From a2575b24e5f48943f4f0b66b6632b917fe803116 Mon Sep 17 00:00:00 2001
From: Koichi ITO <koic.ito@gmail.com>
Date: Fri, 27 Mar 2026 11:47:34 +0900
Subject: [PATCH] Use accessor method in `server_context_with_meta` instead of
 ivar

## Motivation and Context

`server_context_with_meta` reads `@server_context` (the instance variable)
directly instead of calling the `server_context` accessor method.
This prevents subclasses from overriding `server_context`. Ffor example,
to provide thread-local context in multi-threaded servers like Puma.

Fixes #271.

## How Has This Been Tested?

Added a regression test and passed.

## Breaking Changes

None. This restores the expected behavior of `attr_accessor :server_context`.
---
 lib/mcp/server.rb       |  8 ++++----
 test/mcp/server_test.rb | 26 ++++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/lib/mcp/server.rb b/lib/mcp/server.rb
index 52552072..7646b296 100644
--- a/lib/mcp/server.rb
+++ b/lib/mcp/server.rb
@@ -531,14 +531,14 @@ def call_prompt_template_with_args(prompt, args, server_context)
 
     def server_context_with_meta(request)
       meta = request[:_meta]
-      if meta && @server_context.is_a?(Hash)
-        context = @server_context.dup
+      if meta && server_context.is_a?(Hash)
+        context = server_context.dup
         context[:_meta] = meta
         context
-      elsif meta && @server_context.nil?
+      elsif meta && server_context.nil?
         { _meta: meta }
       else
-        @server_context
+        server_context
       end
     end
   end
diff --git a/test/mcp/server_test.rb b/test/mcp/server_test.rb
index fac919b6..c7d7ec7d 100644
--- a/test/mcp/server_test.rb
+++ b/test/mcp/server_test.rb
@@ -1731,5 +1731,31 @@ def call(numbers:, strings:, objects:, server_context: nil)
         end
       end
     end
+
+    test "server_context_with_meta uses accessor method, not ivar directly" do
+      subclass = Class.new(Server) do
+        def server_context
+          { custom: "from_accessor" }
+        end
+      end
+
+      server = subclass.new(name: "test", tools: [])
+
+      received_context = nil
+      server.define_tool(name: "ctx_tool") do |server_context:|
+        received_context = server_context
+        Tool::Response.new([{ type: "text", text: "ok" }])
+      end
+
+      request = {
+        jsonrpc: "2.0",
+        method: "tools/call",
+        id: 1,
+        params: { name: "ctx_tool", arguments: {} },
+      }
+
+      server.handle(request)
+      assert_equal "from_accessor", received_context[:custom]
+    end
   end
 end