diff --git a/core/wasm_shims/gettext_shim.cc b/core/wasm_shims/gettext_shim.cc
index e035b46..c2f53a5 100644
--- a/core/wasm_shims/gettext_shim.cc
+++ b/core/wasm_shims/gettext_shim.cc
@@ -1,6 +1,7 @@
 #include <cstddef>
 
+// LinuxCNC source basis: src/emc/rs274ngc/interp_internal.hh maps _() to
+// gettext(), and RS274 sources wrap interpreter diagnostics with _().
 extern "C" char *gettext(const char *msgid) {
     return const_cast<char *>(msgid ? msgid : "");
 }
-
diff --git a/core/wasm_shims/libgen.h b/core/wasm_shims/libgen.h
index 999304f..1763941 100644
--- a/core/wasm_shims/libgen.h
+++ b/core/wasm_shims/libgen.h
@@ -1,6 +1,8 @@
 #ifndef CNC_SIM_WASM_SHIMS_LIBGEN_H
 #define CNC_SIM_WASM_SHIMS_LIBGEN_H
 
+/* LinuxCNC source basis: src/emc/rs274ngc/interp_o_word.cc uses basename()
+   while resolving O-word subroutine names. */
 #ifdef __cplusplus
 extern "C" {
 #endif
diff --git a/core/wasm_shims/structmember.h b/core/wasm_shims/structmember.h
index 8c8ea6c..d3d2ffa 100644
--- a/core/wasm_shims/structmember.h
+++ b/core/wasm_shims/structmember.h
@@ -2,6 +2,8 @@
 
 #include "boost/python/object.hpp"
 
+// LinuxCNC source basis: src/emc/rs274ngc/gcodemodule.cc includes
+// structmember.h for PyMemberDef entries using T_INT, T_DOUBLE, and READONLY.
 #define T_INT 1
 #define T_DOUBLE 2
 #define READONLY 1
diff --git a/test-linuxcnc-wasm-cmake-safe-probe.sh b/test-linuxcnc-wasm-cmake-safe-probe.sh
index 7127eb8..b5db879 100755
--- a/test-linuxcnc-wasm-cmake-safe-probe.sh
+++ b/test-linuxcnc-wasm-cmake-safe-probe.sh
@@ -1391,6 +1391,7 @@ grep -F 'list(APPEND cnc_sim_core_sources ${cnc_sim_linuxcnc_rs274_backend_sourc
 grep -F 'set(cnc_sim_linuxcnc_kinematics_c_sources' core/CMakeLists.txt >/dev/null
 grep -F 'project(cnc_sim_wasm_core LANGUAGES C CXX)' core/CMakeLists.txt >/dev/null
 grep -F 'set(cnc_sim_wasm_safe_preinclude_options "SHELL:-include wctype.h")' core/CMakeLists.txt >/dev/null
+grep -F 'LinuxCNC source basis: src/emc/rs274ngc/interp_internal.hh maps _() to' core/wasm_shims/gettext_shim.cc >/dev/null
 grep -F 'if(EMSCRIPTEN)' core/CMakeLists.txt >/dev/null
 grep -F 'list(APPEND cnc_sim_wasm_safe_preinclude_options "SHELL:-include libgen.h")' core/CMakeLists.txt >/dev/null
 grep -F 'find_path(CNC_SIM_FMT_INCLUDE_DIR fmt/format.h' core/CMakeLists.txt >/dev/null
@@ -1411,8 +1412,10 @@ test -f core/wasm_shims/boost/noncopyable.hpp
 grep -F 'class noncopyable' core/wasm_shims/boost/noncopyable.hpp >/dev/null
 grep -F 'noncopyable(const noncopyable &) = delete;' core/wasm_shims/boost/noncopyable.hpp >/dev/null
 test -f core/wasm_shims/libgen.h
+grep -F 'LinuxCNC source basis: src/emc/rs274ngc/interp_o_word.cc uses basename()' core/wasm_shims/libgen.h >/dev/null
 grep -F 'inline char *basename(const char *path)' core/wasm_shims/libgen.h >/dev/null
 grep -F 'return basename(const_cast<char *>(path));' core/wasm_shims/libgen.h >/dev/null
+grep -F 'LinuxCNC source basis: src/emc/rs274ngc/gcodemodule.cc includes' core/wasm_shims/structmember.h >/dev/null
 grep -F 'LinuxCNC source basis: src/emc/rs274ngc/interp_base.cc uses dlopen(),' core/wasm_shims/dlfcn.cc >/dev/null
 grep -F 'LinuxCNC source basis: src/emc/rs274ngc/interp_base.cc native loader flags.' core/wasm_shims/dlfcn.h >/dev/null
 grep -F 'LinuxCNC source basis: src/emc/rs274ngc/gcodemodule.cc defines _task=0' core/wasm_shims/linuxcnc_runtime_shim.cc >/dev/null