Adebrelimab Combined With Induction Chemotherapy or SHR-8068 for Mismatch Repair-Deficient/Microsatellite Instability-High (dMMR/MSI-H) Locally Advanced Gastric/Gastroesophageal Junction Adenocarcinoma：A Randomized, Non-comparative Phase 2 Study

Inclusion Criteria: * Male or female, age ≥ 18 years * Pathologically confirmed gastric or gastro-oesophageal-junction adenocarcinoma (Siewert II and III only) * dMMR confirmed by IHC or MSI-H confirmed by PCR * Investigator-assessed potentially curative resection feasible before study entry * CT or MRI clinical stage cT ≥ 2 N any M0 per AJCC 8th edition; laparoscopy with peritoneal washing cytology (and peritoneal biopsy if indicated) recommended to exclude peritoneal metastasis * ECOG performance status 0-2 * Able to swallow tablets * Expected survival ≥ 6 months * Laboratory values within 7 days before randomisation: ANC \> 1.5 × 10⁹/L, Hb ≥ 80 g/L, PLT ≥ 75 × 10⁹/L Serum creatinine ≤ 1.5 × ULN or eGFR ≥ 60 mL/min/1.73 m² ALT and AST ≤ 2.5 × ULN; total bilirubin ≤ 1.5 × ULN (or TBIL \> 1.5 × ULN with direct bilirubin ≤ ULN); albumin ≥ 25 g/L INR or PT ≤ 1.5 × ULN and aPTT ≤ 1.5 × ULN (or on anticoagulation within therapeutic range) * Signed written informed consent; able to comply with protocol visits, treatment, labs, biospecimen collection * WOCBP must have negative serum pregnancy test within 72 h before randomisation, not breastfeeding, and use highly effective contraception from screening until 2 months after last adebrelimab/SHR-8068 or 6 months after last chemotherapy, whichever is longer * Men with pregnant partners or WOCBP partners must be surgically sterile or use highly effective contraception during study and for same post-treatment periods; no sperm donati…