Use a deterministic clock for input expression tests

* caching a little bit

* provide CMake with the explicit path to sccache.exe

* map ACTIONS_RESULTS_URL to ACTIONS_CACHE_URL so sccache can upload the
files...

* i removed the parallel oops

* small change

* doing a little bit of flag editing

* update sccache and cache nuget stuff

.github/workflows/build.yml

@@ -30,6 +30,14 @@ jobs:
         with:
           dotnet-version: '8.0.x'
 
+      - name: Cache NuGet packages
+        uses: actions/cache@v5
+        with:
+          path: ~/.nuget/packages
+          key: ${{ runner.os }}-nuget-${{ hashFiles('translator/Translator.sln', '**/*.csproj', '**/*.props', '**/*.targets', '**/packages.lock.json', 'global.json', 'NuGet.config', 'nuget.config') }}
+          restore-keys: |
+            ${{ runner.os }}-nuget-
+
       - name: Restore
         run: dotnet restore translator/Translator.sln
 
@@ -38,3 +46,22 @@ jobs:
 
       - name: Test
         run: dotnet test translator/Translator.sln -c Release --no-build --verbosity normal
+
+  cpp:
+    name: C++ runtime tests (${{ matrix.os }})
+    runs-on: ${{ matrix.os }}
+    timeout-minutes: 10
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [windows-latest, ubuntu-latest, macos-14]
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          persist-credentials: false
+      - name: Configure
+        run: cmake -S runtime/tests -B build/tests -DCMAKE_BUILD_TYPE=Release
+      - name: Build
+        run: cmake --build build/tests --config Release --parallel
+      - name: Test
+        run: ctest --test-dir build/tests -C Release --output-on-failure --no-tests=error

.github/workflows/recomp-test.yml

@@ -28,6 +28,19 @@ jobs:
           path: Launcher/artifacts/downloads
           key: windows-recomp-downloads-${{ hashFiles('Launcher/Prepare-PortableTools.ps1', 'Launcher/Prepare-Dependencies.ps1') }}
 
+      # Install sccache.
+      - name: Run sccache-action
+        uses: mozilla/sccache-action@v0.0.11
+
+      # Tell CMake to use sccache and use GitHub's API.
+      - name: Configure sccache environment
+        shell: pwsh
+        run: |
+          "SCCACHE_GHA_ENABLED=true" | Add-Content -Path $env:GITHUB_ENV
+          "ACTIONS_CACHE_SERVICE_V2=on" | Add-Content -Path $env:GITHUB_ENV
+          "CMAKE_C_COMPILER_LAUNCHER=$env:SCCACHE_PATH" | Add-Content -Path $env:GITHUB_ENV
+          "CMAKE_CXX_COMPILER_LAUNCHER=$env:SCCACHE_PATH" | Add-Content -Path $env:GITHUB_ENV
+
       - name: Prepare the shipped Windows toolchain
         shell: pwsh
         run: ./Launcher/Prepare-PortableTools.ps1
@@ -36,6 +49,13 @@ jobs:
         shell: pwsh
         run: ./Launcher/Prepare-Dependencies.ps1
 
+      # Expose cache token context to the build script.
       - name: Translate, compile the full runtime, and link
         shell: pwsh
-        run: ./Launcher/Test-Recompilation.ps1 -Parallel 3
+        run: ./Launcher/Test-Recompilation.ps1 -Parallel 4
+
+      # Print cache results (even if the build fails)
+      - name: Show sccache stats
+        if: always()
+        shell: pwsh
+        run: sccache --show-stats

.gitignore

@@ -26,6 +26,8 @@ Code.pul
 /build/
 /build-*/
 /native-build/
+/native-build-macos/
+/local-products/
 /dist/
 /out/
 [Bb]in/
@@ -70,3 +72,5 @@ project.lock.json
 *.log
 output.txt
 
+# Operating System
+.DS_Store

Launcher/Build-Installer.ps1

@@ -281,7 +281,7 @@ foreach ($required in @('ToolkitFingerprint','TranslationFingerprint','NativeToo
 
 $manifest = [ordered]@{
     SchemaVersion = 2
-    ProductVersion = '0.2.29'
+    ProductVersion = '0.2.31'
     ExpectedGameId = $pins.GameId
     ExpectedDolSha256 = $pins.DolSha256
     ExpectedRelSha256 = $pins.RelSha256

Launcher/NativeBuildFlags.ps1

@@ -117,12 +117,13 @@ function Get-MkwProjectPins([string]$ProjectFile) {
 }
 
 function Invoke-Checked([string]$FilePath, [string[]]$Arguments, [string]$Description,
-    [string]$LogPrefix = 'MKWCBUILD', [string]$StepId = '') {
+    [string]$LogPrefix = 'MKWCBUILD', [string]$StepId = '', [bool]$WaitForProcessTree = $true) {
     <#
-    Runs a build tool and turns a non-zero exit code into a described failure. Start-Process -Wait
-    is deliberate: it waits for the whole process tree, since a .NET single-file bundle host may
-    hand off to an extracted child that PowerShell's call operator would not wait for. Start-Process
-    doesn't publish $LASTEXITCODE, so this sets it manually for callers that check it.
+    Runs a build tool and turns a non-zero exit code into a described failure. By default,
+    Start-Process -Wait waits for the whole process tree, since a .NET single-file bundle host may
+    hand off to an extracted child that PowerShell's call operator would not wait for. Callers that
+    need to avoid waiting on unrelated descendants can opt into the call-operator path.
+    Start-Process doesn't publish $LASTEXITCODE, so this sets it manually for callers that check it.
     -StepId emits the machine-readable form the installer's progress bar consumes (BuildStepIds in
     WiiCompiled.Setup/InstallProgress.cs); the human sentence stays on the same log line.
     #>
@@ -132,9 +133,14 @@ function Invoke-Checked([string]$FilePath, [string[]]$Arguments, [string]$Descri
         if ($_.Contains('"')) { throw "A native build argument contains an unsupported quote: $_" }
         '"' + $_ + '"'
     })
-    $process = Start-Process -FilePath $FilePath -ArgumentList $quotedArguments `
-        -NoNewWindow -Wait -PassThru
-    $exitCode = $process.ExitCode
+    if ($WaitForProcessTree) {
+        $process = Start-Process -FilePath $FilePath -ArgumentList $quotedArguments `
+            -NoNewWindow -Wait -PassThru
+        $exitCode = $process.ExitCode
+    } else {
+        & $FilePath @Arguments
+        $exitCode = $LASTEXITCODE
+    }
     $global:LASTEXITCODE = $exitCode
     if ($exitCode -ne 0) { throw "$Description failed with exit code $exitCode." }
 }

Launcher/Test-Recompilation.ps1

@@ -136,9 +136,11 @@ try {
         -CxxCompiler (Join-Path $compilerBin 'x86_64-w64-mingw32-clang++.exe') `
         -ResourceCompiler (Join-Path $compilerBin 'x86_64-w64-mingw32-windres.exe') `
         -DependenciesDirectory $dependencies -AdditionalArguments @('-DMKW_BUILD_PRODUCTS=ON')
-    Invoke-Checked $cmake $configure 'Configuring the production Windows runtime'
+    Invoke-Checked $cmake $configure 'Configuring the production Windows runtime' `
+        -WaitForProcessTree $false
     Invoke-Checked $cmake @('--build', $nativeBuild, '--target', 'WiiCompiled', '--parallel', "$Parallel") `
-        'Compiling and linking the synthetic product with the full runtime'
+        'Compiling and linking the synthetic product with the full runtime' `
+        -WaitForProcessTree $false
     Assert-File (Join-Path $nativeBuild 'WiiCompiled.exe') 'Linked synthetic product'
 } finally {
     $env:PATH = $oldPath

Launcher/WiiCompiled.Setup.Common.Cli/WiiCompiled.Setup.Common.Cli.csproj

@@ -6,7 +6,7 @@
     <Nullable>enable</Nullable>
     <RootNamespace>WiiCompiled.Setup.Common.Cli</RootNamespace>
     <AssemblyName>WiiCompiled.Setup.Common.Cli</AssemblyName>
-    <Version>0.2.29</Version>
+    <Version>0.2.31</Version>
     <Authors>patchzy</Authors>
     <Product>WiiCompiled</Product>
     <Description>Packaging-time helper: resolves (downloading if needed) the nodtool binary bundled by build-appimage.sh and Build-Installer.ps1</Description>

Launcher/WiiCompiled.Setup.Common/WiiCompiled.Setup.Common.csproj

@@ -5,7 +5,7 @@
     <Nullable>enable</Nullable>
     <RootNamespace>WiiCompiled.Setup.Common</RootNamespace>
     <AssemblyName>WiiCompiled.Setup.Common</AssemblyName>
-    <Version>0.2.29</Version>
+    <Version>0.2.31</Version>
     <Authors>patchzy</Authors>
     <Product>WiiCompiled</Product>
     <Description>Shared nodtool/Retro-WFC-payload logic used by both the Windows and Linux installers</Description>

Launcher/WiiCompiled.Setup.Linux/Models.cs

@@ -3,7 +3,7 @@ namespace WiiCompiled.Setup.Linux;
 internal static class ProductInfo
 {
     public const string Name = "WiiCompiled";
-    public const string Version = "0.2.29";
+    public const string Version = "0.2.31";
 }
 
 /// <summary>One installed product's record inside install-state.json.</summary>

Launcher/WiiCompiled.Setup.Linux/WiiCompiled.Setup.Linux.csproj

@@ -6,7 +6,7 @@
     <Nullable>enable</Nullable>
     <AssemblyName>WiiCompiled.Setup.Linux</AssemblyName>
     <RootNamespace>WiiCompiled.Setup.Linux</RootNamespace>
-    <Version>0.2.29</Version>
+    <Version>0.2.31</Version>
     <Authors>patchzy</Authors>
     <Product>WiiCompiled</Product>
     <Description>Command-line installer and launcher for WiiCompiled on Linux</Description>

Launcher/WiiCompiled.Setup.Windows/Program.cs

@@ -121,7 +121,7 @@ internal static class PlatformChecks
 internal static class ProductInfo
 {
     public const string Name = "WiiCompiled";
-    public const string Version = "0.2.29";
+    public const string Version = "0.2.31";
 
     /// <summary>
     /// The setup executable is copied into the installation under this name. It is the launcher and

Launcher/WiiCompiled.Setup.Windows/WiiCompiled.Setup.Windows.csproj

@@ -7,7 +7,7 @@
     <AssemblyName>WiiCompiled.Setup</AssemblyName>
     <RootNamespace>WiiCompiled.Setup.Windows</RootNamespace>
     <ApplicationManifest>app.manifest</ApplicationManifest>
-    <Version>0.2.29</Version>
+    <Version>0.2.31</Version>
     <Authors>patchzy</Authors>
     <Product>WiiCompiled</Product>
     <Description>Command-line installer and launcher for WiiCompiled</Description>

runtime/CMakeLists.txt

@@ -269,68 +269,8 @@ target_include_directories(mkw_platform PUBLIC "${CMAKE_CURRENT_LIST_DIR}/includ
 target_compile_features(mkw_platform PUBLIC cxx_std_17)
 set_target_properties(mkw_platform PROPERTIES UNITY_BUILD OFF)
 
-# Keep these independent from Aurora's BUILD_TESTING option: they validate the
-# project's host-platform contracts, not Aurora's third-party test suite.
 enable_testing()
-add_executable(mkw_platform_paths_tests "${CMAKE_CURRENT_LIST_DIR}/tests/platform_paths_tests.cpp")
-target_link_libraries(mkw_platform_paths_tests PRIVATE mkw_platform)
-target_compile_features(mkw_platform_paths_tests PRIVATE cxx_std_17)
-add_test(NAME mkw_platform_paths_tests COMMAND mkw_platform_paths_tests)
-
-add_executable(mkw_nand_settings_tests "${CMAKE_CURRENT_LIST_DIR}/tests/nand_settings_tests.cpp")
-target_include_directories(mkw_nand_settings_tests PRIVATE "${CMAKE_CURRENT_LIST_DIR}/include")
-target_compile_features(mkw_nand_settings_tests PRIVATE cxx_std_17)
-add_test(NAME mkw_nand_settings_tests COMMAND mkw_nand_settings_tests)
-
-# The input expression engine is self-contained, so it can be exercised without
-# linking the runtime or SDL.
-add_executable(mkw_input_expr_tests
-    "${CMAKE_CURRENT_LIST_DIR}/tests/test_expr.cpp"
-    "${CMAKE_CURRENT_LIST_DIR}/src/input_expr.cpp")
-target_include_directories(mkw_input_expr_tests PRIVATE "${CMAKE_CURRENT_LIST_DIR}/include")
-target_compile_features(mkw_input_expr_tests PRIVATE cxx_std_17)
-add_test(NAME mkw_input_expr_tests COMMAND mkw_input_expr_tests)
-
-# HostContext deliberately keeps the platform-specific context primitive out
-# of fiber_manager.cpp. Exercise the Linux libco handoff directly so future
-# refactors cannot silently remove its headers, implementation, or link edge.
-if(MKW_PLATFORM_LINUX)
-    add_executable(mkw_linux_host_context_tests
-        "${CMAKE_CURRENT_LIST_DIR}/tests/host_context_tests.cpp"
-        "${CMAKE_CURRENT_LIST_DIR}/src/host_context.cpp")
-    target_include_directories(mkw_linux_host_context_tests PRIVATE
-        "${CMAKE_CURRENT_LIST_DIR}/include"
-        "${CMAKE_CURRENT_LIST_DIR}/third_party/libco")
-    target_compile_features(mkw_linux_host_context_tests PRIVATE cxx_std_17)
-    target_link_libraries(mkw_linux_host_context_tests PRIVATE mkw::libco)
-    add_test(NAME mkw_linux_host_context_tests COMMAND mkw_linux_host_context_tests)
-endif()
-
-if(MKW_PLATFORM_MACOS)
-    # Exercise the Apple Silicon context ABI and the public host-memory
-    # contracts separately from translated products.
-    enable_language(ASM)
-    add_executable(mkw_macos_context_abi_tests
-        "${CMAKE_CURRENT_LIST_DIR}/tests/macos_context_abi_tests.cpp"
-        "${CMAKE_CURRENT_LIST_DIR}/src/platform/macos/co_switch.S")
-    target_compile_features(mkw_macos_context_abi_tests PRIVATE cxx_std_17)
-    add_test(NAME mkw_macos_context_abi_tests COMMAND mkw_macos_context_abi_tests)
-
-    add_executable(mkw_macos_host_context_tests
-        "${CMAKE_CURRENT_LIST_DIR}/tests/host_context_tests.cpp"
-        "${CMAKE_CURRENT_LIST_DIR}/src/host_context.cpp"
-        "${CMAKE_CURRENT_LIST_DIR}/src/platform/macos/co_switch.S")
-    target_include_directories(mkw_macos_host_context_tests PRIVATE "${CMAKE_CURRENT_LIST_DIR}/include")
-    target_compile_features(mkw_macos_host_context_tests PRIVATE cxx_std_17)
-    add_test(NAME mkw_macos_host_context_tests COMMAND mkw_macos_host_context_tests)
-
-    add_executable(mkw_macos_guest_flat_memory_tests
-        "${CMAKE_CURRENT_LIST_DIR}/tests/macos_guest_flat_memory_tests.cpp"
-        "${CMAKE_CURRENT_LIST_DIR}/src/guest_flat_memory_macos.cpp")
-    target_include_directories(mkw_macos_guest_flat_memory_tests PRIVATE "${CMAKE_CURRENT_LIST_DIR}/include")
-    target_compile_features(mkw_macos_guest_flat_memory_tests PRIVATE cxx_std_17)
-    add_test(NAME mkw_macos_guest_flat_memory_tests COMMAND mkw_macos_guest_flat_memory_tests)
-endif()
+add_subdirectory(tests)
 
 # The translator emits the complete, content-addressed source graph. Consuming
 # this one manifest keeps configure independent of the 28k generated function

runtime/include/nand_path.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include "runtime_config.h"
+#include "nand_settings.h"
 #include "runtime_log.h"
 #include "system_bridge.h"
 
@@ -163,7 +164,7 @@ inline std::filesystem::path CreateManagedNandRoot() {
     return root;
 }
 
-inline std::filesystem::path DiscoverNandRootPath() {
+inline std::filesystem::path ResolveNandRootPath() {
     const std::string configPath = RuntimeConfigFile::NandRoot();
     if (!configPath.empty()) {
         const auto path = ResolveConfiguredPath(configPath);
@@ -179,4 +180,16 @@ inline std::filesystem::path DiscoverNandRootPath() {
     return CreateManagedNandRoot();
 }
 
+inline std::filesystem::path DiscoverNandRootPath() {
+    static const auto root = [] {
+        const auto resolved = ResolveNandRootPath();
+        std::string error;
+        if (!RuntimeNandSettings::Ensure(resolved, error)) {
+            FailNandRoot(error.c_str(), RuntimeNandSettings::FilePath(resolved));
+        }
+        return resolved;
+    }();
+    return root;
+}
+
 } // namespace RuntimeNandPath

runtime/include/nand_save_probe.h

@@ -0,0 +1,59 @@
+#pragma once
+
+#include <filesystem>
+#include <fstream>
+#include <istream>
+
+namespace RuntimeNandSave {
+
+enum class Contents { Missing, Blank, Nonzero, Error };
+enum class ReadAction { Proceed, Missing, Error, RecoveryNeeded };
+
+// A failed read is not evidence that a save is blank. Check badbit before EOF:
+// an I/O failure may set both, whereas a successful short final read sets EOF.
+inline Contents InspectStream(std::istream& input) {
+    if (!input) return Contents::Error;
+    char block[4096];
+    for (;;) {
+        input.read(block, sizeof(block));
+        if (input.bad() || (input.fail() && !input.eof())) return Contents::Error;
+        for (std::streamsize i = 0; i < input.gcount(); ++i) {
+            if (block[i] != 0) return Contents::Nonzero;
+        }
+        if (input.eof()) return Contents::Blank;
+    }
+}
+
+inline Contents InspectFile(const std::filesystem::path& path) {
+    std::error_code ec;
+    const auto status = std::filesystem::symlink_status(path, ec);
+    if (ec && ec != std::errc::no_such_file_or_directory) return Contents::Error;
+    if (!std::filesystem::exists(status)) return Contents::Missing;
+    if (!std::filesystem::is_regular_file(path, ec) || ec) return Contents::Error;
+    std::ifstream input(path, std::ios::binary);
+    return InspectStream(input);
+}
+
+// Probe only read-only opens of the actual save and its exact write shadow.
+// No probe writes, removes, or repairs data, and backups are not save aliases.
+inline ReadAction CheckRead(const std::filesystem::path& path, int mode) {
+    const auto name = path.filename();
+    const bool isMain = name == "rksys.dat";
+    if (mode != 1 || (!isMain && name != "rksys.dat.nandsafe.tmp")) return ReadAction::Proceed;
+    const auto contents = InspectFile(path);
+    if (contents == Contents::Error) return ReadAction::Error;
+    if (contents == Contents::Nonzero) return ReadAction::Proceed;
+    if (isMain) {
+        auto shadow = path;
+        shadow += ".nandsafe.tmp";
+        const auto shadowContents = InspectFile(shadow);
+        if (shadowContents == Contents::Error) return ReadAction::Error;
+        // The next write normally discards an old shadow. Preserve a possible
+        // recovery source when there is no usable original, without promoting
+        // an uncommitted (and potentially incomplete) shadow to the real save.
+        if (shadowContents == Contents::Nonzero) return ReadAction::RecoveryNeeded;
+    }
+    return contents == Contents::Blank ? ReadAction::Missing : ReadAction::Proceed;
+}
+
+} // namespace RuntimeNandSave

runtime/include/nand_settings.h

@@ -1,6 +1,9 @@
 #pragma once
 
 #include <array>
+#include <atomic>
+#include <chrono>
+#include <ctime>
 #include <cstdint>
 #include <filesystem>
 #include <fstream>
@@ -9,14 +12,23 @@
 #include <string>
 #include <utility>
 
+#ifdef _WIN32
+#include <windows.h>
+#else
+#include <unistd.h>
+#endif
+
 namespace RuntimeNandSettings {
 
 using Settings = std::map<std::string, std::string>;
 
+inline std::filesystem::path FilePath(const std::filesystem::path& root) {
+    return root / "title/00000001/00000002/data/setting.txt";
+}
+
 // Wii setting.txt is a 256-byte buffer encrypted with a rotating XOR key.
 inline std::optional<Settings> Read(const std::filesystem::path& nandRoot) {
-    std::ifstream input(nandRoot / "title/00000001/00000002/data/setting.txt",
-                        std::ios::binary);
+    std::ifstream input(FilePath(nandRoot), std::ios::binary);
     std::array<uint8_t, 256> bytes{};
     if (!input.read(reinterpret_cast<char*>(bytes.data()), bytes.size())) {
         return std::nullopt;
@@ -66,4 +78,143 @@ inline bool HasIdentity(const Settings& settings) {
     return true;
 }
 
+// Dolphin's normal (non-deterministic) first-boot algorithm. It is independent
+// of the ES device ID. Matching another NAND requires that NAND's saved serial.
+inline std::string GenerateSerial(std::time_t now) {
+    if (now < 0) {
+        return {};
+    }
+    const auto digits = std::to_string(now % 1000000000);
+    return std::string(9 - digits.size(), '0') + digits;
+}
+
+// This recompilation targets the European disc. These are Dolphin's PAL boot
+// defaults; an existing setting.txt always takes precedence, in every region.
+inline std::optional<std::array<uint8_t, 256>> EncodeNew(const std::string& serial) {
+    const Settings identity{{"SERNO", serial}, {"CODE", "LEH"}, {"AREA", "EUR"}, {"GAME", "EU"}};
+    if (!HasIdentity(identity)) {
+        return std::nullopt;
+    }
+    std::array<uint8_t, 256> bytes{};
+    size_t position = 0;
+    uint32_t key = 0x73B5DBFAu;
+    const auto writeByte = [&](char value) {
+        bytes[position++] = static_cast<uint8_t>(value) ^ static_cast<uint8_t>(key);
+        key = (key << 1) | (key >> 31);
+    };
+    for (const std::string& line : {std::string("AREA=EUR\r\n"), std::string("MODEL=RVL-001(EUR)\r\n"),
+             std::string("DVD=0\r\n"), std::string("MPCH=0x7FFE\r\n"), std::string("CODE=LEH\r\n"),
+             "SERNO=" + serial + "\r\n", std::string("VIDEO=PAL\r\n"), std::string("GAME=EU\r\n")}) {
+        for (;;) {
+            if (position + line.size() > bytes.size()) {
+                return std::nullopt;
+            }
+            const auto start = position;
+            const auto savedKey = key;
+            bool hasNull = false;
+            for (const char value : line) {
+                writeByte(value);
+                hasNull |= bytes[position - 1] == 0;
+            }
+            if (!hasNull) {
+                break;
+            }
+            // Nintendo stops at an encoded NUL. Dolphin inserts an extra LF
+            // before this line and retries with the shifted encryption key.
+            position = start;
+            key = savedKey;
+            writeByte('\n');
+        }
+    }
+    return bytes; // The unused tail stays raw zero, as in Dolphin.
+}
+
+// Atomically claim our own scratch directory. A collision belongs to another
+// launch (or a previous crashed launch); leave it untouched and try another name.
+inline std::optional<std::filesystem::path> CreateScratchDirectory(
+    const std::filesystem::path& parent, const std::string& token, std::error_code& ec) {
+    for (unsigned attempt = 0; attempt < 128; ++attempt) {
+        const auto candidate = parent / (".setting-init-" + token + "-" + std::to_string(attempt));
+        ec.clear();
+        if (std::filesystem::create_directory(candidate, ec)) return candidate;
+        if (ec && ec != std::errc::file_exists) return std::nullopt;
+    }
+    ec = std::make_error_code(std::errc::file_exists);
+    return std::nullopt;
+}
+
+// Never replace an existing file, including an unreadable or damaged one.
+// Publish a complete file atomically so simultaneous launches use one identity.
+inline bool Ensure(const std::filesystem::path& root, std::string& error,
+                   std::time_t now = std::time(nullptr)) {
+    const auto path = FilePath(root);
+    std::error_code ec;
+    const auto status = std::filesystem::symlink_status(path, ec);
+    if (ec && ec != std::errc::no_such_file_or_directory) {
+        error = "Cannot inspect NAND setting.txt: " + ec.message();
+        return false;
+    }
+    if (std::filesystem::exists(status)) {
+        const auto existing = Read(root);
+        if (existing && HasIdentity(*existing)) {
+            return true;
+        }
+        error = "Existing NAND setting.txt is unreadable or invalid; restore it from this console's backup";
+        return false;
+    }
+
+    const auto bytes = EncodeNew(GenerateSerial(now));
+    if (!bytes) {
+        error = "Cannot initialize NAND settings: invalid system clock";
+        return false;
+    }
+    ec.clear();
+    std::filesystem::create_directories(path.parent_path(), ec);
+    if (ec) {
+        error = "Cannot create NAND settings directory: " + ec.message();
+        return false;
+    }
+    static std::atomic<unsigned> sequence{0};
+#ifdef _WIN32
+    const auto processId = GetCurrentProcessId();
+#else
+    const auto processId = getpid();
+#endif
+    const auto scratch = CreateScratchDirectory(path.parent_path(),
+        std::to_string(processId) + "-" + std::to_string(
+            std::chrono::steady_clock::now().time_since_epoch().count()) + "-" +
+            std::to_string(sequence++), ec);
+    if (!scratch) {
+        error = "Cannot create temporary NAND settings directory: " + ec.message();
+        return false;
+    }
+    const auto temporary = *scratch / "setting.txt";
+    bool written = false;
+    {
+        std::ofstream output(temporary, std::ios::binary);
+        output.write(reinterpret_cast<const char*>(bytes->data()), bytes->size());
+        output.close();
+        written = static_cast<bool>(output);
+    }
+    bool published = false;
+    if (written) {
+#ifdef _WIN32
+        published = MoveFileExW(temporary.c_str(), path.c_str(), MOVEFILE_WRITE_THROUGH) != 0;
+#else
+        published = ::link(temporary.c_str(), path.c_str()) == 0;
+#endif
+    }
+    std::filesystem::remove(temporary, ec);
+    std::filesystem::remove(*scratch, ec);
+    // A competing launcher may have published its settings first. Always read
+    // the winner from NAND rather than using our unpersisted candidate serial.
+    const auto persisted = Read(root);
+    if (persisted && HasIdentity(*persisted)) {
+        return true;
+    }
+    error = published ? "Cannot read newly initialized NAND setting.txt" :
+                        "Cannot persist NAND setting.txt; check NAND directory permissions";
+    return false;
+}
+
 } // namespace RuntimeNandSettings

runtime/include/sc_serial_contract.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <charconv>
+#include <cstddef>
+#include <cstdint>
+#include <string_view>
+#include <system_error>
+
+namespace RuntimeScSerial {
+
+// SCGetProductSN's output is a u32, not a character buffer. DWC loads
+// that word and formats it with the product code to construct csnum.
+template <typename RangeValidator, typename WordWriter>
+uint32_t Write(std::string_view serial, uint32_t address,
+               RangeValidator&& contains, WordWriter&& write32) {
+    if (serial.empty() || serial.size() > 9 ||
+        serial.find_first_not_of("0123456789") != std::string_view::npos) return 0;
+    uint32_t number = 0;
+    const auto parsed = std::from_chars(serial.data(), serial.data() + serial.size(), number);
+    if (parsed.ec != std::errc{} || parsed.ptr != serial.data() + serial.size() ||
+        !address || !contains(address, sizeof(uint32_t))) return 0;
+    write32(address, number);
+    return 1;
+}
+
+} // namespace RuntimeScSerial

runtime/src/hle/sc.cpp

@@ -1,6 +1,7 @@
 #include "hle_stubs.h"
 
 #include "console_identity.h"
+#include "sc_serial_contract.h"
 #include <cstdlib>
 #include <cstddef>
 #include <cstdint>
@@ -97,12 +98,9 @@ PPC_NATIVE_OVERRIDE(801B2424, SCGetProductCode_HLE, uint32_t, (), ());
 extern "C" uint32_t SCGetProductSN_HLE(uint32_t serialAddress)
 {
     const std::string& serial = RuntimeConsoleIdentity::Current().serial;
-    if (!serialAddress || !Memory::Contains(serialAddress, serial.size() + 1)) {
-        return 0;
-    }
-    std::memcpy(Memory::GetPointer(serialAddress, serial.size() + 1),
-                serial.c_str(), serial.size() + 1);
-    return 1;
+    return RuntimeScSerial::Write(serial, serialAddress,
+        [](uint32_t address, size_t size) { return Memory::Contains(address, size); },
+        [](uint32_t address, uint32_t value) { Memory::Write32(address, value); });
 }
 
 PPC_NATIVE_OVERRIDE(801B2460, SCGetProductSN_HLE, uint32_t, (uint32_t serialAddress), (serialAddress));

runtime/src/hle/storage/nand_api.cpp

@@ -3,6 +3,7 @@
 // Shared state and helpers live in nand_internal.h.
 
 #include "nand_internal.h"
+#include "nand_file_ops.h"
 
 // ============================================================================
 // Local helpers
@@ -93,6 +94,9 @@ extern "C" int32_t NANDOpen_HLE(uint32_t pathPtr, uint32_t fileInfoPtr, uint32_t
 
     const std::filesystem::path hostPath = TranslateNandPath(path);
 
+    if (const auto result = NandCheckSystemSaveRead("NANDOpen", hostPath, mode))
+        return *result;
+
     // Existing-file write opens go through a shadow copy seeded from the original, so a
     // crash between NANDWrite and NANDClose cannot leave a torn file (the game patches
     // sub-ranges, e.g. ghost saves at a non-zero offset). New files still create in place.
@@ -375,11 +379,15 @@ extern "C" int32_t NANDMove_HLE(uint32_t srcPathPtr, uint32_t dstPathPtr) {
     }
 
     std::error_code ec;
-    std::filesystem::rename(srcHost, dstHost, ec);
+    NandMove(srcHost, dstHost, ec);
     if (!ec) {
         return NAND_RESULT_OK;
     }
 
+    if (ec == std::errc::file_exists) {
+        return NAND_RESULT_EXISTS;
+    }
+
     LogNandError("NANDMove", "FAILED error=%d message='%s'", ec.value(), ec.message().c_str());
     return NAND_RESULT_UNKNOWN;
 }

runtime/src/hle/storage/nand_async.cpp

@@ -411,6 +411,8 @@ extern "C" int32_t NANDSafeOpen_HLE(uint32_t pathPtr, uint32_t fileInfoPtr, uint
     if (mode == 1) {
         // Read-only safe open reads the original in place; the library builds no scratch
         // copy for this case.
+        if (const auto result = NandCheckSystemSaveRead("NANDSafeOpen", hostPath, mode))
+            return *result;
         FILE* file = NandFopen(hostPath, "rb");
         if (!file && IsFaceLibResourcePath(path) && SeedFaceLibResource(hostPath)) {
             file = NandFopen(hostPath, "rb");

runtime/src/hle/storage/nand_file_ops.cpp

@@ -0,0 +1,115 @@
+#include "nand_file_ops.h"
+
+#include <atomic>
+#include <cerrno>
+#include <chrono>
+#include <filesystem>
+#include <string>
+#include <system_error>
+
+#ifdef _WIN32
+#include <windows.h>
+#elif defined(__linux__)
+#include <fcntl.h>
+#include <linux/fs.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+#elif defined(__APPLE__)
+#include <stdio.h>
+#endif
+
+namespace {
+
+// Unlike std::filesystem::rename on POSIX, this cannot overwrite a destination
+// created by another writer between checking it and publishing the move.
+void RenameNoReplace(const std::filesystem::path& source,
+                     const std::filesystem::path& destination, std::error_code& ec) {
+#ifdef _WIN32
+    if (MoveFileExW(source.c_str(), destination.c_str(), 0)) ec.clear();
+    else ec = std::error_code(GetLastError(), std::system_category());
+#else
+#ifdef __linux__
+    const auto result = syscall(SYS_renameat2, AT_FDCWD, source.c_str(),
+                                AT_FDCWD, destination.c_str(), RENAME_NOREPLACE);
+#else
+    const auto result = renamex_np(source.c_str(), destination.c_str(), RENAME_EXCL);
+#endif
+    if (result == 0) {
+        ec.clear();
+        return;
+    }
+    ec = std::error_code(errno, std::generic_category());
+    if (ec != std::errc::function_not_supported && ec != std::errc::invalid_argument &&
+        ec != std::errc::operation_not_supported) return;
+
+    // Older filesystems may lack exclusive rename. Linking also publishes
+    // without replacement; never fall back to an overwriting rename.
+    std::filesystem::create_hard_link(source, destination, ec);
+    if (!ec) std::filesystem::remove(source, ec);
+#endif
+}
+
+struct StagedMove {
+    std::filesystem::path directory;
+    std::filesystem::path file;
+    ~StagedMove() {
+        std::error_code ignored;
+        std::filesystem::remove(file, ignored);
+        std::filesystem::remove(directory, ignored);
+    }
+};
+
+} // namespace
+
+// NANDMove does not replace an existing entry. Riivolution save redirects can
+// put the destination on a different filesystem from the guest's /tmp files.
+void NandMove(const std::filesystem::path& source, const std::filesystem::path& destination,
+              std::error_code& ec) {
+    namespace fs = std::filesystem;
+    const auto status = fs::symlink_status(destination, ec);
+    if (ec && ec != std::errc::no_such_file_or_directory) return;
+    ec.clear();
+    if (fs::exists(status)) {
+        ec = std::make_error_code(std::errc::file_exists);
+        return;
+    }
+    RenameNoReplace(source, destination, ec);
+    if (ec != std::errc::cross_device_link) return;
+
+    // Do not turn a directory move into a partially completed recursive copy,
+    // or follow a symlink and delete the link after copying its target.
+    const auto sourceStatus = fs::symlink_status(source, ec);
+    if (ec) return;
+    if (!fs::is_regular_file(sourceStatus)) {
+        ec = std::make_error_code(std::errc::cross_device_link);
+        return;
+    }
+
+    static std::atomic<unsigned long long> sequence{0};
+    const auto stamp = std::chrono::steady_clock::now().time_since_epoch().count();
+    fs::path stagingDirectory;
+    bool created = false;
+    for (int attempt = 0; attempt < 64; ++attempt) {
+        stagingDirectory = destination.parent_path() /
+            (".nand-move-" + std::to_string(stamp) + "-" + std::to_string(sequence++));
+        created = fs::create_directory(stagingDirectory, ec);
+        if (created) break;
+        if (ec && ec != std::errc::file_exists) return;
+    }
+    if (!created) {
+        ec = std::make_error_code(std::errc::file_exists);
+        return;
+    }
+
+    const StagedMove staging{stagingDirectory, stagingDirectory / "data"};
+    const auto& staged = staging.file;
+    fs::copy_file(source, staged, fs::copy_options::none, ec);
+    if (!ec) {
+        // Publication is a same-filesystem rename: readers never see a partial
+        // copy. Keep the source until the complete destination is in place.
+        RenameNoReplace(staged, destination, ec);
+        if (!ec) fs::remove(source, ec);
+    }
+    // A failed source removal leaves both complete copies and reports failure.
+    // Staging cleanup preserves ec, including on exceptions.
+}

runtime/src/hle/storage/nand_file_ops.h

@@ -0,0 +1,12 @@
+#pragma once
+
+#include <filesystem>
+#include <system_error>
+
+// Move without replacing an existing entry. Cross-filesystem regular files are
+// staged at the destination before removing the source. On failure the source
+// remains; a failed source removal can leave both complete copies.
+// The caller must keep the source stable for the duration of the move; NAND HLE
+// calls run synchronously on the cooperative guest thread without yielding.
+void NandMove(const std::filesystem::path& source, const std::filesystem::path& destination,
+              std::error_code& ec);

runtime/src/hle/storage/nand_fs.cpp

@@ -411,6 +411,26 @@ bool IsFaceLibResourcePath(const char* path) {
     return std::strcmp(path, "/shared2/menu/FaceLib/RFL_Res.dat") == 0;
 }
 
+std::optional<int32_t> NandCheckSystemSaveRead(const char* who,
+    const std::filesystem::path& hostPath, int mode, bool ios) {
+    const auto action = RuntimeNandSave::CheckRead(hostPath, mode);
+    if (action == RuntimeNandSave::ReadAction::Proceed) return std::nullopt;
+    if (action == RuntimeNandSave::ReadAction::Missing) {
+        LogNandWarning(who, "treating empty or zero-filled system save '%s' as missing",
+                       HostPathText(hostPath).c_str());
+        return ios ? ISFS_ENOENT : NAND_RESULT_NOEXISTS;
+    }
+    if (action == RuntimeNandSave::ReadAction::RecoveryNeeded) {
+        LogNandError(who, "system save '%s' is missing or blank but its .nandsafe.tmp contains data; "
+                         "back up both files before attempting recovery",
+                     HostPathText(hostPath).c_str());
+    } else {
+        LogNandError(who, "could not inspect system save '%s' or its write shadow; leaving data untouched",
+                     HostPathText(hostPath).c_str());
+    }
+    return ios ? ISFS_EIO : NAND_RESULT_UNKNOWN;
+}
+
 // Create directories recursively
 bool CreateDirectoryPath(const std::filesystem::path& path) {
     if (path.empty()) {

runtime/src/hle/storage/nand_internal.h

@@ -9,6 +9,7 @@
 #include "hle/runtime_parse_helpers.h"
 #include "memory.h"
 #include "nand_path.h"
+#include "nand_save_probe.h"
 #include "hle/net/network.h"
 #include "recomp_mod_loader.h"
 #include "runtime_config.h"
@@ -26,6 +27,7 @@
 #include <deque>
 #include <map>
 #include <mutex>
+#include <optional>
 #include <vector>
 #include <filesystem>
 #include <string>
@@ -56,6 +58,11 @@ constexpr uint32_t kNandTitleIdLo = 0x524D4350; // "RMCP" fallback
 void LogNandError(const char* func, const char* fmt, ...);
 void LogNandWarning(const char* func, const char* fmt, ...);
 
+// An empty optional means continue opening normally; otherwise return the
+// supplied NAND/IOS error without exposing a failed scan as a missing save.
+std::optional<int32_t> NandCheckSystemSaveRead(const char* who,
+    const std::filesystem::path& hostPath, int mode, bool ios = false);
+
 // ============================================================================
 // File Descriptor Management
 // ============================================================================

runtime/src/hle/storage/nand_isfs.cpp

@@ -391,6 +391,9 @@ extern "C" int32_t NAND_IOS_Open_HLE(uint32_t pathPtr, uint32_t mode) {
     
     // It's a NAND file path
     const std::filesystem::path hostPath = TranslateNandPath(path);
+
+    if (const auto result = NandCheckSystemSaveRead("IOS_Open", hostPath, mode, true))
+        return *result;
     
     // Seed FaceLib resources before the existence check so every open mode can
     // still find them on a fresh managed NAND.

runtime/src/input_expr.cpp

@@ -9,11 +9,24 @@
 #include <unordered_map>
 
 namespace InputExpr {
+#ifdef MKW_INPUT_EXPR_TEST_CLOCK
+// Only the standalone test target supplies this clock; runtime builds use the
+// steady clock directly, with no mutable override or extra runtime state.
+std::chrono::steady_clock::time_point TestClockNow();
+#endif
 namespace {
 
 using Clock = std::chrono::steady_clock;
 using FSec = std::chrono::duration<double>;
 
+static Clock::time_point Now() {
+#ifdef MKW_INPUT_EXPR_TEST_CLOCK
+    return TestClockNow();
+#else
+    return Clock::now();
+#endif
+}
+
 enum class Kind {
     Literal, Input, Not, Add, Sub, Mul, Div, And, Or, Xor,
     Greater, Less, Equal,
@@ -56,7 +69,7 @@ struct Node {
     mutable bool state = false;
     mutable unsigned taps = 0;
     mutable double value = 0.0;
-    mutable Clock::time_point mark = Clock::now();
+    mutable Clock::time_point mark = Now();
     mutable bool marked = false;
 };
 
@@ -400,7 +413,7 @@ double Eval(const Node& node, const InputSource& source) {
         return std::copysign(std::max(0.0, std::abs(v) - dz) / (1.0 - dz), v);
     }
     case Kind::FnTimer: {
-        const auto now = Clock::now();
+        const auto now = Now();
         if (!node.marked) {
             node.mark = now;
             node.marked = true;
@@ -431,7 +444,7 @@ double Eval(const Node& node, const InputSource& source) {
         return node.state ? 1.0 : 0.0;
     }
     case Kind::FnHold: {
-        const auto now = Clock::now();
+        const auto now = Now();
         if (!node.marked) {
             node.mark = now;
             node.marked = true;
@@ -448,7 +461,7 @@ double Eval(const Node& node, const InputSource& source) {
         return node.state ? 1.0 : 0.0;
     }
     case Kind::FnTap: {
-        const auto now = Clock::now();
+        const auto now = Now();
         if (!node.marked) {
             node.mark = now;
             node.marked = true;
@@ -480,7 +493,7 @@ double Eval(const Node& node, const InputSource& source) {
         return desired == node.taps ? 1.0 : 0.0;
     }
     case Kind::FnPulse: {
-        const auto now = Clock::now();
+        const auto now = Now();
         const double input = Arg(node, 0, source);
         if (input < kConditionThreshold) {
             node.released = true;
@@ -502,7 +515,7 @@ double Eval(const Node& node, const InputSource& source) {
         return node.state ? 1.0 : 0.0;
     }
     case Kind::FnSmooth: {
-        const auto now = Clock::now();
+        const auto now = Now();
         if (!node.marked) {
             node.mark = now;
             node.marked = true;

runtime/src/platform/host_platform.cpp

@@ -46,6 +46,13 @@ std::optional<std::filesystem::path> ExecutableDirectory() noexcept {
     std::error_code ec;
     const auto resolved = std::filesystem::weakly_canonical(path, ec);
     return (ec ? std::filesystem::path(path) : resolved).parent_path();
+#elif defined(__linux__)
+    std::error_code ec;
+    const auto executable = std::filesystem::read_symlink("/proc/self/exe", ec);
+    if (ec) {
+        return std::nullopt;
+    }
+    return executable.parent_path();
 #else
     return std::nullopt;
 #endif

runtime/tests/CMakeLists.txt

@@ -0,0 +1,64 @@
+cmake_minimum_required(VERSION 3.16)
+
+# Share the same test registrations with the full runtime build, while allowing
+# CI and developers to run them without translated game files or Aurora.
+if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+    project(WiiCompiledRuntimeTests LANGUAGES C CXX)
+    enable_testing()
+endif()
+
+get_filename_component(runtime_root "${CMAKE_CURRENT_LIST_DIR}/.." ABSOLUTE)
+find_package(Threads REQUIRED)
+
+function(mkw_add_test name)
+    add_executable(${name} ${ARGN})
+    target_include_directories(${name} PRIVATE "${runtime_root}/include")
+    target_compile_features(${name} PRIVATE cxx_std_17)
+    target_link_libraries(${name} PRIVATE Threads::Threads)
+    add_test(NAME ${name} COMMAND ${name})
+endfunction()
+
+if(NOT TARGET mkw_platform)
+    add_library(mkw_platform STATIC "${runtime_root}/src/platform/host_platform.cpp")
+    target_include_directories(mkw_platform PUBLIC "${runtime_root}/include")
+    target_compile_features(mkw_platform PUBLIC cxx_std_17)
+endif()
+if(WIN32)
+    target_link_libraries(mkw_platform PUBLIC shell32 ole32)
+endif()
+mkw_add_test(mkw_platform_paths_tests platform_paths_tests.cpp)
+target_link_libraries(mkw_platform_paths_tests PRIVATE mkw_platform)
+
+mkw_add_test(mkw_nand_save_tests nand_save_tests.cpp)
+mkw_add_test(mkw_nand_move_tests nand_move_tests.cpp
+    "${runtime_root}/src/hle/storage/nand_file_ops.cpp")
+target_include_directories(mkw_nand_move_tests PRIVATE "${runtime_root}/src/hle/storage")
+mkw_add_test(mkw_nand_settings_tests nand_settings_tests.cpp)
+mkw_add_test(mkw_sc_serial_tests sc_serial_tests.cpp)
+mkw_add_test(mkw_input_expr_tests test_expr.cpp "${runtime_root}/src/input_expr.cpp")
+target_compile_definitions(mkw_input_expr_tests PRIVATE MKW_INPUT_EXPR_TEST_CLOCK)
+
+if(WIN32)
+    mkw_add_test(mkw_windows_host_context_tests host_context_tests.cpp
+        "${runtime_root}/src/host_context.cpp")
+elseif(CMAKE_SYSTEM_NAME STREQUAL "Linux")
+    if(NOT TARGET mkw::libco)
+        add_library(mkw_libco STATIC "${runtime_root}/third_party/libco/libco.c")
+        add_library(mkw::libco ALIAS mkw_libco)
+        target_include_directories(mkw_libco PUBLIC "${runtime_root}/third_party/libco")
+    endif()
+    mkw_add_test(mkw_linux_host_context_tests host_context_tests.cpp
+        "${runtime_root}/src/host_context.cpp")
+    target_link_libraries(mkw_linux_host_context_tests PRIVATE mkw::libco)
+elseif(APPLE)
+    if(NOT CMAKE_SYSTEM_PROCESSOR MATCHES "^(arm64|ARM64|aarch64)$")
+        message(FATAL_ERROR "The macOS runtime tests require Apple Silicon")
+    endif()
+    enable_language(ASM)
+    set(context_asm "${runtime_root}/src/platform/macos/co_switch.S")
+    mkw_add_test(mkw_macos_context_abi_tests macos_context_abi_tests.cpp "${context_asm}")
+    mkw_add_test(mkw_macos_host_context_tests host_context_tests.cpp
+        "${runtime_root}/src/host_context.cpp" "${context_asm}")
+    mkw_add_test(mkw_macos_guest_flat_memory_tests macos_guest_flat_memory_tests.cpp
+        "${runtime_root}/src/guest_flat_memory_macos.cpp")
+endif()

runtime/tests/nand_move_tests.cpp

@@ -0,0 +1,181 @@
+#include "nand_file_ops.h"
+
+#include <atomic>
+#include <chrono>
+#include <fstream>
+#include <functional>
+#include <iterator>
+#include <string>
+#include <thread>
+#include <iostream>
+#include <stdexcept>
+
+#ifdef __linux__
+#include <csignal>
+#include <sys/resource.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#endif
+
+namespace fs = std::filesystem;
+
+static void Require(bool condition, const char* message) {
+    if (!condition) throw std::runtime_error(message);
+}
+
+static void Write(const fs::path& path, const std::string& data) {
+    std::ofstream output(path, std::ios::binary);
+    output << data;
+    output.close();
+    Require(bool(output), "Fixture write failed");
+}
+
+static std::string Read(const fs::path& path) {
+    std::ifstream input(path, std::ios::binary);
+    Require(bool(input), "Fixture read failed");
+    return {std::istreambuf_iterator<char>(input), std::istreambuf_iterator<char>()};
+}
+
+// Competing moves must have exactly one winner, retain the losing source, and
+// publish the winner's complete contents. Exercise both direct and staged moves.
+static void CheckCompetingMoves(const fs::path& sourceRoot, const fs::path& destinationRoot) {
+    const auto left = sourceRoot / "race-left";
+    const auto right = sourceRoot / "race-right";
+    const auto target = destinationRoot / "race-target";
+    const std::string leftBytes(65536, 'L'), rightBytes(65536, 'R');
+    for (int attempt = 0; attempt < 128; ++attempt) {
+        Write(left, leftBytes);
+        Write(right, rightBytes);
+        std::atomic<int> ready{0};
+        std::error_code leftError, rightError;
+        auto move = [&](const fs::path& source, std::error_code& ec) {
+            ++ready;
+            while (ready.load() != 2) std::this_thread::yield();
+            NandMove(source, target, ec);
+        };
+        std::thread first(move, std::cref(left), std::ref(leftError));
+        std::thread second(move, std::cref(right), std::ref(rightError));
+        first.join();
+        second.join();
+        Require(bool(leftError) != bool(rightError), "Competing moves must have exactly one winner");
+        const bool leftWon = !leftError;
+        Require((leftWon ? rightError : leftError) == std::errc::file_exists,
+                "Losing move must report an existing destination");
+        Require(Read(target) == (leftWon ? leftBytes : rightBytes), "Winner's contents were overwritten");
+        Require(!fs::exists(leftWon ? left : right), "Winning source was not removed");
+        Require(Read(leftWon ? right : left) == (leftWon ? rightBytes : leftBytes),
+                "Losing source must remain intact");
+        fs::remove(leftWon ? right : left);
+        fs::remove(target);
+    }
+}
+
+int main() {
+    const auto name = "wiicomp-nand-move-" +
+        std::to_string(std::chrono::steady_clock::now().time_since_epoch().count());
+    const auto root = fs::temp_directory_path() / name;
+    fs::path other;
+    try {
+        fs::create_directory(root);
+        const auto source = root / "banner.bin";
+        const auto destination = root / "moved.bin";
+        std::error_code ec;
+        Write(source, "banner");
+        NandMove(source, destination, ec);
+        Require(!ec && !fs::exists(source) && Read(destination) == "banner", "Same-device move failed");
+        CheckCompetingMoves(root, root);
+        Write(source, "keep source");
+        NandMove(source, destination, ec);
+        Require(ec == std::errc::file_exists && Read(source) == "keep source" && Read(destination) == "banner",
+                "Existing destination must not be overwritten");
+        NandMove(root / "missing", root / "absent", ec);
+        Require(bool(ec) && !fs::exists(root / "absent"), "Missing source must fail");
+        NandMove(source, root / "missing-parent/file", ec);
+        Require(bool(ec) && Read(source) == "keep source", "Missing parent must preserve source");
+        fs::create_directory(root / "directory");
+        Write(root / "directory/child", "child");
+        NandMove(root / "directory", root / "renamed-directory", ec);
+        Require(!ec && Read(root / "renamed-directory/child") == "child", "Same-device directory move regressed");
+
+#ifndef _WIN32
+        fs::create_symlink(root / "missing", root / "same-link");
+        NandMove(root / "same-link", root / "moved-link", ec);
+        Require(!ec && fs::is_symlink(fs::symlink_status(root / "moved-link")) &&
+                !fs::is_symlink(fs::symlink_status(root / "same-link")), "Same-device symlink move regressed");
+#endif
+
+#ifdef __linux__
+        // /dev/shm is a separate tmpfs on ordinary Linux systems, including CI
+        // and WSL. Fail rather than silently passing without exercising EXDEV.
+        other = fs::path("/dev/shm") / name;
+        fs::create_directory(other);
+        struct stat left{}, right{};
+        Require(::stat(root.c_str(), &left) == 0 && ::stat(other.c_str(), &right) == 0 && left.st_dev != right.st_dev,
+                "Cross-device test requires /tmp and /dev/shm on separate filesystems");
+        CheckCompetingMoves(root, other);
+        Require(fs::is_empty(other), "Competing moves left staging files behind");
+        const auto target = other / "banner.bin";
+        const std::string bytes = std::string(8192, '\0') + "banner payload";
+        Write(source, bytes);
+        fs::rename(source, target, ec);
+        Require(ec == std::errc::cross_device_link, "Fixture must reproduce the original EXDEV failure");
+        NandMove(source, target, ec);
+        Require(!ec && !fs::exists(source) && Read(target) == bytes, "Cross-device move must preserve every byte");
+
+        Write(source, "do not overwrite");
+        NandMove(source, target, ec);
+        Require(ec == std::errc::file_exists && Read(source) == "do not overwrite" && Read(target) == bytes,
+                "Cross-device move must preserve an existing destination");
+        fs::remove(target);
+        fs::create_symlink(other / "missing", target);
+        NandMove(source, target, ec);
+        Require(ec == std::errc::file_exists && fs::is_symlink(target) && Read(source) == "do not overwrite",
+                "Dangling destination symlink must not be replaced");
+        fs::remove(target);
+
+        NandMove(root / "renamed-directory", other / "directory", ec);
+        Require(ec == std::errc::cross_device_link && Read(root / "renamed-directory/child") == "child" &&
+                !fs::exists(other / "directory"), "Unsupported directory move must leave source intact");
+        fs::create_symlink(source, root / "link");
+        NandMove(root / "link", other / "link", ec);
+        Require(ec == std::errc::cross_device_link && fs::is_symlink(root / "link") && !fs::exists(other / "link"),
+                "Cross-device source symlinks must not be dereferenced");
+
+        // Force a real write failure after a partial copy without filling disk.
+        Write(source, bytes);
+        struct rlimit saved{}, limited{};
+        Require(getrlimit(RLIMIT_FSIZE, &saved) == 0, "Cannot read file-size limit");
+        limited = saved;
+        limited.rlim_cur = 1024;
+        const auto oldHandler = std::signal(SIGXFSZ, SIG_IGN);
+        Require(setrlimit(RLIMIT_FSIZE, &limited) == 0, "Cannot set file-size limit");
+        NandMove(source, target, ec);
+        const auto copyError = ec;
+        const auto restored = setrlimit(RLIMIT_FSIZE, &saved);
+        std::signal(SIGXFSZ, oldHandler);
+        Require(restored == 0, "Cannot restore file-size limit");
+        Require(bool(copyError) && Read(source) == bytes && !fs::exists(target) && fs::is_empty(other),
+                "Failed copy must retain source and remove partial staging files");
+
+        Require(geteuid() != 0, "Run permission tests as an unprivileged user");
+        fs::permissions(root, fs::perms::owner_read | fs::perms::owner_exec);
+        NandMove(source, target, ec);
+        fs::permissions(root, fs::perms::owner_all);
+        Require(bool(ec) && Read(source) == bytes && Read(target) == bytes,
+                "Failed source deletion must leave both complete copies");
+        Require(std::distance(fs::directory_iterator(other), fs::directory_iterator{}) == 1,
+                "Move must clean up staging directory");
+        fs::remove_all(other);
+#endif
+        fs::remove_all(root);
+        std::cout << "NAND move tests passed\n";
+        return 0;
+    } catch (const std::exception& error) {
+        std::cerr << error.what() << '\n';
+        std::error_code ignored;
+        fs::permissions(root, fs::perms::owner_all, ignored);
+        fs::remove_all(root, ignored);
+        if (!other.empty()) fs::remove_all(other, ignored);
+        return 1;
+    }
+}

runtime/tests/nand_save_tests.cpp

@@ -0,0 +1,142 @@
+#include "nand_save_probe.h"
+
+#include <algorithm>
+#include <chrono>
+#include <iostream>
+#include <sstream>
+#include <stdexcept>
+
+#ifdef _WIN32
+#include <windows.h>
+#endif
+
+namespace fs = std::filesystem;
+using RuntimeNandSave::ReadAction;
+using RuntimeNandSave::Contents;
+
+static void Require(bool condition, const char* message) {
+    if (!condition) throw std::runtime_error(message);
+}
+
+static void Write(const fs::path& path, const std::string& bytes) {
+    fs::create_directories(path.parent_path());
+    std::ofstream output(path, std::ios::binary);
+    output.write(bytes.data(), bytes.size());
+    output.close();
+    Require(static_cast<bool>(output), "Fixture write failed");
+}
+
+static std::string Read(const fs::path& path) {
+    std::ifstream input(path, std::ios::binary);
+    Require(static_cast<bool>(input), "Fixture read failed");
+    return {std::istreambuf_iterator<char>(input), std::istreambuf_iterator<char>()};
+}
+
+// A disk error after zero-filled blocks must not look like a blank file's EOF.
+class FailingDisk : public std::streambuf {
+    int blocks;
+public:
+    explicit FailingDisk(int zeroBlocks) : blocks(zeroBlocks) {}
+    std::streamsize xsgetn(char* buffer, std::streamsize length) override {
+        if (blocks-- <= 0) throw std::runtime_error("injected read failure");
+        std::fill(buffer, buffer + length, '\0');
+        return length;
+    }
+};
+
+int main() {
+    const auto root = fs::temp_directory_path() / ("wiicomp-save-scenarios-" +
+        std::to_string(std::chrono::steady_clock::now().time_since_epoch().count()));
+    try {
+        const auto save = root / "title/00010004/524d4350/data/rksys.dat";
+        const auto shadow = fs::path(save.native() + fs::path(".nandsafe.tmp").native());
+        // Save inspection must leave unrelated NAND data alone. Settings
+        // initialization is covered separately by nand_settings_tests.
+        const auto settingsPath = root / "title/00000001/00000002/data/setting.txt";
+        const std::string identity(256, '\x5a');
+        Write(settingsPath, identity);
+        Require(RuntimeNandSave::CheckRead(save, 1) == ReadAction::Proceed, "Fresh profile follows normal missing-file handling");
+        Require(!fs::exists(save), "Probing fresh profile must not create a save");
+
+        // First launch interrupted before save initialization, including block
+        // boundaries and a full-sized synthetic zero-filled allocation.
+        for (const size_t size : {size_t(0), size_t(1), size_t(4095), size_t(4096), size_t(4097), size_t(3 * 1024 * 1024)}) {
+            const std::string bytes(size, '\0');
+            Write(save, bytes);
+            Require(RuntimeNandSave::CheckRead(save, 1) == ReadAction::Missing, "Blank save should be offered first-save recovery");
+            Require(Read(save) == bytes, "Blank-save detection must not modify the file");
+            for (int mode : {2, 3}) {
+                Require(RuntimeNandSave::CheckRead(save, mode) == ReadAction::Proceed, "Write opens must remain available for initialization");
+            }
+        }
+
+        // Existing saves, imported saves, partial/corrupt saves, and a zero
+        // prefix with data only in the final byte are all left to the game.
+        std::string existing(3 * 1024 * 1024, '\0');
+        existing.replace(0, 8, "RKSD0006");
+        existing[10000] = 42;
+        for (const std::string& bytes : {existing, std::string("RKSD"), std::string("damaged-header"),
+                 std::string(8192, '\0') + "x", std::string(8191, '\0') + "x"}) {
+            Write(save, bytes);
+            Require(RuntimeNandSave::CheckRead(save, 1) == ReadAction::Proceed, "Never hide a save containing any data");
+            Require(Read(save) == bytes, "Existing/partial save must be byte-identical after inspection");
+        }
+
+        // Interrupted replacement: retain a committed original regardless of
+        // whether the shadow is blank, partial, or contains a complete header.
+        Write(save, existing);
+        for (const std::string& bytes : {std::string(), std::string(4096, '\0'), std::string("RKSD"), existing}) {
+            Write(shadow, bytes);
+            Require(RuntimeNandSave::CheckRead(save, 1) == ReadAction::Proceed, "Committed original takes precedence over write shadow");
+            Require(Read(save) == existing && Read(shadow) == bytes, "Probe must preserve both sides of an interrupted write");
+        }
+        // No usable original: do not let missing-save recovery discard the
+        // only possible recovery source, and do not auto-promote that shadow.
+        for (const bool mainExists : {false, true}) {
+            fs::remove(save);
+            if (mainExists) Write(save, std::string(4096, '\0'));
+            Write(shadow, existing);
+            Require(RuntimeNandSave::CheckRead(save, 1) == ReadAction::RecoveryNeeded, "Preserve recovery candidate when original is missing or blank");
+            Require(Read(shadow) == existing, "Recovery candidate must remain unchanged");
+            Require(fs::exists(save) == mainExists, "Do not promote shadow automatically");
+        }
+        Write(shadow, std::string(4096, '\0'));
+        Require(RuntimeNandSave::CheckRead(save, 1) == ReadAction::Missing, "Two blank files may use first-save recovery");
+        fs::remove(shadow);
+
+        for (const char* name : {"rksys.dat.bak", "rksys.dat.backup", "rksys.dat2", "banner.bin", "setting.txt"}) {
+            const auto unrelated = save.parent_path() / name;
+            Write(unrelated, std::string(4096, '\0'));
+            Require(RuntimeNandSave::CheckRead(unrelated, 1) == ReadAction::Proceed, "Do not classify backups or unrelated files as missing saves");
+        }
+        for (int blocks : {0, 1, 2}) {
+            FailingDisk disk(blocks);
+            std::istream input(&disk);
+            Require(RuntimeNandSave::InspectStream(input) == Contents::Error, "Read failure must remain an error, including after zero-filled blocks");
+        }
+        std::istringstream badEof;
+        badEof.setstate(std::ios::badbit | std::ios::eofbit);
+        Require(RuntimeNandSave::InspectStream(badEof) == Contents::Error, "Badbit plus EOF must not imply a blank save");
+
+#ifdef _WIN32
+        Write(save, existing);
+        const HANDLE locked = CreateFileW(save.c_str(), GENERIC_READ, 0, nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
+        Require(locked != INVALID_HANDLE_VALUE, "Could not lock fixture");
+        const auto lockedResult = RuntimeNandSave::CheckRead(save, 1);
+        CloseHandle(locked);
+        Require(lockedResult == ReadAction::Error, "Sharing/access failure must not report a missing save");
+        Require(Read(save) == existing, "Locked save must survive inspection unchanged");
+        Require(SetFileAttributesW(save.c_str(), FILE_ATTRIBUTE_READONLY) != 0, "Set fixture read-only");
+        const auto readOnlyResult = RuntimeNandSave::CheckRead(save, 1);
+        SetFileAttributesW(save.c_str(), FILE_ATTRIBUTE_NORMAL);
+        Require(readOnlyResult == ReadAction::Proceed && Read(save) == existing, "Readable read-only save remains available");
+#endif
+        Require(Read(settingsPath) == identity, "Save inspection must not change NAND settings");
+        fs::remove_all(root);
+        std::cout << "NAND save startup, preservation, interrupted-write and I/O failure scenarios passed\n";
+        return 0;
+    } catch (const std::exception& error) {
+        std::cerr << error.what() << " (fixtures retained at " << root << ")\n";
+        return 1;
+    }
+}

runtime/tests/nand_settings_tests.cpp

@@ -3,22 +3,78 @@
 #include <chrono>
 #include <iostream>
 #include <stdexcept>
+#include <thread>
+#include <vector>
 
-static void Require(bool condition) {
+static void Require(bool condition, const char* message = "NAND settings check failed") {
     if (!condition) {
-        throw std::runtime_error("NAND settings check failed");
+        throw std::runtime_error(message);
     }
 }
 
+static std::string ReadBytes(const std::filesystem::path& path) {
+    std::ifstream input(path, std::ios::binary);
+    return {std::istreambuf_iterator<char>(input), std::istreambuf_iterator<char>()};
+}
+
 int main() {
     const auto root = std::filesystem::temp_directory_path() /
         ("wiicomp-nand-settings-" + std::to_string(
             std::chrono::steady_clock::now().time_since_epoch().count()));
     const auto path = root / "title/00000001/00000002/data/setting.txt";
     try {
+        using namespace RuntimeNandSettings;
+        Require(GenerateSerial(1800000123) == "800000123", "Dolphin timestamp modulo");
+        Require(GenerateSerial(1000000001) == "000000001", "Dolphin leading zero padding");
+        Require(GenerateSerial(-1).empty(), "Invalid clock must not supply an identity");
+        // Golden bytes generated by Dolphin's unmodified SettingsHandler.cpp
+        // (upstream 2026-09-06), PAL boot fields and synthetic serial 000000001.
+        // Everything after this prefix is raw zero padding to 256 bytes.
+        const std::string goldenHex =
+            "bba6ac929a0bc96b7eed83d27f33a1e7e73d9b836d8b47c59ee23df6b275baab"
+            "bec9d9dead03cc7a3bdafee50c30ab9fb86194e119fe4ba19eff62d5ec3aacb3"
+            "b5c9d9e3977eac0943d7ff903120a49ef024eafe1cf77be79cf6229a823aabf0f0";
+        std::array<uint8_t, 256> golden{};
+        for (size_t i = 0; i < goldenHex.size() / 2; ++i) {
+            golden[i] = static_cast<uint8_t>(std::stoul(goldenHex.substr(i * 2, 2), nullptr, 16));
+        }
+        Require(EncodeNew("000000001") == golden, "Exact Dolphin writer golden fixture");
+        std::string error;
         Require(!RuntimeNandSettings::Read(root));
         Require(!std::filesystem::exists(root));
         std::filesystem::create_directories(path.parent_path());
+        const auto scratchParent = root / "scratch-collisions";
+        std::filesystem::create_directories(scratchParent / ".setting-init-fixed-0");
+        const auto sentinel = scratchParent / ".setting-init-fixed-0" / "setting.txt";
+        { std::ofstream output(sentinel); output << "another launch owns this"; }
+        const auto occupiedFile = scratchParent / ".setting-init-fixed-1";
+        { std::ofstream output(occupiedFile); output << "leave this file alone"; }
+        std::error_code scratchError;
+        const auto claimed = CreateScratchDirectory(scratchParent, "fixed", scratchError);
+        Require(claimed && *claimed == scratchParent / ".setting-init-fixed-2" && !scratchError,
+                "Retry collisions with both existing directories and files");
+        Require(ReadBytes(sentinel) == "another launch owns this" &&
+                ReadBytes(occupiedFile) == "leave this file alone", "Never modify another launch's scratch data");
+        Require(!CreateScratchDirectory(occupiedFile / "not-a-directory", "fixed", scratchError) && scratchError,
+                "Real filesystem errors must fail rather than retry indefinitely");
+
+        // Force all claimants to use the same token; this deterministically
+        // exercises the collision path even when host clock precision is high.
+        std::array<std::optional<std::filesystem::path>, 16> claims;
+        std::vector<std::thread> claimants;
+        for (size_t i = 0; i < claims.size(); ++i) {
+            claimants.emplace_back([&, i] {
+                std::error_code ec;
+                claims[i] = CreateScratchDirectory(scratchParent, "shared", ec);
+            });
+        }
+        for (auto& claimant : claimants) claimant.join();
+        for (size_t i = 0; i < claims.size(); ++i) {
+            Require(claims[i].has_value(), "Every concurrent claimant must acquire a scratch directory");
+            for (size_t j = 0; j < i; ++j) {
+                Require(claims[i] != claims[j], "Concurrent claimants must own different scratch directories");
+            }
+        }
         const std::string plain = "AREA=USA\r\n\nCODE=LU\r\nSERNO=987654321\r\nGAME=US\r\n";
         std::array<uint8_t, 256> fixture{};
         for (size_t i = 0; i < fixture.size(); ++i) {
@@ -35,6 +91,7 @@ int main() {
         Require(settings && RuntimeNandSettings::HasIdentity(*settings));
         Require(settings->at("SERNO") == "987654321" && settings->at("CODE") == "LU");
         Require(settings->at("AREA") == "USA" && settings->at("GAME") == "US");
+        Require(Ensure(root, error, 1800000123), "Existing imported NAND must work");
         std::array<uint8_t, 256> after{};
         {
             std::ifstream input(path, std::ios::binary);
@@ -54,6 +111,67 @@ int main() {
         Require(!RuntimeNandSettings::HasIdentity(*settings));
         std::filesystem::resize_file(path, 128);
         Require(!RuntimeNandSettings::Read(root));
+        const auto damaged = ReadBytes(path);
+        Require(!Ensure(root, error, 1800000123), "Do not replace a truncated identity");
+        Require(ReadBytes(path) == damaged, "Damaged file must remain untouched");
+
+        const auto fresh = root / "fresh";
+        Require(Ensure(fresh, error, 1800000123), "Missing setting.txt must initialize");
+        const auto generated = Read(fresh);
+        Require(generated && HasIdentity(*generated), "Generated file must be readable");
+        Require(generated->at("SERNO") == "800000123", "Persist Dolphin-generated serial");
+        Require(generated->at("CODE") == "LEH" && generated->at("AREA") == "EUR" &&
+                generated->at("GAME") == "EU", "PAL first-boot fields");
+        Require(generated->at("MODEL") == "RVL-001(EUR)" && generated->at("VIDEO") == "PAL" &&
+                generated->at("DVD") == "0" && generated->at("MPCH") == "0x7FFE",
+                "Complete Dolphin boot settings");
+        const auto firstBoot = ReadBytes(FilePath(fresh));
+        Require(firstBoot.size() == 256 && firstBoot.back() == 0, "Dolphin buffer size and raw zero padding");
+        Require(Ensure(fresh, error, 1900000999), "Second boot");
+        Require(ReadBytes(FilePath(fresh)) == firstBoot, "Second boot must not change any bytes");
+
+        const auto blocked = root / "blocked";
+        { std::ofstream output(blocked); output << "file obstructing NAND directory"; }
+        Require(!Ensure(blocked, error, 1800000123), "Write failure must not return an ephemeral identity");
+        Require(!Ensure(root / "bad-clock", error, -1), "Clock failure must not initialize");
+
+        const auto concurrent = root / "concurrent";
+        std::array<bool, 16> results{};
+        std::vector<std::thread> workers;
+        for (size_t i = 0; i < results.size(); ++i) {
+            workers.emplace_back([&, i] {
+                std::string detail;
+                results[i] = Ensure(concurrent, detail, 1800000001 + i);
+            });
+        }
+        for (auto& worker : workers) worker.join();
+        for (const bool result : results) Require(result, "Concurrent boot must read the persisted winner");
+        const auto winner = ReadBytes(FilePath(concurrent));
+        Require(Read(concurrent) && HasIdentity(*Read(concurrent)), "Concurrent boot must persist valid settings");
+        Require(Ensure(concurrent, error, 1900000999), "Boot after concurrent initialization");
+        Require(ReadBytes(FilePath(concurrent)) == winner, "Concurrent winner must remain stable");
+
+        // Independently decode as Nintendo does: stop at the first encoded NUL.
+        // Exercise serials that force Dolphin's extra-LF escaping, not only
+        // values that happen to work with a plain rotating-XOR encoder.
+        bool sawExtraLf = false;
+        for (int serial = 1; serial <= 10000; ++serial) {
+            const auto number = GenerateSerial(1000000000 + serial);
+            const auto encoded = EncodeNew(number);
+            Require(encoded.has_value(), "Serial encoding must fit");
+            std::string decoded;
+            for (size_t i = 0; i < encoded->size() && (*encoded)[i] != 0; ++i) {
+                const unsigned shift = i % 32;
+                const uint32_t key = shift == 0 ? 0x73B5DBFAu :
+                    (0x73B5DBFAu << shift) | (0x73B5DBFAu >> (32 - shift));
+                decoded += static_cast<char>((*encoded)[i] ^ static_cast<uint8_t>(key));
+            }
+            Require(decoded.find("SERNO=" + number + "\r\n") != std::string::npos &&
+                    decoded.find("GAME=EU\r\n") != std::string::npos,
+                    "Encoded NUL must not truncate settings");
+            sawExtraLf |= decoded.find("\r\n\n") != std::string::npos;
+        }
+        Require(sawExtraLf, "Exercise Dolphin LF escape path");
         std::filesystem::remove_all(root);
         std::cout << "NAND settings checks passed\n";
         return 0;

runtime/tests/sc_serial_tests.cpp

@@ -0,0 +1,81 @@
+#include "sc_serial_contract.h"
+#include "nand_settings.h"
+
+#include <algorithm>
+#include <array>
+#include <iostream>
+#include <iomanip>
+#include <stdexcept>
+#include <string>
+
+static void Require(bool condition, const char* message) {
+    if (!condition) throw std::runtime_error(message);
+}
+
+static uint32_t ReadWord(const unsigned char* bytes) {
+    return (uint32_t(bytes[0]) << 24) | (uint32_t(bytes[1]) << 16) |
+           (uint32_t(bytes[2]) << 8) | uint32_t(bytes[3]);
+}
+
+int main(int argc, char** argv) {
+    try {
+        // Feed real generator + SC ABI outputs to the upstream bot decoder.
+        // Usage: mkw_sc_serial_tests --timestamp-vectors <unix-seconds> ...
+        if (argc > 1 && std::string(argv[1]) == "--timestamp-vectors") {
+            for (int i = 2; i < argc; ++i) {
+                const auto timestamp = std::stoll(argv[i]);
+                const auto serial = RuntimeNandSettings::GenerateSerial(static_cast<std::time_t>(timestamp));
+                std::array<unsigned char, 4> output{};
+                Require(RuntimeScSerial::Write(serial, 4,
+                    [](uint32_t address, size_t size) { return address == 4 && size == 4; },
+                    [&](uint32_t, uint32_t value) {
+                        for (unsigned j = 0; j < 4; ++j)
+                            output[j] = static_cast<unsigned char>(value >> (24 - 8 * j));
+                    }) == 1, "Generated serial must pass SC ABI");
+                std::cout << timestamp << '\t' << serial << "\tLEH"
+                          << std::setfill('0') << std::setw(9) << ReadWord(output.data()) << '\n';
+            }
+            return 0;
+        }
+        // Reproduce the reported csnums from the old string-writing override.
+        const unsigned char old7886[] = {'7', '8', '8', '6'};
+        const unsigned char old7618[] = {'7', '6', '1', '8'};
+        Require(ReadWord(old7886) == 926431286, "Reproduce shared LEH926431286");
+        Require(ReadWord(old7618) == 926298424, "Reproduce shared LEH926298424");
+
+        std::array<unsigned char, 16> memory;
+        size_t available = 4;
+        unsigned writes = 0;
+        const auto contains = [&](uint32_t address, size_t size) {
+            return address == 4 && size <= available;
+        };
+        const auto write32 = [&](uint32_t address, uint32_t value) {
+            ++writes;
+            for (unsigned i = 0; i < 4; ++i)
+                memory[address + i] = static_cast<unsigned char>(value >> (24 - 8 * i));
+        };
+        for (const auto& pair : {std::pair{"788600001", 788600001u}, {"788699999", 788699999u},
+                 {"761800001", 761800001u}, {"761899999", 761899999u},
+                 {"012345678", 12345678u}, {"000000001", 1u}, {"999999999", 999999999u}}) {
+            memory.fill(0xa5);
+            writes = 0;
+            Require(RuntimeScSerial::Write(pair.first, 4, contains, write32) == 1, "Accept an exactly four-byte output buffer");
+            Require(writes == 1 && ReadWord(memory.data() + 4) == pair.second, "Return full numeric serial, including digits after common prefix");
+            for (size_t i = 0; i < memory.size(); ++i)
+                if (i < 4 || i >= 8) Require(memory[i] == 0xa5, "Do not overwrite adjacent guest stack data");
+        }
+        for (const char* serial : {"", "1234567890", "7886x1234", "-12345678", "+12345678"}) {
+            writes = 0;
+            Require(RuntimeScSerial::Write(serial, 4, contains, write32) == 0 && writes == 0, "Reject malformed serial without a write");
+        }
+        writes = 0;
+        Require(RuntimeScSerial::Write("788600001", 0, contains, write32) == 0 && writes == 0, "Reject null output");
+        available = 3;
+        Require(RuntimeScSerial::Write("788600001", 4, contains, write32) == 0 && writes == 0, "Reject undersized output");
+        std::cout << "SC serial collision reproduction, numeric output and memory-boundary tests passed\n";
+        return 0;
+    } catch (const std::exception& error) {
+        std::cerr << error.what() << '\n';
+        return 1;
+    }
+}

runtime/tests/test_expr.cpp

@@ -8,7 +8,14 @@
 #include <cstdio>
 #include <map>
 #include <string>
-#include <thread>
+#ifndef MKW_INPUT_EXPR_TEST_CLOCK
+#error "Build this test through CMake so the deterministic clock is enabled"
+#endif
+
+static std::chrono::steady_clock::time_point g_now{};
+namespace InputExpr {
+std::chrono::steady_clock::time_point TestClockNow() { return g_now; }
+}
 
 static int g_failures = 0;
 static std::map<std::string, double> g_inputs;
@@ -41,7 +48,7 @@ static bool Pressed(const InputExpr::Expression& e) {
     return e.Evaluate(Source()) > InputExpr::kConditionThreshold;
 }
 
-static void Sleep(int ms) { std::this_thread::sleep_for(std::chrono::milliseconds(ms)); }
+static void AdvanceTime(int ms) { g_now += std::chrono::milliseconds(ms); }
 
 int main() {
     std::printf("Dolphin expression engine\n");
@@ -82,7 +89,7 @@ int main() {
     auto hold = Compile("hold(`H`, 0.05)");
     g_inputs["H"] = 1.0;
     Check(!Pressed(hold), "hold not satisfied immediately");
-    Sleep(70);
+    AdvanceTime(70);
     Check(Pressed(hold), "hold satisfied after the interval");
     g_inputs["H"] = 0.0;
     Check(!Pressed(hold), "hold clears on release");
@@ -93,7 +100,7 @@ int main() {
     pulse.Evaluate(Source());
     g_inputs["P"] = 1.0;
     Check(Pressed(pulse), "pulse fires on rising edge");
-    Sleep(80);
+    AdvanceTime(80);
     Check(!Pressed(pulse), "pulse expires");
 
     // The timing-window idiom seen in shared Dolphin configs.
@@ -102,9 +109,9 @@ int main() {
     window.Evaluate(Source());
     g_inputs["W"] = 1.0;
     Check(!Pressed(window), "window closed before its start");
-    Sleep(90);
+    AdvanceTime(90);
     Check(Pressed(window), "window open between the two pulses");
-    Sleep(90);
+    AdvanceTime(90);
     Check(!Pressed(window), "window closed after its end");
 
     // timer ramps 0..1 and wraps, so a threshold turns it into a square wave.
@@ -114,7 +121,7 @@ int main() {
     int low = 0;
     for (int i = 0; i < 40; ++i) {
         (Pressed(timer) ? high : low)++;
-        Sleep(5);
+        AdvanceTime(5);
     }
     Check(high > 5 && low > 5, "timer alternates high and low");
 
@@ -130,7 +137,7 @@ int main() {
     high = low = 0;
     for (int i = 0; i < 60; ++i) {
         (Pressed(dolphinLine) ? high : low)++;
-        Sleep(2);
+        AdvanceTime(2);
     }
     Check(high > 5 && low > 5, "LB alternates via timer(0.01)");
 
@@ -192,7 +199,7 @@ int main() {
         auto sm = Compile("smooth(`A`, 0)");
         g_inputs["A"] = 1.0;
         sm.Evaluate(Source());
-        Sleep(5);
+        AdvanceTime(5);
         Check(std::isfinite(sm.Evaluate(Source())), "smooth with a zero rate stays finite");
     }