Send this the moment the portfolio changes on your side: a withdrawal, a
trade, a deposit. Collateral value is what sets the margin call price, so a
change CLC does not know about is a margin call price that is wrong.

This is a full replace, not a delta. An asset you leave out is read as zero,
so always send the complete set of holdings.

as_of is when the portfolio was true on your side, not when you sent it. CLC
keeps the newest as_of it has seen and ignores anything older, so two updates
that arrive out of order cannot roll the portfolio backwards. When that happens
the response comes back with applied: false and the state CLC kept.

Deliberately takes no Idempotency-Key: a full replace ordered by as_of is
already safe to repeat, and this endpoint fires far too often to make you mint a
key each time.

Requires scope borrower:write.