Add Microsoft.ModelContextProtocol.HttpServer.Distributed package

[xiangyan99]

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Added the Microsoft.ModelContextProtocol.HttpServer.Distributed package

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• Required for All PRs
  • Read contribution guidelines
  • PR title clearly describes the change
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  • Added comprehensive tests for new/modified functionality
  • Updated servers/Azure.Mcp.Server/CHANGELOG.md and/or servers/Fabric.Mcp.Server/CHANGELOG.md for product changes (features, bug fixes, UI/UX, updated dependencies)
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[Copilot]

Pull request overview

This PR introduces a new Microsoft.ModelContextProtocol.HttpServer.Distributed package that adds distributed session affinity support for MCP HTTP servers, along with a dedicated test project and documentation.

Changes:

• Adds a distributed session affinity infrastructure (HybridCache-based ISessionStore, endpoint filter, listening endpoint resolver, and semantic logging) and wires it via DI/endpoint extension methods.
• Adds comprehensive unit and integration tests covering serialization, options validation, endpoint routing behavior, and real Kestrel multi-server scenarios.
• Defines packaging metadata, local build configuration, and standalone solution/props for the new package, plus README and release notes.

Reviewed changes

Copilot reviewed 29 out of 29 changed files in this pull request and generated 13 comments.

Show a summary per file

File	Description
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/Directory.Build.props	Defines local build defaults (TFM, language, warnings) for the library and tests; note that IsPackable=false currently conflicts with the csproj’s package configuration.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/Directory.Packages.props	Sets package versions for this sub-solution, decoupling it from the repo’s root central package versions.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/Microsoft.ModelContextProtocol.HttpServer.Distributed.slnx	Adds a small solution that includes the new src and test projects for focused development.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/src/Microsoft.ModelContextProtocol.HttpServer.Distributed.csproj	Configures the new library as a NuGet package (ID, version, metadata, AOT compatibility, and runtime dependencies on HybridCache and YARP).
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/src/Abstractions/ISessionStore.cs	Introduces the abstraction for a session ownership store (GetOrClaimOwnershipAsync / RemoveAsync) used by the affinity layer.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/src/Abstractions/SessionOwnerInfo.cs	Defines the SessionOwnerInfo record (owner ID, address, claimed timestamp) that represents session ownership.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/src/Abstractions/SessionAffinityOptions.cs	Adds configurable options for session affinity (forwarder/client configs, HybridCache key, LocalServerAddress with a validation attribute).
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/src/Abstractions/SessionAffinityOptionsValidator.cs	Uses [OptionsValidator] to generate options validation based on SessionAffinityOptions’ data annotations.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/src/Abstractions/ISessionAffinityBuilder.cs	Provides a simple builder interface exposing IServiceCollection for the affinity setup API.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/src/Abstractions/IListeningEndpointResolver.cs	Defines how to resolve the local server address for advertising/forwarding (explicit vs. from server bindings).
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/src/HybridCacheSessionStore.cs	Implements ISessionStore on top of HybridCache, including sliding-style expiration and semantic logging for retrieval/removal.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/src/SessionOwnerInfoSerializer.cs	Adds a source-generated IHybridCacheSerializer<SessionOwnerInfo> using SerializerContext for AOT-safe JSON serialization.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/src/SerializerContext.cs	Declares the JsonSerializerContext with camelCase naming and WhenWritingNull ignore behavior for SessionOwnerInfo.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/src/ListeningEndpointResolver.cs	Implements IListeningEndpointResolver to pick the effective local endpoint from options or IServerAddressesFeature with a priority strategy.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/src/SessionAffinityEndpointFilter.cs	Core endpoint filter that resolves/claims session ownership, forwards non-owned requests via YARP, and cleans up stale sessions.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/src/ServiceCollectionExtensions.cs	Adds AddMcpHttpSessionAffinity to wire up HybridCache (with custom serializer), the session store, YARP, the resolver, and the endpoint filter.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/src/SessionAffinityBuilder.cs	Concrete ISessionAffinityBuilder implementation wrapping the service collection.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/src/MapSessionAffinityExtensions.cs	Provides the WithSessionAffinity endpoint convention extension that injects SessionAffinityEndpointFilter into MapMcp endpoints.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/src/SemanticLogging.cs	Defines event IDs and source-generated LoggerMessage extension methods for structured logging of session and forwarding operations.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/tests/Microsoft.ModelContextProtocol.HttpServer.Distributed.Tests.csproj	Creates the test project with references to the library and test dependencies (xUnit v3, NSubstitute, TestHost, MCP client/server).
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/tests/SessionOwnerInfoSerializerTests.cs	Verifies JSON serialization/deserialization behavior for SessionOwnerInfo including null handling, camelCase naming, and multi-segment buffers.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/tests/SessionAffinityOptionsValidationTests.cs	Tests data-annotation validation, options validator registration, and URI scheme correctness for SessionAffinityOptions.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/tests/ListeningEndpointResolverTests.cs	Thoroughly tests ListeningEndpointResolver across explicit config, binding combinations, localhost detection, and edge cases.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/tests/SessionAffinityEndpointFilterTests.cs	Unit-tests the endpoint filter’s behavior for local vs remote ownership, forwarding errors, 404 cleanup, scheme selection, and restart/stale-session scenarios.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/tests/KeyedServiceTests.cs	Ensures DI registration for the session affinity services works with/without a HybridCache service key and that the session store behaves correctly.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/tests/RealServerIntegrationTests.cs	Adds integration tests using real Kestrel servers and shared cache to validate session affinity and load-balancing semantics end-to-end.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/tests/TESTSERVER_SESSION_AFFINITY.md	Describes design options and tradeoffs for handling session affinity in tests, especially around TestServer vs real Kestrel.
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/README.md	Provides package overview, configuration guidance, and usage samples for enabling distributed session affinity (some API/property names currently diverge from the actual code).
core/Microsoft.ModelContextProtocol.HttpServer.Distributed/RELEASE_NOTES.md	Introduces a release notes file for this package, but the documented version does not yet match the csproj version.