Phoenix File Uploads

Use this skill before implementing ANY file upload functionality.

Canonical FP bar: docs/fcis-engineering-rules.md — Functional Core, Imperative Shell: pure domain modules; side effects at edges. Keep LiveView/controller callbacks thin; delegate business rules to contexts/pure modules.

RULES — Follow these with no exceptions

1. Use manual uploads (NOT auto_upload: true) for form submission patterns 2. Always add upload directory to static_paths() — files won't be accessible without this 3. Handle upload errors — display error_to_string/1 output in templates 4. Validate file types server-side — never trust client MIME types 5. Restart server after changing static_paths() — changes don't apply until restart

Implementation Workflow

Follow these steps in order: