unblockCdcPort
open suspend override fun unblockCdcPort(excluding: Set<String>, waitMillis: Long, holdMillis: Long): Boolean(source)
Opens the port that appeared since excluding was captured and holds DTR asserted, so firmware waiting on a host will run.
The SoftDevice-specific nRF52 erase sketch blocks in while (!Serial) before InternalFS.format(), and Serial only becomes truthy once DTR is asserted — without this the erase never starts. A failure here is therefore safe: the image is written but has destroyed nothing. Never called after the bootloader-driven erase image: the only port present then is the bootloader's own (see MaintenanceUf2.requiresCdcUnblock).
Return
true when a port was claimed and DTR held.