🤖 feat: Support attaching external files to prompts (drag-and-drop / file picker)

[ammar-agent]

Request

Attach external files (from Downloads, Desktop, etc.) to prompts without copying them into the workspace first.

Desired UX: Drag-and-drop or file picker (📎) in chat input.

File types: .txt, .sql, .pdf, .docx, images

Current State

• @ tagging: works for in-project files ✓
• Image paste: works ✓
• File drag-and-drop: not supported ✗

Challenge: Context Management

Large attachments can blow context limits. Need:

• File size / token estimation before send
• Clear limits and warnings
• Strategy for PDFs (text extraction) and DOCX (parsing)

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Generated with mux • Model: anthropic:claude-opus-4-5 • Thinking: high

[ammario]

Suggestion: instead of including drag-and-dropped files into the prompt verbatim we can:

1. ensure the file is visible to the runtime (perhaps first uploading it)
2. insert a reference to the file in the prompt