feat: add opt-in tool output validation

test/mcp/configuration_test.rb

@@ -74,6 +74,14 @@ module MCP
       assert_equal("validate_tool_call_arguments must be a boolean", exception.message)
     end
 
+    test "raises ArgumentError when validate_tool_call_results is not a boolean value" do
+      config = Configuration.new
+      exception = assert_raises(ArgumentError) do
+        config.validate_tool_call_results = "true"
+      end
+      assert_equal("validate_tool_call_results must be a boolean", exception.message)
+    end
+
     test "merges protocol version from other configuration" do
       config1 = Configuration.new(protocol_version: "2025-03-26")
       config2 = Configuration.new(protocol_version: "2025-06-18")
@@ -123,6 +131,40 @@ module MCP
       refute merged.validate_tool_call_arguments
     end
 
+    test "defaults validate_tool_call_results to false" do
+      config = Configuration.new
+      refute config.validate_tool_call_results
+    end
+
+    test "can set validate_tool_call_results to true" do
+      config = Configuration.new(validate_tool_call_results: true)
+      assert config.validate_tool_call_results
+    end
+
+    test "validate_tool_call_results? returns false when not set" do
+      config = Configuration.new
+      refute config.validate_tool_call_results?
+    end
+
+    test "validate_tool_call_results? returns true when set" do
+      config = Configuration.new(validate_tool_call_results: true)
+      assert config.validate_tool_call_results?
+    end
+
+    test "merge preserves validate_tool_call_results from other config" do
+      config1 = Configuration.new(validate_tool_call_results: true)
+      config2 = Configuration.new
+      merged = config1.merge(config2)
+      refute merged.validate_tool_call_results?
+    end
+
+    test "merge preserves validate_tool_call_results from self when other set" do
+      config1 = Configuration.new(validate_tool_call_results: true)
+      config2 = Configuration.new
+      merged = config2.merge(config1)
+      assert merged.validate_tool_call_results
+    end
+
     test "initializes with a default pass-through around_request" do
       config = Configuration.new
       called = false
@@ -183,5 +225,12 @@ module MCP
       end
       assert_equal("validate_tool_call_arguments must be a boolean", exception.message)
     end
+
+    test "raises ArgumentError when validate_tool_call_results is not a boolean" do
+      exception = assert_raises(ArgumentError) do
+        Configuration.new(validate_tool_call_results: "true")
+      end
+      assert_equal("validate_tool_call_results must be a boolean", exception.message)
+    end
   end
 end