ucon#153: MCP error infrastructure for multi-step chains

[withtwoemms]

closes #153

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.34%. Comparing base (837c3ad) to head (5e579e9).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #154      +/-   ##
==========================================
+ Coverage   87.23%   87.34%   +0.11%     
==========================================
  Files          13       13              
  Lines        2138     2149      +11     
  Branches      436      441       +5     
==========================================
+ Hits         1865     1877      +12     
  Misses        184      184              
+ Partials       89       88       -1     

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