// Koru Standard Library: Reactive Stores — the `preorder` event.
// Joined via `~part preorder` in store.kz; merged into the store module at load.
//
// STORE.PREORDER — DFS pre-order forest walk over a [tree] store
//
//   std/store:preorder(tree)
//   ! preorder { entity.val } |> …
//
// The tree-store traversal surface (695_STORE_TREE, TT5). The coordinator
// (create) has already transplanted this site's projection/guard/body into
// qrow/qbody units — identical to query — and emitted a DFS pre-order sweep
// over the synthesized `parent` column (roots first, insertion order; each
// node before its children). The site itself becomes that sweep's call.
// Preorder on a non-[tree] store is rejected by the coordinator with a
// teaching diagnostic (no parent column to walk).
~[keyword|comptime|transform|claims_descendants] pub tor preorder {
    expr: Expression,
    invocation: *const Invocation,
    item: std/compiler:*const Item,
    program: std/compiler:*const Program,
    reporter: std/compiler:*ErrorReporter,
    allocator: std.mem.Allocator
} -> SiteResult