From a7bd96705a0313781977ff2ab53df5f4c3c124b9 Mon Sep 17 00:00:00 2001
From: Koichi ITO <koic.ito@gmail.com>
Date: Fri, 23 Oct 2026 23:08:13 +0700
Subject: [PATCH] Report failed session notifications through the server
 configuration

## Motivation and Context

`ServerSession#notify_progress`, `#notify_log_message`, `#notify_resources_updated` and
`#notify_elicitation_complete` rescue a transport failure and pass it to `@server.report_exception`, which is
private, so the rescue itself raised `NoMethodError`. The failure meant to be reported and swallowed reached
the caller instead, typically a tool reporting progress or logging, whose call then answered Internal error.

The rescues now call `exception_reporter` of the server's configuration, which is what
`Server#report_exception` does, without making that method public.

## How Has This Been Tested?

`test/mcp/server_notification_test.rb`. Against the previous library the new test fails with
`NoMethodError: private method 'report_exception' called for an instance of MCP::Server`.

## Breaking Changes

None.
---
 lib/mcp/server_session.rb            |  8 ++++----
 test/mcp/server_notification_test.rb | 29 ++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/lib/mcp/server_session.rb b/lib/mcp/server_session.rb
index 042b0dc4..2ced2309 100644
--- a/lib/mcp/server_session.rb
+++ b/lib/mcp/server_session.rb
@@ -275,14 +275,14 @@ def send_peer_cancellation(nested_request_id:, related_request_id: nil, reason:
     def notify_elicitation_complete(elicitation_id:)
       send_to_transport(Methods::NOTIFICATIONS_ELICITATION_COMPLETE, { elicitationId: elicitation_id })
     rescue => e
-      @server.report_exception(e, notification: "elicitation_complete")
+      @server.configuration.exception_reporter.call(e, { notification: "elicitation_complete" })
     end
 
     # Sends a resource updated notification to this session only.
     def notify_resources_updated(uri:)
       send_to_transport(Methods::NOTIFICATIONS_RESOURCES_UPDATED, { "uri" => uri })
     rescue => e
-      @server.report_exception(e, notification: "resources_updated")
+      @server.configuration.exception_reporter.call(e, { notification: "resources_updated" })
     end
 
     # Sends a progress notification to this session only.
@@ -296,7 +296,7 @@ def notify_progress(progress_token:, progress:, total: nil, message: nil, relate
 
       send_to_transport(Methods::NOTIFICATIONS_PROGRESS, params, related_request_id: related_request_id)
     rescue => e
-      @server.report_exception(e, notification: "progress")
+      @server.configuration.exception_reporter.call(e, { notification: "progress" })
     end
 
     # Sends a log message notification to this session only.
@@ -320,7 +320,7 @@ def notify_log_message(data:, level:, logger: nil, related_request_id: nil)
 
       send_to_transport(Methods::NOTIFICATIONS_MESSAGE, params, related_request_id: related_request_id)
     rescue => e
-      @server.report_exception(e, { notification: "log_message" })
+      @server.configuration.exception_reporter.call(e, { notification: "log_message" })
     end
 
     private
diff --git a/test/mcp/server_notification_test.rb b/test/mcp/server_notification_test.rb
index ffeb3a8e..c1f32fcf 100644
--- a/test/mcp/server_notification_test.rb
+++ b/test/mcp/server_notification_test.rb
@@ -257,6 +257,35 @@ def send_notification(method, params = nil)
       assert_equal 4, call_count
     end
 
+    test "ServerSession notification methods report transport errors through the server's exception reporter" do
+      transport = Class.new(MockTransport) do
+        def send_notification(method, params = nil)
+          raise StandardError, "Transport error"
+        end
+      end.new(@server)
+      session = ServerSession.new(server: @server, transport: transport)
+      session.configure_logging(MCP::LoggingMessageNotification.new(level: "error"))
+      reported = []
+      @server.configuration.exception_reporter = ->(exception, context) { reported << [exception.message, context] }
+
+      assert_nothing_raised do
+        session.notify_elicitation_complete(elicitation_id: "elicitation-1")
+        session.notify_resources_updated(uri: "file:///a.txt")
+        session.notify_progress(progress_token: "token-1", progress: 1)
+        session.notify_log_message(data: "message", level: "error")
+      end
+
+      assert_equal(
+        [
+          ["Transport error", { notification: "elicitation_complete" }],
+          ["Transport error", { notification: "resources_updated" }],
+          ["Transport error", { notification: "progress" }],
+          ["Transport error", { notification: "log_message" }],
+        ],
+        reported,
+      )
+    end
+
     test "multiple notification methods can be called in sequence" do
       @server.notify_tools_list_changed
       @server.notify_prompts_list_changed