Function with_calibration_tape 

fn with_calibration_tape<T>(
    f: impl FnOnce(&mut Tape<f64>, &mut Vec<f64>) -> T,
) -> T

Runs f on this thread’s calibration tape and adjoint buffer: created on the first call, kept at the largest capacity either ever reached, the tape cleared on every recording. Its own rather than the trading layer’s — that one is the tape a risk pass is recording on, and a calibration inside a risk pass has already been routed away from here.

The buffer is kept for the same reason the tape is: a forty-pillar ladder’s is 2.5 MB, and a fresh allocation of that size per calibration is page faults the sweep then pays for.