fix: mock move_note_to_type_folder collision handling + Rust collision content test

The mock handler now appends -2, -3, etc. when the target path already
exists, matching the Rust unique_dest_path logic.  Previously it would
silently overwrite the existing note's content in MOCK_CONTENT.

Also adds a Rust test that verifies both the moved note and the
pre-existing note retain their respective content after a collision.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src-tauri/src/vault/rename.rs

@@ -826,6 +826,36 @@ mod tests {
         assert!(other_content.contains("[[Weekly Review]]"));
     }
 
+    #[test]
+    fn test_move_note_collision_preserves_both_contents() {
+        let dir = TempDir::new().unwrap();
+        let vault = dir.path();
+        let moving_content =
+            "---\ntype: Quarter\n---\n# Migrate newsletter to Beehiiv\n\nImportant content.\n";
+        let existing_content =
+            "---\ntype: Quarter\n---\n# Feedback for Laputa\n\nCompletely different note.\n";
+        create_test_file(vault, "note/my-note.md", moving_content);
+        create_test_file(vault, "quarter/my-note.md", existing_content);
+
+        let old_path = vault.join("note/my-note.md");
+        let result = move_note_to_type_folder(
+            vault.to_str().unwrap(),
+            old_path.to_str().unwrap(),
+            "Quarter",
+        )
+        .unwrap();
+
+        assert!(result.moved);
+        // Must get a unique path, not the existing file's path
+        assert!(result.new_path.contains("/quarter/my-note-2.md"));
+        // Moved note must retain its own content
+        let moved_content = fs::read_to_string(&result.new_path).unwrap();
+        assert_eq!(moved_content, moving_content);
+        // Existing note must be untouched
+        let untouched = fs::read_to_string(vault.join("quarter/my-note.md")).unwrap();
+        assert_eq!(untouched, existing_content);
+    }
+
     #[test]
     fn test_move_note_empty_type_error() {
         let dir = TempDir::new().unwrap();

src/mock-tauri/mock-handlers.ts

@@ -227,7 +227,16 @@ export const mockHandlers: Record<string, (args: any) => any> = {
     if (currentFolder === slug) return { new_path: args.note_path, updated_links: 0, moved: false }
     const filename = args.note_path.split('/').pop() ?? ''
     const vaultPath = args.vault_path.replace(/\/$/, '')
-    const newPath = `${vaultPath}/${slug}/${filename}`
+    // Handle collisions: append -2, -3, etc. if the target path already exists
+    // (mirrors the Rust unique_dest_path logic).
+    let newPath = `${vaultPath}/${slug}/${filename}`
+    if (newPath in MOCK_CONTENT && newPath !== args.note_path) {
+      const stem = filename.replace(/\.md$/, '')
+      const ext = filename.endsWith('.md') ? '.md' : ''
+      let counter = 2
+      while (`${vaultPath}/${slug}/${stem}-${counter}${ext}` in MOCK_CONTENT) counter++
+      newPath = `${vaultPath}/${slug}/${stem}-${counter}${ext}`
+    }
     const content = MOCK_CONTENT[args.note_path] ?? ''
     delete MOCK_CONTENT[args.note_path]
     MOCK_CONTENT[newPath] = content