Advanced Paste – Phi Silica local testing

How to build, register, and test Phi Silica in Advanced Paste (AP) on a dev machine, plus the few things that actually break it.

How it fits together

AP ships as an unpackaged, self-contained WinUI 3 exe (PowerToys.AdvancedPaste.exe). The Windows AI LanguageModel (Phi Silica) API is a Limited Access Feature (LAF). For it to work, all of these must line up:

1. Package identity — AP runs with identity granted by the sparse MSIX Microsoft.PowerToys.SparseApp.
2. Matching LAF creds — the token/attestation baked into the exe match the registered sparse package's publisher.
3. AI metadata deployed — the Microsoft.Windows.AI*.winmd files ship next to the exe; the AI runtime resolves them at runtime.
4. Model ready — supported hardware and the on-device model downloaded (GetReadyState() == Ready).

Two identities — the baked token must match the registered package's publisher:

Non-secret pairing check: the exe's baked Attestation must equal the registered package's PublisherId.

Build + register (dev loop)

$repo = "X:\GitHub\PowerToys"; $Plat = "ARM64"; $Cfg = "Debug"   # or x64 / Release

# Build AP only (C#; reuses existing C++ outputs):
dotnet restore "$repo\src\modules\AdvancedPaste\AdvancedPaste\AdvancedPaste.csproj" /p:Platform=$Plat
& "$repo\tools\build\build.cmd" -Path "$repo\src\modules\AdvancedPaste\AdvancedPaste" `
    -Platform $Plat -Configuration $Cfg /p:BuildProjectReferences=false

# Register the dev sparse package (creates + trusts a dev cert, grants identity):
pwsh -ExecutionPolicy Bypass -File "$repo\src\PackageIdentity\BuildSparsePackage.ps1" `
    -Platform $Plat -Configuration $Cfg -DevRegister
# Expect: PublisherId djwsxzxb4ksa8, IsDevelopmentMode True

Check the API

PowerToys.AdvancedPaste.exe is a GUI-subsystem app — run directly in a console it prints nothing and returns no exit code. Redirect stdout/stderr and wait:

$exe = "$repo\$Plat\$Cfg\WinUI3Apps\PowerToys.AdvancedPaste.exe"
$o = "$env:TEMP\ap.out"; $e = "$env:TEMP\ap.err"
$p = Start-Process $exe '--check-phi-silica' -Wait -PassThru -WindowStyle Hidden `
        -RedirectStandardOutput $o -RedirectStandardError $e
"exit=$($p.ExitCode)  stdout=$((Get-Content $o -Raw).Trim())"
Get-Content $e -Raw   # stderr: [phi-silica] LAF unlock status: <…>; ReadyState: <…>

--check only reads state; use --prepare to trigger the model download (EnsureReadyAsync). On failure it prints the HRESULT to stderr.

Confirm the running AP has identity:

$apPid = (Get-Process PowerToys.AdvancedPaste -EA SilentlyContinue | Select-Object -First 1).Id
if ($apPid) { & "$repo\src\PackageIdentity\Check-ProcessIdentity.ps1" -ProcessId $apPid }
# Expect a PFN ending in the publisher id that matches the baked attestation

What actually breaks it

• Missing .winmd (most important). The Windows AI runtime resolves Microsoft.Windows.AI*.winmd from the app folder at runtime. If they aren't deployed, GetReadyState() returns NotReady and EnsureReadyAsync() fails with RO_E_METADATA_NAME_NOT_FOUND (0x8000000F) — even though identity, token, and the AI DLLs are all correct. The build emits these winmd into WinUI3Apps\; the installer must harvest them (*.winmd is in the inclusion list of generateAllFileComponents.ps1). Classic symptom: "works from the build output but not from the installer" → check that the installed WinUI3Apps\ contains Microsoft.Windows.AI*.winmd.
• Dev/prod mismatch. A dev-cred exe running against a prod sparse package (or vice versa) makes the LAF unlock silently return Unavailable. Keep the exe and the registered package the same flavor, and verify with the attestation == publisherId check above.
• Forgot to redirect. --check-phi-silica in a console prints nothing — that's the GUI-subsystem quirk, not a result.

Cleanup

pwsh -ExecutionPolicy Bypass -File "$repo\src\PackageIdentity\BuildSparsePackage.ps1" -Unregister

⚠️ This removes any Microsoft.PowerToys.SparseApp registration, including a prod one from an installer — reinstall/repair PowerToys to restore it.