Adding onto this: using this and this, for 1 nm X-rays (~1.2 keV), I think that a tenth of a millimetre (100 μm) of gold would be enough to block ~all of the output from a 1nm runic HOWS (comes out for me as intensity reduced by a factor of about 10^84). This seems intuitively very weird, but remember that gold leaf has a thickness of <1 μm and still looks largely opaque in the visible; I think it's plausible. (That said, it's also very plausible that I've done the calculations wrong or misunderstood something; this is very not my field!)
As @strange_person says, there's no obvious reason Hazō should have to jump straight to gamma rays; it would make perfect sense for him to try "past-past-blue" before "pastest-blue". In fact, this would provide the major advantage that a large enough thickness of stone (e.g. MEW) would probably work to shield him from it, and unlike the gold armour that's a thing that Hazōpilot would plausibly think of immediately ("well, I can't see the light, but if it's light maybe a wall will block it out").
