snapshot: preserve the uncommitted Canary instrumentation (not authored here)

Working-tree snapshot taken 2026-07-28 so this work is not lost. To be clear
about provenance: NONE of this was written in the session that committed it —
it is pre-existing uncommitted work on phase-a-tracing, last committed 2026-07-09,
from the xenia-rs decoder/deadlock investigation. It is recorded verbatim, not
reviewed and not tested.

Contents: 24 tracked modifications (ppc_emit_memory, xex_module, object_table,
shim_utils, xboxkrnl threading/rtl, xevent/xobject/xthread, memory) plus the
untracked probe sources audit_68_host_mem_watch, audit_69_event_signal_watch,
audit_70_semaphore_release_watch, phase_b_snapshot, and cmake/toolchains.

Deliberately excluded: build-cross/ (51 GB of build output) and
vkd3d-proton.cache. Note third_party/snappy is a submodule pointer change whose
target may not be pushed anywhere, so this branch is a preservation record rather
than a guaranteed-buildable tree.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

cmake/XeniaHelpers.cmake

@@ -192,6 +192,12 @@ function(xe_shader_rules_dxbc target shader_dir)
   set(_valid_stages vs hs ds gs ps cs)
   set(_commands)
   set(_bytecode_dir "${shader_dir}/bytecode/d3d12_5_1")
+  # Propagate FXC_PATH from the configure-time env so ninja-spawned python
+  # subprocesses can find fxc.exe (CMake `set(ENV{...})` doesn't reach build).
+  set(_env_prefix "")
+  if(DEFINED ENV{FXC_PATH})
+    set(_env_prefix ${CMAKE_COMMAND} -E env "FXC_PATH=$ENV{FXC_PATH}")
+  endif()
   list(APPEND _commands COMMAND ${CMAKE_COMMAND} -E make_directory "${_bytecode_dir}")
   foreach(src ${_sources})
     get_filename_component(_name ${src} NAME)
@@ -206,7 +212,7 @@ function(xe_shader_rules_dxbc target shader_dir)
     if(NOT _stage IN_LIST _valid_stages)
       continue()
     endif()
-    list(APPEND _commands COMMAND ${Python3_EXECUTABLE} "${_script}" "${src}" "${_bytecode_dir}/${_id}.h")
+    list(APPEND _commands COMMAND ${_env_prefix} ${Python3_EXECUTABLE} "${_script}" "${src}" "${_bytecode_dir}/${_id}.h")
   endforeach()
   add_custom_command(
     OUTPUT "${_stamp}"