이건 누가 눌러도 되나 — 버튼을 숨기는 것은 권한이 아니다

[staff] sale.ring   -> "rang 3000"                        (sales=4 voided=0 refused=0)
[staff] sale.void   -> "sale.void is not yours to press"  (sales=4 voided=0 refused=1)
[staff] drawer.open -> "drawer.open is not yours to press"(sales=4 voided=0 refused=2)

[manager] sale.ring   -> "rang 3000"     (sales=4 voided=0 refused=0)
[manager] sale.void   -> "voided 3000"   (sales=3 voided=1 refused=0)
[manager] drawer.open -> "drawer opened" (sales=3 voided=1 refused=0)

screen ui/pages/register.json sha256:72288a2c655a — one file, both roles
the screen offers 3 buttons and shows all of them to everyone

/// Who this session is. Fixed for its lifetime, never taken from a call.
final String role;

sale.void { "role": "manager" }

final role = args
    .firstWhere((a) => a.startsWith('--role='), orElse: () => '--role=staff')
    .substring('--role='.length);

# The screen may *display* the role it was told. It must never name one — the
# moment "manager" or "staff" appears in a screen definition, some branch is
# being decided in the wrong place.
if grep -qiE '"[^"]*(manager|staff)' register.mbd/ui/pages/register.json; then
  echo "   the screen definition names a role — the rule has leaked out of the tool"
  exit 1
fi

/// Refusals go here as well as into the answer. A refusal that only the
/// person who was refused can see is not much of a control — the point of
/// writing it down is that somebody who was not standing there can read it
/// tomorrow.
final File audit;

audit log holds 2 lines: refused sale.void for role=staff | refused drawer.open for role=staff

AUDIT=$(wc -l < register_server/audit.log | tr -d ' ')
[ "$AUDIT" -eq 2 ] || { echo "   audit log has $AUDIT lines, expected 2"; exit 1; }