c93f9394f5e0aa2e51e321e0efe01d1477ab9030
A new `src/dsl/grammar/sql_expr.rs` authored as a parallel fragment to `expr.rs` (the DSL `WHERE` grammar, ADR-0026). The ADR's stratified ladder lands as named `static` `Node`s, one per precedence tier: or_expr → and_expr → not_expr → predicate → additive → multiplicative → unary → primary Recursion through `Node::Subgrammar` reuses ADR-0026's `MAX_SUBGRAMMAR_DEPTH = 64` cap unchanged; no new walker capability is required. `predicate_tail` follows ADR-0026's factoring (shared operand prefix, infix `NOT` as an explicit branch, no `Optional`-first branch) so `Choice` discriminates cleanly. `name_or_call` factors the identifier-prefix shared between column refs and function calls into a single `Ident` followed by an `Optional` `( call_args )` tail — the same hazard-avoidance shape `predicate_tail` uses. The fragment exports `pub static SQL_OR_EXPR` (test entry) and `pub static SQL_EXPRESSION` (drop-in `Subgrammar(&SQL_OR_EXPR)` that SQL `CommandNode` shapes embed in their `Seq`). No AST builder — every Phase-1 consumer (SELECT projection, WHERE) runs validated SQL as text per ADR-0030 §4/§6. 13 unit tests cover every operator and precedence pair, the full predicate set, `CASE` (searched + simple) including `count(*)` and `count(distinct …)`, parenthesised regrouping, case-insensitive keywords, the depth cap, and a representative set of malformed inputs that do *not* walk. Module registered via one new line in `grammar/mod.rs`.
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