I know that the Mauser bolt shroud features the 'gas shield' flange, but god that's close to your face. Is it unheard of to have gas vents on the action ring up at the breech end of the action on a Mauser 98 action? What about additional gas vents on the bolt?

Go look at the underside of the bolt shank; two long oblong slots or gas vents made specifically forthis purpose. When the bolt is in battery the vents vent downward into the mag box.

The Mauser 98 is a work of art and absolute inginuity !

Designed as a weapon of war in a time of fighting in muddy wet climates with ammo that failed and in terms of bursts due to muzzle plugging with mud and snow this design was revolutionary. The "sloppy" tolerances in the mag follower and bolt was invaluable in adverse condition function.

The exctractor function was such that if a case stuck the extractor woule hang on no matter what, it could not slip, so you either hammered the bolt open and clreared the case or else rip the rim off, but it could not and did not let go.