fix: honor supported_protocol_versions when negotiating initialize (#1093)

crates/rmcp/src/handler/server.rs

@@ -300,6 +300,10 @@ impl<H: ServerHandler> Service<RoleServer> for H {
     fn get_info(&self) -> <RoleServer as ServiceRole>::Info {
         self.get_info()
     }
+
+    fn supported_protocol_versions(&self) -> Cow<'static, [ProtocolVersion]> {
+        ServerHandler::supported_protocol_versions(self)
+    }
 }
 
 macro_rules! server_handler_methods {
@@ -321,10 +325,17 @@ macro_rules! server_handler_methods {
             info.protocol_version = negotiate_protocol_version(
                 &request.protocol_version,
                 info.protocol_version,
+                &self.supported_protocol_versions(),
             );
             std::future::ready(Ok(info))
         }
         /// Return the protocol versions supported by this server.
+        ///
+        /// Defaults to every version this SDK knows. Override it to narrow the
+        /// set to the revisions the server actually implements: the returned
+        /// list is advertised by [`Self::discover`], bounds what `initialize`
+        /// negotiation may agree to, and is what per-request versions are
+        /// validated against.
         fn supported_protocol_versions(&self) -> Cow<'static, [ProtocolVersion]> {
             Cow::Borrowed(ProtocolVersion::KNOWN_VERSIONS)
         }

crates/rmcp/src/handler/server/router.rs

@@ -1,4 +1,4 @@
-use std::sync::Arc;
+use std::{borrow::Cow, sync::Arc};
 
 use prompt::{IntoPromptRoute, PromptRoute};
 use tool::{IntoToolRoute, ToolRoute};
@@ -6,7 +6,10 @@ use tool::{IntoToolRoute, ToolRoute};
 use super::ServerHandler;
 use crate::{
     RoleServer, Service,
-    model::{ClientNotification, ClientRequest, ListPromptsResult, ListToolsResult, ServerResult},
+    model::{
+        ClientNotification, ClientRequest, ListPromptsResult, ListToolsResult, ProtocolVersion,
+        ServerResult,
+    },
     service::NotificationContext,
 };
 
@@ -155,6 +158,10 @@ where
             .list_changed = Some(true);
         info
     }
+
+    fn supported_protocol_versions(&self) -> Cow<'static, [ProtocolVersion]> {
+        ServerHandler::supported_protocol_versions(&self.service)
+    }
 }
 
 #[cfg(test)]