Environment

Visual Studio 2022 / 2025 (Visual Micro)
Board: ESP32-S3 Dev Module (esp32:esp32:esp32s3)
Arduino-ESP32 core: 3.3.7 – 3.3.11 (esp-x32 toolchain 2601)
Host platform in VS: x64 (Debug / Release)
Large C++ project (internet radio), many bundled libraries (AsyncWebServer, audioI2S decoders, etc.)
Problem

I need to control the GCC optimization level and per-file compiler flags for my ESP32-S3 build, but I cannot find a reliable way to do this in Visual Micro.

From the build output, every translation unit is compiled with the core’s default flags, including -Os:

xtensa-esp32s3-elf-g++ ... -Os -Werror=return-type ...
I am hitting intermittent internal compiler errors in the Xtensa GCC toolchain, for example:

internal compiler error: in try_forward_edges, at cfgcleanup.cc
The failing file changes between builds (WebRequest.cpp, Audio.cpp, neaacdec.cpp, mp3_decoder.cpp, celt.cpp, etc.), which suggests a toolchain/optimizer issue, not a syntax error in one source file.

In Arduino IDE / PlatformIO this is usually worked around by adding flags such as:

global: compiler.cpp.extra_flags=-fno-if-conversion
or per-file: lower optimization (-O0 / -O1) on the largest .cpp files
What I have tried

Looked in Visual Micro board / project settings for an “optimization” or “compiler flags” option — nothing obvious that maps to Arduino’s compiler.cpp.extra_flags / build.extra_flags.
Checked whether VS Configuration (Debug vs Release) changes -O — the compile line still shows -Os.
Considered editing the .vcxproj AdditionalOptions, but Visual Micro regenerates Arduino build commands from the board package, so manual MSVC compiler settings do not appear to reach xtensa-esp32s3-elf-g++.
build.extra_flags / upload.extra_flags in board properties appear empty in my .vmps.xml / project metadata.
What I need

A supported way in Visual Micro to:

Set project-wide extra GCC flags (e.g. compiler.cpp.extra_flags=-fno-if-conversion), and/or
Set per-file optimization for selected .cpp files (e.g. Audio.cpp, neaacdec.cpp at -O1 while the rest stays at -Os), and/or
Choose optimization level per VS configuration (Debug = -Og/-O0, Release = -Os/-O2).
Questions

Where is the correct place in Visual Micro to pass Arduino build.flags / compiler.cpp.extra_flags for ESP32?
Is there a platform.local.txt / boards.local.txt workflow that Visual Micro respects when building from VS?
Can per-source-file compiler options be defined in the .vcxproj or a Visual Micro project file without being overwritten?
Is limiting parallel compile jobs the only supported mitigation for GCC ICEs in large ESP32 projects?
Why this matters

Without control over optimizer flags, the only workarounds are retrying the build or downgrading the toolchain — neither is practical for a large, frequently rebuilt project.

Any guidance on the official / supported method would be appreciated.

Thanks.