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    prove_message: RuntimeDescriptor<
        [leaf_index: bigint],

            | {
                leaf: FixedSizeBinary<32>;
                leaf_index: bigint;
                number_of_leaves: bigint;
                proof: FixedSizeBinary<32>[];
                root: FixedSizeBinary<32>;
            }
            | undefined,
    >

    Generate a merkle proof for a committed message identified by leaf_index. The merkle root is stored in the block header as a sp_runtime::generic::DigestItem::Other