[bug]: need to enforce common `decimal_display` across all minted traunches of a grouped asset when validating proofs

[ZZiigguurraatt]

When minting additional traunches of a grouped asset, we have the freedom to define different metadata when minting each traunch.

decimal_display is stored in the asset metadata. Right now when minting, we have a simple check to see if the same decimal_display used for additional traunches is the same as the first traunch:

https://github.com/lightninglabs/taproot-assets/blob/main/tapgarden/seedling.go#L201-L225

However, this isn't really enforced on the client side right now when validating proofs. Therefor, a node minting assets could remove the check above and mint a second traunch with a different decimal_display and then the nodes using the taproot assets from multiple traunches won't really notice and then there could be confusion in the marketplace because different people are assuming different decimal_display values for the asset.

We need to enforce this client side when validating proofs for an asset. Although there might be uses cases for different metadata for different traunches (which is why we have the freedom to change it), decimal_display is one use case in the metadata that it doesn't make sense for it to be able to change from one traunch to another traunch.

[ZZiigguurraatt]

We may just want to ignore any decimal_display defined in metadata for additional traunches instead of compare to the first traunch issuance in the group. It doesn't really make sense to keep embedding that data and taking up more data when we know it should not change from traunch to traunch.

[ZZiigguurraatt]

Wondering, do we have the same issue with the asset name?

[ZZiigguurraatt]

We may just want to ignore any decimal_display defined in metadata for additional traunches instead of compare to the first traunch issuance in the group. It doesn't really make sense to keep embedding that data and taking up more data when we know it should not change from traunch to traunch.

However, places like custom channel data (https://github.com/lightninglabs/taproot-assets/blob/main/rfqmsg/custom_channel_data.go) we have the decimal display for each asset ID tracked in funding_assets, but not the group. If someone funds the channel from an asset_id that is not from the first traunch, the decimal_display won't be tracked if we only store the decimal_display in the first traunch, so we will need to rework the custom channel data format once again.

Similar issue for name.

[guggero]

The asset name is explicitly allowed to be different. Since the name shouldn't be the uniquely ("authoritative") identifying property (that should always be the asset ID or group key).
But yes, the decimal_display value should be compared and asserted against the first mint event. We currently do that only during minting but not at proof verification.

[ZZiigguurraatt]

The asset name is explicitly allowed to be different. Since the name shouldn't be the uniquely ("authoritative") identifying property (that should always be the asset ID or group key).

True, because if someone makes another group_key, they can always give it the same name.

However, why do we have the name at all if it can be different inside the same group or the same across groups?

It seems like name just creates confusion either way since we have no way to enforce it as an identifier. I'm now wondering if we should remove the name completely and use something external like https://spacesprotocol.org/ to enforce uniqueness of a name to a group_key and not even try to enforce names of asset_id at all?