[mono][wasm] Fix AOT + BlazorWebAssemblyLazyLoad startup crash

src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets

@@ -202,6 +202,12 @@ Copyright (c) .NET Foundation. All rights reserved.
       <_WasmWebcilVersion Condition="'$(_WasmWebcilVersion)' == ''">0</_WasmWebcilVersion>
       <_BlazorWebAssemblyJiterpreter>$(BlazorWebAssemblyJiterpreter)</_BlazorWebAssemblyJiterpreter>
       <_BlazorWebAssemblyRuntimeOptions>$(BlazorWebAssemblyRuntimeOptions)</_BlazorWebAssemblyRuntimeOptions>
+      <!-- With AOT, each AOT image hard-binds to every assembly it references when the image is
+           loaded. A BlazorWebAssemblyLazyLoad assembly is not present at runtime startup, so any
+           AOT image that references it would be marked unusable and its methods would fall back to
+           the interpreter (which can then hit unsupported constructs and abort). Enable lazy AOT
+           assembly loading so referenced lazy assemblies are only bound when they are loaded. -->
+      <_BlazorWebAssemblyRuntimeOptions Condition="'$(RunAOTCompilation)' == 'true' and @(BlazorWebAssemblyLazyLoad->Count()) != 0 and !$(_BlazorWebAssemblyRuntimeOptions.Contains('--aot-lazy-assembly-load'))">$([System.String]::Concat('$(_BlazorWebAssemblyRuntimeOptions)', ' --aot-lazy-assembly-load').Trim())</_BlazorWebAssemblyRuntimeOptions>
       <_WasmInlineBootConfig Condition="'$(_WasmInlineBootConfig)' == '' and '$(_TargetingNET100OrLater)' == 'true'">true</_WasmInlineBootConfig>
       <_WasmInlineBootConfig Condition="'$(_WasmInlineBootConfig)' == ''">false</_WasmInlineBootConfig>
       <!-- true = wasm assets will have hard fingerprint; false = wasm assets won't have even soft fingerprint -->

src/mono/wasm/Wasm.Build.Tests/LazyLoadingTests.cs

@@ -73,6 +73,28 @@ public async Task LoadLazyAssemblyTwiceIsIdempotent()
         Assert.False(result.ConsoleOutput.Any(m => m.Contains("must be marked with 'BlazorWebAssemblyLazyLoad'")), "Reloading an already-loaded lazy assembly must not throw the 'must be marked' error");
     }
 
+    [Fact]
+    [TestCategory("native-mono")]
+    public async Task LoadLazyAssemblyWithAOT()
+    {
+        // Regression coverage for https://github.com/dotnet/runtime/issues/125794:
+        // AOT combined with BlazorWebAssemblyLazyLoad must still initialize the runtime
+        // and lazily load assemblies at runtime. AOT is only supported when publishing
+        // in Release, so this exercises the publish + AOT + lazy-load combination that
+        // the Debug build/run tests above do not cover.
+        Configuration config = Configuration.Release;
+        ProjectInfo info = CopyTestAsset(config, aot: true, TestAsset.WasmBasicTestApp, "LazyLoadingTestsAOT");
+        PublishProject(info, config, new PublishOptions(AOT: true, ExtraMSBuildArgs: "-p:TestLazyLoading=true"));
+
+        RunResult result = await RunForPublishWithWebServer(new BrowserRunOptions(
+            config,
+            AOT: true,
+            TestScenario: "LazyLoadingTest"
+        ));
+
+        Assert.True(result.TestOutput.Any(m => m.Contains("FirstName")), "The lazy loading test didn't emit expected message with JSON");
+    }
+
     [Fact]
     public async Task FailOnMissingLazyAssembly()
     {