15. Open Issues

15.1 Choices to settle at implementation time

Where provenance lives: the .crn header or the lock. The tentative policy is that the .crn carries only @intended_targets as a hint, and records such as verified are written into the lock by the compiler (Versioning and Editions).

The type of the reverse-direction IR: one IR that can degenerate, or separate Intent IR and Raw Geometry IR types. The tentative policy is to share the block-array layer and split types at the member layer above it (Architecture).

Legacy .schematic from before 1.13 is unsupported in v1. A numeric-ID mapping could be considered later as an option.

15.2 Untouched topics

Coordinate system. Keep the corner origin and front = +z fixed, or introduce a centre origin, an entrance-relative orientation, or a per-floor local y=0 such as level id=floor2 y=4.

Primitive promotion. Whether hip, flat, and pyramid roofs, columns, arches, and repeat should become semantic primitives. The decision rests on experimental data from the Evaluation Framework.

Interiors. Whether the inside.front prefix suffices or a higher-level room concept is needed, and whether furniture can be served by a def library.

15.3 Language-evolution policy

How to handle breaking changes as Cairn evolves is not settled. The options are a Rust-style “edition” mechanism with year-based opt-in, or announcing changes per release in the CHANGELOG. Note that “edition” already means Java or Bedrock here, so a different term would be needed. For now the latter suffices: CalVer plus @cairn provenance.