@@ -15,6 +15,10 @@ on:
       - 'vm/**'
       - 'Ports/WindowsPort/**'
       - 'maven/windows/**'
+      - 'scripts/gen-windows-uwp-stubs.py'
+      - 'maven/build-engine/src/main/java/com/codename1/builders/WindowsNativeBuilder.java'
+      - 'maven/build-engine/src/test/java/com/codename1/builders/WindowsNativeBuilderArchTest.java'
+      - 'maven/build-engine/src/test/resources/com/codename1/builders/xbox-smoke-AppxManifest.xml'
       - '!vm/**/README.md'
       - '!vm/**/readme.md'
       - '!vm/**/docs/**'
@@ -25,6 +29,10 @@ on:
       - 'vm/**'
       - 'Ports/WindowsPort/**'
       - 'maven/windows/**'
+      - 'scripts/gen-windows-uwp-stubs.py'
+      - 'maven/build-engine/src/main/java/com/codename1/builders/WindowsNativeBuilder.java'
+      - 'maven/build-engine/src/test/java/com/codename1/builders/WindowsNativeBuilderArchTest.java'
+      - 'maven/build-engine/src/test/resources/com/codename1/builders/xbox-smoke-AppxManifest.xml'
 
 concurrency:
   # Only the latest revision needs validation. PR numbers keep forks isolated;
@@ -155,13 +163,156 @@ jobs:
           test -f core/target/classes/com/codename1/ui/Form.class
           test -f windows/target/classes/com/codename1/impl/windows/WindowsImplementation.class
 
+      # A UWP (Xbox Developer Mode) build compiles the desktop-only natives
+      # out and links generated stubs in their place; a native added to one of
+      # those files without regenerating would fail only the UWP link below.
+      - name: UWP stubs are current
+        run: python3 scripts/gen-windows-uwp-stubs.py --check
+
+      # Builds the desktop exe and the UWP one (app partition, WindowsApp.lib
+      # only, /APPCONTAINER): the UWP link is the gate that every Win32 call the
+      # port makes in that build exists inside the app container.
       - name: Cross-compile the native Windows .exe (clang-cl + xwin)
         env:
           CN1_XWIN_SYSROOT: ${{ runner.temp }}/xwin-sdk
           CN1_CLANG_CL: clang-cl
           CN1_LLVM_RC: llvm-rc
+          CN1_UWP_EXE_OUT: ${{ github.workspace }}/uwp-smoke/app.exe
         run: |
           cd vm
           JAVA_HOME="$JDK_8_HOME" mvn -B -pl tests -am test \
             '-Dtest=CleanTargetIntegrationTest#crossCompilesWindowsExeWithXwin' \
             '-Dsurefire.failIfNoSpecifiedTests=false'
+          test -f "$CN1_UWP_EXE_OUT"
+
+      # The development certificate windows.xbox builds create, made by the
+      # builder's own openssl commands; the Windows job signs with it, so a
+      # certificate Windows refuses fails there.
+      - name: Create the Xbox development certificate (WindowsNativeBuilder)
+        env:
+          CN1_XBOX_DEVCERT_OUT: ${{ github.workspace }}/uwp-smoke/devcert
+          RETRY_ONLY_MATCHING: transient
+          RETRY_ATTEMPTS: '3'
+          RETRY_DELAY_SECONDS: '60'
+        run: |
+          set -euo pipefail
+          mkdir -p ~/.codenameone
+          cp maven/UpdateCodenameOne.jar ~/.codenameone/
+          cd maven
+          JAVA_HOME="$JDK_8_HOME" bash ../scripts/ci/retry.sh mvn -B -pl build-engine -am install \
+            -DskipTests -Dmaven.javadoc.skip=true -Plocal-dev-javase
+          JAVA_HOME="$JDK_8_HOME" mvn -B -pl build-engine test -Plocal-dev-javase \
+            '-Dtest=WindowsNativeBuilderArchTest' -Dsurefire.failIfNoSpecifiedTests=false
+          test -s "$CN1_XBOX_DEVCERT_OUT/dev.pfx"
+          test -s "$CN1_XBOX_DEVCERT_OUT/dev.cer"
+
+      # The manifest is pinned to WindowsNativeBuilder.buildXboxAppxManifest by
+      # WindowsNativeBuilderArchTest, so the run below installs what windows.xbox
+      # builds ship.
+      - name: Upload the UWP smoke app
+        uses: actions/upload-artifact@v4
+        with:
+          name: uwp-smoke
+          path: |
+            uwp-smoke/app.exe
+            uwp-smoke/devcert/dev.pfx
+            uwp-smoke/devcert/dev.cer
+            maven/build-engine/src/test/resources/com/codename1/builders/xbox-smoke-AppxManifest.xml
+          if-no-files-found: error
+          retention-days: 3
+
+  # Phase 1's proof without a console: the cross-built UWP app is packed, signed,
+  # installed and launched as a real UWP activation (app container, CoreWindow,
+  # swap chain) on a Windows runner. The app writes a marker into its package
+  # LocalState once its first form has painted; no marker fails the job.
+  uwp-run:
+    name: install + launch the UWP package (Windows x64)
+    needs: cross-compile
+    runs-on: windows-latest
+    timeout-minutes: 20
+    steps:
+      - name: Download the UWP smoke app
+        uses: actions/download-artifact@v4
+        with:
+          name: uwp-smoke
+          path: uwp-smoke
+
+      - name: Pack, sign and install
+        shell: pwsh
+        run: |
+          $ErrorActionPreference = 'Stop'
+          $root = Resolve-Path uwp-smoke
+          $layout = Join-Path $env:RUNNER_TEMP 'uwp-layout'
+          New-Item -ItemType Directory -Force (Join-Path $layout 'Assets') | Out-Null
+          Copy-Item (Join-Path $root 'uwp-smoke/app.exe') (Join-Path $layout 'app.exe')
+          $manifest = Get-ChildItem -Recurse $root -Filter 'xbox-smoke-AppxManifest.xml' | Select-Object -First 1
+          Copy-Item $manifest.FullName (Join-Path $layout 'AppxManifest.xml')
+          Add-Type -AssemblyName System.Drawing
+          foreach ($logo in 'StoreLogo','Square150x150Logo','Square44x44Logo','SplashScreen') {
+            $bmp = New-Object System.Drawing.Bitmap 150,150
+            $g = [System.Drawing.Graphics]::FromImage($bmp); $g.Clear([System.Drawing.Color]::SteelBlue); $g.Dispose()
+            $bmp.Save((Join-Path $layout "Assets/$logo.png"), [System.Drawing.Imaging.ImageFormat]::Png); $bmp.Dispose()
+          }
+          $kit = Get-ChildItem 'C:/Program Files (x86)/Windows Kits/10/bin/*/x64/makeappx.exe' |
+                 Sort-Object FullName -Descending | Select-Object -First 1
+          $bin = $kit.DirectoryName
+          $msix = Join-Path $env:RUNNER_TEMP 'UwpSmoke.msix'
+          & "$bin/makeappx.exe" pack /o /d $layout /p $msix
+          if ($LASTEXITCODE -ne 0) { throw "makeappx failed" }
+          # Signed with the certificate WindowsNativeBuilder created (subject
+          # CN=UwpSmoke, the manifest Publisher; empty PKCS#12 password).
+          $pfx = Join-Path $root 'uwp-smoke/devcert/dev.pfx'
+          $cer = Join-Path $root 'uwp-smoke/devcert/dev.cer'
+          & "$bin/signtool.exe" sign /fd SHA256 /f $pfx $msix
+          if ($LASTEXITCODE -ne 0) { throw "signtool rejected the builder's development certificate" }
+          Import-Certificate -FilePath $cer -CertStoreLocation 'Cert:/LocalMachine/TrustedPeople' | Out-Null
+          $unlock = 'HKLM:/SOFTWARE/Microsoft/Windows/CurrentVersion/AppModelUnlock'
+          New-Item -Force $unlock | Out-Null
+          Set-ItemProperty $unlock AllowAllTrustedApps 1 -Type DWord
+          Set-ItemProperty $unlock AllowDevelopmentWithoutDevLicense 1 -Type DWord
+          Add-AppxPackage -Path $msix
+          Get-AppxPackage com.codename1.uwpsmoke | Format-List Name,PackageFamilyName,InstallLocation,SignatureKind
+
+      - name: Launch and wait for the first frame
+        shell: pwsh
+        run: |
+          $ErrorActionPreference = 'Stop'
+          $pkg = Get-AppxPackage com.codename1.uwpsmoke
+          $pfn = $pkg.PackageFamilyName
+          $state = Join-Path $env:LOCALAPPDATA "Packages/$pfn/LocalState"
+          Start-Process "shell:AppsFolder\$pfn!App"
+          $marker = $null
+          for ($i = 0; $i -lt 90 -and -not $marker; $i++) {
+            Start-Sleep -Seconds 1
+            if (Test-Path $state) {
+              $marker = Get-ChildItem -Recurse $state -Filter 'uwp-smoke.txt' -ErrorAction SilentlyContinue | Select-Object -First 1
+            }
+          }
+          Add-Type -AssemblyName System.Drawing, System.Windows.Forms
+          $b = [System.Windows.Forms.Screen]::PrimaryScreen.Bounds
+          $bmp = New-Object System.Drawing.Bitmap $b.Width, $b.Height
+          $g = [System.Drawing.Graphics]::FromImage($bmp); $g.CopyFromScreen($b.Location, [System.Drawing.Point]::Empty, $b.Size); $g.Dispose()
+          New-Item -ItemType Directory -Force uwp-run | Out-Null
+          $bmp.Save('uwp-run/desktop.png', [System.Drawing.Imaging.ImageFormat]::Png)
+          Get-Process app -ErrorAction SilentlyContinue | Format-Table Id,ProcessName,StartTime
+          if (-not $marker) {
+            Get-WinEvent -LogName 'Microsoft-Windows-AppModel-Runtime/Admin' -MaxEvents 20 -ErrorAction SilentlyContinue |
+              Format-List TimeCreated,Id,Message
+            Get-WinEvent -FilterHashtable @{LogName='Application'; Id=1000,1001} -MaxEvents 5 -ErrorAction SilentlyContinue |
+              Format-List TimeCreated,Message
+            if (Test-Path $state) { Get-ChildItem -Recurse $state | Format-Table FullName,Length }
+            throw "the UWP app wrote no marker in 90s: it did not reach its first frame"
+          }
+          $text = Get-Content $marker.FullName -Raw
+          Write-Host "marker: $text"
+          if ($text -notmatch '^CN1-UWP-STARTED [1-9][0-9]*x[1-9][0-9]*') { throw "unexpected marker: $text" }
+          Get-Process app -ErrorAction SilentlyContinue | Stop-Process -Force
+
+      - name: Upload the desktop capture
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: uwp-run-capture
+          path: uwp-run/
+          if-no-files-found: ignore
+          retention-days: 7
@@ -59,6 +59,60 @@
 #include <wincodec.h>
 #include <stdint.h>
 
+#if defined(CN1_WINDOWS_UWP)
+/*
+ * UWP (Xbox Developer Mode) build: the app container's API partition drops a
+ * few Win32 calls that have a direct app-partition equivalent. They are mapped
+ * here once, so the shared file code reads the same in both builds.
+ * CreateFileW -> CreateFile2 (same handle, same flags, split differently);
+ * CharUpperW -> an invariant-locale LCMapStringEx in place. A template file is
+ * never used by this port, so CreateFile2 ignores that argument.
+ */
+static __inline HANDLE cn1UwpCreateFileW(LPCWSTR name, DWORD access, DWORD share,
+        LPSECURITY_ATTRIBUTES sa, DWORD disposition, DWORD flagsAndAttributes, HANDLE templateFile) {
+    CREATEFILE2_EXTENDED_PARAMETERS ext;
+    (void) templateFile;
+    ZeroMemory(&ext, sizeof(ext));
+    ext.dwSize = sizeof(ext);
+    ext.dwFileAttributes = flagsAndAttributes & 0x0000FFFF;
+    ext.dwFileFlags = flagsAndAttributes & 0xFFF00000;
+    ext.dwSecurityQosFlags = flagsAndAttributes & 0x000F0000;
+    ext.lpSecurityAttributes = sa;
+    return CreateFile2(name, access, share, disposition, &ext);
+}
+#undef CreateFileW
+#define CreateFileW cn1UwpCreateFileW
+
+static __inline HANDLE cn1UwpCreateFileA(LPCSTR name, DWORD access, DWORD share,
+        LPSECURITY_ATTRIBUTES sa, DWORD disposition, DWORD flagsAndAttributes, HANDLE templateFile) {
+    WCHAR wide[MAX_PATH];
+    if (MultiByteToWideChar(CP_UTF8, 0, name, -1, wide, MAX_PATH) <= 0) {
+        SetLastError(ERROR_FILENAME_EXCED_RANGE);
+        return INVALID_HANDLE_VALUE;
+    }
+    return cn1UwpCreateFileW(wide, access, share, sa, disposition, flagsAndAttributes, templateFile);
+}
+#undef CreateFileA
+#define CreateFileA cn1UwpCreateFileA
+
+static __inline LPWSTR cn1UwpCharUpperW(LPWSTR s) {
+    int len = (int) wcslen(s);
+    LCMapStringEx(LOCALE_NAME_INVARIANT, LCMAP_UPPERCASE, s, len, s, len, NULL, NULL, 0);
+    return s;
+}
+#undef CharUpperW
+#define CharUpperW cn1UwpCharUpperW
+
+/* Declared by the SDK for the desktop partition only, but exported by kernel32
+ * on every Windows, the Xbox included. It is how a null dereference becomes a
+ * NullPointerException (cn1WinFaultToException), so the UWP build keeps it.
+ * Developer Mode sideloading does not run the Store's API certification. */
+#ifdef __cplusplus
+extern "C"
+#endif
+WINBASEAPI PVOID WINAPI AddVectoredExceptionHandler(ULONG First, PVECTORED_EXCEPTION_HANDLER Handler);
+#endif /* CN1_WINDOWS_UWP */
+
 #ifdef __cplusplus
 /* C++ method-call macros for the COBJMACROS-style call sites. */
 #include "cn1_windows_comc.h"
@@ -71,6 +125,16 @@ extern "C" {
 /* The ParparVM runtime is C; keep its declarations C-linked under C++. */
 #include "cn1_globals.h"
 
+#if defined(CN1_WINDOWS_UWP)
+/* The app's local data folder (ApplicationData.Current.LocalFolder) into buf,
+ * NUL terminated. Returns 0 when it cannot be read. cn1_windows_corewindow.cpp. */
+int cn1UwpLocalFolder(WCHAR* buf, int capacity);
+#endif
+
+/* COM, the fault handlers and the input ring, shared by every host's
+ * initDisplay. 0 when already initialised. cn1_windows_window.cpp. */
+int cn1WinInitRuntime(void);
+
 /* ------------------------------------------------------------------ events */
 
 /*
 
@@ -22,7 +22,7 @@
  */
 
 /* Native virtual accessibility tree for the lightweight Win32 port. */
-#ifdef _WIN32
+#if defined(_WIN32) && !defined(CN1_WINDOWS_UWP) /* desktop only: stubbed for UWP in cn1_windows_uwp_stubs.c */
 
 /* xwin may provide a newer MSVC STL than the clang-cl installed by the Linux
  * cross-compile runner.  This file uses only the long-stable string/vector
 
@@ -35,7 +35,7 @@
  * and closes.
  */
 
-#ifdef _WIN32
+#if defined(_WIN32) && !defined(CN1_WINDOWS_UWP) /* desktop only: stubbed for UWP in cn1_windows_uwp_stubs.c */
 
 #include "cn1_windows.h"
 #include <mmsystem.h>
 
@@ -36,7 +36,7 @@
  * (negative stride); both are handled when packing into CN1's 0xAARRGGBB ints.
  */
 
-#ifdef _WIN32
+#if defined(_WIN32) && !defined(CN1_WINDOWS_UWP) /* desktop only: stubbed for UWP in cn1_windows_uwp_stubs.c */
 
 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>
 
@@ -25,7 +25,7 @@
 /* Integrated main-window title bar. The window keeps WS_OVERLAPPEDWINDOW:
  * DWM owns the real caption buttons and DefWindowProc owns system commands,
  * resize tracking, caption double-click and the window system menu. */
-#ifdef _WIN32
+#if defined(_WIN32) && !defined(CN1_WINDOWS_UWP) /* desktop only: stubbed for UWP in cn1_windows_uwp_stubs.c */
 #include "cn1_windows.h"
 #include <dwmapi.h>
 #include <windowsx.h>