Module encode 

Top-level bytecode encoder: KeyCard → canonical Vec<u8>.

Per design/SPEC_mk_v0_1.md §3.2 payload field order (closure Q-6):

[bytecode_header   : 1 B]
[stub_count        : 1 B; MUST be ≥ 1]
[policy_id_stubs   : 4 × N B]
[origin_fingerprint: 4 B]   ← present iff bytecode_header bit 2 set
[origin_path       : variable]
[xpub_compact      : 73 B]

Functions

encode_bytecode

Encode a KeyCard to its canonical bytecode form (pre-chunking).