01 Build
The descriptor stays honest; the file claims one extra data byte. The size equations catch it.
02 The 64 bytes — click to corrupt
header/flags
formats
grouping
note (unhashed)
placements
grade_id
Clicking XORs the byte with 0x01 — a single-bit flip, the smallest possible lie. Bytes 28–31 (note) are the only ones the fingerprint ignores; corrupt those and identity holds.
03 Identity & size equations
| grade_id | |
| gid (128-bit) | |
| gid (crockford) | |
| elements | |
| groups L0 / L1 | |
| plane bytes |
The gid hashes grade ‖ frame ‖ shape — computed identically by the C, C++, Rust, Python, and TypeScript implementations (CI proves 96/96 agreement on every push).
04 The O(1) check
GRIT_OK descriptor, shape, and plane bytes agree.
This is the same grit_check that costs 296 ns in C at a load boundary. It evaluates the normative rule order and reports the first failure — corrupt several bytes and it still names the earliest one.
05 Encode → planes → decode, round trip
Planes (hex)
Decoded values & max abs error