[WebToolsE2E] Subsequent Blazor WebAssembly Standalone projects fail to launch after first successful debug session

[joniel-bolocon]

REGRESSION INFO: In May Prerelease 10 (C# Dev Kit 3.31.199 and C# 2.149.34) #3366 will be encountered

INSTALL STEPS

• OS: windows x64
• Install the SDK 10.0.401
• Install VS Code insiders - 1.137.0
• V3 Sept prerelease C#: 2.151.27
• V3 Sept prerelease C# DK: 3.31.218

REPRO STEPS

1. Make sure enable "[Experimental] Enables C# Hot Reload while debugging"
2. Open VS Code > Create .NET Project > Blazor WebAssembly Standalone App
3. Build project successfully. > F5 to run the project
4. Verify the project runs successfully > Stop the project > Close all VS Code programs
5. Open again VS Code > Create .NET Project > Blazor WebAssembly Standalone App
6. Build project successfully. > F5 to run the project

ACTUAL
After running the first project successfully, the succeeding Blazor WebAssembly Standalone App projects won't run successfully and will encounter the following errors/warnings:

Run via "Start new Instance"

Logs:

The target process exited without raising a CoreCLR started event. Ensure that the target process is configured to use .NET Core. This may be expected if the target process did not run on .NET Core.

Run via "Start without Debugging"

Logs:

A fatal error was encountered. The library 'hostpolicy.dll' required to execute the application was not found in 'C:\Users\v-jbolocon\BlazorApp3\BlazorApp3\bin\Debug\net10.0\'.
Failed to run as a self-contained app.
  - The application was run as a self-contained app because 'C:\Users\v-jbolocon\BlazorApp3\BlazorApp3\bin\Debug\net10.0\BlazorApp3.runtimeconfig.json' did not specify a framework.
  - If this should be a framework-dependent app, specify the appropriate framework in 'C:\Users\v-jbolocon\BlazorApp3\BlazorApp3\bin\Debug\net10.0\BlazorApp3.runtimeconfig.json'.

EXPECTED
Blazor WebAssembly Standalone App templates will consistently run successfully

[LittleLittleCloud]

joniel-bolocon I am not able to reproduce this on my environment, it might be flakiness. could you give it another try by reopen VSCode and rebuild project and relaunch,,

[joniel-bolocon]

I check it again with the latest C# Dev Kit internal prerelease [3.33.194] and C# [2.152.5], but this time I was able to repro the issue in the first run, I tried to reopen VS Code and rebuild the existing project and also tried creating a new project but the issue still persists.

I run via "Start new Instance" and "Start without Debugging"

[cyimperial]

Verified this issue repro in CDK (main): 9.9.512-g6b007c and C# (main): 2.152.5

[JakeRadMSFT]

Finding: orthogonal Web Tools/Blazor launch issue.

The reported Blazor WebAssembly launch failure includes no CoreCLR event, a missing hostpolicy.dll, and a framework-less runtimeconfig. It was verified on C# Dev Kit main 9.9.512-g6b007c with C# 2.152.5; later reports reproduced it on first run even after reopening, rebuilding, or creating a new project.

This is a Web Tools/Blazor launch issue, separate from C# Doctor SDK selection. It needs focused standalone Blazor WebAssembly debug and no-debug launch coverage around runtimeconfig generation.

vs-green PR !779247 does not fix this issue.

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