[zfergus]

Description

Fixes an out-of-bounds read in GCPCollisionTemplate::core_vertex_ids().

• The function indexed m_vertex_ids (one entry per vertex, 4 for Edge3-Edge3) with DOF indices that run up to 11.
• The only caller, TangentialCollisions::build, reads entries 0-3, so the out-of-range values were never used.
• Under -D_GLIBCXX_ASSERTIONS, std::vector::operator[] aborts on the read.
• It now maps each core point to its vertex slot: the core points of primitive A, then those of primitive B.
• finitediff_finitediff gets EIGEN_DONT_VECTORIZE=1 when SIMD is on, like MeshFEMSparse, so matrices our lambdas return and finite-diff reshapes or frees share one alignment.
• Bumps the scalable-ccd pin.

API changes

• core_vertex_ids() returns std::array<index_t, N_CORE_POINTS> instead of std::array<index_t, N_CORE_DOFS>.
• TangentialCollisions::build is the only caller in the codebase and is unaffected.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Full suite (429 tests) in Debug with -D_GLIBCXX_ASSERTIONS passes.
• Smooth friction force no_mu and no_contact_force_multiplier, Smooth friction force jacobian 3D, and Smooth friction force jacobian of a single collision aborted at stl_vector.h:1282 in core_vertex_ids before this change and pass after it.

cmake -B build -DIPC_TOOLKIT_BUILD_TESTS=ON -DCMAKE_BUILD_TYPE=Debug \
    -DCMAKE_CXX_FLAGS=-D_GLIBCXX_ASSERTIONS -DSIMD_CXX_FLAGS=-march=x86-64-v3
cmake --build build -j && ctest --test-dir build -j

Test Configuration:

• OS and Version: CachyOS Linux (kernel 7.2.3, glibc 2.44)
• Compiler and Version: GCC 15.3.0

Checklist

• I have followed the project style guide
• My code follows the clang-format style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.76%. Comparing base (b9d0325) to head (6c8f9da).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #284      +/-   ##
==========================================
- Coverage   96.97%   96.76%   -0.22%     
==========================================
  Files         221      221              
  Lines       22426    22502      +76     
  Branches     1540     1559      +19     
==========================================
+ Hits        21748    21774      +26     
- Misses        678      728      +50     

Flag	Coverage Δ
unittests	96.76% <100.00%> (-0.22%)	⬇️

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