Query and Actual batch swaps of boosted pools are different sometimes

[joaobrunoah]

Sometimes, a batch swap query in a boosted pool returns a slightly different result from the actual swap. It happens because the batch swap of a boosted pool is composed of three steps:

• Wrap TokenIn
• Trade wrapped TokenIn by wrapped TokenOut
• Unwrap TokenOut

In the query mode, the first and third steps (wrap/unwrap) are only previews; we don't execute them, so the rate of the wrapped tokens doesn't change. However, the wrap/unwrap is executed in the actual operation so the total supply and total assets of the wrapped tokens change, and it introduces rounding issues in the order of 1 wei to the token rate. This rounding issue propagates to the boosted pool (2nd step) which uses a fixed 18 decimals rate, so it amplifies the error a bit for 18 decimal tokens.

[jubeira]

I think this is addressed already right?

There's still a difference that can't really be solved without moving tokens around, but that's expected.