This file is the authoritative list of FPM record keys. A key exists once it has
an entry here; its meaning is what its entry says. The specification
(fpm-standard.md) defines the format itself; this registry defines the
vocabulary. keys.json mirrors these entries for tooling and MUST stay in sync.
Registry rules, from specification section 3.6:
- Keys are never removed or reused. A key that turns out badly is marked