[nawaaaaaAaar]

Summary

Fixes #570. Follow-up to my merged #674 and #675.

Reject MultiIndex level names that cannot be represented by CF's whitespace-delimited compress attribute, before resetting indexes or constructing an invalid encoded dataset.

For example, names ("lat name", "lon") currently produce compress="lat name lon"; decoding then raises KeyError: 'lat'. Renaming silently would change the user's coordinate names, so this uses an actionable ValueError instead.

The guard rejects empty/non-string names and any whitespace, not only literal spaces. The docstring documents the error.

Validation

• All 12 new regressions fail against unchanged main, then pass with the guard.
• Cover both index levels, internal/leading/trailing spaces, tab, newline and empty names.
• Verify the input Dataset is unchanged on rejection.
• Relevant coding suite: 26 passed.
• Full suite: 313 passed, 10 skipped.
• Mypy: no issues in 28 source files after installing the repository's type-stub dependencies.
• All pre-commit hooks pass; wheel and sdist build successfully.
• git diff --check: clean.

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[nawaaaaaAaar]

Closing in favor of the earlier #676, which appeared while this implementation was being prepared. Keeping one compression-name validation PR for maintainers to review.

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.10%. Comparing base (a9cebee) to head (b227711).
⚠️ Report is 132 commits behind head on main.

Files with missing lines	Patch %	Lines
cf_xarray/coding.py	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #680      +/-   ##
==========================================
+ Coverage   85.78%   87.10%   +1.31%     
==========================================
  Files          13       16       +3     
  Lines        2364     3357     +993     
  Branches      183      313     +130     
==========================================
+ Hits         2028     2924     +896     
- Misses        303      387      +84     
- Partials       33       46      +13     

Flag	Coverage Δ
mypy	45.99% <0.00%> (+7.46%)	⬆️
unittests	92.85% <100.00%> (-1.14%)	⬇️

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