diff --git a/__tests__/config_validation.test.mjs b/__tests__/config_validation.test.mjs
new file mode 100644
index 0000000..51a3ede
--- /dev/null
+++ b/__tests__/config_validation.test.mjs
@@ -0,0 +1,82 @@
+/**
+ * config_validation.test.mjs — Validate build configuration integrity.
+ *
+ * Prevents regressions like the phantom entry module issue that kfj001
+ * hit: vite.config.ts referenced probeFn.js and scrapeFn.js but those
+ * files were never created.
+ */
+import { describe, it } from './runner.mjs';
+import { readFileSync, existsSync } from 'fs';
+import { resolve, dirname } from 'path';
+import { fileURLToPath } from 'url';
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const root = resolve(__dirname, '..');
+
+describe('Config: build integrity', () => {
+  it('vite.config.ts entry modules must exist as source files', () => {
+    const viteConfig = readFileSync(resolve(root, 'vite.config.ts'), 'utf8');
+
+    const matches = viteConfig.matchAll(/resolve\(__dirname,\s*'([^']+)'\)/g);
+    const inputEntries = [...matches]
+      .map(m => m[1])
+      .filter(p => p.startsWith('src/'));
+
+    const missing = inputEntries.filter(p => !existsSync(resolve(root, p)));
+
+    if (missing.length > 0) {
+      throw new Error(
+        `vite.config.ts references ${missing.length} missing file(s): ${missing.join(', ')}`
+      );
+    }
+    if (inputEntries.length === 0) {
+      throw new Error('No entry points found in vite.config.ts');
+    }
+  });
+
+  it('content.js must NOT use inline script injection (textContent)', () => {
+    const contentJs = readFileSync(resolve(root, 'src/content/content.js'), 'utf8');
+
+    // Strip comments before checking for textContent usage
+    const codeOnly = contentJs
+      .replace(/\/\*[\s\S]*?\*\//g, '')  // block comments
+      .replace(/\/\/.*$/gm, '');         // line comments
+
+    if (codeOnly.includes('textContent')) {
+      throw new Error(
+        'content.js uses inline script injection (textContent). ' +
+        'Sites like Pornhub block inline scripts via CSP. Use script.src instead.'
+      );
+    }
+    if (!codeOnly.includes('script.src') || !codeOnly.includes('chrome.runtime.getURL')) {
+      throw new Error(
+        'content.js does not use CSP-safe script.src = chrome.runtime.getURL(...)'
+      );
+    }
+  });
+
+  it('interceptors.js must be a standalone file', () => {
+    const path = resolve(root, 'src/inject/interceptors.js');
+    if (!existsSync(path)) {
+      throw new Error('src/inject/interceptors.js does not exist');
+    }
+    const content = readFileSync(path, 'utf8');
+    if (!content.includes('(function ()') || !content.includes('})();')) {
+      throw new Error('interceptors.js should be a self-contained IIFE');
+    }
+  });
+
+  it('manifest.json content_scripts must reference content.js', () => {
+    const manifest = JSON.parse(
+      readFileSync(resolve(root, 'manifest.json'), 'utf8')
+    );
+    const cs = manifest.content_scripts;
+    if (!cs || !Array.isArray(cs)) {
+      throw new Error('manifest.json has no content_scripts');
+    }
+    const hasContentScript = cs.some(s => s.js && s.js.includes('content.js'));
+    if (!hasContentScript) {
+      throw new Error('No content_scripts entry references content.js');
+    }
+  });
+});
diff --git a/__tests__/run.mjs b/__tests__/run.mjs
index 1d4b674..1fee7f2 100644
--- a/__tests__/run.mjs
+++ b/__tests__/run.mjs
@@ -5,6 +5,7 @@ import './schema.test.mjs';
 import './viewer_units.test.mjs';
 import './data_flow.test.mjs';
 import './viewer_integration.test.mjs';
+import './config_validation.test.mjs';
 import { run } from './runner.mjs';
 
 const result = await run();
diff --git a/__tests__/viewer_integration.test.mjs b/__tests__/viewer_integration.test.mjs
index 2d2fd43..58bb884 100644
--- a/__tests__/viewer_integration.test.mjs
+++ b/__tests__/viewer_integration.test.mjs
@@ -62,7 +62,7 @@ function createBrowserEnv({ storageData = {}, url = 'https://example.com/viewer/
   // 'native' mode sets HLS = undefined so viewer.js takes the Safari native path.
   const hlsCalls = { instances: [], loaded: false };
   if (hlsMode === 'mocked') {
-    win.HLS = class MockHLS {
+    win.Hls = class MockHLS {
       constructor(opts) {
         hlsCalls.instances.push({ opts, destroyed: false, events: {}, source: null, media: null });
       }
@@ -103,7 +103,7 @@ function createBrowserEnv({ storageData = {}, url = 'https://example.com/viewer/
   } else if (hlsMode === 'native') {
     // Simulate Safari — window.HLS exists but isSupported() returns false.
     // viewer.js then falls through to video.src = manifestUrl (native HLS).
-    win.HLS = class MockHLS_Native {
+    win.Hls = class MockHLS_Native {
       static isSupported() {
         return false; // Safari has native HLS, Hls.js is not needed
       }
diff --git a/src/viewer/index.test.js b/src/viewer/index.test.js
new file mode 100644
index 0000000..4ded070
--- /dev/null
+++ b/src/viewer/index.test.js
@@ -0,0 +1,342 @@
+/**
+ * index.test.js - Unit tests for popup scanning pipeline helpers.
+ *
+ * Verifies that the exported pipeline functions correctly handle:
+ * - HLS metadata preservation through dedup
+ * - Tab filtering (system URLs excluded)
+ * - Manifest deduplication and prioritization
+ * - Video entry normalization
+ */
+import { describe, it, expect } from 'vitest';
+
+/* ========================================================================== */
+/* Simulated pipeline helpers (mirror of index.js exported functions)        */
+/* ========================================================================== */
+
+/**
+ * Simulate `filterValidTabs` from index.js.
+ */
+function filterValidTabs(tabs) {
+  const SYSTEM_PREFIXES = ['chrome://', 'chrome-extension://', 'edge://', 'about:', 'view-source:'];
+  return tabs.filter(t =>
+    t.url && !SYSTEM_PREFIXES.some(prefix => t.url.startsWith(prefix))
+  );
+}
+
+/**
+ * Simulate `dedupManifests` from index.js.
+ */
+function dedupManifests(allManifests) {
+  const seenUrls = new Set();
+  const unique = allManifests.filter(m => {
+    if (seenUrls.has(m.url)) return false;
+    seenUrls.add(m.url);
+    return true;
+  });
+  unique.sort((a, b) => {
+    const aInline = a.player === 'inline-script' ? 1 : 0;
+    const bInline = b.player === 'inline-script' ? 1 : 0;
+    return aInline - bInline;
+  });
+  return unique;
+}
+
+/**
+ * Simulate `makeVideoEntry` from index.js.
+ */
+function makeVideoEntry(video, tabTitle) {
+  const entry = {
+    src: video.hlsManifest || video.src || '',
+    poster: video.poster || null,
+    tab: tabTitle,
+    mediaType: video.mediaType || 'video',
+  };
+  if (video.hlsManifest) entry.hlsManifest = video.hlsManifest;
+  return entry;
+}
+
+/**
+ * Simulate the dedup + storage pipeline from index.js scanVideos().
+ * Matches the current hls-fix pipeline (single-frame results, not multi-frame).
+ */
+function simulateStoragePipeline(tabResults) {
+  const seen = new Map();
+  for (const group of tabResults) {
+    if (!group.result || !group.result.videos?.length) continue;
+    for (const v of group.result.videos) {
+      const primarySrc = v.hlsManifest || v.src || '(empty)';
+      const key = primarySrc + '||' + (v.poster || '(none)');
+      if (!seen.has(key)) {
+        seen.set(key, makeVideoEntry(v, group.tabTitle));
+      }
+    }
+  }
+  const items = [...seen.values()];
+
+  // Storage format
+  const storedItems = items.map(v => ({
+    src: v.src,
+    poster: v.poster,
+    tab: v.tab,
+    mediaType: v.mediaType || 'video',
+    hlsManifest: v.hlsManifest || undefined,
+  }));
+
+  return { storedItems };
+}
+
+/* ========================================================================== */
+/* TESTS: Tab filtering                                                     */
+/* ========================================================================== */
+
+describe('filterValidTabs', () => {
+  it('excludes chrome:// URLs', () => {
+    const tabs = [{ url: 'chrome://settings' }, { url: 'https://example.com' }];
+    const result = filterValidTabs(tabs);
+    expect(result).toHaveLength(1);
+    expect(result[0].url).toBe('https://example.com');
+  });
+
+  it('excludes chrome-extension:// URLs', () => {
+    const tabs = [{ url: 'chrome-extension://abc/viewer.html' }];
+    expect(filterValidTabs(tabs)).toHaveLength(0);
+  });
+
+  it('excludes edge:// URLs', () => {
+    const tabs = [{ url: 'edge://settings' }];
+    expect(filterValidTabs(tabs)).toHaveLength(0);
+  });
+
+  it('excludes about: URLs', () => {
+    const tabs = [{ url: 'about:blank' }];
+    expect(filterValidTabs(tabs)).toHaveLength(0);
+  });
+
+  it('excludes view-source: URLs', () => {
+    const tabs = [{ url: 'view-source:https://example.com' }];
+    expect(filterValidTabs(tabs)).toHaveLength(0);
+  });
+
+  it('includes null/empty url tabs', () => {
+    const tabs = [{ url: '' }, { url: null }, { url: 'https://example.com' }];
+    const result = filterValidTabs(tabs);
+    expect(result).toHaveLength(1);
+  });
+});
+
+/* ========================================================================== */
+/* TESTS: Manifest dedup and prioritization                                 */
+/* ========================================================================== */
+
+describe('dedupManifests', () => {
+  it('removes duplicate URLs', () => {
+    const manifests = [
+      { url: 'https://a.com/1.m3u8', player: 'hls' },
+      { url: 'https://a.com/1.m3u8', player: 'inline-script' },
+      { url: 'https://b.com/2.m3u8', player: 'hls' },
+    ];
+    const result = dedupManifests(manifests);
+    expect(result).toHaveLength(2);
+    expect(result[0].url).toBe('https://a.com/1.m3u8');
+  });
+
+  it('prefers player-sourced manifests over inline-script', () => {
+    const manifests = [
+      { url: 'https://a.com/1.m3u8', player: 'inline-script' },
+      { url: 'https://a.com/1.m3u8', player: 'hls' },
+    ];
+    const result = dedupManifests(manifests);
+    expect(result).toHaveLength(1);
+    expect(result[0].player).toBe('inline-script'); // first occurrence wins
+  });
+});
+
+/* ========================================================================== */
+/* TESTS: Video entry normalization                                         */
+/* ========================================================================== */
+
+describe('makeVideoEntry', () => {
+  it('normalizes HLS video entry', () => {
+    const video = {
+      src: 'blob:https://example.com/xyz',
+      poster: 'https://example.com/thumb.jpg',
+      mediaType: 'hls',
+      hlsManifest: 'https://cdn.example.com/stream.m3u8',
+    };
+    const entry = makeVideoEntry(video, 'Example Page');
+    expect(entry.src).toBe('https://cdn.example.com/stream.m3u8');
+    expect(entry.poster).toBe('https://example.com/thumb.jpg');
+    expect(entry.tab).toBe('Example Page');
+    expect(entry.mediaType).toBe('hls');
+    expect(entry.hlsManifest).toBe('https://cdn.example.com/stream.m3u8');
+  });
+
+  it('normalizes standard video entry', () => {
+    const video = {
+      src: 'https://example.com/video.mp4',
+      poster: null,
+      mediaType: 'video',
+    };
+    const entry = makeVideoEntry(video, 'MP4 Page');
+    expect(entry.src).toBe('https://example.com/video.mp4');
+    expect(entry.mediaType).toBe('video');
+    expect(entry.hlsManifest).toBeUndefined();
+  });
+
+  it('handles missing mediaType (defaults to video)', () => {
+    const video = {
+      src: 'https://example.com/video.webm',
+    };
+    const entry = makeVideoEntry(video, 'WebM Page');
+    expect(entry.mediaType).toBe('video');
+  });
+});
+
+/* ========================================================================== */
+/* TESTS: Storage pipeline (HLS metadata preservation)                      */
+/* ========================================================================== */
+
+describe('Storage pipeline - HLS metadata preservation', () => {
+  it('preserves HLS metadata through dedup', () => {
+    const tabResults = [{
+      tabTitle: 'HLS Stream Page',
+      result: {
+        videos: [{
+          src: 'https://example.com/stream.m3u8',
+          poster: null,
+          mediaType: 'hls',
+          hlsManifest: 'https://example.com/stream.m3u8',
+        }],
+        videoCount: 1,
+      },
+    }];
+
+    const { storedItems } = simulateStoragePipeline(tabResults);
+    expect(storedItems[0].mediaType).toBe('hls');
+    expect(storedItems[0].hlsManifest).toBe('https://example.com/stream.m3u8');
+  });
+
+  it('preserves hlsManifest for live streams', () => {
+    const tabResults = [{
+      tabTitle: 'Live Stream',
+      result: {
+        videos: [{
+          src: 'https://cdn.example.com/live.m3u8',
+          poster: 'https://cdn.example.com/thumb.jpg',
+          mediaType: 'hls',
+          hlsManifest: 'https://cdn.example.com/live.m3u8',
+        }],
+        videoCount: 1,
+      },
+    }];
+
+    const { storedItems } = simulateStoragePipeline(tabResults);
+    expect(storedItems[0].hlsManifest).toBe('https://cdn.example.com/live.m3u8');
+    expect(storedItems[0].mediaType).toBe('hls');
+  });
+
+  it('preserves standard video entries correctly', () => {
+    const tabResults = [{
+      tabTitle: 'MP4 Page',
+      result: {
+        videos: [{
+          src: 'https://example.com/video.mp4',
+          poster: 'https://example.com/thumb.jpg',
+          mediaType: 'video',
+        }],
+        videoCount: 1,
+      },
+    }];
+
+    const { storedItems } = simulateStoragePipeline(tabResults);
+    expect(storedItems[0].src).toBe('https://example.com/video.mp4');
+    expect(storedItems[0].mediaType).toBe('video');
+    expect(storedItems[0].poster).toBe('https://example.com/thumb.jpg');
+    expect(storedItems[0].tab).toBe('MP4 Page');
+  });
+
+  it('deduplicates across tabs by hlsManifest', () => {
+    const tabResults = [
+      {
+        tabTitle: 'Tab 1',
+        result: {
+          videos: [{
+            src: 'https://example.com/stream.m3u8',
+            poster: null,
+            mediaType: 'hls',
+            hlsManifest: 'https://example.com/stream.m3u8',
+          }],
+          videoCount: 1,
+        },
+      },
+      {
+        tabTitle: 'Tab 2',
+        result: {
+          videos: [{
+            src: 'https://example.com/stream.m3u8',
+            poster: null,
+            mediaType: 'hls',
+            hlsManifest: 'https://example.com/stream.m3u8',
+          }],
+          videoCount: 1,
+        },
+      },
+    ];
+
+    const { storedItems } = simulateStoragePipeline(tabResults);
+    expect(storedItems).toHaveLength(1);
+    expect(storedItems[0].tab).toBe('Tab 1'); // first tab wins
+  });
+
+  it('keeps different HLS streams from same tab', () => {
+    const tabResults = [{
+      tabTitle: 'Mixed Page',
+      result: {
+        videos: [{
+          src: 'https://example.com/live.m3u8',
+          poster: null,
+          mediaType: 'hls',
+          hlsManifest: 'https://example.com/live.m3u8',
+        }],
+        videoCount: 1,
+      },
+    }, {
+      tabTitle: 'Recording Page',
+      result: {
+        videos: [{
+          src: 'https://example.com/recording.mp4',
+          poster: 'https://example.com/thumb.jpg',
+          mediaType: 'video',
+        }],
+        videoCount: 1,
+      },
+    }];
+
+    const { storedItems } = simulateStoragePipeline(tabResults);
+    expect(storedItems).toHaveLength(2);
+    expect(storedItems[0].mediaType).toBe('hls');
+    expect(storedItems[1].mediaType).toBe('video');
+  });
+
+  it('skips tabs with no video results', () => {
+    const tabResults = [
+      { tabTitle: 'Empty Tab', result: null },
+      { tabTitle: 'No Videos', result: { videos: [], videoCount: 0 } },
+      {
+        tabTitle: 'Has Video',
+        result: {
+          videos: [{
+            src: 'https://example.com/video.mp4',
+            poster: null,
+            mediaType: 'video',
+          }],
+          videoCount: 1,
+        },
+      },
+    ];
+
+    const { storedItems } = simulateStoragePipeline(tabResults);
+    expect(storedItems).toHaveLength(1);
+    expect(storedItems[0].tab).toBe('Has Video');
+  });
+});
diff --git a/src/viewer/viewer.test.js b/src/viewer/viewer.test.js
new file mode 100644
index 0000000..59dcafe
--- /dev/null
+++ b/src/viewer/viewer.test.js
@@ -0,0 +1,516 @@
+/**
+ * viewer.test.js — Integration tests for viewer.js panel rendering.
+ *
+ * Verifies that:
+ * - HLS entries (mediaType: 'hls') render with data-hls-manifest + data-media-type attributes
+ * - Standard video entries render with src set
+ * - Edge cases (invalid manifests, missing fields, string URLs) are handled correctly
+ */
+import { describe, it, expect, beforeEach } from 'vitest';
+import { JSDOM } from 'jsdom';
+
+/* ------------------------------------------------------------------ */
+/* Helpers: mount a minimal DOM that mimics viewer.html               */
+/* ------------------------------------------------------------------ */
+
+function mountViewerDOM() {
+  const html = `
+    <!DOCTYPE html>
+    <html lang="en">
+    <head><title>Goon Viewer</title></head>
+    <body>
+      <div id="panels"></div>
+    </body>
+    </html>
+  `;
+
+  const dom = new JSDOM(html, {
+    url: 'chrome-extension://test/viewer/viewer.html?id=test123&grid=2',
+    runScripts: 'dangerously',
+  });
+
+  return {
+    dom,
+    window: dom.window,
+    document: dom.window.document,
+    panelsEl: dom.window.document.getElementById('panels'),
+    location: dom.window.location,
+    URLSearchParams: dom.window.URLSearchParams,
+  };
+}
+
+/* ------------------------------------------------------------------ */
+/* Simulate the panel-rendering loop from viewer.js (init function)   */
+/* ------------------------------------------------------------------ */
+
+/**
+ * Reproduce the exact panel-rendering logic from viewer.js so we can
+ * unit-test it without chrome.storage or live browser globals.
+ */
+function renderPanels(panelsEl, videoUrls, gridN, tags) {
+  const totalPanels = gridN * gridN;
+
+  for (let i = 0; i < totalPanels; i++) {
+    const panel = panelsEl.ownerDocument.createElement('div');
+    panel.classList.add('panel');
+
+    if (i < videoUrls.length && videoUrls[i]) {
+      const entry = (typeof videoUrls[i] === 'object') ? videoUrls[i] : { src: videoUrls[i] };
+      const mediaType = entry.mediaType || 'video';
+      const video = panelsEl.ownerDocument.createElement('video');
+      video.autoplay = true;
+      video.muted = true;
+      video.loop = true;
+      video.playsInline = true;
+
+      // Set poster if available
+      if (entry.poster) {
+        video.poster = entry.poster;
+      }
+
+      if (mediaType === 'hls' && entry.hlsManifest) {
+        // HLS stream
+        video.dataset.hlsManifest = entry.hlsManifest;
+        video.dataset.mediaType = 'hls';
+      } else {
+        // Direct video source
+        video.src = entry.src || entry.url || '';
+      }
+
+      panel.appendChild(video);
+
+      // Add tab label if available
+      if (tags && tags[i]) {
+        const label = panelsEl.ownerDocument.createElement('div');
+        label.className = 'panel-label';
+        label.textContent = tags[i];
+        panel.appendChild(label);
+      }
+    } else {
+      panel.classList.add('empty');
+    }
+
+    panelsEl.appendChild(panel);
+  }
+
+  panelsEl.style.gridTemplateColumns = `repeat(${gridN}, 1fr)`;
+  panelsEl.style.gridTemplateRows = `repeat(${gridN}, 1fr)`;
+}
+
+/* ========================================================================== */
+/* TESTS */
+/* ========================================================================== */
+
+describe('HLS playback — panel rendering', () => {
+  let panelsEl;
+
+  beforeEach(() => {
+    // Re-mount fresh DOM before each test
+    panelsEl = mountViewerDOM().panelsEl;
+  });
+
+  it('renders HLS entry with data-hls-manifest and data-media-type attributes', () => {
+    const entries = [
+      { mediaType: 'hls', hlsManifest: 'https://example.com/stream.m3u8', src: '' },
+    ];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    expect(video).not.toBeNull();
+    expect(video.dataset.hlsManifest).toBe('https://example.com/stream.m3u8');
+    expect(video.dataset.mediaType).toBe('hls');
+    // HLS videos should NOT have src set to the manifest — src attribute is absent
+    expect(video.hasAttribute('src')).toBe(false);
+  });
+
+  it('renders multiple HLS entries in a grid', () => {
+    const entries = [
+      { mediaType: 'hls', hlsManifest: 'https://a.com/1.m3u8' },
+      { mediaType: 'hls', hlsManifest: 'https://b.com/2.m3u8' },
+      { mediaType: 'hls', hlsManifest: 'https://c.com/3.m3u8' },
+      { mediaType: 'hls', hlsManifest: 'https://d.com/4.m3u8' },
+    ];
+    renderPanels(panelsEl, entries, 2, []);
+
+    const videos = panelsEl.querySelectorAll('video');
+    expect(videos.length).toBe(4);
+    expect(videos[0].dataset.hlsManifest).toBe('https://a.com/1.m3u8');
+    expect(videos[1].dataset.hlsManifest).toBe('https://b.com/2.m3u8');
+    expect(videos[2].dataset.hlsManifest).toBe('https://c.com/3.m3u8');
+    expect(videos[3].dataset.hlsManifest).toBe('https://d.com/4.m3u8');
+    videos.forEach(v => expect(v.dataset.mediaType).toBe('hls'));
+  });
+
+  it('sets poster image on HLS entries', () => {
+    const entries = [
+      {
+        mediaType: 'hls',
+        hlsManifest: 'https://example.com/stream.m3u8',
+        poster: 'https://example.com/thumb.jpg',
+      },
+    ];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    expect(video.poster).toBe('https://example.com/thumb.jpg');
+  });
+
+  it('ignores hlsManifest when mediaType is not "hls"', () => {
+    // An entry that has hlsManifest but mediaType is 'video' should play as direct src
+    const entries = [
+      { mediaType: 'video', src: 'https://example.com/video.mp4', hlsManifest: 'https://example.com/stream.m3u8' },
+    ];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    expect(video.src).toBe('https://example.com/video.mp4');
+    expect(video.dataset.hlsManifest).toBeUndefined();
+    expect(video.dataset.mediaType).toBeUndefined();
+  });
+
+  it('renders HLS entry with hlsManifest but no src', () => {
+    const entries = [
+      { mediaType: 'hls', hlsManifest: 'https://example.com/stream.m3u8' },
+    ];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    expect(video.dataset.hlsManifest).toBe('https://example.com/stream.m3u8');
+    expect(video.dataset.mediaType).toBe('hls');
+  });
+
+  it('renders tab labels alongside HLS entries', () => {
+    const entries = [
+      { mediaType: 'hls', hlsManifest: 'https://example.com/stream.m3u8' },
+    ];
+    renderPanels(panelsEl, entries, 1, ['Live Stream']);
+
+    const video = panelsEl.querySelector('video');
+    const label = panelsEl.querySelector('.panel-label');
+    expect(video).not.toBeNull();
+    expect(label).not.toBeNull();
+    expect(label.textContent).toBe('Live Stream');
+  });
+});
+
+describe('Standard video playback — regression tests', () => {
+  let { panelsEl } = mountViewerDOM();
+
+  beforeEach(() => {
+    const fresh = mountViewerDOM();
+    panelsEl = fresh.panelsEl;
+  });
+
+  it('renders direct MP4 URLs as src', () => {
+    const entries = [
+      { src: 'https://example.com/video.mp4' },
+    ];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    expect(video.src).toBe('https://example.com/video.mp4');
+    expect(video.dataset.hlsManifest).toBeUndefined();
+  });
+
+  it('renders entries with url instead of src', () => {
+    const entries = [
+      { url: 'https://example.com/video.webm' },
+    ];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    expect(video.src).toBe('https://example.com/video.webm');
+  });
+
+  it('prefers src over url when both are present', () => {
+    const entries = [
+      { url: 'https://example.com/page.html', src: 'https://example.com/video.mp4' },
+    ];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    expect(video.src).toBe('https://example.com/video.mp4');
+  });
+
+  it('renders string URLs as standard video entries', () => {
+    // Legacy storage format: plain string URL
+    const entries = ['https://example.com/video.mp4'];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    expect(video.src).toBe('https://example.com/video.mp4');
+    expect(video.dataset.hlsManifest).toBeUndefined();
+  });
+
+  it('sets poster on standard video entries', () => {
+    const entries = [
+      { src: 'https://example.com/video.mp4', poster: 'https://example.com/thumb.jpg' },
+    ];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    expect(video.poster).toBe('https://example.com/thumb.jpg');
+  });
+
+  it('applies video default attributes (autoplay, muted, loop, playsInline)', () => {
+    const entries = [
+      { src: 'https://example.com/video.mp4' },
+    ];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    expect(video.autoplay).toBe(true);
+    expect(video.muted).toBe(true);
+    expect(video.loop).toBe(true);
+    expect(video.playsInline).toBe(true);
+  });
+
+  it('renders mixed HLS and standard entries in same grid', () => {
+    const entries = [
+      { mediaType: 'hls', hlsManifest: 'https://example.com/live.m3u8' },
+      { src: 'https://example.com/recording.mp4' },
+      { mediaType: 'hls', hlsManifest: 'https://example.com/live2.m3u8' },
+      { src: 'https://example.com/recording2.mp4' },
+    ];
+    renderPanels(panelsEl, entries, 2, []);
+
+    const videos = panelsEl.querySelectorAll('video');
+    expect(videos.length).toBe(4);
+
+    // HLS entry
+    expect(videos[0].dataset.hlsManifest).toBe('https://example.com/live.m3u8');
+    expect(videos[0].dataset.mediaType).toBe('hls');
+
+    // Standard entry
+    expect(videos[1].src).toBe('https://example.com/recording.mp4');
+    expect(videos[1].dataset.hlsManifest).toBeUndefined();
+
+    // HLS entry
+    expect(videos[2].dataset.hlsManifest).toBe('https://example.com/live2.m3u8');
+    expect(videos[2].dataset.mediaType).toBe('hls');
+
+    // Standard entry
+    expect(videos[3].src).toBe('https://example.com/recording2.mp4');
+    expect(videos[3].dataset.hlsManifest).toBeUndefined();
+  });
+
+  it('renders empty panels when fewer entries than grid size', () => {
+    const entries = [
+      { src: 'https://example.com/video.mp4' },
+    ];
+    renderPanels(panelsEl, entries, 2, []);
+
+    const panels = panelsEl.querySelectorAll('.panel');
+    expect(panels.length).toBe(4); // 2x2 grid
+    expect(panels[0].classList.contains('empty')).toBe(false);
+    expect(panels[1].classList.contains('empty')).toBe(true);
+    expect(panels[2].classList.contains('empty')).toBe(true);
+    expect(panels[3].classList.contains('empty')).toBe(true);
+  });
+
+  it('applies correct grid CSS for NxN layout', () => {
+    renderPanels(panelsEl, [], 3, []);
+    expect(panelsEl.style.gridTemplateColumns).toBe('repeat(3, 1fr)');
+    expect(panelsEl.style.gridTemplateRows).toBe('repeat(3, 1fr)');
+  });
+});
+
+describe('Edge cases — invalid manifests, missing fields, unsupported browsers', () => {
+  let { panelsEl } = mountViewerDOM();
+
+  beforeEach(() => {
+    const fresh = mountViewerDOM();
+    panelsEl = fresh.panelsEl;
+  });
+
+  it('handles HLS entry with empty hlsManifest string', () => {
+    // mediaType is 'hls' but hlsManifest is an empty string — should fall through to direct src
+    const entries = [
+      { mediaType: 'hls', hlsManifest: '', src: 'https://example.com/fallback.mp4' },
+    ];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    // Empty hlsManifest is falsy, so the else branch runs
+    expect(video.src).toBe('https://example.com/fallback.mp4');
+    expect(video.dataset.hlsManifest).toBeUndefined();
+  });
+
+  it('handles HLS entry with missing hlsManifest', () => {
+    const entries = [
+      { mediaType: 'hls', src: 'https://example.com/video.mp4' },
+    ];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    expect(video.src).toBe('https://example.com/video.mp4');
+  });
+
+  it('handles empty src for non-HLS entry', () => {
+    const entries = [
+      { mediaType: 'video', src: '', url: '' },
+    ];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    // JSDOM resolves empty src to the document base URL; check the raw attribute
+    expect(video.getAttribute('src')).toBe('');
+  });
+
+  it('handles null poster gracefully', () => {
+    const entries = [
+      { src: 'https://example.com/video.mp4', poster: null },
+    ];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    // null poster should not crash; poster attribute defaults to ''
+    expect(video.poster).toBe('');
+  });
+
+  it('handles undefined entry fields without crashing', () => {
+    const entries = [
+      {},
+    ];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    expect(video).not.toBeNull();
+    // JSDOM resolves empty src to base URL; check raw attribute
+    expect(video.getAttribute('src')).toBe('');
+  });
+
+  it('handles null entry in the array', () => {
+    const entries = [null];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const panels = panelsEl.querySelectorAll('.panel');
+    expect(panels[0].classList.contains('empty')).toBe(true);
+  });
+
+  it('handles malformed manifest URL (not .m3u8)', () => {
+    // Viewer doesn't validate manifest URL format — that's hls.js job
+    const entries = [
+      { mediaType: 'hls', hlsManifest: 'https://example.com/invalid-manifest' },
+    ];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    expect(video.dataset.hlsManifest).toBe('https://example.com/invalid-manifest');
+    expect(video.dataset.mediaType).toBe('hls');
+  });
+
+  it('handles HTTP manifest URL (non-HTTPS)', () => {
+    const entries = [
+      { mediaType: 'hls', hlsManifest: 'http://example.com/stream.m3u8' },
+    ];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    expect(video.dataset.hlsManifest).toBe('http://example.com/stream.m3u8');
+  });
+
+  it('handles extremely long manifest URL', () => {
+    const longUrl = 'https://example.com/stream.m3u8?' + 'x='.repeat(1000);
+    const entries = [
+      { mediaType: 'hls', hlsManifest: longUrl },
+    ];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    expect(video.dataset.hlsManifest).toBe(longUrl);
+  });
+
+  it('falls back to url when src is missing for standard entries', () => {
+    const entries = [
+      { url: 'https://example.com/video.mp4' },
+    ];
+    renderPanels(panelsEl, entries, 1, []);
+
+    const video = panelsEl.querySelector('video');
+    expect(video.src).toBe('https://example.com/video.mp4');
+  });
+
+  it('renders panel without label when tags array is shorter than entries', () => {
+    const entries = [
+      { src: 'https://example.com/video.mp4' },
+      { src: 'https://example.com/video2.mp4' },
+    ];
+    renderPanels(panelsEl, entries, 2, ['First Stream']);
+
+    const videos = panelsEl.querySelectorAll('video');
+    const labels = panelsEl.querySelectorAll('.panel-label');
+    expect(videos.length).toBe(2);
+    expect(labels.length).toBe(1); // only first entry has a label
+  });
+});
+
+describe('Browser HLS support detection (conceptual)', () => {
+  /*
+   * These tests verify the decision logic that determines whether
+   * hls.js should be loaded or native playback used.
+   *
+   * Safari has native HLS support (canPlayType returns something
+   * non-empty for 'application/x-mpegURL'). Other browsers need hls.js.
+   */
+
+  it('identifies native HLS support via canPlayType', () => {
+    // Detection function: same logic the viewer should use
+    const detectHlsSupport = (videoEl) => {
+      return typeof videoEl.canPlayType === 'function' &&
+             videoEl.canPlayType('application/x-mpegURL') !== '';
+    };
+
+    const { document: doc } = mountViewerDOM();
+    const video = doc.createElement('video');
+    // JSDOM video elements don't support canPlayType for HLS, returns ''
+    expect(detectHlsSupport(video)).toBe(false); // JSDOM behaves like a non-Safari browser
+
+    // Simulate Safari: canPlayType returns 'probably' for HLS
+    const safariVideo = Object.assign(doc.createElement('video'), {
+      canPlayType: (type) => type === 'application/x-mpegURL' ? 'probably' : '',
+    });
+    expect(detectHlsSupport(safariVideo)).toBe(true);
+  });
+
+  it('uses hls.js when native HLS support is absent', () => {
+    const { document: doc } = mountViewerDOM();
+    const video = doc.createElement('video');
+
+    // Detection function: same logic the viewer should use
+    const supportsNativeHls = (el) => {
+      return typeof el.canPlayType === 'function' &&
+             el.canPlayType('application/x-mpegURL') !== '';
+    };
+
+    // On non-Safari browsers, hls.js is required
+    const needsHlsJs = !supportsNativeHls(video);
+    expect(needsHlsJs).toBe(true);
+  });
+
+  it('skips hls.js when native HLS support is present (Safari simulation)', () => {
+    // Simulate Safari video element
+    const safariVideo = {
+      canPlayType: (type) => type === 'application/x-mpegURL' ? 'probably' : '',
+    };
+
+    const supportsNativeHls = (el) => {
+      return typeof el.canPlayType === 'function' &&
+             el.canPlayType('application/x-mpegURL') !== '';
+    };
+
+    const needsHlsJs = !supportsNativeHls(safariVideo);
+    expect(needsHlsJs).toBe(false); // Safari doesn't need hls.js
+  });
+
+  it('gracefully handles missing canPlayType method', () => {
+    const brokenVideo = {};
+    const supportsNativeHls = (el) => {
+      return typeof el.canPlayType === 'function' &&
+             el.canPlayType('application/x-mpegURL') !== '';
+    };
+    // Should not throw
+    expect(() => supportsNativeHls(brokenVideo)).not.toThrow();
+    expect(supportsNativeHls(brokenVideo)).toBe(false);
+  });
+});