Many transceivers use the ALC facility to progressively reduce the drive with worsening mismatch. PicAStar has no such ALC system and doesn't need it.
Picswr provides the facility to shut down the PA if reflected power is above a specified level for a specified time interval. The power level is specified in the reflected calibration window. The time interval is determined by R13 / C7 on Picswr circuit board. My default provision is > 4w for approx 8 seconds. This arrangement allows you to tune at full power for eight seconds or more. The 'shut down' output is an open collector NPN transistor.
The reflected calibration screen has an extra data entry box for 'Mismatch Watts'