diff --git a/check-linuxcnc-wasm-shims-source-map.sh b/check-linuxcnc-wasm-shims-source-map.sh
index 661c364..fd38b42 100755
--- a/check-linuxcnc-wasm-shims-source-map.sh
+++ b/check-linuxcnc-wasm-shims-source-map.sh
@@ -31,6 +31,8 @@ grep -F 'Cannot use polar coordinate on a machine lacking X or Y axes' \
     "$linuxcnc_root/src/emc/rs274ngc/interp_internal.cc" >/dev/null
 grep -F 'int _task = 0;' "$linuxcnc_root/src/emc/rs274ngc/gcodemodule.cc" >/dev/null
 grep -F 'int _task = 1;' "$linuxcnc_root/src/emc/task/emctaskmain.cc" >/dev/null
+grep -F '{ "interpreter", PyInit_interpreter },' "$linuxcnc_root/src/emc/rs274ngc/gcodemodule.cc" >/dev/null
+grep -F '{ "emccanon", PyInit_emccanon },' "$linuxcnc_root/src/emc/rs274ngc/gcodemodule.cc" >/dev/null
 grep -F 'struct _inittab builtin_modules[]' "$linuxcnc_root/src/emc/task/taskclass.cc" >/dev/null
 grep -F 'int Interp::fetch_hal_param(' "$linuxcnc_root/src/emc/rs274ngc/interp_namedparams.cc" >/dev/null
 grep -F 'hal_get_pin_value_by_name(hal_name, &type, &ptr, &conn)' \
@@ -47,6 +49,11 @@ grep -F 'int hal_get_pin_value_by_name(' "$linuxcnc_root/src/hal/hal_lib.c" >/de
 grep -F 'int hal_get_signal_value_by_name(' "$linuxcnc_root/src/hal/hal_lib.c" >/dev/null
 grep -F 'int hal_get_param_value_by_name(' "$linuxcnc_root/src/hal/hal_lib.c" >/dev/null
 grep -F 'wordexp(basename, &exp_result, 0);' "$linuxcnc_root/src/emc/rs274ngc/rs274ngc_pre.cc" >/dev/null
+grep -F 'wordexp(settings->program_prefix, &exp_result, 0);' \
+    "$linuxcnc_root/src/emc/rs274ngc/rs274ngc_pre.cc" >/dev/null
+grep -F 'wordexp(settings->subroutines[dct], &exp_result, 0);' \
+    "$linuxcnc_root/src/emc/rs274ngc/rs274ngc_pre.cc" >/dev/null
+grep -F 'wordfree(&exp_result);' "$linuxcnc_root/src/emc/rs274ngc/rs274ngc_pre.cc" >/dev/null
 grep -F '#include "nml_intf/emc_nml.hh"' "$linuxcnc_root/src/emc/sai/dummyemcstat.cc" >/dev/null
 grep -F 'EMC_STAT *emcStatus = new EMC_STAT;' "$linuxcnc_root/src/emc/sai/dummyemcstat.cc" >/dev/null
 grep -F 'int NMLmsg::automatically_clear = 1;' \
@@ -229,6 +236,32 @@ for needle in [
 ]:
     if needle not in nml_status_shim:
         raise SystemExit(f"NML status shim missing LinuxCNC constructor boundary: {needle}")
+for needle in [
+    "int _task = 0;",
+    'extern "C" PyObject *PyInit_interpreter(void)',
+    'extern "C" PyObject *PyInit_emccanon(void)',
+    'extern "C" PyObject *PyInit_gcode(void)',
+    "return nullptr;",
+    'struct _inittab builtin_modules[] = {',
+    '{"interpreter", PyInit_interpreter}',
+    '{"emccanon", PyInit_emccanon}',
+]:
+    if needle not in runtime_shim:
+        raise SystemExit(f"linuxcnc runtime shim missing preview/builtin module boundary: {needle}")
+for needle in [
+    "std::string expand_home_directory(const char *words)",
+    "std::string expand_environment_variables(const std::string &words)",
+    "extern \"C\" int wordexp(const char *words, wordexp_t *pwordexp, int)",
+    "return WRDE_BADVAL;",
+    "return WRDE_NOSPACE;",
+    "pwordexp->we_wordc = 1;",
+    "pwordexp->we_offs = 0;",
+    "extern \"C\" void wordfree(wordexp_t *pwordexp)",
+    "pwordexp->we_wordc = 0;",
+    "pwordexp->we_wordv = nullptr;",
+]:
+    if needle not in runtime_shim:
+        raise SystemExit(f"linuxcnc runtime shim missing limited wordexp boundary: {needle}")
 for needle in [
     'extern "C" int hal_get_pin_value_by_name',
     'extern "C" int hal_get_signal_value_by_name',
@@ -322,7 +355,11 @@ for phrase in [
     "dynamic loading unavailable",
     "unavailable HAL lookup",
     "must leave HAL values unavailable",
+    "preview `_task=0`",
+    "builtin module stubs",
     "must not switch browser-safe probes into task mode",
+    "single-word `wordexp()` path expansion",
+    "`wordfree()` cleanup",
     "must not become a shell expansion feature",
     "must not become Python execution",
     "keeping Python execution disabled",
diff --git a/docs/linuxcnc-wasm-shims-source-map.md b/docs/linuxcnc-wasm-shims-source-map.md
index d48c0d7..bab4b27 100644
--- a/docs/linuxcnc-wasm-shims-source-map.md
+++ b/docs/linuxcnc-wasm-shims-source-map.md
@@ -17,7 +17,7 @@ only; it must not add CNC behavior and must not expand the temporary smoke parse
 | `core/wasm_shims/dlfcn.cc` | `src/emc/rs274ngc/interp_base.cc` | Satisfies LinuxCNC `interp_base.cc` dynamic loader calls and RTLD flags for browser-safe probes while keeping dynamic loading unavailable. |
 | `core/wasm_shims/emc_status_shim.cc` | `src/emc/sai/dummyemcstat.cc` | Provides the detached LinuxCNC `EMC_STAT` singleton shape without task/NML startup. |
 | `core/wasm_shims/gettext_shim.cc` | `src/emc/rs274ngc/interp_internal.hh` | Preserves LinuxCNC `_()` diagnostic call sites by satisfying `gettext()` while leaving browser gettext catalogs unavailable. |
-| `core/wasm_shims/linuxcnc_runtime_shim.cc` | `src/emc/rs274ngc/gcodemodule.cc`, `src/emc/task/emctaskmain.cc`, `src/emc/task/taskclass.cc`, `src/emc/rs274ngc/interp_namedparams.cc`, `include/hal.h`, `src/hal/hal_lib.c`, `src/emc/rs274ngc/rs274ngc_pre.cc` | Keeps preview/task, builtin Python module, unavailable HAL lookup, and `wordexp()` edges compile-safe. |
+| `core/wasm_shims/linuxcnc_runtime_shim.cc` | `src/emc/rs274ngc/gcodemodule.cc`, `src/emc/task/emctaskmain.cc`, `src/emc/task/taskclass.cc`, `src/emc/rs274ngc/interp_namedparams.cc`, `include/hal.h`, `src/hal/hal_lib.c`, `src/emc/rs274ngc/rs274ngc_pre.cc` | Keeps preview/task, builtin module stubs, unavailable HAL lookup, and `wordexp()` edges compile-safe. |
 | `core/wasm_shims/nml_status_shim.cc` | `src/libnml/nml/nmlmsg.cc`, `src/libnml/nml/stat_msg.cc` | Provides LinuxCNC NML status constructors, clear behavior, and `RCS_STAT_MSG` default status fields needed by source-linked EMC status objects. |
 | `core/wasm_shims/python_c_api_shim.cc` | `src/emc/rs274ngc/interp_python.cc`, `src/emc/rs274ngc/interp_namedparams.cc`, `src/emc/rs274ngc/gcodemodule.cc`, `src/emc/pythonplugin/python_plugin.cc` | Satisfies Python C API symbols while Python/Boost.Python remap paths remain tracked blockers. |
 | `core/wasm_shims/rcs_print_shim.cc` | `src/libnml/rcs/rcs_print.cc`, `src/libnml/rcs/rcs_print.hh` | Provides the LinuxCNC `rcs_print_error` split entry points used by NML validation without native print routing. |
@@ -36,15 +36,20 @@ only; it must not add CNC behavior and must not expand the temporary smoke parse
 - `core/wasm_shims/emc_status_shim.cc` must stay limited to the detached
   LinuxCNC `EMC_STAT` singleton from `src/emc/sai/dummyemcstat.cc`; it must not
   pull in task startup, NML channels, or operator callback behavior.
-- `core/wasm_shims/linuxcnc_runtime_shim.cc` must keep `_task=0` for preview,
+- `core/wasm_shims/linuxcnc_runtime_shim.cc` must keep preview `_task=0`,
   matching `src/emc/rs274ngc/gcodemodule.cc`; it must not switch browser-safe probes into task mode.
+- The runtime shim's builtin module stubs must match LinuxCNC's
+  `interpreter`/`emccanon` inittab shape from `gcodemodule.cc` and
+  `taskclass.cc` while returning null module pointers; they must not become
+  Python execution.
 - The HAL lookup shim covers `hal_get_pin_value_by_name()`,
   `hal_get_signal_value_by_name()`, and `hal_get_param_value_by_name()` from
   `src/emc/rs274ngc/interp_namedparams.cc`, `include/hal.h`, and
   `src/hal/hal_lib.c`; it must leave HAL values unavailable by returning `-1`,
   `HAL_TYPE_UNINITIALIZED`, and null data pointers.
-- `wordexp()` support is limited to the browser-safe path expansion needed by
-  `src/emc/rs274ngc/rs274ngc_pre.cc`; it must not become a shell expansion feature.
+- `wordexp()` support is limited to the single-word `wordexp()` path expansion
+  and `wordfree()` cleanup needed by `src/emc/rs274ngc/rs274ngc_pre.cc` for
+  basename, program prefix, and subroutine-directory lookups; it must not become a shell expansion feature.
 
 ## Python Shim Boundaries