// Feature 1 / Step 1.2 — pack-expansion forms PARSE in all four positions.
//
// Parse-only probe. Spread reuses the existing `spread_expr` node (its operand
// carries projection `xs.field` / type-application `F(Ts)`); closure-sig packs
// use `ClosureTypeExpr.pack_name` + the new `pack_projection`. Sema/lowering
// arrive in Phase 2 — do NOT expect this to compile/run yet. The authoritative
// checks are the parser unit tests in src/parser.zig ("parse pack expansion: …").

// 1. Tuple value position — `(..pack)` / `(..pack.field)`:
tv1 :: () => (..xs);
tv2 :: () => (..xs.value);
tv3 :: () => (a, ..xs, b);            // mixed positional + spread

// 2. Tuple type position — `(..F(Ts))` / `(..F(Ts.Arg))`:
tt1 :: (x: (..ValueListenable(Ts)))       => x;
tt2 :: (x: (..ValueListenable(Ts.Arg)))   => x;

// 3. Call-arg position — `..pack` / `..pack.field` (reuses spread_expr):
ca1 :: () => f(..xs);
ca2 :: () => f(..xs.value);

// 4. Closure-sig position — `Closure(..Ts)` / `Closure(..Ts.Arg)`:
cs1 :: (cb: Closure(..Ts) -> s32)         => cb;
cs2 :: (cb: Closure(..sources.T) -> s32)  => cb;