# Design

The compiler owns marking semantics. `center-line-style` remains segment
scoped because a bidirectional road segment shares one centre-line decision.
`edge-line-style` is scoped to `{ roadId, side }`, since a directional
carriageway has independently editable left and right outside edges.

`double: true` is valid only with yellow solid centre lines. Generation emits
two 0.32m-separated parallel polygons for each normal solid mark, preserving
junction cutback and crosswalk/stop-line clearance. This keeps the existing
solid line implementation and avoids a separate geometry pipeline.

Road edge lines use the existing road-edge offset geometry. A solid style is
one continuous buffered offset line; a dashed style uses deterministic 2m
marks at 4m spacing. Both carry `effective_style`, source IDs, side, and
native provenance.

The Workbench uses one marking form with an explicit selected target type.
Only a centre-line target exposes the double-yellow option; lane separators
and edge lines retain the ordinary colour/pattern choices. Staged changes pass
through the existing save and regenerate flow, so browser, compiler and
Blender read the same persisted override.