Error messages expose raw tuple repr in NodeTypeError

[nathanjmcdougall]

NodeTypeError messages in document.py use f-string interpolation of key tuples:

msg = f"Value at {keys} is not a list"

This produces messages like Value at ('repos',) is not a list - the tuple syntax is implementation noise for users.

Affected locations

• remove_from_list (~line 392)
• find_index (~line 484)

Suggested fix

Format keys as a human-readable path string (e.g. repos or repos > 0 > steps) before interpolation. Apply consistently to both methods.