I've succcessfully figured out how to make manual coin control transactions with the lnd wallet over grpc (in Python, but I'll probably rewrite in golang). Will prob drop it on github shortly. Will require a PR on lnd though, although it's minor.
Longer term goal has been to do something like this: build a kind of 'sidecar daemon' that runs against lnd and passively coinjoins using 'SNICKER' (see it on my joinmarket.me blog). I've also done some PSBT code that may be useful in btcsuite/btcuti.
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