Make MCPStdioServerConfig.args optional across all SDKs

[stephentoub]

Summary

The runtime schema (@github/copilot 1.0.51-2) now allows args to be omitted from stdio MCP server configurations. This PR updates the user-facing types across all five SDKs to match, and adds E2E test coverage for the omitted-args case.

Changes

Type changes:

SDK	Before	After
Node.js	args: string[]	args?: string[]
Go	json:"args"	json:"args,omitempty"
Python	args: list[str]	args: NotRequired[list[str]]
Rust	#[serde(default)]	#[serde(default, skip_serializing_if = "Vec::is_empty")]
.NET	IList<string> Args { get => field ??= []; set; }	IList<string>? Args { get; set; }

E2E tests: Each SDK now has a test that creates a session with MCPStdioServerConfig omitting args entirely, verifying the session creates and responds successfully.

Validation

• All SDK builds pass (Node.js, Go, .NET, Rust)
• TypeScript type-check passes
• Generated wire types already had args as optional — this aligns user-facing types

Fixes #1231

[Copilot]

Pull request overview

Updates the public SDK surface area (and accompanying E2E scenarios) to align with the updated runtime schema allowing MCPStdioServerConfig.args to be omitted for stdio/local MCP server configurations.

Changes:

• Made args optional/omittable in user-facing MCP stdio config types across Node.js, Go, Python, Rust, and .NET.
• Added cross-SDK E2E tests validating session creation and basic prompting works when args is omitted.
• Added new replay snapshots supporting the new E2E scenarios.

Show a summary per file

File	Description
test/snapshots/mcp_and_agents/should_accept_mcp_server_configuration_without_args.yaml	New replay snapshot for “should accept … without args” scenario.
test/snapshots/mcp_and_agents/accept_mcp_server_config_without_args.yaml	New replay snapshot for “accept … without args” scenario.
rust/tests/e2e/mcp_and_agents.rs	Adds Rust E2E coverage for omitted args.
rust/src/types.rs	Omits args from serialization when empty (treats omitted as default empty).
python/e2e/test_mcp_and_agents_e2e.py	Adds Python E2E coverage for omitted args.
python/copilot/session.py	Updates Python MCP stdio config typing to reflect optional args.
nodejs/test/e2e/mcp_and_agents.e2e.test.ts	Adds Node.js E2E coverage for omitted args.
nodejs/src/types.ts	Makes MCPStdioServerConfig.args optional in TS types.
go/types.go	Adds omitempty to omit args when unset/empty during JSON marshaling.
go/internal/e2e/mcp_and_agents_e2e_test.go	Adds Go E2E coverage for omitted args.
dotnet/test/E2E/SessionMcpAndAgentConfigE2ETests.cs	Adds .NET E2E coverage for omitted args.
dotnet/src/Types.cs	Makes Args nullable so it can be omitted on the wire when unset.

Copilot's findings

• Files reviewed: 12/12 changed files
• Comments generated: 1

[github-actions]

Cross-SDK Consistency Review ✅

This PR does an excellent job maintaining feature parity across all five SDK implementations. Here's a summary of the consistency analysis:

Changes Reviewed

SDK	Change	Serialization behavior
Node.js	args: string[] → args?: string[]	Field absent when not provided
Go	json:"args" → json:"args,omitempty"	Field omitted when nil/empty
Python	args: list[str] → args: NotRequired[list[str]]	Field absent when not provided
.NET	IList<string> Args { get => field ??= []; set; } → IList<string>? Args { get; set; }	Field omitted when null (via WhenWritingNull in TypesJsonContext and SerializerOptionsForMessageFormatter)
Rust	#[serde(default)] → #[serde(default, skip_serializing_if = "Vec::is_empty")]	Field omitted when empty

All five implementations now correctly omit args from the wire format when not supplied, aligning with the updated runtime schema.

E2E Coverage

E2E tests were added for all five SDKs, and the two snapshot YAML files correctly cover all test naming patterns:

• accept_mcp_server_config_without_args.yaml → Go and Rust tests
• should_accept_mcp_server_configuration_without_args.yaml → Node.js, Python, and .NET tests

Notes

• The .NET Args nullability change is safe because the SDK's JsonSerializerOptions configures DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull globally, ensuring null Args is omitted rather than serialized as "args": null.
• The Rust approach (Vec<String> with skip_serializing_if) is idiomatic — empty args and absent args are treated equivalently on the wire, which is the correct behavior here.

No cross-SDK inconsistencies found. 🎉

Generated by SDK Consistency Review Agent for issue #1347 · ● 549.2K · ◷