zerodds-lang-rules

Maps the common AST onto the language CSTs.

The rules are data, not code. A rule is a RuleV2 value: it names an L-side pattern over the model, an R-side pattern over a language CST, and the correspondences between them. It can be compared, serialised, and checked for completeness. Two languages' treatment of @optional is a diff between two values, not a reading of two emitters three thousand lines apart.

Rules are minimal and positive: small rules that compose, monotone and add-only, with no negative application conditions. One rule maps a struct to a type declaration; a second maps a member to a field; a third adds a derive. A single rule doing all three could not be reused for the members of a union.

The engine is seesaw's v2 layer — seesaw_core::v2. The crate carries both rule layers side by side until the 1.1.0 cut, so binding the crate is not by itself enough to land on the right one.

See docs/specs/zerodds-lang-cst-1.0.md §2 to §4.