[WIP] Address feedback from review on canvas origami implementation

DistFiles/localization/en/Bloom.xlf

@@ -1361,7 +1361,7 @@
         <source xml:lang="en">Image</source>
         <note>ID: EditTab.CustomPage.Image</note>
       </trans-unit>
-      <trans-unit id="EditTab.CustomPage.Canvas" sil:dynamic="true">
+      <trans-unit id="EditTab.CustomPage.Canvas" sil:dynamic="true" translate="no">
         <source xml:lang="en">Canvas</source>
         <note>ID: EditTab.CustomPage.Canvas</note>
       </trans-unit>
@@ -1877,9 +1877,10 @@
         <note>ID: EditTab.ImageMetadata.Corrupt.MoreInfo</note>
         <note>label of a button to click to display a website with more information</note>
       </trans-unit>
-      <trans-unit id="EditTab.Image.CutImage" sil:dynamic="true">
+      <trans-unit id="EditTab.Image.CutImage" sil:dynamic="true" translate="no">
         <source xml:lang="en">Cut image</source>
         <note>ID: EditTab.Image.CutImage</note>
+        <note>Obsolete as of 6.3</note>
       </trans-unit>
       <trans-unit id="EditTab.Image.EditMetadata" sil:dynamic="true">
         <source xml:lang="en">Edit image credits, copyright, &amp; license</source>

src/BloomBrowserUI/bookEdit/css/editMode.less

@@ -1376,10 +1376,9 @@ canvas.moving {
     pointer-events: none;
     background-color: transparent;
 
-    // background images can't be manually resized
+    // background images can't be manually resized, but they can be cropped
     &.bloom-backgroundImage-control-frame {
-        .bloom-ui-canvas-element-resize-handle,
-        .bloom-ui-canvas-element-side-handle {
+        .bloom-ui-canvas-element-resize-handle {
             display: none;
         }
     }

src/BloomBrowserUI/bookEdit/js/CanvasElementManager.ts

@@ -2693,7 +2693,7 @@ export class CanvasElementManager {
                     !useSizeOfNewImage && // not waiting for new dimensions
                     imgOrVideo.classList.contains("bloom-imageLoadError")) // error occurred while trying to load
             ) {
-                // Image is in an error state; we probably won't ever get useful dimensions. Just leave
+                // Image is a placeholder or in an error state; we probably won't ever get useful dimensions. Just leave
                 // the canvas element the shape it is.
                 return;
             }

src/BloomBrowserUI/bookEdit/js/bloomImages.ts

@@ -36,12 +36,17 @@ export const kImageContainerSelector = `.${kImageContainerClass}`;
 // We don't use actual placeHolder.png files anymore, but we do continue to use
 // src="placeHolder.png" to mark placeholders
 export function isPlaceHolderImage(
-    filename: string | null | undefined,
+    url: string | null | undefined,
 ): boolean {
-    if (!filename) {
+    if (!url) {
         return false;
     }
-    return filename.toLowerCase().endsWith("placeholder.png");
+    // Extract just the filename part to handle cases like "placeHolder.png?cachebust=12345"
+    // or paths like "book/placeHolder.png"
+    const urlLower = url.toLowerCase();
+    const questionMarkIndex = urlLower.indexOf("?");
+    const pathPart = questionMarkIndex >= 0 ? urlLower.substring(0, questionMarkIndex) : urlLower;
+    return pathPart.endsWith("placeholder.png");
 }
 
 export function cleanupImages() {

src/BloomExe/Book/Book.cs

@@ -5190,10 +5190,10 @@ ref coverImageFileName
             );
             // We no longer put placeHolder.png files in books (BL-15441) but we still need to detect when the placeholder
             // is called for, so here we return placeHolder.png instead of null. Callers of this method should handle this special case.
-            if (
-                !ImageUtils.IsPlaceholderImageFilename(coverImagePath)
-                && !RobustFile.Exists(coverImagePath)
-            )
+            if (ImageUtils.IsPlaceholderImageFilename(coverImagePath))
+                return coverImagePath;
+
+            if (!RobustFile.Exists(coverImagePath))
             {
                 // And the filename might be multiply-HTML encoded.
                 while (coverImagePath.Contains("&"))

src/BloomExe/BookThumbNailer.cs

@@ -243,6 +243,7 @@ internal static bool CreateThumbnailOfCoverImage(
                     BloomFileLocator.BrowserRoot
                 );
                 imageSrc = Path.Combine(bloomRoot, "images", "placeHolder.png");
+                // Enhance: We are unnecessarily running some image checks/processing below even in the placeholder case.
             }
             if (!IsCoverImageSrcValid(imageSrc, options))
             {

src/BloomExe/Publish/BloomPub/BloomPubMaker.cs

@@ -727,8 +727,9 @@ private static void StripImgIfWeCannotFindFile(SafeXmlDocument dom, string bookF
                 var imgElt in dom.SafeSelectNodes("//img[@src]").Cast<SafeXmlElement>().ToArray()
             )
             {
-                // As of BL-15441, we don't use real files for place holders but we still mark them with src="placeHolder.png".
-                // Don't strip these - we want them to persist in template books, and for other books we are already removing them elsewhere.
+                // As of BL-15441, we don't use real files for place holders (except in templates) but we still mark them with src="placeHolder.png".
+                // Don't strip them here -- we want them to persist in template books. For other books we are already removing them
+                // elsewhere (see line 540 where we delete placeHolder.png from the book folder).
                 string src = imgElt.GetAttribute("src");
                 if (ImageUtils.IsPlaceholderImageFilename(src))
                     continue;

src/BloomExe/web/BloomServer.cs

@@ -748,6 +748,9 @@ private bool ProcessImageFileRequest(IRequestInfo info)
                     }
                     else if (ImageUtils.IsPlaceholderImageFilename(imageFile))
                     {
+                        // BL-15441: We no longer use real files for placeholders, but the HTML still references placeHolder.png.
+                        // The placeholder is displayed via CSS. Return a 404 so the browser knows there's no file.
+                        info.WriteError(404);
                         return true;
                     }
                     // If the user does add a video or widget, these placeholder .svgs will get copied to the