Function parse_coinbase_height 

fn parse_coinbase_height(
    script_sig: &[u8],
) -> Result<(Height, Vec<u8>), SerializationError>

Parses the BIP-34 block-height prefix of a non-genesis coinbase script and returns the height along with the trailing miner data.

Consensus

A coinbase transaction for a block at block height greater than 0 MUST have a script that, as its first item, encodes the block height height as follows. For height in the range {1 .. 16}, the encoding is a single byte of value 0x50 + height. Otherwise, let heightBytes be the signed little-endian representation of height, using the minimum nonzero number of bytes such that the most significant byte is < 0x80. The length of heightBytes MUST be in the range {1 .. 5}. Then the encoding is the length of heightBytes encoded as one byte, followed by heightBytes itself. This matches the encoding used by Bitcoin in the implementation of BIP-34 (but the description here is to be considered normative).

https://zips.z.cash/protocol/protocol.pdf#txnconsensus

Strategy

Rather than parsing the height bytes ourselves, we read a candidate height directly off the wire (using the prefix shape to locate the bytes), then re-encode it via zcash_script::pattern::push_num — the same primitive used by [zcash_transparent::bundle::TxIn::coinbase] to build coinbase inputs — and require byte-exact equality. Any non-canonical input (wrong shape, non-minimal length, oversize, negative, signed-bit games) fails this check.