feat(call): introduce StreamingHandler, HandlerKind, ResponseStream + INVALID_OPERATION_TYPE (ADR-049)

Add the foundational types for ADR-049 streaming handlers:
- StreamingHandler, ResponseStream type aliases and HandlerKind enum
  (Once | Stream) in registration.rs, with make_streaming_handler() helper
- CallError::invalid_operation_type() in wire.rs (sixth protocol code,
  retryable: false)
- HandlerRegistration.handler flipped from Handler to HandlerKind;
  HandlerRegistration::new() now takes HandlerKind
- OperationRegistryBuilder absorbs wrapping: with_local/with_leaf/
  with_leaf_provenance wrap raw Handler in HandlerKind::Once for
  Query/Mutation; new with_local_streaming/with_leaf_streaming take a
  StreamingHandler and wrap in HandlerKind::Stream for Subscription.
  Builder validates kind matches spec.op_type (mismatch = startup error)
- OperationRegistry::register() returns Result<(), String> with a clear
  mismatch message; all call sites updated to handle the Result
- invoke() matches on HandlerKind: Once -> existing path; Stream ->
  INVALID_OPERATION_TYPE error envelope (guards against silent
  truncation; invoke_streaming() added in a downstream task)
- OverlayOperationEnv::invoke_with_policy matches on HandlerKind:
  Once -> dispatch; Stream -> INVALID_OPERATION_TYPE (composition is
  request/response-only)
- Migrated every HandlerRegistration::new() construction site (~95)
  to wrap raw Handler in HandlerKind::Once(handler); the builder sites
  are handled by the builder-absorbs-wrapping change
- Updated two websocket subscription tests that relied on Subscription
  ops dispatching via invoke() to expect INVALID_OPERATION_TYPE
- Added unit tests for invoke/register validation and
  make_streaming_handler

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

@@ -17,7 +17,9 @@ use std::sync::Arc;
 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, HandlerRegistration, OperationProvenance};
+use alknet_call::registry::registration::{
+    make_handler, HandlerKind, HandlerRegistration, OperationProvenance,
+};
 use alknet_call::registry::spec::{
     AccessControl, ErrorDefinition, OperationSpec, OperationType, Visibility,
 };
@@ -469,7 +471,7 @@ impl FromOpenAPI {
         let capabilities = Capabilities::new();
         Ok(HandlerRegistration::new(
             spec,
-            handler,
+            HandlerKind::Once(handler),
             OperationProvenance::FromOpenAPI,
             None,
             None,
@@ -1151,7 +1153,10 @@ mod tests {
             .unwrap();
         let registration = &bundles[0];
         let ctx = noop_context("req-10", Capabilities::new());
-        let response = (registration.handler)(serde_json::json!({}), ctx).await;
+        let response = match &registration.handler {
+            HandlerKind::Once(h) => h(serde_json::json!({}), ctx).await,
+            _ => panic!("expected Once handler"),
+        };
         assert_eq!(response.request_id, "req-10");
         match response.result {
             Ok(v) => assert_eq!(v, serde_json::json!({"ok":true})),
@@ -1176,7 +1181,10 @@ mod tests {
             .unwrap();
         let registration = &bundles[0];
         let ctx = noop_context("req-11", Capabilities::new());
-        let response = (registration.handler)(serde_json::json!({}), ctx).await;
+        let response = match &registration.handler {
+            HandlerKind::Once(h) => h(serde_json::json!({}), ctx).await,
+            _ => panic!("expected Once handler"),
+        };
         match response.result {
             Err(e) => {
                 assert_eq!(e.code, "HTTP_404");
@@ -1201,7 +1209,10 @@ mod tests {
             .unwrap();
         let registration = &bundles[0];
         let ctx = noop_context("req-12", Capabilities::new());
-        let response = (registration.handler)(serde_json::json!({}), ctx).await;
+        let response = match &registration.handler {
+            HandlerKind::Once(h) => h(serde_json::json!({}), ctx).await,
+            _ => panic!("expected Once handler"),
+        };
         assert!(response.result.is_ok());
         let last = response.result.unwrap();
         assert_eq!(last, serde_json::json!({"n":2}));
@@ -1447,11 +1458,16 @@ mod tests {
             .unwrap();
         let registration = &bundles[0];
         let ctx = noop_context("req-16", Capabilities::new());
-        let response = (registration.handler)(
-            serde_json::json!({"id":"42","filter":"new","body":{"name":"widget"}}),
-            ctx,
-        )
-        .await;
+        let response = match &registration.handler {
+            HandlerKind::Once(h) => {
+                h(
+                    serde_json::json!({"id":"42","filter":"new","body":{"name":"widget"}}),
+                    ctx,
+                )
+                .await
+            }
+            _ => panic!("expected Once handler"),
+        };
         assert!(
             response.result.is_ok(),
             "expected Ok, got {:?}",
@@ -1483,7 +1499,10 @@ mod tests {
         let registration = &bundles[0];
         let caps = Capabilities::new().with_http_token("openai", "sk-test-token".to_string());
         let ctx = noop_context("req-17", caps);
-        let _ = (registration.handler)(serde_json::json!({}), ctx).await;
+        let _ = match &registration.handler {
+            HandlerKind::Once(h) => h(serde_json::json!({}), ctx).await,
+            _ => panic!("expected Once handler"),
+        };
         let captured = rx.await.unwrap();
         assert_eq!(
             captured.headers.get("authorization").unwrap(),
@@ -1519,7 +1538,10 @@ mod tests {
             .unwrap();
         let registration = &bundles[0];
         let ctx = noop_context("req-18", Capabilities::new());
-        let response = (registration.handler)(serde_json::json!({}), ctx).await;
+        let response = match &registration.handler {
+            HandlerKind::Once(h) => h(serde_json::json!({}), ctx).await,
+            _ => panic!("expected Once handler"),
+        };
         match response.result {
             Ok(Value::String(s)) => assert_eq!(s, "hello world"),
             other => panic!("expected String, got {other:?}"),
@@ -1540,7 +1562,10 @@ mod tests {
             .unwrap();
         let registration = &bundles[0];
         let ctx = noop_context("req-19", Capabilities::new());
-        let response = (registration.handler)(serde_json::json!({}), ctx).await;
+        let response = match &registration.handler {
+            HandlerKind::Once(h) => h(serde_json::json!({}), ctx).await,
+            _ => panic!("expected Once handler"),
+        };
         match response.result {
             Err(e) => assert_eq!(e.code, "HTTP_500"),
             other => panic!("expected HTTP_500, got {other:?}"),