.NET: Add Azure Blob Storage session persistence

[Korolev Dmitry (DeagleGross)]

Motivation & Context

Hosted agents need durable session state to continue conversations across HTTP requests, process restarts, and multiple application instances. In-memory storage is useful for development, but it loses state when the process stops. This change adds Azure Blob Storage as an opt-in durable session store for hosted .NET agents.

Description & Review Guide

• What are the major changes?
  • Adds the Microsoft.Agents.AI.Hosting.AzureStorage package with AzureBlobAgentSessionStore, configuration options, and WithAzureBlobSessionStore registration helpers.
  • Persists serialized AgentSession JSON using stable, bounded SHA-256 blob names partitioned by the hosted agent registration name.
  • Supports session creation, retrieval, overwrite, deletion, optional container creation, and blob name prefixes.
  • Uses the standard hosted-agent isolation wrapper by default and supports configurable dependency injection lifetime.
  • Updates AgentWebChat to use Azure Blob Storage when AZURE_STORAGE_BLOB_CONNECTION_STRING and AZURE_STORAGE_BLOB_CONTAINER_NAME are configured, with in-memory storage as the development fallback.
  • Adds Azurite coverage and an in-memory ASP.NET Core server test that exercises agent resolution, two HTTP turns, session restoration, and blob persistence. A live Azure Blob test is included but remains explicitly skipped until CI has a provisioned Storage account and data permissions.
• What is the impact of these changes?
  • Hosted .NET agents can opt into durable Azure Blob Storage session persistence without changing existing default behavior.
  • Session state can survive process restarts and be shared across application instances.
• What do you want reviewers to focus on?
  • The stable blob naming format and storage lifecycle behavior.
  • Dependency injection registration, user isolation defaults, and service lifetime handling.
  • The end-to-end hosted-agent tests that verify session continuity and the resulting blob record.

Related Issue

No related issue or overlapping open pull request was found.

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change. If it is a breaking change, add the breaking change label (or add "[BREAKING]" to the title prefix, before or after any language prefix), and a workflow keeps the label and title prefix in sync automatically.

[Copilot]

Pull Request Overview

This PR adds Azure Blob Storage integration for agent thread persistence to the Microsoft Agent Framework. It introduces a new project Microsoft.Agents.AI.Hosting.AzureStorage that provides an implementation of AgentThreadStore using Azure Blob Storage, along with corresponding unit tests.

Key Changes:

• New AzureBlobAgentThreadStore implementation for persisting agent threads to Azure Blob Storage
• Extension methods to configure agents with Azure Blob thread store
• Unit tests with Azurite emulator support for local testing
• CI/CD workflow updates to start Azurite for running tests

Reviewed Changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
dotnet/src/Microsoft.Agents.AI.Hosting.AzureStorage/Blob/AzureBlobAgentThreadStore.cs	Core implementation for Azure Blob Storage thread persistence
dotnet/src/Microsoft.Agents.AI.Hosting.AzureStorage/Blob/AzureBlobAgentThreadStoreOptions.cs	Configuration options for the blob store
dotnet/src/Microsoft.Agents.AI.Hosting.AzureStorage/HostedAgentBuilderExtensions.Blob.cs	Extension methods for configuring agents with blob storage
dotnet/tests/Microsoft.Agents.AI.Hosting.AzureStorage.UnitTests/AzureBlobAgentThreadStoreTests.cs	Unit tests for the blob store implementation
dotnet/tests/Microsoft.Agents.AI.Hosting.AzureStorage.UnitTests/TestRunner.cs	Test helper for running agent scenarios
dotnet/tests/Microsoft.Agents.AI.Hosting.AzureStorage.UnitTests/Mock/MockChatClient.cs	Mock chat client for testing
dotnet/tests/Microsoft.Agents.AI.Hosting.AzureStorage.UnitTests/AzureStorageEmulatorAvailabilityHelper.cs	Helper for checking Azurite availability
dotnet/samples/AgentWebChat/AgentWebChat.AgentHost/Program.cs	Sample code demonstrating blob storage usage
.github/workflows/dotnet-build-and-test.yml	CI workflow updated to start Azurite

Comments suppressed due to low confidence (1)

dotnet/tests/Microsoft.Agents.AI.Hosting.AzureStorage.UnitTests/Mock/MockChatClient.cs:28

• This assignment to lastUserMessage is useless, since its value is never read.

 ChatMessage lastUserMessage = messageList.LastOrDefault(m => m.Role == ChatRole.User)
?? new ChatMessage(ChatRole.User, "No user message");