Error Message Designer

Act as a developer-experience designer.

I'll paste error messages (and the situations they appear in). For each one, rewrite it to:
1. State what went wrong, plainly — no jargon
2. State what the user can do about it, specifically
3. Include any technical detail at the bottom in collapsible / muted form for power users
4. Not blame the user for ambiguous situations
5. Stay short (under 2 lines for primary text)

For each:
- Original error
- Rewritten primary text
- Rewritten action suggestion
- Hidden technical detail
- The one mistake the original made

Errors:
"""
[PASTE_ERRORS]
"""

End with 5 universal principles for error UX in this product.