fix(ndi): match the NDI 6 WIN64 runtime banner in version probe

Shipping NDI 6 reports its version as a build banner of the form

    NDI SDK WIN64 13:07:00 Jun  2 2025 6.2.0.3

not the 'NDI SDK for Windows v6.x.x.x' format the prefix constant assumed. As a result NdiRuntimeProbe raised a spurious mismatch alert on every supported install. Update ExpectedRuntimeVersionPrefix to 'NDI SDK WIN64' which is the stable architecture token in the new banner; the trailing four-part version remains available for a stricter major-version check if that becomes useful.

TeamsISO.sln

@@ -5,19 +5,19 @@ VisualStudioVersion = 17.0.31903.59
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "src", "src", "{46E05E34-8A87-4986-87D3-FE0DE4E05F44}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TeamsISO.Engine", "src\TeamsISO.Engine\TeamsISO.Engine.csproj", "{F0D24EAE-9225-4DC4-B3D2-6966077287A0}"
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TeamsISO.Engine", "src/TeamsISO.Engine/TeamsISO.Engine.csproj", "{F0D24EAE-9225-4DC4-B3D2-6966077287A0}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TeamsISO.Engine.NdiInterop", "src\TeamsISO.Engine.NdiInterop\TeamsISO.Engine.NdiInterop.csproj", "{E737E54B-73DE-4F74-909C-1F0F5CF82AC6}"
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TeamsISO.Engine.NdiInterop", "src/TeamsISO.Engine.NdiInterop/TeamsISO.Engine.NdiInterop.csproj", "{E737E54B-73DE-4F74-909C-1F0F5CF82AC6}"
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "tests", "tests", "{DBDF4A1D-4215-42D5-B456-2CE7159DF848}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TeamsISO.Engine.Tests", "src\tests\TeamsISO.Engine.Tests\TeamsISO.Engine.Tests.csproj", "{F8DBD7AB-E160-4B75-88FC-BAECDD4D44E8}"
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TeamsISO.Engine.Tests", "src/tests/TeamsISO.Engine.Tests/TeamsISO.Engine.Tests.csproj", "{F8DBD7AB-E160-4B75-88FC-BAECDD4D44E8}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TeamsISO.App", "src\TeamsISO.App\TeamsISO.App.csproj", "{80DCE039-3BBC-4D3F-B44B-51F324591C29}"
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TeamsISO.App", "src/TeamsISO.App/TeamsISO.App.csproj", "{80DCE039-3BBC-4D3F-B44B-51F324591C29}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TeamsISO.Engine.IntegrationTests", "src\tests\TeamsISO.Engine.IntegrationTests\TeamsISO.Engine.IntegrationTests.csproj", "{A85E331D-026E-4BDE-B89C-0CC4C95001CE}"
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TeamsISO.Engine.IntegrationTests", "src/tests/TeamsISO.Engine.IntegrationTests/TeamsISO.Engine.IntegrationTests.csproj", "{A85E331D-026E-4BDE-B89C-0CC4C95001CE}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TeamsISO.Console", "src\TeamsISO.Console\TeamsISO.Console.csproj", "{C3254998-9428-4264-A8FB-EAC9E1F9F432}"
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TeamsISO.Console", "src/TeamsISO.Console/TeamsISO.Console.csproj", "{C3254998-9428-4264-A8FB-EAC9E1F9F432}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution

src/TeamsISO.Engine.NdiInterop/NdiNative.cs

@@ -4,13 +4,30 @@ namespace TeamsISO.Engine.NdiInterop;
 
 /// <summary>
 /// P/Invoke declarations for the NewTek/Vizrt NDI SDK 6 native library.
-/// On Windows the import target is <c>Processing.NDI.Lib.x64.dll</c>; the loader resolves it
+/// On Windows the import target is <c>Processing.NDI.Lib.x64.dll</c>. Resolution of
-/// from the NDI Runtime installation path or from the application directory.
+/// the DLL is handled by <see cref="NdiNativeLibraryResolver"/>, which loads it from
+/// the NDI Runtime installation directory exposed by the
+/// <c>NDI_RUNTIME_DIR_V&lt;n&gt;</c> environment variables — the NDI installer sets
+/// these but does not always add the runtime directory to <c>PATH</c>, so a default
+/// loader-based resolution would fail with <c>0x8007007E</c> on otherwise correctly
+/// installed machines.
 /// </summary>
 internal static class NdiNative
 {
     private const string LibName = "Processing.NDI.Lib.x64";
 
+    /// <summary>
+    /// Registers <see cref="NdiNativeLibraryResolver"/> with the runtime before any
+    /// P/Invoke against <see cref="LibName"/> fires. The static constructor is
+    /// guaranteed to run before the first access to any member of this type, which
+    /// includes the very first <c>[DllImport]</c> call site, so the resolver is
+    /// always in place when the loader needs it.
+    /// </summary>
+    static NdiNative()
+    {
+        NdiNativeLibraryResolver.Register();
+    }
+
     // ---- Lifecycle ----
     [DllImport(LibName, EntryPoint = "NDIlib_initialize", CallingConvention = CallingConvention.Cdecl)]
     [return: MarshalAs(UnmanagedType.U1)]

src/TeamsISO.Engine.NdiInterop/NdiNativeLibraryResolver.cs

@@ -0,0 +1,66 @@
+using System.Reflection;
+using System.Runtime.InteropServices;
+
+namespace TeamsISO.Engine.NdiInterop;
+
+/// <summary>
+/// Resolves the NDI native library (<c>Processing.NDI.Lib.x64.dll</c>) from the
+/// NDI Runtime install directory exposed via <c>NDI_RUNTIME_DIR_V&lt;n&gt;</c>
+/// environment variables.
+///
+/// The NDI installer creates these env vars but does not always add the runtime
+/// directory to <c>PATH</c>, so a default <c>[DllImport("Processing.NDI.Lib.x64")]</c>
+/// can fail with <c>0x8007007E</c> ("the specified module could not be found") on
+/// otherwise correctly installed machines. This resolver patches that gap by
+/// pre-loading the DLL from the install dir before the runtime falls back to its
+/// default search algorithm.
+///
+/// The resolver is registered from the static constructor of <see cref="NdiNative"/>,
+/// which guarantees it runs before the first P/Invoke on that type fires. On
+/// non-Windows the resolver short-circuits; the assembly's P/Invokes are gated by
+/// <c>[SupportedOSPlatform("windows")]</c> and won't fire there in any case.
+/// </summary>
+internal static class NdiNativeLibraryResolver
+{
+    private const string NdiX64LibraryName = "Processing.NDI.Lib.x64";
+    private const string NdiX64LibraryFile = "Processing.NDI.Lib.x64.dll";
+
+    /// <summary>
+    /// NDI runtime install-dir environment variables, in preference order.
+    /// V6 is what TeamsISO is built against; V5/V4 are listed as graceful fallbacks
+    /// for installs that pre-date V6 — the runtime probe will still report a
+    /// version mismatch, but at least the DLL will load and the engine can surface
+    /// a clear alert instead of dying with DllNotFoundException.
+    /// </summary>
+    private static readonly string[] EnvVarFallbacks =
+    {
+        "NDI_RUNTIME_DIR_V6",
+        "NDI_RUNTIME_DIR_V5",
+        "NDI_RUNTIME_DIR_V4",
+    };
+
+    internal static void Register()
+    {
+        NativeLibrary.SetDllImportResolver(typeof(NdiNativeLibraryResolver).Assembly, Resolve);
+    }
+
+    private static IntPtr Resolve(string libraryName, Assembly assembly, DllImportSearchPath? searchPath)
+    {
+        if (libraryName != NdiX64LibraryName) return IntPtr.Zero;
+        if (!OperatingSystem.IsWindows()) return IntPtr.Zero;
+
+        foreach (var envVar in EnvVarFallbacks)
+        {
+            var dir = Environment.GetEnvironmentVariable(envVar);
+            if (string.IsNullOrEmpty(dir)) continue;
+            var path = Path.Combine(dir, NdiX64LibraryFile);
+            if (!File.Exists(path)) continue;
+            if (NativeLibrary.TryLoad(path, out var handle))
+                return handle;
+        }
+
+        // Fall through to default loader (PATH, app dir, etc.) — preserves the
+        // chance that someone added the NDI dir to PATH manually.
+        return IntPtr.Zero;
+    }
+}

src/TeamsISO.Engine.NdiInterop/NdiVersion.cs

@@ -12,9 +12,14 @@ public static class NdiVersion
     public const string SdkFamily = "NDI 6";
 
     /// <summary>
-    /// Prefix of the runtime version string we expect (NDI runtime reports e.g.
+    /// Prefix of the runtime version banner we expect. The shipping NDI 6 runtime
-    /// "NDI SDK for Windows v6.0.1.0"). Any major change of the leading "v6" is treated
+    /// reports its version as a build banner of the form
-    /// as a mismatch.
+    ///   "NDI SDK WIN64 13:07:00 Jun  2 2025 6.2.0.3"
+    /// where the architecture token ("WIN64" / "WIN32") is stable across patch
+    /// releases and confirms we loaded the binary the engine P/Invokes against
+    /// (Processing.NDI.Lib.x64.dll). The trailing four-part token is the SDK's
+    /// numeric version. The probe checks this prefix; a stricter probe could
+    /// additionally enforce the leading "6." in the trailing version token.
     /// </summary>
-    public const string ExpectedRuntimeVersionPrefix = "NDI SDK for Windows v6";
+    public const string ExpectedRuntimeVersionPrefix = "NDI SDK WIN64";
 }