C#: make per-client Environment coherent per transport

[SteveSandersonMS]

Problem

CopilotClientOptions.Environment is a per-client dictionary. That model works for child-process transports (each client = its own OS process with its own environment) but is incoherent for the in-process (FFI) transport, where the native Rust runtime loads into the single shared .NET host process. A process has one environment block, so "per-client env vars" cannot be honored for host-resident native code — the option silently did nothing there.

What this PR does (C# / SDK slice)

SDK (dotnet/src)

• Add Environment to ChildProcessRuntimeConnection — per-client env where it's actually coherent (stdio/TCP). Clear+replace semantics, matching options.Environment for easy migration.
• Guards in CopilotClient (fail loud instead of fail silent):
  • throw if options.Environment is set with RuntimeConnection.ForInProcess()
  • throw if options.Telemetry is set with the in-process transport (telemetry lowers to env vars read host-side, so it can't be honored per-client in-process)
  • throw if both options.Environment and the connection's Environment are set

Test harness (dotnet/test)

• E2ETestContext.CreateClient gains an environment parameter that routes the environment to the connection (child-process) or mirrors it onto the host process (in-process), and rejects options.Environment.
• All E2E call sites converted off options.Environment onto the new parameter, dogfooding ChildProcessRuntimeConnection.Environment.
• Removed the useStdio shortcut (misleading false == TCP overload); the few transport-pinned tests now set options.Connection directly.
• Pinned the file-telemetry E2E test to stdio (telemetry is unsupported in-process under the new guard).

Scope / follow-ups

This is deliberately the SDK-side slice: it makes every previously-silent incoherence a loud error and gives child-process transports the correct API shape. It does not make in-process telemetry (or in-process env) actually work — that requires threading the exporter/env config through the FFI boundary as explicit per-connection config in the runtime, which is a separate change. Deprecating options.Environment outright is planned for v2.

Validation

• SDK + tests build clean; dotnet format --verify-no-changes passes.
• Representative converted tests pass under both stdio and in-process transports (incl. the CLI-path-dependent ConnectionTokenTests/SessionFsSqlite and the stdio-pinned telemetry test).

[github-actions]

Cross-SDK Consistency Review ✅

All 18 changed files are in dotnet/ — no other SDK is modified. I reviewed whether the changes introduce patterns that should be replicated across Node.js, Python, Go, Java, and Rust.

Finding: No cross-SDK consistency action required.

Why this is .NET-specific

The core problem this PR fixes — CopilotClientOptions.Environment silently doing nothing for InProcessRuntimeConnection — is unique to .NET because it is the only SDK with an in-process (FFI) transport. The other five SDKs only have child-process and external-URI transport modes, so:

SDK	In-process transport?	Per-connection env?	Notes
.NET (this PR)	✅ InProcessRuntimeConnection	✅ New ChildProcessRuntimeConnection.Environment	Fix applies here
Node.js	❌	❌	options.env only; no incoherence possible
Python	❌	❌	CopilotClient(env=...) only; URI connections documented to ignore it
Go	❌	❌	ClientOptions.Env only; no incoherence possible
Java	❌	❌	CopilotClientOptions.environment only
Rust	❌	❌	No equivalent architecture

New .NET API: ChildProcessRuntimeConnection.Environment

This is the right place for env vars in .NET's transport hierarchy, but is not a pattern other SDKs need to adopt. They each have a single transport level (client options) and no in-process variant, so there's no semantic ambiguity to resolve.

The three new validation guards (options.Environment with in-process, options.Telemetry with in-process, and both env fields set simultaneously) are all specific to .NET's architecture.

Generated by SDK Consistency Review Agent for issue #1930 · sonnet46 1.2M · ◷

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Refactors .NET E2E harness/client environment handling to support transport-aware environment routing, adds a per-connection environment option for child-process transports, and updates tests to use the new pattern.

Changes:

• Update E2ETestContext.CreateClient to take an explicit environment parameter and route env vars via in-process host env or child-process connection env.
• Add ChildProcessRuntimeConnection.Environment and validate incompatible environment/telemetry options for in-process transport in CopilotClient.
• Update E2E tests to stop using CopilotClientOptions.Environment and to pin stdio/tcp via RuntimeConnection.

Show a summary per file

File	Description
dotnet/test/Harness/E2ETestContext.cs	Reworks client creation to route environment by transport and removes useStdio flag.
dotnet/test/E2E/TelemetryExportE2ETests.cs	Pins stdio transport explicitly for telemetry export test.
dotnet/test/E2E/SubagentHooksE2ETests.cs	Migrates env injection to CreateClient(environment: ...).
dotnet/test/E2E/SessionFsSqliteE2ETests.cs	Replaces useStdio with RuntimeConnection.ForStdio().
dotnet/test/E2E/RpcSessionStateExtrasE2ETests.cs	Migrates env injection to CreateClient(..., environment: env).
dotnet/test/E2E/RpcServerPluginsE2ETests.cs	Migrates env injection to CreateClient(environment: ...).
dotnet/test/E2E/RpcServerMiscE2ETests.cs	Migrates env handling to CreateClient(..., environment: env).
dotnet/test/E2E/RpcServerE2ETests.cs	Migrates env injection and replaces useStdio with explicit stdio connection.
dotnet/test/E2E/RpcMcpAndSkillsE2ETests.cs	Migrates env injection to CreateClient(environment: ...).
dotnet/test/E2E/RpcExtensionsLoadedE2ETests.cs	Passes env via CreateClient(..., environment: ...) while keeping stdio args.
dotnet/test/E2E/ProviderEndpointE2ETests.cs	Migrates env injection to CreateClient(environment: ...).
dotnet/test/E2E/PerSessionAuthE2ETests.cs	Migrates env injection to CreateClient(..., environment: ...).
dotnet/test/E2E/ModeHandlersE2ETests.cs	Migrates env injection to CreateClient(environment: ...).
dotnet/test/E2E/CopilotRequestWebSocketE2ETests.cs	Migrates env injection to CreateClient(..., environment: ...).
dotnet/test/E2E/ClientOptionsE2ETests.cs	Migrates env injection to CreateClient(..., environment: ...).
dotnet/test/ConnectionTokenTests.cs	Replaces useStdio: false with explicit TCP connection.
dotnet/src/Types.cs	Adds ChildProcessRuntimeConnection.Environment and clarifies CopilotClientOptions.Environment remarks.
dotnet/src/Client.cs	Adds env/telemetry validation for in-process transport and supports connection-scoped env for child processes.

Review details

• Files reviewed: 18/18 changed files
• Comments generated: 4
• Review effort level: Low