refactor: consolidate JsonRpc trait implementations with macros

- Replace ~890 lines of repetitive trait implementations with concise macros
- Add impl_jsonrpc_request! and impl_jsonrpc_notification! macros in schema/mod.rs
- Add feature flags for unstable ACP methods (session_model, session_fork, etc.)
- All tests pass, no functional changes

Author: nikomatsakis

src/sacp/Cargo.toml

@@ -8,6 +8,22 @@ repository = "https://github.com/symposium-dev/symposium-acp"
 keywords = ["acp", "agent", "protocol", "ai"]
 categories = ["development-tools"]
 
+[features]
+default = []
+
+# Forward unstable features from agent-client-protocol-schema.
+# Enable these to get support for the corresponding unstable ACP methods.
+unstable = [
+    "unstable_session_model",
+    "unstable_session_fork",
+    "unstable_session_resume",
+    "unstable_session_close",
+]
+unstable_session_model = ["agent-client-protocol-schema/unstable_session_model"]
+unstable_session_fork = ["agent-client-protocol-schema/unstable_session_fork"]
+unstable_session_resume = ["agent-client-protocol-schema/unstable_session_resume"]
+unstable_session_close = ["agent-client-protocol-schema/unstable_session_close"]
+
 [dependencies]
 agent-client-protocol-schema.workspace = true
 sacp-derive = { version = "11.0.0", path = "../sacp-derive" }

src/sacp/src/schema/agent_to_client/notifications.rs

@@ -1,32 +1,3 @@
 use crate::schema::SessionNotification;
-use serde::Serialize;
 
-use crate::jsonrpc::{JsonRpcMessage, JsonRpcNotification};
-
-const METHOD_SESSION_UPDATE: &str = "session/update";
-
-// Agent -> Client notifications
-// These are one-way messages that agents send to clients/editors
-
-impl JsonRpcMessage for SessionNotification {
-    fn matches_method(method: &str) -> bool {
-        method == METHOD_SESSION_UPDATE
-    }
-
-    fn method(&self) -> &str {
-        METHOD_SESSION_UPDATE
-    }
-
-    fn to_untyped_message(&self) -> Result<crate::UntypedMessage, crate::Error> {
-        crate::UntypedMessage::new(self.method(), self)
-    }
-
-    fn parse_message(method: &str, params: &impl Serialize) -> Result<Self, crate::Error> {
-        if !Self::matches_method(method) {
-            return Err(crate::Error::method_not_found());
-        }
-        crate::util::json_cast(params)
-    }
-}
-
-impl JsonRpcNotification for SessionNotification {}
+impl_jsonrpc_notification!(SessionNotification, "session/update");