Description

After upgrading a .NET hosted Foundry agent from Microsoft.Agents.AI.Foundry.Hosting 1.3.0-preview.260423.1 to 1.8.0-preview.260528.1, the agent deploys and starts, but fails after the agent invokes a local .NET tool registered through AIFunctionFactory.Create(...).

The platform/container logs show:

mount:
/app: mount failed: No such file or directory.

Local tool pattern

The agent registers a local function tool with AIFunctionFactory.Create(...), for example:

AIAgent agent = new AIProjectClient(projectEndpoint, new DefaultAzureCredential())
    .AsAIAgent(
        model: deployment,
        instructions: "...",
        name: "sow-agent",
        tools:
        [
            AIFunctionFactory.Create(GetAvailableHotels, "GetAvailableHotels",
                "Gets a list of available hotels in Seattle with details about amenities and pricing.")
        ]);

The hosting setup uses:

var builder = AgentHost.CreateBuilder(args);
builder.Services.AddFoundryResponses(agent);
builder.RegisterProtocol("responses", endpoints => endpoints.MapFoundryResponses());

var app = builder.Build();
app.Run();

Suspected regression area

Microsoft.Agents.AI.Foundry.Hosting 1.8.0-preview.260528.1 introduced file-backed session/checkpoint behavior in the Foundry hosting layer, including FileSystemAgentSessionStore.

The failure happens after local tool invocation, so it may be related to new hosted-session, checkpoint, tool-call state, or local function execution behavior introduced between 1.3.0-preview.260423.1 and 1.8.0-preview.260528.1.

Related public Microsoft Agent Framework items:

• .NET: Hosting updates to declarative workflows #5589
• .NET: [Bug]: FileSystemJsonCheckPointStore for Agent Workflow , RetrieveIndexAsync(SessionId) returns all checkpoint entries instead of filtering by SessionId #5942
• .NET: fix: filter filesystem checkpoint index by session #6132