The canonical limit values as NAMED constants (A14/A18) — construction sites use these, never a string literal, so a spelling cannot drift in the one field hosts branch on.

max_children/0, max_concurrent/0 and max_depth/0 are SPAWN/ADMISSION refusals: in elixir they surface as a verb error, never as a settled TaskResult (A17), so the port never emits them. The spelling is pinned here regardless, so that if one ever does settle it settles with the same word as every other port.