Refactor CDN detection into shared constants with test framework

Moved all CDN detection logic and constants into a shared constants.js
file that is used by both background.js and popup.js. This provides:

- Declarative CDN_RULES: Each CDN has clear detection conditions
  (e.g., Akamai ← x-akamai-request-id OR server contains "akamai")
- Single source of truth for detection logic, header lists, colors, etc.
- Test framework with 27 test cases covering all supported CDNs

The rules are self-documenting - looking at CDN_RULES makes it obvious
why a response is detected as a particular CDN.

Also added `just test` command to run the test suite.

Author: bartTC

CF Cache Status/CF Cache Status Extension/Resources/background.js

@@ -3,10 +3,11 @@
  *
  * Intercepts HTTP responses to extract CDN cache headers and updates
  * the toolbar badge with the cache status (HIT/MISS/etc).
- *
- * Supports: Cloudflare, CloudFront, Fastly, Akamai, Bunny CDN, Varnish
  */
 
+// Import shared constants (loaded via manifest.json)
+// Uses: TRACKED_HEADERS, STATUS_COLORS, detectCDN, parseCacheStatus
+
 // =============================================================================
 // State Management
 // =============================================================================
@@ -17,122 +18,12 @@ const tabData = new Map();
 /** Tracks tabs with pending navigations to capture only the first main request */
 const pendingNavigations = new Set();
 
-// =============================================================================
-// Configuration
-// =============================================================================
-
-/** HTTP headers to capture from responses */
-const TRACKED_HEADERS = [
-  // Cloudflare
-  'cf-cache-status', 'cf-ray', 'cf-pop',
-  // CloudFront
-  'x-amz-cf-id', 'x-amz-cf-pop',
-  // Fastly
-  'x-served-by', 'x-cache-hits', 'x-timer',
-  // Akamai
-  'x-akamai-request-id',
-  // Bunny CDN
-  'cdn-cache', 'cdn-pullzone', 'cdn-requestid',
-  // Generic (CloudFront, Fastly, Akamai, Varnish, KeyCDN, etc.)
-  'x-cache', 'x-cache-status', 'x-varnish', 'x-edge-location', 'via',
-  // Standard cache headers
-  'age', 'cache-control', 'expires', 'etag', 'last-modified', 'vary', 'pragma',
-  // Response metadata
-  'server', 'content-type'
-];
-
-/** Badge colors for each cache status */
-const STATUS_COLORS = {
-  'HIT':         { badge: '#22c55e', text: '#fff' },  // Green
-  'MISS':        { badge: '#ef4444', text: '#fff' },  // Red
-  'EXPIRED':     { badge: '#eab308', text: '#000' },  // Yellow
-  'STALE':       { badge: '#eab308', text: '#000' },  // Yellow
-  'REVALIDATED': { badge: '#eab308', text: '#000' },  // Yellow
-  'REFRESH':     { badge: '#eab308', text: '#000' },  // Yellow
-  'BYPASS':      { badge: '#6b7280', text: '#fff' },  // Gray
-  'DYNAMIC':     { badge: '#6b7280', text: '#fff' },  // Gray
-  'ERROR':       { badge: '#ef4444', text: '#fff' },  // Red
-  'NONE':        { badge: '#6b7280', text: '#fff' }   // Gray (no CDN)
-};
-
-// =============================================================================
-// CDN Detection
-// =============================================================================
-
-/**
- * Detects the CDN provider based on response headers.
- * @param {Object} headers - Lowercase header name to value mapping
- * @returns {string|null} CDN identifier or null if not detected
- */
-function detectCDN(headers) {
-  if (headers['cf-cache-status'] || headers['cf-ray']) return 'cloudflare';
-  if (headers['x-amz-cf-id'] || headers['x-amz-cf-pop']) return 'cloudfront';
-  if (headers['x-served-by'] || headers['x-timer']) return 'fastly';
-  if (headers['x-akamai-request-id']) return 'akamai';
-  if (headers['cdn-cache'] || headers['cdn-pullzone']) return 'bunny';
-  if (headers['x-varnish']) return 'varnish';
-
-  // Check server header for CDN hints
-  const server = (headers['server'] || '').toLowerCase();
-  if (server.includes('akamai')) return 'akamai';
-
-  // Check x-cache with via header for additional hints
-  if (headers['x-cache']) {
-    const via = (headers['via'] || '').toLowerCase();
-    if (via.includes('cloudfront')) return 'cloudfront';
-    if (via.includes('varnish')) return 'varnish';
-    if (via.includes('akamai')) return 'akamai';
-    return 'cdn';  // Generic CDN
-  }
-
-  return null;
-}
-
-/**
- * Parses cache status from headers based on the detected CDN.
- * @param {Object} headers - Lowercase header name to value mapping
- * @param {string} cdn - CDN identifier from detectCDN()
- * @returns {string|null} Normalized cache status (HIT, MISS, etc.) or null
- */
-function parseCacheStatus(headers, cdn) {
-  // Cloudflare uses its own header
-  if (cdn === 'cloudflare') {
-    return headers['cf-cache-status']?.toUpperCase() || null;
-  }
-
-  // Bunny CDN uses cdn-cache header
-  if (cdn === 'bunny') {
-    const status = headers['cdn-cache'];
-    if (status) {
-      const lower = status.toLowerCase();
-      if (lower.includes('hit')) return 'HIT';
-      if (lower.includes('miss')) return 'MISS';
-    }
-    return null;
-  }
-
-  // Most CDNs use x-cache header (CloudFront, Fastly, Akamai, Varnish, etc.)
-  const xCache = headers['x-cache'] || headers['x-cache-status'];
-  if (xCache) {
-    const lower = xCache.toLowerCase();
-    if (lower.includes('hit')) return 'HIT';
-    if (lower.includes('miss')) return 'MISS';
-    if (lower.includes('refresh')) return 'REFRESH';
-    if (lower.includes('error')) return 'ERROR';
-    if (lower.includes('pass')) return 'BYPASS';
-    if (lower.includes('expired')) return 'EXPIRED';
-  }
-
-  return null;
-}
-
 // =============================================================================
 // Badge Management
 // =============================================================================
 
 /**
  * Updates the toolbar badge text and color for a tab.
- * Sets both globally and per-tab (Safari has inconsistent per-tab support).
  * @param {number} tabId - Browser tab ID
  * @param {string|null} status - Cache status (HIT, MISS, etc.)
  * @param {string|null} cdn - CDN identifier
@@ -141,19 +32,16 @@ function updateBadge(tabId, status, cdn) {
   const displayStatus = status || 'NONE';
   const colors = STATUS_COLORS[displayStatus] || STATUS_COLORS['NONE'];
 
-  // Map status to shortened badge text
   const badgeTextMap = {
     'HIT': 'HIT', 'MISS': 'MISS', 'EXPIRED': 'EXP', 'STALE': 'STL',
     'REVALIDATED': 'REV', 'BYPASS': 'BYP', 'DYNAMIC': 'DYN',
     'REFRESH': 'REF', 'ERROR': 'ERR'
   };
   const badgeText = status ? (badgeTextMap[status] || status.substring(0, 3)) : '';
 
-  // Set badge globally (Safari doesn't always support per-tab badges)
   browser.action.setBadgeText({ text: badgeText });
   browser.action.setBadgeBackgroundColor({ color: colors.badge });
 
-  // Also try per-tab for browsers that support it
   try {
     browser.action.setBadgeText({ text: badgeText, tabId });
     browser.action.setBadgeBackgroundColor({ color: colors.badge, tabId });
@@ -163,7 +51,7 @@ function updateBadge(tabId, status, cdn) {
 }
 
 /**
- * Clears the badge, setting it globally and per-tab.
+ * Clears the badge for a tab.
  * @param {number} tabId - Browser tab ID
  */
 function clearBadge(tabId) {
@@ -181,26 +69,25 @@ function clearBadge(tabId) {
 
 // Track navigation start to capture only the first main document request
 browser.webNavigation.onBeforeNavigate.addListener((details) => {
-  if (details.frameId === 0) {  // Main frame only
+  if (details.frameId === 0) {
     pendingNavigations.add(details.tabId);
-    tabData.delete(details.tabId);  // Clear stale data
+    tabData.delete(details.tabId);
   }
 });
 
 // Update URL after navigation completes (handles redirects)
 browser.webNavigation.onCompleted.addListener((details) => {
-  if (details.frameId === 0) {  // Main frame only
+  if (details.frameId === 0) {
     const data = tabData.get(details.tabId);
     if (data && data.url !== details.url) {
-      data.url = details.url;  // Update to final URL after redirects
+      data.url = details.url;
     }
   }
 });
 
 // Capture response headers for main document requests
 browser.webRequest.onHeadersReceived.addListener(
   (details) => {
-    // Only process main frame requests we're expecting
     if (details.type !== 'main_frame' || details.frameId !== 0) return;
     if (!pendingNavigations.has(details.tabId)) return;
 
@@ -215,11 +102,10 @@ browser.webRequest.onHeadersReceived.addListener(
       }
     }
 
-    // Detect CDN and parse status
+    // Detect CDN and parse status using shared functions
     const cdn = detectCDN(headers);
     const status = parseCacheStatus(headers, cdn);
 
-    // Store data for popup
     tabData.set(details.tabId, {
       url: details.url,
       headers,
@@ -275,13 +161,11 @@ browser.runtime.onMessage.addListener((message, sender, sendResponse) => {
     sendResponse(tabData.get(message.tabId) || null);
   }
 
-  // Handle performance data from content script
   if (message.type === 'performanceData' && sender.tab) {
     const existing = tabData.get(sender.tab.id);
     if (existing) {
       existing.performance = message.metrics;
     } else {
-      // Store performance data even if no cache headers yet
       tabData.set(sender.tab.id, {
         url: sender.tab.url,
         headers: {},