Function apply_header_ops 

pub fn apply_header_ops(headers: &mut HeaderMap, ops: &HeaderOps)

Apply header manipulation ops in the frozen order (DW-028): set (replace-all), add (append), rename (relabel every value), then remove — see HeaderOps for the rationale. Every name/value was validated representable at config publish; the if let Ok skips are generation-tear backstops (never a panic, never a 500), the same posture as the respond-action headers.