Node-Sparing Short-Course Radiotherapy (25 Gy/5 Fractions) Combined With Chemoimmunotherapy as Neoadjuvant Treatment for Locally Advanced Esophageal Squamous Cell Carcinoma：A Prospective Single-Arm, Phase II Study

Inclusion Criteria: * Written informed consent before enrollment. * Age 18 to 75 years, any sex. * Treatment-naive esophageal squamous cell carcinoma confirmed by pathology and PET-CT. * Clinical stage cT1b-3N1-2M0 or cT2-3N0M0 (stage II/III according to the AJCC 9th edition). * Disease assessed as amenable to R0 surgical resection before treatment. * At least one measurable lesion according to RECIST v1.1. * ECOG performance status 0-1. * Adequate organ function: absolute neutrophil count ≥1,500/mm³; platelets ≥100,000/mm³; hemoglobin ≥9 g/dL; serum creatinine ≤1.5 mg/dL and/or creatinine clearance ≥60 mL/min; bilirubin ≤1.5×ULN; AST and ALT ≤1.5×ULN; no blood components or hematopoietic growth factors within 14 days. * For women of childbearing potential: medically accepted contraception during treatment and for 3 months afterward; negative serum or urine HCG within 7 days before enrollment; not breastfeeding. * For men who are not surgically sterile: agreement to use medically accepted contraception with their partner during treatment and for 3 months afterward. * Willingness to participate and comply with safety and survival follow-up. Exclusion Criteria: * Prior radiotherapy, chemotherapy, prolonged/high-dose corticosteroid therapy, surgery, or molecular targeted therapy. * Previous or concurrent other malignancy. * Prior PD-1/PD-L1 therapy; known allergy to macromolecular protein preparations or any component of PD-1 therapy. * Active autoimmune disease or relevant autoimmune disease history as specified in the protocol. * Immunosuppressive agents for immunosuppression within 2 weeks before enrollment. * Symptomatic pleural or peritoneal effusion requiring therapeutic puncture or drainage. * Poorly controlled clinically significant cardiac disease as specified in the protocol. * Abnormal coagulation with bleeding tendency or thrombolytic/anticoagulant therapy. * Recent gastrointestinal conditions associated with bleeding or perforation risk. * Severe bleeding within 3 months, hemoptysis within 4 weeks, or thromboembolic event within 12 months according to protocol thresholds. * Active infection or unexplained fever \>38.5°C during screening or before first dose. * Abdominal fistula, gastrointestinal perforation, or intra-abdominal abscess within 4 weeks before study treatment. * History/current pulmonary fibrosis, interstitial pneumonia, pneumoconiosis, radiation pneumonitis, drug-related pneumonitis, or severe pulmonary dysfunction. * Congenital/acquired immunodeficiency including HIV infection, or active hepatitis outside protocol-defined limits. * Participation in another clinical study or completion of a previous clinical study within 1 month; anticipated need for other systemic anticancer therapy. * Live vaccine within 4 weeks before study treatment or anticipated during the study. * Known history of psychotropic drug abuse, alcohol abuse, or illicit drug abuse. * Unable or unwilling to bear self-paid portions of study-related examinations or treatment. * Any other condition considered by the investigator to compromise participant safety, study completion, or data/sample collection.