SOR - Fix BPT rates on swap with add/remove liquidity step

[brunoguerios]

Closes #2452

[changeset-bot]

🦋 Changeset detected

Latest commit: 78dc526

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
backend	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[brunoguerios]

@jubeira - tagging you so you can provide feedback on the expected behavior:

Comparing this tenderly simulation with the SOR I found out that the SOR was applying rates to the bptAmountIn on the swapExit givenIn operation while on-chain math wasn’t.
The logical conclusion is that we shouldn’t consider rates on these cases, but I’m not sure of the expected behavior.
So, my assumption is that:

• we shouldn’t take BPT priceRate into account when swapping it with its pool tokens (i.e. swapExit/swapJoin)
• we should take BPT priceRate into account when swapping it with a token in another pool (i.e. regular swap in a nested pool)

Let me know if you think that makes sense.

[jubeira]

Yes, that's correct. In any case in a nested pool the rate of the bpt token will be consumed via a rate provider, so it shouldn't be a special case.