fix: paste Excel/spreadsheet copies as text instead of image (#2960)

The image-paste handlers scanned the clipboard for an image file item and
acted on it without checking for co-present text. Excel/Word/spreadsheet
copies place BOTH a rendered bitmap and text/plain on the clipboard, so the
image always won and cells pasted as an uploaded image.

Prefer text when text/plain is present; only treat a paste as an image when
the clipboard is image-only (screenshots, copy-image, Finder file copies have
no text/plain). Fixes the CodeMirror markdown editor and the mdviewer
live-preview paste paths.

Author: abose

src-mdviewer/src/components/editor.js

@@ -711,6 +711,14 @@ function handleImagePaste(e, contentEl) {
     if (!items) {
         return false;
     }
+    // Spreadsheet/word-processor copies (e.g. Excel cells) place BOTH a rendered
+    // bitmap AND plain text on the clipboard. Genuine image copies (screenshots,
+    // copy-image) carry no text/plain. Prefer text when present so such copies
+    // paste as text, not an uploaded image. See issue #2960.
+    const pastedText = e.clipboardData.getData && e.clipboardData.getData("text/plain");
+    if (pastedText && pastedText.length > 0) {
+        return false;
+    }
     for (let i = 0; i < items.length; i++) {
         if (items[i].kind === "file" && ALLOWED_IMAGE_TYPES.includes(items[i].type)) {
             e.preventDefault();

src/editor/EditorCommandHandlers.js

@@ -1299,6 +1299,16 @@ define(function (require, exports, module) {
             return false;
         }
 
+        // Spreadsheet/word-processor copies (e.g. Excel cells) place BOTH a rendered
+        // bitmap AND plain text on the clipboard. Genuine image copies (screenshots,
+        // copy-image from a browser/file manager) carry no text/plain. When text is
+        // present, prefer the normal text paste instead of uploading the bitmap so
+        // Excel cells paste as text, not an image. See issue #2960.
+        const pastedText = event.clipboardData.getData && event.clipboardData.getData("text/plain");
+        if (pastedText && pastedText.length > 0) {
+            return false;
+        }
+
         // Only handle in markdown files
         const doc = editor.document;
         if (!doc || !doc.file) {