Immutable shares are limited to what you can pay for with 10 passes right
now.  This certainly needs to be lifted but until it is we don't want spurious
test failures telling us about the limit.

Mutable shares are limited to what you can pay for with 1 pass right now
because the client doesn't know how to compute the right number of passes and
always spends 1 pass.

Integer division lets this number be zero sometimes.

If enough valid passes are supplied for the amount of storage requested then
allow the operation to succeed.  Otherwise, fail with an error.

We do so by introducing a limitation that the client must be configured with
an issuer and it must match the issuer announced by any storage server the
client is to talk to.

The client will decline to speak to any storage server without a matching
issuer.

Although ... the client resource doesn't really the part of the redeemer that
needs the announcement.  Maybe that part of the redeemer belongs somewhere
else.  Probably.

lots of mess to clean up though

Passes cannot be constructed until we know how we're going to use them since
they are derived from the unblinded tokens and an operation-specific message.