Fix G_K exponential degradation in damage model

[sbryngelson]

User description

Summary

• The continuous damage factor was applied to G_K/G inside the stress component loop (do i = strxb, strxe), causing the shear modulus to be compounded by the damage factor on each iteration
• With N stress components, this produced an effective G_K * damage^N instead of the intended G_K * damage
• Fix moves the damage application before the loop in both cons-to-prim and prim-to-cons paths

Test plan

• Verify damage model test cases produce physically correct stress degradation
• Golden file regeneration likely needed for damage model cases

🤖 Generated with Claude Code

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CodeAnt-AI Description

Apply damage factor once to shear modulus to stop exponential weakening

What Changed

• The damage multiplier is applied a single time to the shear modulus before iterating stress components instead of being multiplied inside the component loop.
• Shear contribution to pressure and elastic stress now uses the correctly degraded shear modulus rather than an N-times compounded reduction.
• No change to user-facing inputs; results for damage-model cases will change to the physically intended stress degradation.

Impact

✅ Correcter stress degradation for damage cases
✅ Restored shear strength in damaged cells
✅ Fewer unexpected differences in damage-model outputs

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[cubic-dev-ai]

No issues found across 1 file

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

[Copilot]

Pull request overview

This PR fixes a critical bug in the continuous damage model for hypoelastic materials. The damage factor was incorrectly applied to the shear modulus G_K/G inside the stress component loop, causing exponential degradation with each stress component iteration. The fix moves the damage application to before the loop in both the conservative-to-primitive and primitive-to-conservative conversion paths.

Changes:

• Move damage factor application for G_K outside the stress loop in s_convert_conservative_to_primitive_variables
• Move damage factor application for G outside the stress loop in s_convert_primitive_to_conservative_variables

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 44.04%. Comparing base (d048c4b) to head (e9ad948).
⚠️ Report is 19 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1227      +/-   ##
==========================================
- Coverage   44.07%   44.04%   -0.03%     
==========================================
  Files          70       70              
  Lines       20431    20498      +67     
  Branches     1974     1991      +17     
==========================================
+ Hits         9004     9029      +25     
- Misses      10291    10329      +38     
- Partials     1136     1140       +4     

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[sbryngelson]

Superseded by #1242 (batched HPC-sensitive fixes)