.NET: [Bug]: Shell="cmd" echoes commands containing quotes instead of executing them and reports exit 0

Start in ShellResolver.StatelessArgvForCommand, which builds the cmd /d /c argv, and in the Cmd branch of LocalShellExecutor.RunStatelessAsync, where the elements are added through ProcessStartInfo.ArgumentList. Run the 25-line reproduction on Windows to confirm that quoted commands are echoed with exit 0. Done means quoted commands such as echo "quoted value" return the correct stdout with the right exit code on Windows. Wait for maintainer agreement on the /s approach before you start.

Observed Behavior

LocalShellExecutor in stateless mode with Shell = "cmd" does not execute commands that contain double quotes. It prints the command text as if it were the program output and reports ExitCode == 0, so the caller has no signal that nothing ran.

LocalShellExecutor.RunAsync("powershell -NoProfile -Command \"Write-Output hello\"")
  stdout: Write-Output hello        ExitCode: 0     <-- command echoed, never executed

LocalShellExecutor.RunAsync("echo \"quoted value\"")
  stdout: \"quoted value\"          ExitCode: 0     <-- quotes arrived escaped as \" and were printed

The second case shows the mechanism: the child process receives the quote as literal \". For commands that do run despite this, their arguments are corrupted the same way.

This is the shape models emit all the time, for example powershell -NoProfile -Command "...", git commit -m "message", or echo "text". On Windows the tool silently returns a success with wrong output, which is worse than an error because the model has no reason to retry.

Expected Behavior

Quoted commands execute normally:

RunAsync("powershell -NoProfile -Command \"Write-Output hello\"")  -> stdout: hello           ExitCode: 0
RunAsync("echo \"quoted value\"")                                  -> stdout: "quoted value"   ExitCode: 0

Steps to Reproduce

1. On Windows, create a console project targeting net10.0 and add Microsoft.Agents.AI.Tools.Shell (prerelease).
2. Construct LocalShellExecutor in ShellMode.Stateless with Shell = "cmd".
3. RunAsync a command containing a double quote, for example powershell -NoProfile -Command "Write-Output hello".
4. Observe Stdout == "Write-Output hello" with ExitCode == 0: the command was echoed, not executed.

Minimal Reproduction

using Microsoft.Agents.AI.Tools.Shell;

await using var shell = new LocalShellExecutor(new LocalShellExecutorOptions
{
    Mode = ShellMode.Stateless,
    Shell = "cmd",
    AcknowledgeUnsafe = true, // unrelated to this bug: only disables the approval wrapper
    WorkingDirectory = Directory.GetCurrentDirectory(),
    Timeout = TimeSpan.FromSeconds(30),
});

var nested = await shell.RunAsync("powershell -NoProfile -Command \"Write-Output hello\"", default);
Console.WriteLine($"stdout=[{nested.Stdout.Trim()}] exit={nested.ExitCode}");
// actual:   stdout=[Write-Output hello] exit=0
// expected: stdout=[hello] exit=0

var quoted = await shell.RunAsync("echo \"quoted value\"", default);
Console.WriteLine($"stdout=[{quoted.Stdout.Trim()}] exit={quoted.ExitCode}");
// actual:   stdout=[\"quoted value\"] exit=0
// expected: stdout=["quoted value"] exit=0

Error Messages and Stack Traces

None. That is part of the problem: no exception, no stderr, exit code 0.

Package Versions

• Microsoft.Agents.AI.Tools.Shell 1.27.0-preview.261030.1
• (transitive) Microsoft.Agents.AI.Abstractions 1.27.0, Microsoft.Extensions.AI 10.10.0

.NET Version

.NET 10.0.402 SDK, runtime 10.0.9.

Operating System

Windows

Regression

Unknown

Additional Context

Cause. ShellResolver.StatelessArgvForCommand builds cmd /d /c <command> and LocalShellExecutor.RunStatelessAsync adds each element through ProcessStartInfo.ArgumentList. .NET escapes " as \" when it flattens ArgumentList into a command line, and cmd.exe has no notion of an escaped quote, so it terminates the /c argument at the first \" and treats the rest as text to print. cmd.exe documents /s as the way to pass a full command line: with /s, the outer pair of quotes is stripped and the remainder is used verbatim.

Suggested fix. For ShellKind.Cmd, bypass ArgumentList and set the command line as a single Arguments string:

startInfo.Arguments = $"/d /s /c \"{command}\"";

That is the same approach powershell/bash do not need, so it can stay inside the Cmd branch of RunStatelessAsync.

The persistent path (ShellSession) uses the same ArgumentList for its launch argv, but since persistent mode is not supported for cmd.exe, only stateless is affected.

Workaround. Build the command line manually for cmd instead of going through ArgumentList (what a downstream consumer does today), or avoid cmd by using Shell = "pwsh", which changes how bash-style commands in model output behave.

AI assistance. The analysis, the reproduction program and this report were prepared with an AI coding assistant. Every command output quoted here was produced by actually running the reproduction; none of it is predicted or paraphrased. Package versions, API names and source references were checked against the published package and the repository's main branch.

Verification. Reproduced locally before filing:

• OS: Windows 10.0.26300.9711
• SDK: .NET SDK 10.0.402, runtime 10.0.9
• Package: Microsoft.Agents.AI.Tools.Shell 1.27.0-preview.261030.1
• How: dotnet run on the 25-line console project in Minimal Reproduction above
• Output: stdout=[Write-Output hello] exit=0, stdout=[\"quoted value\"] exit=0

Acknowledgements

• I searched existing issues and did not find a duplicate (searched cmd quote, ArgumentList, LocalShellExecutor, Tools.Shell, and open issues/PRs with shell in the title; every existing shell issue targets the other SDK implementation, none target the .NET one).
• I personally verified this behavior and the reproduction details are authentic.
• I will wait for explicit maintainer agreement before starting implementation of a non-trivial change.