Function to_miniscript_descriptor 

pub fn to_miniscript_descriptor(
    d: &Descriptor,
    chain: u32,
) -> Result<Descriptor<DescriptorPublicKey>, Error>

Convert an md1 Descriptor AST to a miniscript::Descriptor<DescriptorPublicKey> for chain (the multipath alt selector). The trailing wildcard /* remains for miniscript::Descriptor::at_derivation_index to resolve.

chain is resolved in-place during key construction (multipath alt substituted into each DescriptorXKey.derivation_path); the resulting Descriptor is single-path.

Errors

• Error::MissingPubkey / Error::InvalidXpubBytes / Error::MissingExplicitOrigin propagated from expand_per_at_n.
• Error::AddressDerivationFailed wrapping any miniscript-layer failure (type check, context error, unsupported fragment) or arity mismatch raised by the converter.