A 28-year-old woman from Mumbai presents with progressive epigastric pain, early satiety, and weight loss over 6 months. Upper endoscopy reveals diffuse gastric wall thickening with poor distensibility. Histopathology shows the cellular morphology marked as **A** in the diagram — cells with abundant intracellular mucin and peripherally displaced nuclei. Genetic testing reveals a heterozygous CDH1 mutation. Which of the following is the most appropriate management strategy for this patient?