RIDL intermediate representation.
The v2 schema (proto/ridl/ir/v2/ir.proto) is compiled from its protobuf
source by build.rs (protox + prost-build, ADR-0006 decision 3) and
exposed as [v2]. v2 is the typl surface plus the ridl interaction layer
(ridl language reference §3–§14) with exact decimal values — every numeric
value is a canonical decimal string, never a floating-point field (ADR-0007
decision 9, ADR-0008 decision 12). The v1 schema was removed when its last
consumer moved to v2 (task 6 of the E2 plan), mirroring the E1 v0→v1
retirement.