[bug]: `DecodeAssetPayReq` not working right with `group_key` defined

[ZZiigguurraatt]

I'm trying to use DecodeAssetPayReq with a group_key defined but I'm getting the error

error deriving asset amount: error querying ask price: OracleError(code=0, msg=Unsupported subject asset)

even though my price oracle is configured for the group_key. Then I look at the code and I see that DecodeAssetPayReq tries to request the price of the first asset_id in the group:

taproot-assets/rpcserver.go

Lines 9667 to 9720 in 8ff0ae9

	// The group key is a bit more involved. We first need to sync the asset
	// group, then fetch the leaves that are associated with this group key.
	// From there, we can look up the asset ID of one of the group's
	// tranches.
	case len(payReq.GroupKey) != 0:
	var (
	groupKey *btcec.PublicKey
	err error
	)
	if len(payReq.GroupKey) == 32 {
	groupKey, err = schnorr.ParsePubKey(payReq.GroupKey)
	} else {
	groupKey, err = btcec.ParsePubKey(payReq.GroupKey)
	}
	if err != nil {
	return nil, fmt.Errorf("error parsing group "+
	"key: %w", err)
	}
	assetID, err = r.syncAssetGroup(ctx, *groupKey)
	if err != nil {
	return nil, fmt.Errorf("error syncing asset group: %w",
	err)
	}
	tapdLog.Debugf("Resolved asset ID %v for group key %x",
	assetID.String(), groupKey.SerializeCompressed())
	}
	// With the inputs validated, we'll first call out to lnd to decode the
	// payment request.
	rpcCtx, _, rawClient := r.cfg.Lnd.Client.RawClientWithMacAuth(ctx)
	payReqInfo, err := rawClient.DecodePayReq(rpcCtx, &lnrpc.PayReqString{
	PayReq: payReq.PayReqString,
	})
	if err != nil {
	return nil, fmt.Errorf("unable to fetch channel: %w", err)
	}
	resp := tchrpc.AssetPayReqResponse{
	PayReq: payReqInfo,
	}
	// Next, we'll fetch the information for this asset ID through the addr
	// book. This'll automatically fetch the asset if needed.
	assetGroup, err := r.cfg.AddrBook.QueryAssetInfo(
	ctx, asset.NewSpecifierFromId(assetID),
	)
	if err != nil {
	return nil, fmt.Errorf("unable to fetch asset info for "+
	"asset_id=%x: %w", assetID[:], err)
	}

but my price oracle doesn't know about all the asset tranches, so that is why I'm thinking it is failing.

I don't think DecodeAssetPayReq should query the price oracle based on the first asset_id in the group. Instead, it should query the price oracle based on the group_key, I think that is what all the other RPC do that support group_key.