debug: add comprehensive logging for image caching

Add debug logs prefixed with [image-preload], [image-cache], [sw-image-cache],
and [reader-header] to track:
- When images are preloaded
- Service Worker availability and controller status
- Image fetch success/failure
- Service Worker intercepting and caching image requests
- Image loading in ReaderHeader component
- Cache hits/misses in Service Worker

This will help debug why images aren't available offline.

src/components/ReaderHeader.tsx

@@ -37,6 +37,17 @@ const ReaderHeader: React.FC<ReaderHeaderProps> = ({
   onHighlightCountClick
 }) => {
   const cachedImage = useImageCache(image)
+  
+  // Debug: Log image loading state
+  React.useEffect(() => {
+    if (image) {
+      console.log('[reader-header] Image provided:', image)
+      if (cachedImage) {
+        console.log('[reader-header] Using cached image URL:', cachedImage)
+      }
+    }
+  }, [image, cachedImage])
+  
   const { textColor } = useAdaptiveTextColor(cachedImage)
   const formattedDate = published ? format(new Date(published * 1000), 'MMM d, yyyy') : null
   const isLongSummary = summary && summary.length > 150
@@ -80,7 +91,21 @@ const ReaderHeader: React.FC<ReaderHeaderProps> = ({
       <>
         <div className="reader-hero-image">
           {cachedImage ? (
-            <img src={cachedImage} alt={title || 'Article image'} />
+            <img 
+              src={cachedImage} 
+              alt={title || 'Article image'}
+              onLoad={() => {
+                console.log('[reader-header] ✅ Image loaded successfully:', cachedImage)
+              }}
+              onError={(e) => {
+                console.error('[reader-header] ❌ Image failed to load:', cachedImage, {
+                  error: e,
+                  target: e.currentTarget,
+                  naturalWidth: e.currentTarget.naturalWidth,
+                  naturalHeight: e.currentTarget.naturalHeight
+                })
+              }}
+            />
           ) : (
             <div className="reader-hero-placeholder">
               <FontAwesomeIcon icon={faNewspaper} />

src/hooks/useImageCache.ts

@@ -12,6 +12,34 @@ export function useImageCache(
   // Service Worker handles everything - just return the URL as-is
   // The Service Worker will intercept fetch requests and cache them
   // Make sure images use standard <img src> tags for SW interception
+  
+  // Debug: Log when image URL is provided
+  if (imageUrl) {
+    console.log('[image-cache] useImageCache hook called with URL:', imageUrl)
+    
+    // Check if Service Worker is available
+    if ('serviceWorker' in navigator) {
+      if (navigator.serviceWorker.controller) {
+        console.log('[image-cache] ✅ Service Worker controller is active')
+      } else {
+        console.warn('[image-cache] ⚠️ Service Worker not controlling page - checking registration...')
+        navigator.serviceWorker.getRegistration().then((reg) => {
+          if (reg) {
+            console.log('[image-cache] Service Worker registered but not controlling:', {
+              active: !!reg.active,
+              installing: !!reg.installing,
+              waiting: !!reg.waiting
+            })
+          } else {
+            console.warn('[image-cache] ❌ No Service Worker registration found')
+          }
+        })
+      }
+    } else {
+      console.warn('[image-cache] ❌ Service Workers not supported in this browser')
+    }
+  }
+  
   return imageUrl
 }
 
@@ -34,18 +62,49 @@ export function useCacheImageOnLoad(
  * images are cached before going offline
  */
 export function preloadImage(imageUrl: string | undefined): void {
-  if (!imageUrl) return
+  if (!imageUrl) {
+    console.log('[image-preload] Skipping - no image URL provided')
+    return
+  }
+  
+  console.log('[image-preload] Preloading image:', imageUrl)
+  
+  // Check if Service Worker is available
+  if ('serviceWorker' in navigator && navigator.serviceWorker.controller) {
+    console.log('[image-preload] ✅ Service Worker is active')
+  } else {
+    console.warn('[image-preload] ⚠️ Service Worker not active - images may not cache')
+  }
   
   // Create a link element with rel=prefetch or use Image object to trigger fetch
   // Service Worker will intercept and cache the request
   const img = new Image()
+  
+  img.onload = () => {
+    console.log('[image-preload] ✅ Image loaded successfully:', imageUrl)
+  }
+  
+  img.onerror = (err) => {
+    console.error('[image-preload] ❌ Image failed to load:', imageUrl, err)
+  }
+  
   img.src = imageUrl
+  console.log('[image-preload] Created Image() object with src:', imageUrl)
   
   // Also try using fetch to explicitly trigger Service Worker
   // This ensures the image is cached even if <img> tag hasn't rendered yet
-  fetch(imageUrl, { mode: 'no-cors' }).catch(() => {
-    // Ignore errors - image might not be CORS-enabled, but SW will still cache it
-    // The Image() approach above will work for most cases
-  })
+  fetch(imageUrl, { mode: 'no-cors' })
+    .then((response) => {
+      console.log('[image-preload] ✅ Fetch successful for image:', imageUrl, {
+        status: response.status,
+        type: response.type,
+        url: response.url
+      })
+    })
+    .catch((err) => {
+      console.warn('[image-preload] ⚠️ Fetch failed (may be CORS issue, Image() should still work):', imageUrl, err)
+      // Ignore errors - image might not be CORS-enabled, but SW will still cache it
+      // The Image() approach above will work for most cases
+    })
 }
 

src/sw.ts

@@ -31,6 +31,15 @@ registerRoute(
                     /\.(jpg|jpeg|png|gif|webp|svg)$/i.test(url.pathname)
     // Cache all images, not just cross-origin ones
     // This ensures article images from any source get cached
+    
+    if (isImage) {
+      console.log('[sw-image-cache] Intercepting image request:', {
+        url: url.href,
+        destination: request.destination,
+        method: request.method
+      })
+    }
+    
     return isImage
   },
   new StaleWhileRevalidate({
@@ -43,6 +52,29 @@ registerRoute(
       new CacheableResponsePlugin({
         statuses: [0, 200],
       }),
+      {
+        cacheKeyWillBeUsed: async ({ request }) => {
+          console.log('[sw-image-cache] Cache key generated for:', request.url)
+          return request
+        },
+        cacheWillUpdate: async ({ response }) => {
+          console.log('[sw-image-cache] Caching response:', {
+            url: response.url,
+            status: response.status,
+            type: response.type,
+            ok: response.ok
+          })
+          return response.ok ? response : null
+        },
+        cachedResponseWillBeUsed: async ({ cachedResponse, request }) => {
+          if (cachedResponse) {
+            console.log('[sw-image-cache] ✅ Serving from cache:', request.url)
+          } else {
+            console.log('[sw-image-cache] ❌ No cached response found:', request.url)
+          }
+          return cachedResponse || null
+        }
+      }
     ],
   })
 )