Refine media state handling and fix CellImageBuilder errors

- Update MediaService delegation tests in src/mediaHandlers.test.ts to use mock.results for more reliable instance retrieval.
- Fix CellImageBuilder failure in src/mediaHandlers.ts by using public Shopify thumbnail URLs for synced items and direct Drive thumbnail endpoints for non-synced items.
- Fallback to IMAGE() formula in the spreadsheet for Drive items to avoid authentication issues with native cell images.
- Add test_*.txt to .gitignore to keep the workspace clean.
- Ensure all tests pass with updated log expectations and mock data.

src/mediaHandlers.ts

@@ -84,7 +84,54 @@ export function saveMediaChanges(sku: string, finalState: any[]) {
        throw new Error("Product must be synced to Shopify before saving media changes.")
   }
 
-  return mediaService.processMediaChanges(sku, finalState, product.shopify_id)
+  const logs = mediaService.processMediaChanges(sku, finalState, product.shopify_id)
+
+  // Update Sheet Thumbnail (Top of Gallery)
+  try {
+      // Refresh state to get Shopify CDN URLs
+      const latestState = mediaService.getUnifiedMediaState(sku, product.shopify_id);
+      const sorted = latestState.sort((a, b) => (a.galleryOrder || 0) - (b.galleryOrder || 0));
+      const firstItem = sorted[0];
+
+      if (firstItem) {
+          const ss = new GASSpreadsheetService();
+          const row = ss.getRowNumberByColumnValue("product_inventory", "sku", sku);
+          if (row) {
+              // Decide on the most reliable URL for the spreadsheet
+              // 1. If it's a synced Shopify item, use the Shopify preview image URL (public)
+              // 2. Otherwise (Drive item or adoption), use the dedicated Drive thumbnail endpoint
+              const isShopifyThumb = firstItem.thumbnail && firstItem.thumbnail.startsWith('http');
+              const driveThumbUrl = `https://drive.google.com/thumbnail?id=${firstItem.driveId}&sz=w400`;
+              const thumbUrl = isShopifyThumb ? firstItem.thumbnail : driveThumbUrl;
+
+              // Use CellImageBuilder for native in-cell image (Shopify only)
+              try {
+                  // CellImageBuilder is picky about URLs and often fails with Drive's redirects/auth
+                  // even if the file is public. Formula-based IMAGE() is more robust for Drive.
+                  if (!isShopifyThumb) throw new Error("Use formula for Drive thumbnails");
+
+                  const image = SpreadsheetApp.newCellImage()
+                    .setSourceUrl(thumbUrl)
+                    .setAltTextTitle(sku)
+                    .setAltTextDescription(`Thumbnail for ${sku}`)
+                    .build();
+                  ss.setCellValueByColumnName("product_inventory", row, "thumbnail", image);
+                  logs.push(`Updated sheet thumbnail for SKU ${sku}`);
+              } catch (builderErr) {
+                  // Fallback to formula
+                  ss.setCellValueByColumnName("product_inventory", row, "thumbnail", `=IMAGE("${thumbUrl}")`);
+                  logs.push(`Updated sheet thumbnail (Formula) for SKU ${sku}`);
+              }
+          } else {
+              logs.push(`Warning: Could not find row for SKU ${sku} to update thumbnail.`);
+          }
+      }
+  } catch (e) {
+      console.warn("Failed to update sheet thumbnail", e);
+      logs.push(`Warning: Failed to update sheet thumbnail: ${e.message}`);
+  }
+
+  return logs
 }