Web Shell dropped-file intent choice

Problem

The composer currently infers intent from file type: image-only drops become prompt attachments, while ordinary or mixed drops upload to the workspace and insert @ references. File type does not express user intent. A user may want an image persisted in the workspace, or a text file attached only to the next prompt.

Design

When workspace upload is available, a drop containing one or more files opens one modal with their names, sizes, and three actions:

• Reference content uses the existing prompt-attachment ingestion path. The original browser files remain local to the draft. On submit they upload unchanged to the daemon's session attachment store under the workspace-scoped Qwen runtime temp directory. Prompt JSON carries filename-based attachment IDs; the bridge resolves them only at dispatch.
• Upload to workspace uses the existing upload queue, configured upload directory, progress UI, and server-confirmed @ reference insertion.
• Cancel discards the drop.

Every file type can be referenced. Multi-file drops use the same choice as single files; the browser does not pre-disable referencing based on the the files already present in the current draft.

The browser File objects are copied synchronously during the drop event, so the choice does not depend on a DataTransfer after the event returns. The dialog closes if the composer target changes or upload becomes unavailable.

When workspace upload is unavailable, drops keep the existing attachment behavior instead of showing an upload action that cannot succeed. Host-level fileUploadEnabled={false} retains its existing contract and disables all file drag-in. Clipboard paste and the @ panel upload item are unchanged.

File attachment chips are interactive before and after optimistic submission. Opening one shows the referenced file in the right-side preview panel. Completed workspace uploads and their file tags open the same panel by reading the uploaded workspace path. Image attachments retain their existing thumbnail and image-panel behavior.

Storage and compatibility

The default attachment root is ~/.qwen/tmp/<workspace-hash>/attachments/, resolved through Storage.getProjectTempDir() so custom runtime directories continue to work. Each session owns session-<encoded-session-id>/. Files use their stored names as attachment IDs, with (1) suffixes for duplicates. Daemon shutdown and client detach keep the directory; permanent session deletion removes it.

Images and files use the same session_attachments capability, /attachments routes, and attachmentId references. There is no retained media cache, TTL cleanup, in-memory filename index, or legacy mediaId path.

Scope

Attachment admission limits are enforced by ingestion and the daemon rather than by the choice dialog.