diff --git a/toolchain/Containerfile b/toolchain/Containerfile
new file mode 100644
index 0000000..32e5ba0
--- /dev/null
+++ b/toolchain/Containerfile
@@ -0,0 +1,6 @@
+FROM registry.fedoraproject.org/fedora:43
+RUN dnf -y install --setopt=install_weak_deps=False \
+      mingw32-gcc mingw32-gcc-c++ mingw32-winpthreads-static mingw32-headers mingw32-crt \
+      mingw32-binutils meson ninja-build glslang git python3 make cmake file diffutils patch which findutils \
+    && dnf clean all
+WORKDIR /work
diff --git a/toolchain/build.sh b/toolchain/build.sh
new file mode 100755
index 0000000..b875eb6
--- /dev/null
+++ b/toolchain/build.sh
@@ -0,0 +1,18 @@
+#!/bin/bash
+# Reproducible mingw build of the TRL VR mod (DXVK fork + d3d9 proxy + launcher).
+# usage: build.sh <source-tree> <output-dir> [dxvk|proxy|all]
+#   source-tree: TRLVR layout (src/, dxvk-trlvr/, third_party/), mounted read-only.
+#   output-dir : receives dist/{d3d9.dll,d3d9_dxvk.dll,trlvr_launcher.exe}, work/, logs/
+# Env: FIXES=<dir with dxvk-*.patch / proxy-*.patch applied to the in-container copy>
+#      JOBS, EXTRA_CXXFLAGS, EXTRA_LIBS. Needs podman and image legendframe-mingw
+#      (podman build -t legendframe-mingw <this dir>).
+set -euo pipefail
+HERE=$(cd "$(dirname "$0")" && pwd)
+SRC=$(readlink -f "${1:?source tree}"); OUT=$(readlink -m "${2:?output dir}"); WHAT=${3:-all}
+mkdir -p "$OUT"
+FIXMNT=()
+if [ -n "${FIXES:-}" ]; then FIXMNT=(-v "$(readlink -f "$FIXES"):/fixes:ro,Z"); fi
+podman image exists localhost/legendframe-mingw || podman build -t legendframe-mingw "$HERE"
+exec podman run --rm -e JOBS="${JOBS:-}" -e WHAT="$WHAT" -e EXTRA_CXXFLAGS="${EXTRA_CXXFLAGS:-}" -e EXTRA_LIBS="${EXTRA_LIBS:-}" \
+  -v "$SRC:/src:ro,Z" -v "$OUT:/out:Z" -v "$HERE/shims:/shims:ro,Z" -v "$HERE/container-build.sh:/container-build.sh:ro,Z" \
+  "${FIXMNT[@]}" localhost/legendframe-mingw bash /container-build.sh
diff --git a/toolchain/container-build.sh b/toolchain/container-build.sh
new file mode 100755
index 0000000..abdf58a
--- /dev/null
+++ b/toolchain/container-build.sh
@@ -0,0 +1,93 @@
+#!/bin/bash
+# Runs INSIDE the legendframe-mingw container. Invoked by build.sh.
+#   /src     read-only source tree (TRLVR layout: src/, dxvk-trlvr/, third_party/)
+#   /out     writable output dir
+#   /shims   read-only toolchain/shims
+#   /fixes   optional read-only dir of *.patch files applied to the COPY (patch -p1)
+# Env: JOBS, WHAT=all|dxvk|proxy
+set -euo pipefail
+JOBS=${JOBS:-$(nproc)}
+WHAT=${WHAT:-all}
+W=/out/work
+mkdir -p "$W" /out/dist /out/logs
+
+ts() { date +%s; }
+
+if [ "$WHAT" = all ] || [ "$WHAT" = dxvk ]; then
+  t0=$(ts)
+  echo "=== DXVK: copy tree"
+  rm -rf "$W/dxvk-trlvr" "$W/b-dxvk"
+  cp -r /src/dxvk-trlvr "$W/dxvk-trlvr"; rm -rf "$W/dxvk-trlvr/build-win32"
+  for p in /fixes/dxvk-*.patch; do [ -f "$p" ] && (cd "$W/dxvk-trlvr" && patch -p1 < "$p"); done || true
+  cd "$W/dxvk-trlvr"
+  # Same options as build_dxvk.bat (d3d9 only), mingw cross file, asserts off.
+  meson setup --backend ninja --cross-file build-win32.txt --buildtype release \
+      -Denable_d3d8=false -Denable_d3d10=false -Denable_d3d11=false -Denable_dxgi=false \
+      -Db_ndebug=if-release "$W/b-dxvk" .
+  ninja -C "$W/b-dxvk" -j"$JOBS"
+  i686-w64-mingw32-strip -o /out/dist/d3d9_dxvk.dll "$W/b-dxvk/src/d3d9/d3d9.dll"
+  echo "DXVK_SECONDS=$(( $(ts) - t0 ))"
+fi
+
+if [ "$WHAT" = all ] || [ "$WHAT" = proxy ]; then
+  t0=$(ts)
+  echo "=== proxy + launcher: copy tree"
+  rm -rf "$W/src" "$W/obj" "$W/third_party"; mkdir -p "$W/obj" "$W/third_party"
+  cp -r /src/src "$W/src"
+  for d in openvr openxr imgui; do [ -d /src/third_party/$d ] && cp -r /src/third_party/$d "$W/third_party/"; done
+  for p in /fixes/proxy-*.patch; do [ -f "$p" ] && (cd "$W" && patch -p1 < "$p"); done || true
+  cd "$W"
+  # Struct-returning OpenVR virtuals: MSVC and GCC disagree on thiscall+sret, so route the
+  # calls through trlvr_abi::call_sret (see shims/seh_compat.h). Mechanical rewrite, diffed.
+  mkdir -p "$W/abi-orig"; rm -rf "$W/abi-orig/src"; cp -r "$W/src" "$W/abi-orig/src"
+  SRET='GetEyeToHeadTransform|GetProjectionMatrix|GetSeatedZeroPoseToStandingAbsoluteTrackingPose|GetRawZeroPoseToStandingAbsoluteTrackingPose|GetMatrix34TrackedDeviceProperty|GetHiddenAreaMesh|GetCurrentFadeColor|GetHeadsetViewMode'
+  find "$W/src" -name '*.cpp' -o -name '*.h' | xargs sed -i -E \
+    "s/\b([A-Za-z_][A-Za-z0-9_]*)->($SRET)\(\)/trlvr_abi::call_sret(\1, \&std::remove_pointer_t<decltype(\1)>::\2)/g; \
+     s/\b([A-Za-z_][A-Za-z0-9_]*)->($SRET)\(/trlvr_abi::call_sret(\1, \&std::remove_pointer_t<decltype(\1)>::\2, /g"
+  (cd "$W" && diff -ru abi-orig/src src > /out/abi-fix.diff) || true
+  echo "ABI rewrite sites: $(grep -c '^+.*call_sret' /out/abi-fix.diff || true)"
+  # Source list, defines and include dirs come straight from build.bat.
+  SRCS=$(grep -E '^set SRC=%SRC% "%ROOT%[^"]+\.cpp"' /src/build.bat | sed -E 's/.*%ROOT%([^"]+)"/\1/; s#\\#/#g')
+  IMGUI_SRCS=""
+  if [ -d "$W/third_party/imgui" ]; then
+    for f in $(grep -oE 'for %%F in \(([a-z0-9_ ]+)\)' /src/build.bat | sed -E 's/.*\((.*)\)/\1/'); do IMGUI_SRCS="$IMGUI_SRCS third_party/imgui/$f.cpp"; done
+  fi
+  DEFS=$(grep -E '^set CFLAGS=' /src/build.bat | grep -oE '/D[A-Za-z_0-9]+' | sed 's#^/D#-D#' | tr '\n' ' ')
+  INC="-I$W/third_party/openvr/headers -I$W/third_party/openxr/include -I$W/third_party/imgui -I/src/dxvk-trlvr/src/d3d9 -I/src/dxvk-trlvr/include/vulkan/include"
+  # -include seh_compat.h: MSVC __try/__except shim + _ReturnAddress + sret helper; sources stay unmodified.
+  CXXFLAGS="-std=gnu++17 -O2 $DEFS -fno-strict-aliasing -include /shims/seh_compat.h $INC ${EXTRA_CXXFLAGS:-}"
+  echo "sources: $(echo $SRCS $IMGUI_SRCS | wc -w); defs: $DEFS"
+  objs=(); pids=()
+  for s in $SRCS $IMGUI_SRCS; do
+    s=${s%.cpp}
+    o="$W/obj/$(echo $s | tr / _).o"; objs+=("$o")
+    f="$W/$s.cpp"; [ -f "$f" ] || f="$W/src/${s#src/}.cpp"
+    i686-w64-mingw32-g++ $CXXFLAGS -c "$f" -o "$o" > "${o%.o}.log" 2>&1 &
+    pids+=($!)
+    while [ "$(jobs -r | wc -l)" -ge "$JOBS" ]; do sleep 0.2; done
+  done
+  rc=0; for p in "${pids[@]}"; do wait "$p" || rc=1; done
+  cat "$W"/obj/*.log | grep -E "error|Error" | head -80 || true
+  [ $rc = 0 ] || { echo "PROXY COMPILE FAILED"; exit 1; }
+  # GNU ld wants a name after a bare LIBRARY keyword (MSVC link does not).
+  sed 's/^LIBRARY[[:space:]]*$/LIBRARY "d3d9.dll"/' "$W/src/proxy/d3d9.def" > "$W/d3d9.mingw.def"
+  XRLIB=""; [ -f "$W/third_party/openxr/lib/win32/openxr_loader.lib" ] && XRLIB="$W/third_party/openxr/lib/win32/openxr_loader.lib"
+  # Not linking d3d9: this DLL is d3d9.dll. --kill-at = undecorated stdcall exports like MSVC.
+  i686-w64-mingw32-g++ -shared -static -static-libgcc -static-libstdc++ -s \
+      -o /out/dist/d3d9.dll "${objs[@]}" "$W/d3d9.mingw.def" $XRLIB \
+      -Wl,--kill-at -Wl,--enable-stdcall-fixup -Wl,--subsystem,windows -Wl,--large-address-aware \
+      -Wl,-Map,/out/dist/d3d9.map \
+      -ldxguid -luser32 -lkernel32 -ladvapi32 -lgdi32 -ldwmapi ${EXTRA_LIBS:-}
+  # Launcher: its own exe (large-address-aware bit must be in the file).
+  i686-w64-mingw32-g++ -std=gnu++17 -O2 -DWIN32 -DNDEBUG -D_CRT_SECURE_NO_WARNINGS \
+      -include /shims/seh_compat.h -static -static-libgcc -static-libstdc++ -s \
+      -o /out/dist/trlvr_launcher.exe "$W/src/launcher/main.cpp" \
+      -mwindows -municode -Wl,--large-address-aware -luser32 -lkernel32 -lshell32
+  # d3d9.dll links openxr_loader statically (MSVC delay-loads it): the loader must ship beside it.
+  if [ -f /src/third_party/openxr/bin/win32/openxr_loader.dll ]; then
+    cp /src/third_party/openxr/bin/win32/openxr_loader.dll /out/dist/
+    echo "NOTE: dist/openxr_loader.dll must be installed next to d3d9.dll (static import)"
+  fi
+  echo "PROXY_SECONDS=$(( $(ts) - t0 ))"
+fi
+ls -l /out/dist
diff --git a/toolchain/run-trio.sh b/toolchain/run-trio.sh
new file mode 100755
index 0000000..1cdf833
--- /dev/null
+++ b/toolchain/run-trio.sh
@@ -0,0 +1,42 @@
+#!/bin/bash
+# usage: run-trio.sh <label> <dist dir> [key=value ini overrides...]
+# Swaps the trio into the game dir, launches headless-style (DISPLAY=:1, 90 s), kills, restores.
+LABEL=$1; DIST=$(readlink -f $2); shift 2
+G="/home/steamos/.local/share/Steam/steamapps/common/Tomb Raider Legend"; ST=/home/steamos/.local/share/Steam
+B=/home/steamos/Games/LegendFrame/build-m1; L=$B/logs/$LABEL; mkdir -p $L
+pgrep trl_vr && { echo "game running"; exit 1; }
+# verify shipped state
+(cd $B/shipped/1.0.0 && grep -E " (d3d9.dll|d3d9_dxvk.dll|trlvr_launcher.exe|openvr_api.dll|trl_vr.exe)$" SHA256SUMS | sed "s# # $G/#;s#  *$G/# $G/#" >/dev/null)
+for f in d3d9.dll d3d9_dxvk.dll trlvr_launcher.exe; do
+  want=$(grep " $f\$" $B/shipped/1.0.0/SHA256SUMS | cut -d' ' -f1); have=$(sha256sum "$G/$f" | cut -d' ' -f1)
+  [ "$want" = "$have" ] || { echo "game-dir $f is not the shipped one; abort"; exit 2; }
+done
+mkdir -p $B/shipped/backup-$LABEL; cp -p "$G"/trlvr.ini "$G"/trlvr.log "$G"/trlvr.log.prev "$G"/trlvr_launcher.log $B/shipped/backup-$LABEL/ 2>/dev/null
+restore() {
+  cp -p $B/shipped/1.0.0/d3d9.dll $B/shipped/1.0.0/d3d9_dxvk.dll $B/shipped/1.0.0/trlvr_launcher.exe "$G/"
+  cp -p $B/shipped/backup-$LABEL/trlvr.ini "$G/trlvr.ini"
+  rm -f "$G/openxr_loader.dll" "$G/trlvr_crash.dmp"
+  [ -f $B/shipped/backup-$LABEL/trlvr.log ] && cp -p $B/shipped/backup-$LABEL/trlvr.log "$G/"
+  [ -f $B/shipped/backup-$LABEL/trlvr.log.prev ] && cp -p $B/shipped/backup-$LABEL/trlvr.log.prev "$G/"
+  [ -f $B/shipped/backup-$LABEL/trlvr_launcher.log ] && cp -p $B/shipped/backup-$LABEL/trlvr_launcher.log "$G/"
+  (cd "$G" && sha256sum d3d9.dll d3d9_dxvk.dll trlvr_launcher.exe trlvr.ini) > $L/restore-sha.txt
+}
+trap restore EXIT
+for kv in "$@"; do
+  k=${kv%%=*}; v=${kv#*=}
+  if grep -q "^$k=" "$G/trlvr.ini"; then sed -i "s|^$k=.*|$k=$v|" "$G/trlvr.ini"; else sed -i "/^\[vr\]/a $k=$v" "$G/trlvr.ini"; fi
+done
+cp $DIST/d3d9.dll $DIST/d3d9_dxvk.dll $DIST/trlvr_launcher.exe "$G/"
+[ -f $DIST/openxr_loader.dll ] && cp $DIST/openxr_loader.dll "$G/"
+T0=$(date +%s)
+SP=$(pgrep -x steam | head -1)
+(
+  while IFS= read -r -d '' kv; do export "$kv"; done < /proc/$SP/environ
+  export DISPLAY=:1 STEAM_COMPAT_DATA_PATH=$ST/steamapps/compatdata/7000 STEAM_COMPAT_CLIENT_INSTALL_PATH=$ST
+  export WINEDLLOVERRIDES="d3d9=n,b" SteamAppId=7000 SteamGameId=7000
+  timeout 90 $ST/steamapps/common/SteamLinuxRuntime_4-arm64/_v2-entry-point --verb=waitforexitandrun -- "$ST/steamapps/common/Proton 11.0 (ARM64)/proton" waitforexitandrun "$G/trlvr_launcher.exe" > $L/run.out 2>&1
+)
+pkill trl_vr; pkill trlvr_launch; sleep 3
+cp "$G"/trlvr.log "$G"/trlvr_launcher.log $L/ 2>/dev/null; cp "$G"/trl_vr_d3d9.log $L/ 2>/dev/null; cp "$G"/trlvr_crash.dmp $L/ 2>/dev/null
+for f in vrserver vrcompositor; do awk -v t="$(date -d @$T0 '+%b %d %H:%M:%S')" '1' ~/.local/share/Steam/logs/$f.txt | tail -n 4000 > $L/$f.tail.txt; done
+echo "ran $((`date +%s`-T0)) s"
diff --git a/toolchain/shims/seh_compat.h b/toolchain/shims/seh_compat.h
new file mode 100644
index 0000000..d17af5f
--- /dev/null
+++ b/toolchain/shims/seh_compat.h
@@ -0,0 +1,106 @@
+// seh_compat.h -- MSVC __try/__except(EXCEPTION_EXECUTE_HANDLER) for i686 mingw-w64.
+//
+// GCC has no __try/__except on 32-bit Windows. The TRL VR mod only uses the
+// catch-everything form, with no filter expression use, no __finally, and no
+// GetExceptionCode. This header maps that form onto a hand-registered x86 SEH
+// frame (fs:[0] chain) + __builtin_setjmp/longjmp, so nesting with foreign SEH
+// frames (the game's, the CRT's) keeps its order, exactly like MSVC's.
+//
+//   __try { A } __except(EXCEPTION_EXECUTE_HANDLER) { B }
+// becomes
+//   if (Scope s; (s.arm(), __builtin_setjmp(s.jb)) == 0) { A } else { B }
+//
+// Injected with -include so the mod's sources stay unmodified. Not applicable
+// to x86_64 (native SEH there). Hardware faults only (not C++ throws).
+#pragma once
+#if defined(__MINGW32__) && defined(__i386__) && !defined(TRLVR_SEH_COMPAT_DONE)
+#define TRLVR_SEH_COMPAT_DONE 1
+// libstdc++ defines its own __try/__catch macros (bits/exception_defines.h) and
+// would clobber ours if first included later; pull the whole library in now.
+#ifndef MINGW_HAS_SECURE_API
+#define MINGW_HAS_SECURE_API 1   // swprintf_s and friends, as MSVC provides
+#endif
+#ifdef __cplusplus
+#include <bits/stdc++.h>
+#endif
+#include <windows.h>
+#include <setjmp.h>
+
+namespace seh_compat {
+// Raw x86 SEH frame on the FS:[0] chain (what MSVC's __try does). On a fault the
+// handler redirects the thread into resume(), which __builtin_longjmp's back to the
+// guard and runs the else-branch. No C++ EH, no unwinding through ntdll frames.
+// Design and code from the probe-clang lane (probe-clang/seh_compat.h).
+struct Scope {
+    Scope* prev;                       // == EXCEPTION_REGISTRATION_RECORD layout
+    void*  handler;
+    void*  jb[5];                      // __builtin_setjmp buffer
+    bool   armed;
+    Scope() : armed(false) {}
+    ~Scope() { disarm(); }
+    void arm();
+    void disarm() { if (armed) { asm volatile("movl %0, %%fs:0" :: "r"(prev) : "memory"); armed = false; } }
+};
+__attribute__((noreturn, noinline, used)) static void __cdecl resume(Scope* s) {
+    s->disarm();
+    __builtin_longjmp(s->jb, 1);
+}
+static EXCEPTION_DISPOSITION __cdecl handler(EXCEPTION_RECORD* rec, void* est, CONTEXT* ctx, void*) {
+    if (rec->ExceptionFlags & (EXCEPTION_UNWINDING | EXCEPTION_EXIT_UNWIND)) return ExceptionContinueSearch;
+    DWORD* sp = reinterpret_cast<DWORD*>(ctx->Esp) - 2;       // fake cdecl call: [ret][arg]
+    sp[0] = 0; sp[1] = reinterpret_cast<DWORD>(est);
+    ctx->Esp = reinterpret_cast<DWORD>(sp);
+    ctx->Eip = reinterpret_cast<DWORD>(&resume);
+    return ExceptionContinueExecution;
+}
+__attribute__((noinline)) inline void Scope::arm() {
+    asm volatile("movl %%fs:0, %0" : "=r"(prev));
+    handler = reinterpret_cast<void*>(&seh_compat::handler);
+    asm volatile("movl %0, %%fs:0" :: "r"(this) : "memory");
+    armed = true;
+}
+}
+
+#include <intrin.h>
+// MSVC intrinsic; mingw's <intrin.h> declares it without a definition.
+#undef _ReturnAddress
+#define _ReturnAddress() __builtin_return_address(0)
+
+#undef __try
+#undef __except
+// The asm barrier matters: without it GCC -O2 schedules __builtin_setjmp's save of ESP into jb[]
+// AFTER the first guarded load, so a fault on that first load longjmps with a garbage ESP.
+#define __try if (::seh_compat::Scope seh_scope_; (seh_scope_.arm(), __builtin_setjmp(seh_scope_.jb)) == 0 && ({ __asm__ __volatile__("" ::: "memory"); 1; }))
+#define __except(x) else
+
+// ---------------------------------------------------------------------------
+// GCC/MSVC thiscall mismatch for virtuals that return a struct in memory:
+// MSVC passes `this` in ECX and the hidden return pointer first on the stack;
+// GCC puts the hidden pointer in ECX and `this` on the stack. OpenVR's
+// openvr_api.dll (MSVC ABI) therefore needs these called by hand.
+// container-build.sh rewrites `obj->GetEyeToHeadTransform(a)` (and the other
+// struct-returning OpenVR methods) to
+//   trlvr_abi::call_sret(obj, &decltype(*obj)::GetEyeToHeadTransform, a)
+// on its working copy and saves the result as abi-fix.diff.
+#if __has_include(<openvr.h>)
+#include <openvr.h>
+#include <type_traits>
+namespace trlvr_abi
+{
+    template <class R, class C, class... A>
+    inline R call_sret(C* obj, R (C::*pmf)(A...), A... args)
+    {
+        static_assert(sizeof(pmf) == 2 * sizeof(void*), "unexpected pmf layout");
+        size_t words[2];
+        __builtin_memcpy(words, &pmf, sizeof(words));
+        // Itanium-style PMF to a virtual: first word = vtable byte offset + 1.
+        const size_t slot = (words[0] - 1) / sizeof(void*);
+        void** vtbl = *reinterpret_cast<void***>(obj);
+        typedef void (__attribute__((thiscall)) *Fn)(void*, R*, A...);
+        R out{};
+        reinterpret_cast<Fn>(vtbl[slot])(obj, &out, args...);
+        return out;
+    }
+}
+#endif
+#endif
diff --git a/toolchain/test/seh_test.cpp b/toolchain/test/seh_test.cpp
new file mode 100644
index 0000000..3e5b62d
--- /dev/null
+++ b/toolchain/test/seh_test.cpp
@@ -0,0 +1,68 @@
+// Runtime check of shims/seh_compat.h (no game involved). Built with -include seh_compat.h.
+// usage: seh_test.exe <logfile>   (stdout is swallowed by Proton, so results go to the file too)
+#include <windows.h>
+#include <cstdio>
+
+static FILE* g_log;
+static void say(const char* fmt, int v = 0)
+{
+    char b[256]; snprintf(b, sizeof b, fmt, v);
+    if (g_log) { fputs(b, g_log); fputc('\n', g_log); fflush(g_log); }
+    puts(b); fflush(stdout);
+}
+
+static volatile int* volatile g_null = nullptr;
+static int __attribute__((noinline)) faulting_callee(int x) { return *g_null + x; }
+typedef int (*Fn)(int);
+static volatile Fn g_fn = faulting_callee;
+static int __attribute__((noinline)) good_callee(int x) { return x * 2; }
+
+static bool peek(volatile int* p, int* out)
+{
+    __try { *out = *p; return true; }
+    __except (EXCEPTION_EXECUTE_HANDLER) { return false; }
+}
+
+int main(int argc, char** argv)
+{
+    if (argc > 1) g_log = fopen(argv[1], "w");
+    int failures = 0;
+    say("start");
+
+    // 1. null read inside __try
+    int got = 0;
+    if (!peek(g_null, &got)) say("recovered (null read)"); else { say("FAIL null read not caught"); ++failures; }
+
+    // 2. guarded call through a function pointer into faulting code
+    volatile int r2 = 0;
+    __try { r2 = g_fn(1); say("FAIL call did not fault"); ++failures; }
+    __except (EXCEPTION_EXECUTE_HANDLER) { r2 = -1; }
+    if (r2 == -1) say("recovered (faulting call through function pointer)");
+
+    // 3. no fault: body runs, `return` leaves the frame cleanly
+    int ok = 0;
+    if (peek(&got, &ok) && ok == got) say("ok (no-fault path returns from inside __try)"); else { say("FAIL no-fault path"); ++failures; }
+
+    // 4. nested: inner fault is caught by the inner handler, outer body continues
+    int stage = 0;
+    __try {
+        __try { (void)*g_null; stage = 1; }
+        __except (EXCEPTION_EXECUTE_HANDLER) { stage = 2; }
+        stage += 10;
+    }
+    __except (EXCEPTION_EXECUTE_HANDLER) { stage = -99; }
+    if (stage == 12) say("recovered (nested)"); else { say("FAIL nested stage=%d", stage); ++failures; }
+
+    // 5. many faults in a row (frame chain must not leak or corrupt)
+    int n = 0;
+    for (int i = 0; i < 2000; ++i) { int t; if (!peek(g_null, &t)) ++n; }
+    if (n == 2000) say("recovered (2000 consecutive faults)"); else { say("FAIL repeated faults n=%d", n); ++failures; }
+
+    // 6. FS:[0] chain intact afterwards: a function pointer call that does NOT fault still works
+    if (g_fn != nullptr && good_callee(21) == 42) say("ok (chain intact)"); else ++failures;
+
+    // 7. unguarded fault still reaches the unhandled path? skipped on purpose (would kill the process)
+    say(failures ? "RESULT FAIL" : "RESULT PASS");
+    if (g_log) fclose(g_log);
+    return failures ? 1 : 0;
+}
diff --git a/toolchain/test/seh_test.sh b/toolchain/test/seh_test.sh
new file mode 100755
index 0000000..4641fbe
--- /dev/null
+++ b/toolchain/test/seh_test.sh
@@ -0,0 +1,25 @@
+#!/bin/bash
+# Build and run the seh_compat runtime check headless under Proton (scratch prefix, no game).
+# usage: seh_test.sh <output dir>
+set -uo pipefail
+HERE=$(cd "$(dirname "$0")/.." && pwd)
+OUT=$(readlink -m "${1:?output dir}"); mkdir -p "$OUT"
+podman image exists localhost/legendframe-mingw || podman build -t legendframe-mingw "$HERE"
+podman run --rm -v "$HERE:/tc:ro,Z" -v "$OUT:/out:Z" localhost/legendframe-mingw \
+  i686-w64-mingw32-g++ -std=gnu++17 -O2 -DWIN32 -DNDEBUG -include /tc/shims/seh_compat.h \
+    -static -static-libgcc -static-libstdc++ -o /out/seh_test.exe /tc/test/seh_test.cpp || exit 70
+ST=$HOME/.local/share/Steam; SP=$(pgrep -x steam | head -1)
+[ -n "$SP" ] || { echo "steam not running" >&2; exit 71; }
+PFX=$HOME/Games/LegendFrame/build-m2c/pfx; mkdir -p "$PFX"
+rm -f "$OUT/seh_test.log"
+(
+  while IFS= read -r -d '' kv; do export "$kv"; done < "/proc/$SP/environ"
+  export DISPLAY=:1 STEAM_COMPAT_DATA_PATH="$PFX" STEAM_COMPAT_CLIENT_INSTALL_PATH="$ST" SteamAppId=0 SteamGameId=0
+  cd "$OUT"
+  timeout "${TIMEOUT:-120}" "$ST/steamapps/common/SteamLinuxRuntime_4-arm64/_v2-entry-point" --verb=waitforexitandrun -- \
+    "$ST/steamapps/common/Proton 11.0 (ARM64)/proton" waitforexitandrun "$OUT/seh_test.exe" "Z:/${OUT#/}/seh_test.log" > "$OUT/seh_test.out" 2>&1
+  echo $? > "$OUT/exitcode"
+)
+cat "$OUT/seh_test.log" 2>/dev/null || tail -20 "$OUT/seh_test.out"
+echo "exit code $(cat "$OUT/exitcode")"
+exit "$(cat "$OUT/exitcode")"