It was not documented explicitly anywhere, but the len/wsl argument to
STV_NewObject() is the amount of space to allocate for all
OBJ_VARATTRs combined which are going to be written to this
object. For now, these are OA_HEADERS and OA_VARY only (see
include/tbl/obj_attr.h).

So for one, there is no reason to force this argument be greater than
zero when we know that no OBJ_VARATTRs are going to be set.

Secondly, this might actually represent a minor shortcoming of the
stevedore API, because the amount of space which a stevedore
implementation actually needs might be larger than what the simple
stevedores use. So for now, the semantics of this argument are, more
specifically, "the equivalent of space for OBJ_VARATTRs as for simple
storage". In practice, this probably does not matter much...

But even before this clarification, the API was not used consistently:

For the call from vrb_pull(), the maximum request body size (to cache)
was used as the wsl argument, yet it has nothing to do with the object
body size, it specifies the amount of space to allocate for variable
sized object attributes (see above).

For the call from cnt_synth(), a somehow arbitrary value of 1KB was
used.

In both cases, the amount of space actually required is zero, because
the only attribute used on the objects created is OA_LEN, which is
fixed and thus always present.