sdk: Expose disabled MCP servers across languages

[connor4312]

Why

SDK consumers can supply MCP servers and plugin directories per session, but cannot currently prevent a discovered server from starting before the first turn. The global disabledMcpServers setting avoids startup but persists user state and has the wrong scope.

This addresses https://github.com/github/copilot-mcp-core/issues/2056.

Companion runtime contract PR: https://github.com/github/copilot-agent-runtime/pull/14727

What

Expose session-scoped disabled MCP server names on create and resume across all six SDKs:

• Node: disabledMcpServers
• Python: disabled_mcp_servers
• Go: DisabledMCPServers
• .NET: DisabledMcpServers
• Java: setDisabledMcpServers(...)
• Rust: with_disabled_mcp_servers(...)

The exact names are forwarded as disabledMcpServers without writing global settings. Omission preserves existing behavior; Python and Go also preserve an explicitly empty list.

The Node E2E coverage uses real plugin-provided stdio servers and the built-in github-mcp-server to prove:

• a separate post-create non-MCP RPC does not start MCP;
• the first user message starts enabled plugin servers but never spawns disabled ones;
• a disabled built-in GitHub MCP makes no /mcp request;
• an enabled control reaches connected;
• cold resume applies the session-scoped disabled set before startup.

Testing

• Node build, typecheck, format check, lint, and unit tests
• Node disabled-MCP E2E against the locally built runtime: 3/3 passed
• Go tests
• Rust formatting and 204 library tests
• Cross-language serialization/copy tests added for Python, Java, and .NET; those toolchains were unavailable locally
• Persistent local proof covered first-message startup, no-global-mutation, direct list, and cold resume

Release note

The option is backward-compatible and targets the existing legacy session.create / session.resume wire field. After the runtime contract PR is released, SDK codegen can be refreshed to expose the same field through generated sessions.open options.

[Copilot]

Pull request overview

Adds session-scoped disabled MCP server configuration across all six SDKs without modifying global settings.

Changes:

• Exposes and forwards disabled server names during create and resume.
• Adds serialization, cloning, and E2E coverage.
• Documents cross-language configuration names and behavior.

Show a summary per file

File	Description
test/harness/test-mcp-server.mjs	Adds configurable server names and startup markers.
test/harness/replayingCapiProxy.ts	Adds a hermetic /mcp transport mock.
rust/src/wire.rs	Adds create and resume wire fields.
rust/src/types.rs	Adds Rust configuration APIs and tests.
python/test_client.py	Tests Python forwarding and omission semantics.
python/copilot/client.py	Adds Python create and resume options.
nodejs/test/e2e/disabled_mcp_servers.e2e.test.ts	Tests create, built-in, and cold-resume behavior.
nodejs/test/client.test.ts	Tests Node.js request forwarding.
nodejs/src/types.ts	Defines the Node.js public option.
nodejs/src/client.ts	Forwards the Node.js option.
java/src/test/java/com/github/copilot/SessionRequestBuilderTest.java	Tests Java request serialization.
java/src/test/java/com/github/copilot/ConfigCloneTest.java	Tests Java configuration cloning.
java/src/main/java/com/github/copilot/SessionRequestBuilder.java	Copies configuration into requests.
java/src/main/java/com/github/copilot/rpc/SessionConfig.java	Adds Java create-session configuration.
java/src/main/java/com/github/copilot/rpc/ResumeSessionRequest.java	Adds the Java resume wire field.
java/src/main/java/com/github/copilot/rpc/ResumeSessionConfig.java	Adds Java resume configuration.
java/src/main/java/com/github/copilot/rpc/CreateSessionRequest.java	Adds the Java create wire field.
go/types.go	Adds Go public and wire fields.
go/client.go	Preserves nil versus empty Go lists.
go/client_test.go	Tests Go serialization semantics.
dotnet/test/Unit/SerializationTests.cs	Tests .NET wire serialization.
dotnet/test/Unit/CloneTests.cs	Tests .NET collection cloning.
dotnet/src/Types.cs	Adds the .NET public property.
dotnet/src/Client.cs	Forwards the .NET property.
docs/features/mcp.md	Documents session-scoped disabling.

Review details

• Files reviewed: 25/25 changed files
• Comments generated: 1
• Review effort level: Balanced

[Copilot]

Review details

Suppressed comments (1)

nodejs/test/e2e/disabled_mcp_servers.e2e.test.ts:439

• This cold-resume test uses the global 30-second Vitest timeout, even though both polling helpers below allow up to 60 seconds and the test starts two runtimes. On slower CI hosts, Vitest can abort a valid run before those waits complete. Give this test the same explicit extended timeout as the two preceding MCP tests.

 "applies disabled plugin MCP servers on cold stdio resume",
async () => {

• Files reviewed: 25/25 changed files
• Comments generated: 0 new
• Review effort level: Balanced

[Copilot]

Review details

• Files reviewed: 25/25 changed files
• Comments generated: 0 new
• Review effort level: Balanced