Node::DynamicSubgrammar factories build a Node from the WalkContext and
must Box::leak it (the Node enum's combinator children are &'static).
Leaking per walk grew unbounded under per-keystroke completion
(handoff-12 §2.1).
resolve_dynamic now memoizes on the schema state a factory reads
(table columns, current column, user-listed columns) keyed by factory
fn-pointer. Each distinct value-list shape leaks exactly once — total
leak bounded by distinct (schema × form) combinations, not keystroke
count. TableColumn gains Hash for the cache key.
The handoff's original arena sketch needed a lifetime-generic Node
(major refactor); memoization gets the same bound without it.
claude@clouddev1
9bbb96e735