ToME: the Tales of Maj'Eyal

Oneshot while resting at full health in Normal / Adventure

and that's bud because... well, lets see what could it be.

lets start with this.
there were the same number of "light retaliation" as the physical attacks received.
and yes here it is "deactivates chant of fortitude".
they are all int he same message, therefore you were hit by a single multi-hit talent. also, they can only retaliate in melee.
stealth + flurry is most likely.
also, there are 4 critical damage messages, and you stopped resting right after the first crit, so you cant blame "slept through the damage".

now again, which part of this is supposed to be a bug?

edit
btw, pretty sure the second lvl of the steal category increase your damage while stealthed, and then you also have "lethality" wich may increase the crit mod, so, the damage can ramp up.

Yes a stealth flurry. The point is not that it kept resting after the damage, which was a single turn.

The point is that I believe the balance goal was to not allow oneshotting in normal. My character had 2 +life items and a decent investment in constitution.

it did stop resting after the first hit.
the problem is that flurry, is a talent that has multiple hits.
all 6 hits are supposed to happen at the same turn, so after you stopped resting, the rogue continued and dealt another 3 blows.
there is no bug here.

Not to mention that an Orc Grand Master Assassin is very out of depth for a level 24.

Sounds like it came from a vault, offhand. Had you opened any, on that level? Dreadfell vaults are notoriously out of depth.