Constant ABI_VERSION 

pub const ABI_VERSION: u32 = 4;

Current ABI version. Bump on any breaking change to instruction encoding, constant representation, or function-table layout.

v2: Value::Message wire tag 5. v3: Message.reply_cap; Value::Cap wire tag 6 (FlowCap). v4: Value::Str tag 7, Value::Bytes tag 8.