fix(desktop): handle OS-dropped folders — detect directories via stat, route to attachContextFolderPath

[thedavidweng]

What

When a folder is dragged from Finder/Explorer into the Desktop composer, the browser File API does not expose isDirectory, so the drop handler treated it as a regular file. On submit, readFileDataUrl threw EISDIR, and the gateway received no data_url — producing:

file not found on gateway and no data_url provided

Changes

1. main.cjs — new hermes:fs:isDirectory IPC handler that stat-checks the resolved path (uses existing resolveRequestedPathForIpc for path safety).

2. preload.cjs — expose the new IPC method as window.hermesDesktop.isDirectory(path).

3. use-composer-actions.ts — in attachDroppedItems, before the image/file branch for OS drops, check isDirectory via the new IPC call. If true, route through attachContextFolderPath — matching the existing in-app folder drag behavior (creates a kind: 'folder' attachment with @folder: ref).

4. global.d.ts — add isDirectory to the hermesDesktop type definition.

What is NOT included

• Copy-paste of folders — the clipboard handler (handlePaste in composer/index.tsx) only processes image blobs. Detecting folder paste events requires a different approach (the clipboard API doesn't expose file-system paths for pasted directories). This is a separate concern.
• Remote gateway folder support — when the gateway is remote, the folder path from the client machine won't resolve on the server. The existing in-app folder drag already has this limitation; extending it to OS drops is out of scope here.

Testing

1. Drag a folder from Finder into the Desktop composer → should appear as a folder attachment (not a file)
2. Send a message → agent should receive the @folder: reference and be able to list its contents
3. Drag a file from Finder → should still work as before (image or file attachment)
4. In-app folder drag from project tree → should still work as before

Closes #44581

[teknium1]

Thanks for the focused Desktop reproduction and fix direction. This is an automated hermes-sweeper review; the reported behavior is already implemented on current main through a more direct drop-time detector.

• a488fcf107d1c61400db4274c0baf357b908c772 (fix(desktop): detect dropped folders so they attach as @folder refs) detects folders with DataTransferItem.webkitGetAsEntry() in apps/desktop/src/app/chat/hooks/use-composer-actions.ts:176-205.
• The current code emits dropped directories as path-only isDirectory entries at apps/desktop/src/app/chat/hooks/use-composer-actions.ts:165-173, then routes them to attachContextFolderPath at :527-539, producing @folder: attachments.
• Regression coverage is present at apps/desktop/src/app/chat/hooks/use-composer-actions.test.ts:124-187, including folder, file, mixed-drop, and deduplication cases.
• The fix is included in v2026.7.1; the timeline's related merged PR fix(desktop): detect dropped folders so they attach as @folder refs #56029 delivered the current implementation.

Closing as implemented on main.