feat(ui): collapsible sidebar + rail, off-canvas mobile drawers, responsive layout

- Left sidebar collapses (topbar menu button); rail collapses (topbar button + strip).
- <=860px / portrait: sidebar + rail become off-canvas drawers over main with a
  scrim, closed by default; main goes full-width single-column.
- Smooth transitions; crossing the breakpoint resets to a sane default.
- New components/chrome.js owns toggle + drawer state.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

public/app.js

@@ -10,6 +10,7 @@ import { renderRightrail } from './components/rightrail.js';
 import { emit, state } from './state.js';
 import { el, mount } from './dom.js';
 import { attachDropzone } from './components/dropzone.js';
+import { initChrome } from './components/chrome.js';
 
 const VIEWS = {
   home:            () => import('./views/home.js'),
@@ -72,6 +73,7 @@ async function init() {
   renderTopbar(document.getElementById('topbar'));
   renderSidebar(document.getElementById('sidebar'));
   renderRightrail(document.getElementById('rightrail'));
+  initChrome();
   attachDropzone(document.getElementById('main'));
   route(renderView);
   pollPending();

public/components/chrome.js

@@ -0,0 +1,76 @@
+// Collapsible chrome controller: left sidebar + right companion rail.
+// Desktop → panels shrink the grid (state persisted). Narrow/portrait → panels
+// become off-canvas drawers over the main area with a scrim; closed by default.
+//
+// State lives as classes on #shell: `sidebar-collapsed` / `rail-collapsed`.
+// rightrail.js also toggles `rail-collapsed` (its own strip) + the same key, so
+// a MutationObserver keeps the scrim in sync no matter who toggles.
+
+const SB_KEY = 'void_sidebar_collapsed';
+const RAIL_KEY = 'void_rail_collapsed';
+
+const shell = () => document.getElementById('shell');
+const isNarrow = () => window.matchMedia('(max-width: 860px)').matches;
+
+function syncScrim() {
+  const s = shell();
+  if (!s) return;
+  const anyOpen = isNarrow() &&
+    (!s.classList.contains('sidebar-collapsed') || !s.classList.contains('rail-collapsed'));
+  document.body.classList.toggle('drawer-open', anyOpen);
+}
+
+export function toggleSidebar() {
+  const s = shell();
+  const opening = s.classList.contains('sidebar-collapsed');
+  s.classList.toggle('sidebar-collapsed');
+  if (opening && isNarrow()) s.classList.add('rail-collapsed'); // one drawer at a time
+  if (!isNarrow()) localStorage.setItem(SB_KEY, String(!opening));
+}
+
+export function toggleRail() {
+  const s = shell();
+  const opening = s.classList.contains('rail-collapsed');
+  s.classList.toggle('rail-collapsed');
+  if (opening && isNarrow()) s.classList.add('sidebar-collapsed');
+  localStorage.setItem(RAIL_KEY, String(!opening));
+}
+
+function closeDrawers() {
+  shell().classList.add('sidebar-collapsed', 'rail-collapsed');
+}
+
+export function initChrome() {
+  const s = shell();
+  if (!s) return;
+
+  if (!document.getElementById('scrim')) {
+    const scrim = document.createElement('div');
+    scrim.id = 'scrim';
+    scrim.addEventListener('click', closeDrawers);
+    document.body.appendChild(scrim);
+  }
+
+  // Initial state.
+  if (isNarrow()) {
+    s.classList.add('sidebar-collapsed', 'rail-collapsed'); // drawers closed on phones/portrait
+  } else if (localStorage.getItem(SB_KEY) === 'true') {
+    s.classList.add('sidebar-collapsed'); // restore desktop preference (rail handled by rightrail.js)
+  }
+
+  // Keep the scrim correct whenever shell classes change (covers rightrail's own toggle).
+  new MutationObserver(syncScrim).observe(s, { attributes: true, attributeFilter: ['class'] });
+
+  // Crossing the breakpoint: collapse to a sane default for the new mode.
+  let wasNarrow = isNarrow();
+  window.addEventListener('resize', () => {
+    const narrow = isNarrow();
+    if (narrow === wasNarrow) return;
+    wasNarrow = narrow;
+    if (narrow) closeDrawers();
+    else s.classList.remove('sidebar-collapsed'); // show the sidebar again on desktop
+    syncScrim();
+  });
+
+  syncScrim();
+}

public/components/topbar.js

@@ -4,6 +4,7 @@
 import { el, mount, clear } from '../dom.js';
 import { navigate } from '../router.js';
 import { on } from '../state.js';
+import { toggleSidebar, toggleRail } from './chrome.js';
 
 function captureModal() {
   const root = document.getElementById('modal-root');
@@ -37,11 +38,13 @@ export function renderTopbar(root) {
   const bell = el('button', { class: 'icon-btn', onclick: () => navigate('/inbox') }, 'Inbox');
 
   mount(root,
+    el('button', { class: 'chrome-toggle', title: 'Toggle menu', onclick: toggleSidebar }, '☰'),
     el('div', { class: 'brand' }, 'VOID'),
     el('button', { class: 'icon-btn', onclick: captureModal }, '+ Capture'),
     el('div', { class: 'topbar-search' }, searchInput),
     el('div', { class: 'topbar-spacer' }),
     bell,
+    el('button', { class: 'chrome-toggle', title: 'Toggle companion chat', onclick: toggleRail }, '◆'),
     el('button', { class: 'icon-btn', onclick: () => alert('Agent-switching ships post-Plan-2.') }, 'Owner')
   );
 

public/style.css

@@ -240,3 +240,65 @@ ul.plain li:last-child { border-bottom: none; }
 .tile.status-unknown .dot { background: var(--muted); }
 .tile-go { color: var(--lb); font-size: 11px; opacity: 0; transition: opacity .25s; }
 .tile:hover .tile-go { opacity: 1; }
+
+/* ===== Collapsible chrome + responsive layout (Plan 6 polish) ===== */
+:root { --sidebar-w-min: 0px; }
+#shell { transition: grid-template-columns .22s ease; }
+#sidebar, #rightrail { transition: transform .22s ease; }
+
+/* Desktop collapse — shrink the grid columns */
+#shell.sidebar-collapsed { grid-template-columns: var(--sidebar-w-min) 1fr var(--rail-w); }
+#shell.sidebar-collapsed.rail-collapsed { grid-template-columns: var(--sidebar-w-min) 1fr var(--rail-w-min); }
+#shell.rail-collapsed { grid-template-columns: var(--sidebar-w) 1fr var(--rail-w-min); }
+#shell.sidebar-collapsed #sidebar { overflow: hidden; border-right: none; }
+/* Hide chat body when the rail is collapsed so the thin strip stays clean */
+#shell.rail-collapsed .rail-chat { display: none; }
+
+/* Topbar toggle buttons */
+.chrome-toggle {
+  background: transparent; border: 1px solid var(--border); color: var(--text);
+  width: 34px; height: 30px; border-radius: 4px; cursor: pointer; font-size: 15px; line-height: 1; flex: none;
+}
+.chrome-toggle:hover { border-color: var(--accent-dim); color: var(--accent); }
+
+/* Scrim behind mobile drawers */
+#scrim {
+  position: fixed; inset: var(--topbar-h) 0 0 0; background: rgba(0,0,0,.5);
+  z-index: 40; opacity: 0; pointer-events: none; transition: opacity .22s;
+}
+body.drawer-open #scrim { opacity: 1; pointer-events: auto; }
+
+/* Hide the chat-only toggle button on wide screens (rail has its own strip);
+   show it on narrow screens where the rail is an off-canvas drawer. */
+.rail-toggle-btn { display: none; }
+
+/* ---- Narrow / mobile / vertical: off-canvas drawers, single-column main ---- */
+@media (max-width: 860px) {
+  #shell,
+  #shell.sidebar-collapsed,
+  #shell.rail-collapsed,
+  #shell.sidebar-collapsed.rail-collapsed {
+    grid-template-columns: 1fr;
+    grid-template-areas: "topbar" "main";
+  }
+  #sidebar, #rightrail {
+    position: fixed; top: var(--topbar-h); bottom: 0; z-index: 50;
+  }
+  #sidebar  { left: 0;  width: min(82vw, 300px); transform: translateX(-100%); border-right: 1px solid var(--border); }
+  #rightrail{ right: 0; width: min(90vw, 360px); transform: translateX(100%); }
+  /* A drawer is OPEN when its collapse class is absent */
+  #shell:not(.sidebar-collapsed) #sidebar { transform: translateX(0); box-shadow: 6px 0 28px rgba(0,0,0,.6); }
+  #shell:not(.rail-collapsed)   #rightrail{ transform: translateX(0); box-shadow: -6px 0 28px rgba(0,0,0,.6); }
+  #shell:not(.rail-collapsed) .rail-chat { display: flex; flex-direction: column; height: 100%; }
+  #main { padding: 16px 18px; }
+  .topbar-search { max-width: none; }
+  .rail-toggle-btn { display: inline-block; }
+}
+
+/* Very narrow phones — tighten the topbar so toggles + search fit */
+@media (max-width: 520px) {
+  #topbar { padding: 0 8px; gap: 8px; }
+  .brand { display: none; }
+  #main { padding: 14px 12px; }
+  /* Sacred Valley cards already collapse to 1 column at <=900px (see grid rules) */
+}