009 empty branch no binding

// Test: Empty branch {} rejects binding attempts
//
// NEGATIVE TEST - This should fail shape checking
//
// When a branch is declared with {} (empty), it means "no payload to bind"
// Attempting to bind with `| done x |>` should be a shape checker error
//
// This is the counterpart to 020_008 which tests { * } allowing bindings

~import "$std/io"

// Event with empty payload - nothing to bind
~event signal_done {}
| done {}

~proc signal_done {
    return .{ .done = .{} };
}

// INVALID: trying to bind `x` to a {} branch
// Shape checker should reject this
~signal_done()
| done x |> std.io:println(text: "should not compile")