Finding-I from doc/reviewer/external-audit-2026-05-30.md.
Root cause: CGAL+Eigen at -O3 drives cc1plus peak RAM to ~700 MB per
Unity compilation unit (batch size 4) on ARM64. With the 1600 MB
container limit the 2nd or 3rd TU reliably triggered OOM-kill, so
test-cgal was gated off via `if: false` since 2026-05-26.
Fix: new CMake option CONFORMALLAB_LOW_MEMORY_BUILD=ON applies four
orthogonal memory-saving measures to conformallab_cgal_tests:
1. -O0 (no debug info): optimizer passes entirely skipped → cc1plus
peak drops from ~700 MB to ~150-200 MB per TU on ARM64.
Omitting -g avoids the additional object-file / linker RAM cost.
2. CONFORMALLAB_USE_PCH=OFF: saves the one-time ~200 MB PCH
compilation cost; each TU re-parses CGAL headers (fast at -O0).
3. UNITY_BUILD_BATCH_SIZE=1: one source file per cc1plus invocation,
removing the "4-file template-explosion" per-unit multiplier.
4. -Wl,--no-keep-memory (GNU ld): linker releases symbol tables after
each input file → ~15-25 % less linker RSS.
Verified locally with cmake -DCONFORMALLAB_LOW_MEMORY_BUILD=ON:
277/277 CGAL tests pass, 31 s runtime (vs 2 s at -O3 — expected;
tests run 15× slower without optimizer but all correct).
CI workflow changes (cpp-tests.yml):
- test-cgal re-enabled: `if: github.event_name == 'pull_request'`
- Configure step adds -DCONFORMALLAB_LOW_MEMORY_BUILD=ON
- Container memory: 1600m → 2000m (--memory-swap=3000m for 1 GB swap
headroom), using ~half of the Pi's 3-4 GB while leaving OS margin.
CLAUDE.md updated: new flag added to compile-time options table; CI
status row corrected from DISABLED to active.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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