Prevent Villager from restocking in Vanilla game?

Is it possible to (and, if so, how do you) spawn in a villager which is incapable of restocking?

I’m going to make a guided Skyblock-like map, with the villager’s trades representing different progression tasks (e.g. get 64 cobblestone); I want to make this in an entirely Vanilla way. I want to disable "grinding" for the rewards, however; they should be finite even if they require renewable resources.

(I actually do want, if possible, some custom trades to be gated behind level progression; this would make for an extra degree of freedom in the design; but that’s not a hard requirement and is out of primary scope of this question.)

• Can one program it to think that its job block must be a Dragon Egg or Barrier block (which it will never find, thus never claim, thus never restock)?
• Can one create a Nitwit (villager unable to claim a job site) who has been, nevertheless, spawned in with some artificial trading ability?
• If one simply assigns it a job block, which is encased in Barrier at y=0, can a crafty player nevertheless convince the villager to abandon it in favor of an accessible one?

Generally: is there any way to do this without mods?

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This is related to, but not a duplicate of, “How do I prevent new villager trades from spawning?”.

• That question concerns how to prevent villagers from unlocking new trades when the villager levels up
• I am asking how to prevent them from restocking existing trades when they are exhausted