Major update for v1 and tests

src/utils/imageLoading.js

@@ -0,0 +1,52 @@
+/**
+ * Image-loading helpers used by photo upload and slot assignment.
+ *
+ * Before this module: `useTemplate.assignImageToSlot` and `UploadTab.getImageSize`
+ * each had their own inline `new Image() + onload + onerror` Promise wrapper,
+ * and `App.handlePhotoEditComplete` had a third variant using callbacks
+ * instead of a Promise. The three wrappers had subtly different error
+ * handling — one rejected with a generic message, another logged to the
+ * console, the third silently swallowed errors and used a fallback path.
+ *
+ * Centralizing here gives every caller the same behavior: a clean Promise
+ * that resolves to dimensions or rejects with a descriptive Error. The
+ * App.jsx photo-edit flow still uses the lower-level callback form because
+ * its onload handler runs synchronously before its setEditingElement call
+ * (timing matters for the Filerobot modal teardown sequence) — but the
+ * other two consumers go through `loadImageDimensions`.
+ */
+
+/**
+ * Load an image and resolve to its natural pixel dimensions.
+ *
+ * Resolves with `{ width, height }` from `naturalWidth`/`naturalHeight`,
+ * falling back to `width`/`height` for the rare case where naturalWidth is 0
+ * (some Safari versions report this for SVG sources without intrinsic size).
+ *
+ * Rejects with a descriptive Error if the image fails to load. Callers
+ * should `await` and use try/catch — not `.then(undefined, () => fallback)`,
+ * which would silently mask bugs.
+ *
+ * @param {string} src - data:, blob:, or remote URL
+ * @returns {Promise<{ width: number, height: number }>}
+ */
+export function loadImageDimensions(src) {
+  return new Promise((resolve, reject) => {
+    const img = new window.Image();
+    img.onload = () => resolve({
+      width: img.naturalWidth || img.width,
+      height: img.naturalHeight || img.height,
+    });
+    img.onerror = () => reject(new Error(`Failed to load image: ${truncate(src, 80)}`));
+    img.src = src;
+  });
+}
+
+/**
+ * Truncate a URL for use in error messages. Long data: URLs in stack traces
+ * blow up log readers; the first 80 chars are enough to identify the type.
+ */
+function truncate(s, n) {
+  if (typeof s !== 'string') return String(s);
+  return s.length > n ? `${s.slice(0, n)}…` : s;
+}