The phase a prompt step runs in, named by the planner that cut it: a whole
planned chunk (exactly the step's chunk size), a tail (any other number
of positions above one: what is left after the whole chunks, or a piece a
snapshot boundary cuts short), or decode, a single position, which appends
through the one-position read.
The phase a prompt step runs in, named by the planner that cut it: a whole planned
chunk(exactly the step's chunk size), atail(any other number of positions above one: what is left after the whole chunks, or a piece a snapshot boundary cuts short), ordecode, a single position, which appends through the one-position read.