TSIG RR is stripped on packet parsing.

src/knot/server/zone-load.c

src/knot/server/zones.c

src/libknot/dname.c

src/libknot/packet/pkt.c

src/libknot/packet/pkt.h

src/libknot/tsig-op.c

src/libknot/tsig-op.h

src/libknot/updates/xfr-in.c