What causes "Invalid mode" in microsoft/autogen?

Use only the defined HumanInputMode values: NEVER, ALWAYS, AUTO (AUTO is the default)

microsoft/autogen · error · InvalidOperationException

Invalid mode

Error message

Invalid mode

What it means

Unreachable-in-practice defensive throw at the end of HumanInputMiddleware.InvokeAsync. The method handles HumanInputMode.NEVER, ALWAYS, and AUTO explicitly; the InvalidOperationException only fires if 'mode' holds an enum value outside those three (e.g. (HumanInputMode)99 cast from an int or from a bad config parse).

Source

Thrown at dotnet/src/AutoGen/Middleware/HumanInputMiddleware.cs:84

        {
            if (await isTermination(context.Messages, cancellationToken) is false)
            {
                return await agent.GenerateReplyAsync(context.Messages, context.Options, cancellationToken);
            }

            this.writeLine(prompt);
            var input = getInput();
            if (input == exitKeyword)
            {
                return new TextMessage(Role.Assistant, GroupChatExtension.TERMINATE, agent.Name);
            }

            input ??= string.Empty;

            return new TextMessage(Role.Assistant, input, agent.Name);
        }

        throw new InvalidOperationException("Invalid mode");
    }

    private async Task<bool> DefaultIsTermination(IEnumerable<IMessage> messages, CancellationToken _)
    {
        return messages?.Last().IsGroupChatTerminateMessage() is true;
    }

    private string? GetInput()
    {
        return Console.ReadLine();
    }

    private void WriteLine(string message)
    {
        Console.WriteLine(message);
    }
}

View on GitHub (pinned to 027ecf0a37)

Solutions

Use only the defined HumanInputMode values: NEVER, ALWAYS, AUTO (AUTO is the default)
Validate external input with Enum.IsDefined<HumanInputMode>(value) before constructing the middleware
If a new enum member was added upstream, upgrade AutoGen so the middleware handles it

Example fix

// before
var mode = (HumanInputMode)int.Parse(args[0]); // 7 -> invalid
var mw = new HumanInputMiddleware(mode: mode);
// after
var raw = int.Parse(args[0]);
var mode = Enum.IsDefined<HumanInputMode>(raw) ? (HumanInputMode)raw : HumanInputMode.AUTO;
var mw = new HumanInputMiddleware(mode: mode);

Defensive patterns

Strategy: validation

Validate before calling

if (!Enum.IsDefined<HumanInputMode>(mode)) throw new ArgumentOutOfRangeException(nameof(mode));
var middleware = new HumanInputMiddleware(mode: mode);

Type guard

static bool IsValidMode(HumanInputMode mode) => mode is HumanInputMode.NEVER or HumanInputMode.ALWAYS or HumanInputMode.AUTO;

Prevention

Never construct enum values via unchecked casts from external input; validate with Enum.IsDefined
Parse mode strings with Enum.TryParse<HumanInputMode>(s, ignoreCase, out _) plus IsDefined
Default to AUTO when input is unparsable instead of propagating a bad value

When it happens

Trigger: Constructing HumanInputMiddleware with a mode produced by an unchecked cast: (HumanInputMode)42, or parsing a numeric/string config value into the enum without Enum.IsDefined validation.

Common situations: Driving HumanInputMode from appsettings or CLI args where an out-of-range integer is accepted by the compiler/parser; interop code that passes raw ints across a boundary; refactoring that adds a new enum member not yet handled here.

Related errors

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/a90d695670825893. Report an issue: GitHub.