Feature: QuickLook thumbnail cards for pasted/dropped document files

[gjouret]

Summary

When pasting or dragging a non-image file (PDF, SVG, DOCX, PPTX, XLSX, Pages, Keynote, Numbers, etc.) into a note, FSNotes now generates a QuickLook thumbnail of the document and inserts a centered Markdown table with the thumbnail image and a clickable link to the original file:

| Thumbnail |
|:---:|
| ![document_thumb.png](assets/document_thumb.png) |
| [document.pptx](assets/document.pptx) |

This replaces the previous behavior where non-image files were either inserted as generic file icons (PDF) or plain text links (DOCX, PPTX, etc.).

Supported File Types

Any file type with a macOS QuickLook plugin gets a thumbnail, including:

Type	Examples
PDF	.pdf
Vector graphics	.svg
Microsoft Office	.docx, .pptx, .xlsx
Apple iWork	.pages, .keynote, .numbers
Other	Any format with a QuickLook generator

Regular image files (PNG, JPG, GIF, TIFF, WebP, HEIC) continue to use the existing inline NSTextAttachment rendering — they don't need the thumbnail card since they already display natively.

How It Works

Thumbnail generation

Uses QLThumbnailGenerator (QuickLookThumbnailing framework) to generate a 480×480 thumbnail at screen scale. The thumbnail is saved as a PNG alongside the original file in the note's assets/ directory (TextBundle) or i/ directory (plain notes).

Paste and drag-and-drop

Both paths are handled:

1. Paste (Cmd+V): Detects PDF data on the pasteboard (com.adobe.pdf type), saves it, and generates a thumbnail card. Other document types typically arrive via file URL paste.
2. Drag-and-drop from Finder: performDragOperation() intercepts local file URL drops before handleAttributedText(). Previously, handleAttributedText fired first and inserted non-image files as NSTextAttachment objects with image syntax — causing broken images, crashes (EXC_BAD_ACCESS in updateCounters due to thread-safety race), and no thumbnails.

Inline rendering

After inserting the markdown table, the note is saved to disk synchronously and reloaded via note.load(), which calls loadImagesAndFiles() to convert ![](path) patterns into NSTextAttachment objects. This ensures the thumbnail renders inline immediately — not just after app restart.

Asset link handling in Preview mode

Three supporting fixes ensure links work in Preview mode:

1. Relative path resolution (String+.swift createURL(for:)) — resolves paths like assets/file.pdf against the note's directory, since the WKWebView's base URL is MPreview.bundle.
2. File opening (MPreviewView.swift HandlerOpen) — NSWorkspace.shared.open(url) opens files in their default app (e.g., Preview.app for PDFs, Word for DOCX) instead of revealing in Finder.
3. External URL support — HTTP/HTTPS links open in the default browser.
4. Image loading for export — buildPage() runs loadImages() for all modes (including print: true used by Share as PDF), so thumbnail images appear in exported PDFs.

Files Changed

File	Change
EditTextView.swift	Unified saveFileWithThumbnail() using QLThumbnailGenerator; removed PDF-specific savePDFWithThumbnail(); file URL interception in performDragOperation()
String+.swift	Relative asset path resolution in createURL(for:)
MPreviewView.swift	HandlerOpen: open files/URLs instead of revealing; buildPage(): always run loadImages()

Previous Issue

Supersedes #1920 (PDF-specific implementation).

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