PCE-Guided Reliability-Aware Intraday Reserve Dispatch with Wind Headroom and Fast-Start Backup

High shares of renewable generation make intraday dispatch sensitive to forecast error, reserve deliverability, and credible equipment outages. This paper presents a Polynomial Chaos Expansion (PCE)-guided reliability-aware reserve policy that coordinates thermal reserve, withheld wind-power headroom, and fast-start backup. The PCE output shapes the hourly probabilistic reserve band, whereas loss-of-load probability (LOLP) and expected energy not supplied (EENS) are independently evaluated on held-out scenarios. A paired six-policy ablation separates the contributions of PCE shaping, wind headroom, and fast-start backup. The results show that wind headroom without firm backup is not equivalent to thermal reserve, whereas adding fast-start backup restores reliability and yields the least-cost reliable policy; relative to the feasible PCE thermal-only policy, the complete joint policy reduces held-out cost by 7.59% while retaining a comparable LOLP. In a posterior unit-outage trajectory, the joint policy markedly reduces unserved energy through fast-start deployment and available wind headroom. A separate exact-dual Benders benchmark reaches the same objective as the single-cut benchmark with fewer iterations and less recorded CPU time.