Error, GatewayClient, MxStatus, MxValue as ClientMxValue,
@@ -136,6 +137,52 @@ async fn event_stream_preserves_order_and_drop_cancels_server_stream() {
     assert!(state.stream_dropped.load(Ordering::SeqCst));
 }
 
+#[tokio::test]
+async fn acknowledge_alarm_returns_reply_with_native_status() {
+    let state = Arc::new(FakeState::default());
+    let endpoint = spawn_fake_gateway(state.clone()).await;
+    let client = GatewayClient::connect(ClientOptions::new(endpoint))
+        .await
+        .unwrap();
+
+    let reply = client
+        .acknowledge_alarm(AcknowledgeAlarmRequest {
+            session_id: "session-fixture".to_owned(),
+            client_correlation_id: "corr-1".to_owned(),
+            alarm_full_reference: "Tank01.Level.HiHi".to_owned(),
+            comment: "investigating".to_owned(),
+            operator_user: "alice".to_owned(),
+        })
+        .await
+        .unwrap();
+
+    assert_eq!(
+        reply.protocol_status.as_ref().unwrap().code,
+        ProtocolStatusCode::Ok as i32
+    );
+    assert_eq!(reply.status.as_ref().unwrap().success, 1);
+}
+
+#[tokio::test]
+async fn query_active_alarms_streams_snapshot_rows() {
+    let state = Arc::new(FakeState::default());
+    let endpoint = spawn_fake_gateway(state.clone()).await;
+    let client = GatewayClient::connect(ClientOptions::new(endpoint))
+        .await
+        .unwrap();
+
+    let mut stream = client
+        .query_active_alarms(QueryActiveAlarmsRequest {
+            session_id: "session-fixture".to_owned(),
+            ..QueryActiveAlarmsRequest::default()
+        })
+        .await
+        .unwrap();
+
+    let first = stream.next().await.unwrap().unwrap();
+    assert_eq!(first.alarm_full_reference, "Tank01.Level.HiHi");
+}
+
 #[test]
 fn value_conversion_fixtures_keep_typed_projection_and_raw_metadata() {
     let fixture = behavior_fixture("values/value-conversion-cases.json");
@@ -335,6 +382,43 @@ impl MxAccessGateway for FakeGateway {
             dropped: self.state.stream_dropped.clone(),
         }))
     }
+
+    async fn acknowledge_alarm(
+        &self,
+        _request: Request<AcknowledgeAlarmRequest>,
+    ) -> Result<Response<AcknowledgeAlarmReply>, Status> {
+        Ok(Response::new(AcknowledgeAlarmReply {
+            session_id: "session-fixture".to_owned(),
+            correlation_id: "corr-1".to_owned(),
+            protocol_status: Some(ok_status("ack ok")),
+            status: Some(MxStatusProxy {
+                success: 1,
+                category: MxStatusCategory::Ok as i32,
+                detected_by: MxStatusSource::RespondingLmx as i32,
+                ..MxStatusProxy::default()
+            }),
+            ..AcknowledgeAlarmReply::default()
+        }))
+    }
+
+    type QueryActiveAlarmsStream =
+        Pin<Box<dyn Stream<Item = Result<ActiveAlarmSnapshot, Status>> + Send + 'static>>;
+
+    async fn query_active_alarms(
+        &self,
+        _request: Request<QueryActiveAlarmsRequest>,
+    ) -> Result<Response<Self::QueryActiveAlarmsStream>, Status> {
+        let (sender, receiver) = mpsc::channel(4);
+        sender
+            .send(Ok(ActiveAlarmSnapshot {
+                alarm_full_reference: "Tank01.Level.HiHi".to_owned(),
+                ..ActiveAlarmSnapshot::default()
+            }))
+            .await
+            .unwrap();
+        let stream = ReceiverStream::new(receiver);
+        Ok(Response::new(Box::pin(stream)))
+    }
 }
 
 struct DropAwareStream {