js/desktop/src/features/compose/markdown-editor.tsx

@@ -1,11 +1,12 @@
 import { useEffect, useRef } from 'react';
 import { Crepe } from '@milkdown/crepe';
-import { editorViewCtx } from '@milkdown/kit/core';
+import { editorViewCtx, editorViewOptionsCtx } from '@milkdown/kit/core';
 import { Selection } from '@milkdown/kit/prose/state';
 import '@milkdown/crepe/theme/common/style.css';
 import '@milkdown/crepe/theme/frame-dark.css';
 import './markdown-editor.css';
 import { cn } from '@/lib/utils';
+import { transferFiles } from '@/lib/data-transfer';
 
 interface MarkdownEditorProps {
   /** Initial markdown. The editor owns its content after mount; edits flow out
@@ -80,6 +81,21 @@ export function MarkdownEditor({
           onChangeRef.current?.(markdown);
         });
       });
+
+      // Decline dropped files: they belong in the compose attachment strip
+      // (the drop zone still receives them), not inlined into the document.
+      // Without this the editor parses the drag's HTML into an image node with
+      // an ephemeral blob:/localhost src, which then leaks into the markdown.
+      crepe.editor.config((ctx) => {
+        ctx.update(editorViewOptionsCtx, (prev) => ({
+          ...prev,
+          handleDrop: (view, event, slice, moved) => {
+            const data = event.dataTransfer;
+            if (data && transferFiles(data).length > 0) return true;
+            return prev.handleDrop?.(view, event, slice, moved) ?? false;
+          },
+        }));
+      });
     }
 
     crepe.create().then(() => {

js/desktop/src/hooks/use-file-input.ts

@@ -1,23 +1,11 @@
 import { useCallback, useEffect, useRef, useState } from 'react';
+import { transferFiles } from '@/lib/data-transfer';
 
 interface UseFileInputOptions {
   onFilesSelected: (files: File[]) => void;
   enabled: boolean;
 }
 
-/**
- * Files carried by a paste. A pasted image is usually exposed only through
- * `items` (`getAsFile`), with `files` left empty, so read `items` first and
- * fall back to `files` for the rare clipboard that populates only the latter.
- */
-function clipboardFiles(data: DataTransfer): File[] {
-  const fromItems = Array.from(data.items)
-    .filter((item) => item.kind === 'file')
-    .map((item) => item.getAsFile())
-    .filter((file): file is File => file !== null);
-  return fromItems.length > 0 ? fromItems : Array.from(data.files);
-}
-
 export function useFileInput({
   onFilesSelected,
   enabled,
@@ -61,9 +49,8 @@ export function useFileInput({
   useEffect(() => {
     if (!enabled) return;
 
-    // Capture phase so file pastes always become attachments — ProseMirror
-    // (the markdown editor) would otherwise inline a pasted image as an
-    // ephemeral blob: URL and get stuck on its "uploading" placeholder.
+    // Capture phase so file pastes always become attachments — the markdown
+    // editor would otherwise inline a pasted image as an ephemeral blob: URL.
     const handlePaste = (e: ClipboardEvent) => {
       const data = e.clipboardData;
       if (!data) return;
@@ -74,7 +61,7 @@ export function useFileInput({
       // list an *empty* text/plain entry that must not block the attachment.
       if (data.getData('text/plain').trim().length > 0) return;
 
-      const files = clipboardFiles(data);
+      const files = transferFiles(data);
       if (files.length === 0) return;
       e.preventDefault();
       e.stopPropagation();

js/desktop/src/lib/data-transfer.ts

@@ -0,0 +1,12 @@
+/**
+ * Files carried by a paste or drag {@link DataTransfer}. Pasted/dragged images
+ * frequently surface only through `items` (`getAsFile`), with `files` left
+ * empty, so read `items` first and fall back to `files`.
+ */
+export function transferFiles(data: DataTransfer): File[] {
+  const fromItems = Array.from(data.items)
+    .filter((item) => item.kind === 'file')
+    .map((item) => item.getAsFile())
+    .filter((file): file is File => file !== null);
+  return fromItems.length > 0 ? fromItems : Array.from(data.files);
+}