I agree with both points of view, in ways, both Rindert and Kristijan. The downdraft design forces the steam to pass through the glowing char, largely addressing the concern of exposing H2O to cracking temperatures.
But, at shut down the effect of heat producing steam will take over, leading to condensation in the system, and drying of the fuel. Also, if steam production was excessive in operation I might imagine it making “wormholes” through the char bed, avoiding cracking.
The only ways I see to avoid these problems would be “just in time” feeding of damp char, impossible to achieve without advanced sensing, or avoiding damp char, introducing steam as in the steam cooled nozzle designs, or a water metering carburetor, as suggested by Max, @gasman.
Great progress and innovation in design anyways, as has been said, probably the most compact gasifier to ever run a passenger vehicle. Once the bugs are worked out it will be a marvel.