feat: add streaming core domain model

crates/crank-core/src/protocol.rs

@@ -1,5 +1,7 @@
 use serde::{Deserialize, Serialize};
 
+use crate::streaming::{ExecutionMode, TransportBehavior};
+
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum Protocol {
@@ -40,3 +42,41 @@ pub enum ExportMode {
     Portable,
     Bundle,
 }
+
+impl Protocol {
+    pub fn supports_execution_mode(self, mode: ExecutionMode) -> bool {
+        match self {
+            Self::Rest => true,
+            Self::Graphql => matches!(mode, ExecutionMode::Unary),
+            Self::Grpc => true,
+        }
+    }
+
+    pub fn supports_transport_behavior(self, behavior: TransportBehavior) -> bool {
+        match self {
+            Self::Rest => true,
+            Self::Graphql => matches!(behavior, TransportBehavior::RequestResponse),
+            Self::Grpc => !matches!(behavior, TransportBehavior::DeferredResult),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Protocol;
+    use crate::streaming::{ExecutionMode, TransportBehavior};
+
+    #[test]
+    fn graphql_support_matrix_is_restricted() {
+        assert!(Protocol::Graphql.supports_execution_mode(ExecutionMode::Unary));
+        assert!(!Protocol::Graphql.supports_execution_mode(ExecutionMode::Window));
+        assert!(!Protocol::Graphql.supports_execution_mode(ExecutionMode::Session));
+        assert!(!Protocol::Graphql.supports_transport_behavior(TransportBehavior::ServerStream));
+    }
+
+    #[test]
+    fn grpc_supports_session_but_not_deferred_result() {
+        assert!(Protocol::Grpc.supports_execution_mode(ExecutionMode::Session));
+        assert!(!Protocol::Grpc.supports_transport_behavior(TransportBehavior::DeferredResult));
+    }
+}