Add mux_index contact annotation

[alejoe91]

Fixes #367

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.96%. Comparing base (9279d1f) to head (1c636b2).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #368      +/-   ##
==========================================
+ Coverage   89.92%   89.96%   +0.04%     
==========================================
  Files          12       12              
  Lines        2044     2043       -1     
==========================================
  Hits         1838     1838              
+ Misses        206      205       -1     

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