Summary

• Added focused unit coverage for native VM vmMain argument packing.
• Refactored the native VM_Call argument slot packing into the existing vm_native_module helper so the behavior is directly testable.
• Updated tests/README.md to include unit_vm_native_module in the unit target index.

Risky behavior now covered

• Native vmMain calls with fewer than three arguments now have tests proving missing argument slots are zero-filled.
• Full three-argument native calls now have tests proving argument order is preserved.
• The helper respects the native argument slot limit without writing beyond the provided array.

Test files added/updated

• Updated tests/unit/test_vm_native_module.c
• Updated tests/README.md

Why this reduces regression risk

Recent native VM loading fixes made standalone/full-conversion native modules more important. A regression in VM_Call argument packing can corrupt native UI/game module behavior, especially zero-argument calls like API-version probes that previously risked observing stack garbage. These unit tests pin that behavior without requiring game data or a graphics environment.

Validation

• cmake --build build-coverage --target unit_vm_native_module && ctest --test-dir build-coverage -R '^unit_vm_native_module$' --output-on-failure — passed
• cmake --build build-coverage --target idtech3_server — passed (pre-existing vm_x86.c variadic macro warnings only)
• cmake --build build-coverage --target unit_macros unit_qmath unit_surfaceflags unit_qhelpers unit_crc unit_pathutil unit_msg unit_info unit_cm_bounds unit_parse unit_endian unit_vm_native_module && ctest --test-dir build-coverage -R '^unit_' --output-on-failure — 12/12 passed