Apps like Zwift have control only over initiating those procedures.
What Zwift needs to know and implement is described in common spec documents.
On the bluetooth side of things those are the Cycling Power Service spec and the FTMS spec.
In the FTMS spec look for section 4.16.2.20 Spin Down Control Procedure:
And that is appendix 3:
In the Cycling Power Service look for section 3.4.2.16 Start Enhanced Offset Compensation Procedure:
You can search for and downwoad those and other related documents at: GATT specifications
Full documents are at (downloads a pdf): Cycling Power Service, Fitness Machine Service