Fail pending Streamable HTTP requests on POST 405

lib/ruby_llm/mcp/native/transports/streamable_http.rb

@@ -406,6 +406,7 @@ def handle_response(response, request_id, original_message)
               handle_authorization_challenge(response, request_id, original_message)
             when 405
               # Method not allowed - acceptable for some endpoints
+              fail_pending_request(request_id, response) if request_id
               nil
             when 400...500
               handle_client_error(response)
@@ -418,6 +419,19 @@ def handle_response(response, request_id, original_message)
             end
           end
 
+          def fail_pending_request(request_id, response)
+            response_body = response.respond_to?(:body) ? response.body.to_s : "Unknown error"
+            error = Errors::TransportError.new(
+              code: response.status,
+              message: "HTTP request failed: #{response.status} - #{response_body}"
+            )
+
+            @pending_mutex.synchronize do
+              queue = @pending_requests.delete(request_id.to_s)
+              queue&.push(error)
+            end
+          end
+
           def handle_success_response(response, request_id, _original_message)
             content_type = response.respond_to?(:headers) ? response.headers["content-type"] : nil
 

spec/ruby_llm/mcp/native/transports/streamable_http_spec.rb

@@ -2207,6 +2207,28 @@
           /no OAuth provider configured/
         )
       end
+
+      it "delivers a POST 405 response to the pending request instead of timing out" do
+        short_timeout_transport = described_class.new(
+          url: TestServerManager::HTTP_SERVER_URL,
+          request_timeout: 100,
+          coordinator: mock_coordinator,
+          options: { headers: {} }
+        )
+
+        stub_request(:post, TestServerManager::HTTP_SERVER_URL)
+          .to_return(status: 405, body: "Method Not Allowed")
+
+        expect do
+          short_timeout_transport.request({ "method" => "tools/list", "id" => "post-405" })
+        end.to raise_error(RubyLLM::MCP::Errors::TransportError) { |error|
+          expect(error.code).to eq(405)
+          expect(error.message).to match(/405/)
+        }
+
+        pending_requests = short_timeout_transport.instance_variable_get(:@pending_requests)
+        expect(pending_requests).not_to have_key("post-405")
+      end
     end
   end