FIX: guard gRPC layout terminal enumeration against null terminals

[pl170491]

Summary

• guard gRPC layout terminal enumeration against None and invalid terminal objects
• add focused unit coverage for invalid terminal entries and enumeration failure

Notes

• This replaces the earlier fork-based PR so CI can run without fork OIDC/provenance restrictions.

closes #2028

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 5 complexity · 0 duplication

Metric	Results
Complexity	5
Duplication	0

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 63.15789% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.33%. Comparing base (5cbae21) to head (134f3a3).
⚠️ Report is 90 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2040      +/-   ##
==========================================
- Coverage   70.20%   69.33%   -0.88%     
==========================================
  Files         261      264       +3     
  Lines       42416    43366     +950     
==========================================
+ Hits        29779    30066     +287     
- Misses      12637    13300     +663     

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[svandenb-dev]

LGTM