feat: add overlay image loading state

src/server/request-handler.ts

@@ -619,6 +619,12 @@ function htmlPage(): string {
         color: var(--timeline-text);
       }
 
+      .overlay-media {
+        position: relative;
+        min-height: 48vh;
+        background: var(--timeline-surface-strong);
+      }
+
       .overlay-card header {
         padding: 16px 18px;
         border-bottom: 1px solid var(--timeline-border);
@@ -635,6 +641,43 @@ function htmlPage(): string {
         max-height: 78vh;
         object-fit: contain;
         background: var(--timeline-surface-strong);
+        transition: opacity 120ms ease;
+      }
+
+      .overlay-card.loading img {
+        opacity: 0;
+      }
+
+      .overlay-loading {
+        position: absolute;
+        inset: 0;
+        display: none;
+        place-items: center;
+        gap: 10px;
+        padding: 24px;
+        text-align: center;
+        color: var(--timeline-text-muted);
+      }
+
+      .overlay-loading.active {
+        display: grid;
+      }
+
+      .overlay-loading .spinner {
+        opacity: 1;
+        transform: scale(1);
+        animation: spin 0.8s linear infinite;
+      }
+
+      .overlay-loading.error .spinner {
+        animation: none;
+        opacity: 0.45;
+      }
+
+      .overlay-loading strong {
+        color: var(--timeline-text);
+        font-size: 0.92rem;
+        font-weight: 600;
       }
 
       .close {
@@ -1015,9 +1058,15 @@ function htmlPage(): string {
             <span>Close</span>
           </button>
         </header>
+        <div class="overlay-media">
+          <div class="overlay-loading" id="overlay-loading" aria-live="polite" aria-atomic="true">
+            <span class="spinner active" aria-hidden="true"></span>
+            <strong id="overlay-loading-text">Loading full-size image...</strong>
+          </div>
           <img id="overlay-image" alt="" />
         </div>
       </div>
+    </div>
 
     <script src="https://unpkg.com/leaflet@1.9.4/dist/leaflet.js" integrity="sha256-20nQCchB9co0qIjJZRGuk2/Z9VM+kNiyxNV1lvTlZBo=" crossorigin=""></script>
     <script type="module">
@@ -1079,6 +1128,8 @@ function htmlPage(): string {
       const overlay = mustGet("overlay");
       const overlayTitle = mustGet("overlay-title");
       const overlayImage = mustGet("overlay-image");
+      const overlayLoading = mustGet("overlay-loading");
+      const overlayLoadingText = mustGet("overlay-loading-text");
       const closeOverlay = mustGet("close-overlay");
       const photoList = mustGet("photo-list");
       const emptyState = mustGet("empty-state");
@@ -1104,6 +1155,7 @@ function htmlPage(): string {
       const importStatus = mustGet("share-status");
       const importButton = mustGet("load-share");
       const stopImportButton = mustGet("cancel-share");
+      let overlayLoadToken = 0;
 
       function mustGet(id) {
         const element = document.getElementById(id);
@@ -1568,11 +1620,34 @@ function htmlPage(): string {
       }
 
       function openOverlay(photo) {
+        const requestToken = ++overlayLoadToken;
         overlay.classList.add("open");
         overlay.setAttribute("aria-hidden", "false");
         overlayTitle.textContent = photo.name;
-        overlayImage.src = photo.fullUrl;
         overlayImage.alt = photo.name;
+        overlay.classList.add("loading");
+        overlayLoading.classList.add("active");
+        overlayLoading.classList.remove("error");
+        overlayLoadingText.textContent = "Loading full-size image...";
+        overlayImage.onload = () => {
+          if (requestToken !== overlayLoadToken) {
+            return;
+          }
+          overlay.classList.remove("loading");
+          overlayLoading.classList.remove("active");
+          overlayLoading.classList.remove("error");
+        };
+        overlayImage.onerror = () => {
+          if (requestToken !== overlayLoadToken) {
+            return;
+          }
+          overlayLoadingText.textContent = "Could not load full-size image.";
+          overlay.classList.remove("loading");
+          overlayLoading.classList.add("error");
+          overlayLoading.classList.add("active");
+        };
+        overlayImage.removeAttribute("src");
+        overlayImage.src = photo.fullUrl;
       }
 
       function createPhotoMarkerIcon(photo) {
@@ -1588,8 +1663,13 @@ function htmlPage(): string {
       }
 
       function closeOverlayView() {
+        overlayLoadToken += 1;
         overlay.classList.remove("open");
         overlay.setAttribute("aria-hidden", "true");
+        overlay.classList.remove("loading");
+        overlayLoading.classList.remove("active");
+        overlayLoading.classList.remove("error");
+        overlayLoadingText.textContent = "Loading full-size image...";
         overlayImage.removeAttribute("src");
       }