Bounded key/value metadata bag for IaC marking and customer tags.
See .rfcs/object-annotations.md §2. Limits: ≤16 entries; keys 1–128
chars matching ^[A-Za-z][A-Za-z0-9._/-]{0,127}$; values 0–256 chars
matching URL-safe ASCII; total serialized ≤4096 bytes. Keys starting
with c1/ are reserved for server-managed use and rejected on write.
Step sequences for this policy. The map must include a baseline entry keyed
by the lowercased policy type (e.g., "grant"). Additional entries with
opaque keys can be added for conditional routing via the rules array.