Add Docker Files to Workspace generates invalid tasks.json referencing a non-existent .sln file when C# Dev Kit is installed

[v-amyang]

OS: Win 10
Build Version: 20260902.2

Repro Steps:

1. Install C# Dev Kit
2. Create a new project: dotnet new mvc -n DotnetApp0903
3. Open the project folder in VS Code->Add Docker Files to Workspace
4. Inspect the generated .vscode/tasks.json.

Expect:
Generated tasks.json should reference the existing project file(DotnetApp0903.csproj) instead of a non-existent solution file.

Actual:
Generates invalid tasks.json referencing a non-existent .sln file and lead to build image failed.

More Info:

1. This issue doesn't repro when separately install C# extension
2. The project was created using: dotnet new mvc
3. The generated project contains DotnetApp0903.csproj and no .sln file.
4. Running "dotnet build" succeeds.

[bwateratmsft]

Traced this; it's an external change in C# DevKit that cascades down. I opened dotnet/vscode-csharp#9748.

Workaround

For anyone who hits this issue, you can fix it by replacing the long .sln path with ${workspaceFolder}/MyProject.csproj, in .vscode/tasks.json. Note, forward slash is preferred, even on Windows.

Example--
Was:

{
    "version": "2.0.0",
    "tasks": [
        {
            "label": "build",
            "command": "dotnet",
            "type": "process",
            "args": [
                "build",
                "./${workspaceFolder}/c:/Users/username/AppData/Roaming/Code/User/workspaceStorage/22c32d0c33cd5e83b81d8a0fec294120/ms-dotnettools.csdevkit/MyProject-55ffe9f3.sln", // This is the busted line
                "/property:GenerateFullPaths=true",
                "/consoleloggerparameters:NoSummary;ForceNoAlign"
            ],
            "problemMatcher": "$msCompile"
        },
        // ...
    ]
}

Fixed:

{
    "version": "2.0.0",
    "tasks": [
        {
            "label": "build",
            "command": "dotnet",
            "type": "process",
            "args": [
                "build",
                "${workspaceFolder}/MyProject.csproj", // This is fixed
                "/property:GenerateFullPaths=true",
                "/consoleloggerparameters:NoSummary;ForceNoAlign"
            ],
            "problemMatcher": "$msCompile"
        },
        // ...
    ]
}

This must be done in the task named "build", but should be done in all of them.