feat: add device badge and data attributes to buildTileHTML (task-9)

- Show <span class="device-badge"> after tile name when _sources.length > 1
  and session.deviceName is present (multi-source federation context)
- Add data-session-key and data-source-url attributes to tile article
  element for unique session identification across sources
- Tests: 3 new tests covering badge visibility, badge omission for single
  source, and presence of new data attributes

muxplex/frontend/app.js

@@ -468,9 +468,9 @@ function buildTileHTML(session, index, mobile) {
   const lastLines = snapshot.split('\n').slice(-20).join('\n');
 
   return (
-    `<article class="${classes}" data-session="${escapedName}" tabindex="0" role="listitem" aria-label="${escapedName}">` +
+    `<article class="${classes}" data-session="${escapedName}" data-session-key="${escapeHtml(session.sessionKey || name)}" data-source-url="${escapeHtml(session.sourceUrl || '')}" tabindex="0" role="listitem" aria-label="${escapedName}">` +
     `<div class="tile-header">` +
-    `<span class="tile-name">${escapeHtml(name)}</span>` +
+    `<span class="tile-name">${escapeHtml(name)}${_sources.length > 1 && session.deviceName ? '<span class="device-badge">' + escapeHtml(session.deviceName) + '</span>' : ''}</span>` +
     `<span class="tile-meta">${bellHtml}<span class="tile-time">${escapeHtml(timeStr)}</span></span>` +
     `</div>` +
     `<div class="tile-body"><pre>${ansiToHtml(lastLines)}</pre></div>` +

muxplex/frontend/tests/test_app.mjs

@@ -2338,6 +2338,43 @@ test('getVisibleSessions hides local sessions by name but not remote sessions wi
   app._setServerSettings(null);
 });
 
+// --- buildTileHTML device badge (task-9) ---
+
+test('buildTileHTML shows device-badge when session has deviceName and multiple sources', () => {
+  app._setSources([
+    { url: '', name: 'This device', type: 'local', status: 'authenticated', backoffMs: 2000 },
+    { url: 'https://remote.example.com', name: 'Remote', type: 'remote', status: 'authenticated', backoffMs: 2000 },
+  ]);
+  const session = { name: 'work', deviceName: 'Laptop', sourceUrl: '', sessionKey: '::work', snapshot: '' };
+  const html = app.buildTileHTML(session, 0, false);
+  assert.ok(html.includes('device-badge'), 'should show device-badge when _sources.length > 1 and session has deviceName');
+  assert.ok(html.includes('Laptop'), 'device-badge should contain the deviceName');
+  app._setSources([]);
+});
+
+test('buildTileHTML omits device-badge when only one source configured', () => {
+  app._setSources([
+    { url: '', name: 'This device', type: 'local', status: 'authenticated', backoffMs: 2000 },
+  ]);
+  const session = { name: 'work', deviceName: 'Laptop', sourceUrl: '', sessionKey: '::work', snapshot: '' };
+  const html = app.buildTileHTML(session, 0, false);
+  assert.ok(!html.includes('device-badge'), 'should NOT show device-badge when _sources.length is 1');
+  app._setSources([]);
+});
+
+test('buildTileHTML includes data-session-key and data-source-url attributes on article element', () => {
+  const session = {
+    name: 'work',
+    deviceName: 'Laptop',
+    sourceUrl: 'https://remote.example.com',
+    sessionKey: 'https://remote.example.com::work',
+    snapshot: '',
+  };
+  const html = app.buildTileHTML(session, 0, false);
+  assert.ok(html.includes('data-session-key='), 'article should have data-session-key attribute');
+  assert.ok(html.includes('data-source-url='), 'article should have data-source-url attribute');
+});
+
 test('pollSessions sets unreachable and applies exponential backoff on network error', async () => {
   const mockStatusEl = { textContent: '', className: '' };
   const mockGrid = { innerHTML: '' };