The String() version of BlockNumberOrHash uses decimal for all block numbers, including negative ones used to indicate labels. Switch to using BlockNumber.String() which encodes it correctly for use in the JSON-RPC API.
Currently rpc.BlockNumber is marshalled to JSON as a numeric value, which is
wrong because BlockNumber.UnmarshalJSON() wants it to either be hex-encoded
or string "earliest"/"latest"/"pending". As a result, the call chain
rpc.BlockNumberOrHashWithNumber(123) -> json.Marshal() -> json.Unmarshal()
fails with error "cannot unmarshal object into Go value of type string".
- returned headers didn't include mixHash
- returned transactions didn't include signature fields
- empty transaction input was returned as "", but should be "0x"
- returned receipts didn't include the bloom filter
- "root" in receipts was missing 0x prefix
