[transfix]

Problem

glibc's <signal.h> (bits/types/siginfo_t.h) defines

#define si_value _sifields._rt.si_sigval

so any TU that includes <signal.h> before <cvc/core/world_units.h> fails to compile:

world_units.h:147:28: error: expected ',' or '...' before '.' token
  147 |   double to_display(double si_value, dimension d) const;

Found building volrover3's GeometryDialog.cpp, IsosurfaceDialog.cpp, ProceduralGeometryDialog.cpp and SDFDialog.cpp against the installed 3.5.0 prefix (transfix/volrover#48).

Changes

• world_units::to_display / world_units::format: renamed the si_value parameter to canonical_value in the header, world_units.cpp and docs/WORLD_UNITS_API.md. The name pairs with from_display's display_value and drops the si_* prefix, which glibc and musl use for siginfo_t accessor macros. Only parameter names change, so there is no API or ABI change.
• cvc/utility/utility.h: the audit below found one more real clash. glibc's (and macOS's) <sys/param.h> and GLib define function-like MIN(a,b)/MAX(a,b) macros, which expand the declarations of the cvc::MIN/cvc::MAX templates. The declarator names are now parenthesized (const T &(MIN)(...)). Existing callers are unchanged: cvc::MIN(a, b), unqualified MIN(a, b), MIN<int>(...) and &cvc::MAX<long> all still compile.
• New system_macro_headers_test (C++20, registered in all five places): the TU includes <signal.h>, <sys/param.h>, <sys/stat.h> and <sys/types.h> on POSIX, or <windows.h> behind the repo's usual WIN32_LEAN_AND_MEAN + NOMINMAX guards, before a representative public header from every module in the cvc target. It leaves out cvc/gl/* (cvcGL, needs VTK/GL), hdf5_utils.h, project_verts.h (CGAL) and the CUDA headers. If a header regresses, this test stops compiling. Its two small TESTs call world_units and (cvc::MIN)/(cvc::MAX).

Macro-name audit of inc/

Every identifier token in all 262 public headers (comments and strings stripped) was checked against:

Source	Macros	Result
~50 glibc/POSIX headers (signal.h, sys/{stat,types,sysmacros,param,wait,socket,...}.h, errno.h, stdio.h, unistd.h, netinet/*, ...)	7,855	si_value and MIN/MAX (both fixed). The other hits are intentional uses (NULL, UINT32_MAX, std::isfinite, ...).
mingw-w64 <windows.h>, full and with WIN32_LEAN_AND_MEAN+NOMINMAX	27,332 / 18,604	Only RGB, which appears only as the enumerator pixel_format::RGB and is never followed by (, so the function-like macro can't expand.
Explicit list: si_value si_pid si_uid si_addr si_status si_band si_code si_errno sa_handler sa_sigaction st_atime st_mtime st_ctime errno stdin stdout stderr major minor makedev unix linux min max small near far interface ERROR DELETE IN OUT OPTIONAL TRUE FALSE, plus common Win32 A/W names and BSD sys/param.h helpers	—	Nothing beyond the above. Lowercase min/max (about 70 uses, e.g. voxels::min(), std::numeric_limits<>::max()) only clash with <windows.h> without NOMINMAX, which the repo already handles by convention (config.h, magick_io.cpp, (max)() in async_lane.h).
X11 (Xlib.h, Xutil.h, glx.h), informational	8,590	#define None 0L collides with gl::Switch::None and ariadne::BorderShow::None. Not changed here: the only fix is renaming public enumerators/constants, an API change that deserves its own PR.

Verification

Tested locally with g++ 11, -std=c++20, against this tree's inc/ plus the installed 3.5.0 SDK's headers and defines; gtest was a local stub, not committed.

• Repro: a TU containing just #include <signal.h> then #include <cvc/core/world_units.h> fails on master and compiles with this branch.
• New test on master's headers: fails with world_units.h:147/163 and utility.h:77/78 errors. On this branch: compiles with no warnings under -Wall -Wextra, also under -std=gnu++20. Linked against libcvc 3.5.0, both TESTs pass.
• world_units.cpp: compiles, including with -include signal.h.
• check_test_targets.py: OK: all 161 test executables reach TEST_TARGETS.
• clang-format: emulated git clang-format --diff origin/master reports 0 files to reformat, and the new file is also clean when checked in full. The system headers sit in their own #ifndef _WIN32 block, so include regrouping can't move them after the libcvc headers.
• Includes: all 28 <cvc/...> includes in the test resolve in inc/ and are installed via install(DIRECTORY inc/cvc/).
• Not checked locally: Windows/MSVC and macOS, which are left to CI.