A multicenter randomized controlled trial of prophylactic intraperitoneal normothermic chemotherapy for resectable locally advanced gastric/gastroesophageal junction adenocarcinoma (cT4a >= 4 cm or cN2-3)

INTERVENTION: Experimental group:Intraoperative placement of the abdominal chemotherapy port and postoperative prophylactic intraperitoneal normothermic chemotherapy;Control group:none; CONDITION: Resectable locally advanced gastric/gastric‐cardiac junction adenocarcinoma (cT4a >= 4cm or cN2‐3) PRIMARY OUTCOME: Event‐free survival; SECONDARY OUTCOME: Overall survival;disease‐free survival;Peritoneum recurrence‐free survival and safety; INCLUSION CRITERIA: 1. Histologically confirmed gastric/gastroesophageal junction adenocarcinoma; 2. Resectable by CT assessment and meets at least one of the following: cT4a, tumor maximum diameter >= 4 cm, or cN2‐3, estimated metastatic lymph nodes >= 3; 3. No distant metastasis (cM0); 4. Esophageal invasion <= 3 cm; 5. Age >= 18 years, ECOG PS 0‐1; 6. No prior chemotherapy, radiotherapy, targeted therapy, or immunotherapy; 7. Not residual gastric cancer or recurrent cancer; 8. Laparoscopic exploration P0/CY0; 9. No need for combined thoracoabdominal incision, Appleby procedure, or combined pancreaticoduodenectomy; 10. No gastrointestinal obstruction; 11. Major organ function meets criteria (ANC >= 1.5 × 10^9/L, PLT >= 100 × 10^9/L, Hb >= 90 g/L, TBil <= 1.5 × ULN, ALT/AST <= 2.5 × ULN, CrCl >= 50 mL/min); 12. Cohort C: thyroid function and myocardial markers show no clinically significant abnormalities; 13. Negative pregnancy test for