diff --git a/frontend/css/main.css b/frontend/css/main.css
index bbc6c26..86429ce 100644
--- a/frontend/css/main.css
+++ b/frontend/css/main.css
@@ -32,6 +32,65 @@ body {
   font-size: 16px;
 }
 
+/* Workspace switcher (Phase 3 MVP). Sits in sidebar-header below the logo.
+   Three render modes via JS: dropdown (>1 ws), static text (1 ws),
+   muted empty state (0 ws). */
+.workspace-switcher { position: relative; margin-top: 12px; }
+.workspace-switcher-button {
+  display: flex; align-items: center; justify-content: space-between;
+  width: 100%; padding: 8px 10px;
+  background: var(--bg-card); border: 1px solid var(--border);
+  border-radius: var(--radius); color: var(--text-primary);
+  font-size: 13px; cursor: pointer; transition: all var(--transition);
+}
+.workspace-switcher-button:hover { border-color: var(--accent); }
+.workspace-switcher-static {
+  display: block; padding: 4px 2px;
+  color: var(--text-primary); font-size: 13px; font-weight: 500;
+}
+.workspace-switcher-static::before {
+  content: 'Workspace';
+  display: block;
+  font-size: 10px; text-transform: uppercase; letter-spacing: 0.5px;
+  color: var(--text-muted); margin-bottom: 2px;
+}
+.workspace-switcher-empty {
+  display: block; padding: 8px 10px;
+  color: var(--text-muted); font-size: 12px; font-style: italic;
+}
+.workspace-switcher-button .chev {
+  flex-shrink: 0; margin-left: 8px; color: var(--text-muted);
+  transition: transform var(--transition);
+}
+.workspace-switcher.open .chev { transform: rotate(180deg); }
+.workspace-switcher-menu {
+  display: none;
+  position: absolute; top: calc(100% + 4px); left: 0; right: 0;
+  background: var(--bg-card); border: 1px solid var(--border);
+  border-radius: var(--radius); box-shadow: 0 4px 12px rgba(0,0,0,0.3);
+  max-height: 320px; overflow-y: auto; z-index: 100;
+}
+.workspace-switcher.open .workspace-switcher-menu { display: block; }
+.workspace-switcher-item {
+  display: flex; align-items: center; gap: 8px;
+  padding: 10px 12px; cursor: pointer;
+  border-bottom: 1px solid var(--border);
+  color: var(--text-primary); font-size: 13px;
+}
+.workspace-switcher-item:last-child { border-bottom: none; }
+.workspace-switcher-item:hover { background: var(--bg-input); }
+.workspace-switcher-item.current { font-weight: 600; }
+.workspace-switcher-item .check {
+  flex-shrink: 0; color: var(--accent); width: 14px;
+}
+.workspace-switcher-item .ws-meta { flex: 1; min-width: 0; }
+.workspace-switcher-item .ws-name {
+  white-space: nowrap; overflow: hidden; text-overflow: ellipsis;
+}
+.workspace-switcher-item .ws-org {
+  font-size: 11px; color: var(--text-muted); margin-top: 2px;
+}
+
 .nav-links {
   flex: 1;
   padding: 12px 8px;
diff --git a/frontend/index.html b/frontend/index.html
index 5be30e5..747051a 100644
--- a/frontend/index.html
+++ b/frontend/index.html
@@ -31,6 +31,7 @@
         </svg>
         <span>ScreenTinker</span>
       </div>
+      <div class="workspace-switcher" id="workspaceSwitcher"></div>
     </div>
     <ul class="nav-links">
       <li><a href="#/" class="nav-link active" data-view="dashboard">
diff --git a/frontend/js/api.js b/frontend/js/api.js
index d5409e2..778f491 100644
--- a/frontend/js/api.js
+++ b/frontend/js/api.js
@@ -156,6 +156,7 @@ export const api = {
   // Current user
   getMe: () => request('/auth/me'),
   updateMe: (data) => request('/auth/me', { method: 'PUT', body: JSON.stringify(data) }),
+  switchWorkspace: (workspaceId) => request('/auth/switch-workspace', { method: 'POST', body: JSON.stringify({ workspace_id: workspaceId }) }),
 
   // Admin - Users
   getUsers: () => request('/auth/users'),
diff --git a/frontend/js/app.js b/frontend/js/app.js
index 4b17160..22c5820 100644
--- a/frontend/js/app.js
+++ b/frontend/js/app.js
@@ -21,6 +21,7 @@ import * as playlists from './views/playlists.js';
 import { applyBranding } from './branding.js';
 import { t } from './i18n.js';
 import { isPlatformAdmin } from './utils.js';
+import { renderWorkspaceSwitcher } from './components/workspace-switcher.js';
 
 const app = document.getElementById('app');
 const sidebar = document.querySelector('.sidebar');
@@ -94,6 +95,9 @@ async function refreshCurrentUser() {
     if (!res.ok) return;
     const fresh = await res.json();
     localStorage.setItem('user', JSON.stringify(fresh));
+    // Re-render the workspace switcher on every /me refresh - cheap, and keeps
+    // the dropdown in sync if a workspace was added/removed in another tab.
+    renderWorkspaceSwitcher(fresh);
     window.dispatchEvent(new CustomEvent('user-refreshed', { detail: fresh }));
   } catch {}
 }
diff --git a/frontend/js/components/workspace-switcher.js b/frontend/js/components/workspace-switcher.js
new file mode 100644
index 0000000..cf0367d
--- /dev/null
+++ b/frontend/js/components/workspace-switcher.js
@@ -0,0 +1,91 @@
+import { api } from '../api.js';
+import { showToast } from './toast.js';
+
+// Render the workspace switcher inside #workspaceSwitcher based on the
+// /api/auth/me response. Three modes:
+//   - 0 accessible workspaces: muted "No workspace" placeholder
+//   - 1 accessible workspace: workspace name as static text
+//   - >1 accessible workspaces: dropdown button + menu with click-to-switch
+export function renderWorkspaceSwitcher(me) {
+  const container = document.getElementById('workspaceSwitcher');
+  if (!container) return;
+
+  const list = Array.isArray(me?.accessible_workspaces) ? me.accessible_workspaces : [];
+  const currentId = me?.current_workspace_id || null;
+
+  if (list.length === 0) {
+    container.classList.remove('open');
+    container.innerHTML = `<span class="workspace-switcher-empty">No workspace</span>`;
+    return;
+  }
+
+  if (list.length === 1) {
+    container.classList.remove('open');
+    container.innerHTML = `<span class="workspace-switcher-static">${esc(list[0].name)}</span>`;
+    return;
+  }
+
+  // >1: dropdown. Alpha sort by workspace name for MVP (no recently-used yet).
+  const sorted = [...list].sort((a, b) => a.name.localeCompare(b.name));
+  const current = sorted.find(w => w.id === currentId) || sorted[0];
+
+  container.innerHTML = `
+    <button class="workspace-switcher-button" type="button" aria-haspopup="listbox" aria-expanded="false">
+      <span class="ws-name" style="overflow:hidden;text-overflow:ellipsis;white-space:nowrap">${esc(current.name)}</span>
+      <svg class="chev" width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
+        <polyline points="6 9 12 15 18 9"/>
+      </svg>
+    </button>
+    <div class="workspace-switcher-menu" role="listbox">
+      ${sorted.map(w => `
+        <div class="workspace-switcher-item ${w.id === currentId ? 'current' : ''}" data-workspace-id="${esc(w.id)}" role="option">
+          <svg class="check" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="3" style="${w.id === currentId ? '' : 'visibility:hidden'}">
+            <polyline points="20 6 9 17 4 12"/>
+          </svg>
+          <div class="ws-meta">
+            <div class="ws-name">${esc(w.name)}</div>
+            <div class="ws-org">${esc(w.organization_name || '')}</div>
+          </div>
+        </div>
+      `).join('')}
+    </div>
+  `;
+
+  const button = container.querySelector('.workspace-switcher-button');
+  button.addEventListener('click', (e) => {
+    e.stopPropagation();
+    const opening = !container.classList.contains('open');
+    container.classList.toggle('open');
+    button.setAttribute('aria-expanded', String(opening));
+  });
+
+  container.querySelectorAll('.workspace-switcher-item').forEach(item => {
+    item.addEventListener('click', async () => {
+      const wsId = item.dataset.workspaceId;
+      if (wsId === currentId) { container.classList.remove('open'); return; }
+      try {
+        const resp = await api.switchWorkspace(wsId);
+        if (resp?.token) {
+          localStorage.setItem('token', resp.token);
+          window.location.reload();
+        } else {
+          showToast('Switch returned no token', 'error');
+        }
+      } catch (err) {
+        showToast(err.message || 'Failed to switch workspace', 'error');
+      }
+    });
+  });
+
+  // Click-outside closes the menu.
+  document.addEventListener('click', (e) => {
+    if (!container.contains(e.target)) {
+      container.classList.remove('open');
+      button.setAttribute('aria-expanded', 'false');
+    }
+  });
+}
+
+function esc(s) {
+  return String(s ?? '').replace(/[&<>"']/g, c => ({ '&':'&amp;','<':'&lt;','>':'&gt;','"':'&quot;',"'":'&#39;' }[c]));
+}
diff --git a/frontend/sw-admin.js b/frontend/sw-admin.js
index 94d9ad9..26575ba 100644
--- a/frontend/sw-admin.js
+++ b/frontend/sw-admin.js
@@ -1,4 +1,8 @@
-const CACHE = 'rd-admin-v1';
+// Service worker for the admin SPA. Bumped to v2 to invalidate the cache-first
+// caches that were shipping stale JS to existing clients (the server already
+// sends Cache-Control: no-cache + ETag, but the previous SW intercepted before
+// any of that mattered). Strategy is now network-first with offline fallback.
+const CACHE = 'rd-admin-v2';
 
 self.addEventListener('install', e => {
   e.waitUntil(caches.open(CACHE).then(c => c.addAll([
@@ -15,7 +19,18 @@ self.addEventListener('activate', e => {
 });
 
 self.addEventListener('fetch', e => {
-  // Network first for API, cache first for static
+  // Don't intercept API or socket.io traffic - those need to hit the network unmediated.
   if (e.request.url.includes('/api/') || e.request.url.includes('/socket.io/')) return;
-  e.respondWith(caches.match(e.request).then(r => r || fetch(e.request)));
+  // Network-first: respect the server's Cache-Control: no-cache + ETag (304s
+  // stay fast); fall back to cache only when offline. Re-populate the cache
+  // on every successful fetch so the offline fallback stays current.
+  e.respondWith(
+    fetch(e.request)
+      .then(resp => {
+        const copy = resp.clone();
+        caches.open(CACHE).then(c => c.put(e.request, copy)).catch(() => {});
+        return resp;
+      })
+      .catch(() => caches.match(e.request))
+  );
 });
diff --git a/server/routes/auth.js b/server/routes/auth.js
index 23ccc0d..dbbb612 100644
--- a/server/routes/auth.js
+++ b/server/routes/auth.js
@@ -293,14 +293,32 @@ function getMicrosoftProfile(accessToken) {
 // roles, and the list of accessible workspaces. Legacy fields (user object at
 // the top level) are preserved so existing frontend code continues to work.
 router.get('/me', requireAuth, resolveTenancy, (req, res) => {
-  const accessible = db.prepare(`
-    SELECT w.id, w.name, w.organization_id, o.name AS organization_name, wm.role AS workspace_role
-    FROM workspace_members wm
-    JOIN workspaces w ON w.id = wm.workspace_id
-    JOIN organizations o ON o.id = w.organization_id
-    WHERE wm.user_id = ?
-    ORDER BY o.name, w.name
-  `).all(req.user.id);
+  // Platform admins see every workspace in the system (via the LEFT JOIN they
+  // still get their own workspace_role for direct memberships; NULL elsewhere,
+  // matching accessContext's actingAs semantics). Regular users see only
+  // workspaces they have a direct workspace_members row in. Role is read from
+  // the signed JWT (not user-supplied), so non-admins cannot reach the admin
+  // branch. No cap on the admin list yet - revisit at 50+ workspaces when
+  // dropdown UX without search starts to degrade.
+  const isPlatformAdmin = req.user.role === 'platform_admin' || req.user.role === 'superadmin';
+  const accessible = isPlatformAdmin
+    ? db.prepare(`
+        SELECT w.id, w.name, w.organization_id, o.name AS organization_name,
+               wm.role AS workspace_role
+        FROM workspaces w
+        JOIN organizations o ON o.id = w.organization_id
+        LEFT JOIN workspace_members wm ON wm.workspace_id = w.id AND wm.user_id = ?
+        ORDER BY o.name, w.name
+      `).all(req.user.id)
+    : db.prepare(`
+        SELECT w.id, w.name, w.organization_id, o.name AS organization_name,
+               wm.role AS workspace_role
+        FROM workspace_members wm
+        JOIN workspaces w ON w.id = wm.workspace_id
+        JOIN organizations o ON o.id = w.organization_id
+        WHERE wm.user_id = ?
+        ORDER BY o.name, w.name
+      `).all(req.user.id);
 
   const currentOrg = req.organizationId
     ? db.prepare('SELECT id, name FROM organizations WHERE id = ?').get(req.organizationId)