@layer layout {
  /* ===== App shell — sidebar + main ===== */
  .app-shell {
    display: grid;
    grid-template-columns: var(--sidebar-w) 1fr;
    height: 100dvh;
    overflow: hidden;
  }

  .main {
    display: flex;
    flex-direction: column;
    height: 100dvh;
    overflow: hidden;
    background: var(--bg);
  }

  .main__yield {
    flex: 1; min-height: 0;
    overflow-y: auto;
    padding: var(--s-8);
  }
  .main__yield--chat { padding: 0; overflow: hidden; }

  /* ===== Primitives ===== */
  .stack { display: flex; flex-direction: column; gap: var(--s-4); }
  .stack--sm { gap: var(--s-2); }
  .stack--lg { gap: var(--s-6); }

  .cluster { display: flex; flex-wrap: wrap; gap: var(--s-3); align-items: center; }
  .cluster--end { justify-content: flex-end; }
  .cluster--between { justify-content: space-between; }
  .cluster--tight { gap: var(--s-1); }

  .grid { display: grid; gap: var(--s-3); }
  .auto-grid {
    display: grid; gap: var(--s-3);
    grid-template-columns: repeat(auto-fill, minmax(min(100%, 15rem), 1fr));
  }

  .narrow { max-width: var(--content-w); margin-inline: auto; }

  .divider {
    height: 1px;
    background: var(--border);
    border: none;
  }

  /* ===== Responsive ===== */
  .sb-toggle {
    display: none;
    position: fixed;
    top: 0.625rem;
    left: 0.625rem;
    z-index: 200;
    width: 2.25rem;
    height: 2.25rem;
    border-radius: var(--r);
    background: var(--surface);
    border: 1px solid var(--border);
    align-items: center;
    justify-content: center;
    color: var(--text-2);
    box-shadow: var(--shadow-sm);
  }

  .sb-backdrop {
    display: none;
    position: fixed;
    inset: 0;
    z-index: 90;
    background: rgb(0 0 0 / 0.4);
  }
  .sb-backdrop--visible { display: block; }

  @media (max-width: 48rem) {
    .sb-toggle { display: flex; }
    .app-shell { grid-template-columns: 1fr; }
    .sidebar {
      position: fixed; inset: 0 auto 0 0; z-index: 100;
      width: var(--sidebar-w);
      transform: translateX(-100%);
      transition: transform .2s ease;
    }
    .sidebar--open { transform: translateX(0); }
    .main__yield { padding: var(--s-4); padding-top: 3.5rem; }
    .main__yield--chat { padding: 0; padding-top: 0; }
    .chat-bar { padding-left: 3.5rem; }
  }
}