feat: Ensure system headers are preserved in streamable HTTP tests

To maintain consistency and ensure the integrity of HTTP headers during tests, system headers like Content-Type are now verified to be preserved. This change enhances the reliability of our testing framework by ensuring essential headers are not inadvertently removed or altered during the testing process.

Signed-off-by: Matthis Holleville <matthish29@gmail.com>

Author: matthisholleville

client/transport/streamable_http_test.go

@@ -267,6 +267,11 @@ func TestStreamableHTTP(t *testing.T) {
 		if headerValues, ok := result["X-Test-Header"].([]any); !ok || len(headerValues) == 0 || headerValues[0] != "test-header-value" {
 			t.Errorf("Expected X-Test-Header to be ['test-header-value'], got %v", result["X-Test-Header"])
 		}
+
+		// Verify system headers are still present
+		if contentType, ok := result["Content-Type"].([]any); !ok || len(contentType) == 0 {
+			t.Errorf("Expected Content-Type header to be preserved")
+		}
 	})
 
 	t.Run("SendRequestWithTimeout", func(t *testing.T) {