Strongly type expAssignments session config across all SDKs

[devm33]

Summary

Strongly types the internal expAssignments session-config field across all six SDKs. Previously each SDK typed it as opaque JSON (Record<string, unknown> / any / dict / JsonElement / JsonNode / serde_json::Value). This replaces those with a concrete CopilotExpAssignmentResponse type (plus ExpConfigEntry) that mirrors the runtime contract from copilot-agent-runtime — the same shape the Copilot CLI fetches from the experimentation service.

This closes a gap from #1750, which forwarded expAssignments but left it loosely typed even though the runtime's in-process type (sessionOptions.ts) is the concrete CopilotExpAssignmentResponse.

Type shape

ExpConfigEntry { Id: string; Parameters: Record<string, string|number|boolean|null> }
CopilotExpAssignmentResponse {
  Features: string[]; Flights: Record<string,string>; Configs: ExpConfigEntry[];
  ParameterGroups?; FlightingVersion?: number; ImpressionId?: string;
  AssignmentContext: string;
}

Wire JSON keys stay PascalCase (Features, Flights, Configs, Id, Parameters, ...); optional fields are omitted when null; and the field keeps its @internal/hidden posture (not part of the broadly advertised public surface) in every language.

Changes per SDK

Each SDK updates the type, the create/resume config field, the wire path, clone/copy logic, and tests.

SDK	Key files	Validation
Node	nodejs/src/types.ts, index.ts	tsc + vitest
Go	go/types.go	build / vet / gofmt / test
Python	python/copilot/client.py, __init__.py	ruff + pytest
Rust	rust/src/types.rs, wire.rs	fmt + clippy -D warnings + test
.NET	dotnet/src/Types.cs, Client.cs	build + serialization tests
Java	new CopilotExpAssignmentResponse.java, ExpConfigEntry.java + rpc/*	spotless + checkstyle + tests

Testing

• Node — tsc --noEmit clean; vitest passing
• Go — go build/vet/gofmt/test passing
• Python — ruff + pytest passing
• Rust — cargo fmt --check, clippy --all-features --all-targets -- -D warnings, cargo test passing
• .NET — dotnet build clean; 46 serialization tests passing
• Java — mvn spotless:check + checkstyle clean; 85 SessionRequestBuilderTest tests passing (JDK 25)

[Copilot]

Pull request overview

Strongly types ExP assignment session configuration across all six SDKs while preserving PascalCase wire serialization.

Changes:

• Adds shared ExP response, configuration-entry, and flag-value types.
• Updates create/resume APIs and wire requests to use the new types.
• Revises serialization, clone, unit, and E2E tests.

Show a summary per file

File	Description
rust/tests/e2e/client_options.rs	Updates ExP forwarding tests.
rust/src/wire.rs	Types create/resume wire fields.
rust/src/types.rs	Adds ExP types, builders, and tests.
python/test_client.py	Tests typed ExP serialization.
python/copilot/client.py	Adds dataclasses and wire conversion.
python/copilot/__init__.py	Exports ExP types.
nodejs/test/client.test.ts	Updates typed payload fixture.
nodejs/src/types.ts	Defines ExP TypeScript types.
nodejs/src/index.ts	Exports ExP types.
java/src/test/java/com/github/copilot/SessionRequestBuilderTest.java	Updates request and clone tests.
java/src/main/java/com/github/copilot/rpc/SessionConfig.java	Types create configuration.
java/src/main/java/com/github/copilot/rpc/ResumeSessionRequest.java	Types resume wire request.
java/src/main/java/com/github/copilot/rpc/ResumeSessionConfig.java	Types resume configuration.
java/src/main/java/com/github/copilot/rpc/ExpConfigEntry.java	Adds ExP configuration entries.
java/src/main/java/com/github/copilot/rpc/CreateSessionRequest.java	Types create wire request.
java/src/main/java/com/github/copilot/rpc/CopilotExpAssignmentResponse.java	Adds ExP response model.
go/types.go	Adds ExP types and request fields.
go/internal/e2e/client_options_e2e_test.go	Updates forwarding scenarios.
go/client_test.go	Updates request serialization tests.
dotnet/test/Unit/SerializationTests.cs	Updates serialization and clone tests.
dotnet/src/Types.cs	Adds ExP models and serializer metadata.
dotnet/src/Client.cs	Types create/resume request records.

Review details

• Files reviewed: 22/22 changed files
• Comments generated: 6
• Review effort level: Medium

[Copilot]

Review details

• Files reviewed: 22/22 changed files
• Comments generated: 1
• Review effort level: Medium

[Copilot]

Review details

Comments suppressed due to low confidence (1)

python/copilot/client.py:3018

• The adjacent comment still describes this as “opaque JSON,” but this path now accepts and serializes a concrete CopilotExpAssignmentResponse. Update the comment so it does not contradict the new API.

            payload["expAssignments"] = _exp_assignment_response_to_dict(exp_assignments)

• Files reviewed: 22/22 changed files
• Comments generated: 1
• Review effort level: Medium

[Copilot]

Review details

• Files reviewed: 22/22 changed files
• Comments generated: 0 new
• Review effort level: Medium

[Copilot]

Review details

• Files reviewed: 22/22 changed files
• Comments generated: 0 new
• Review effort level: Medium

[vijayrathore5983-dev]

Vijay

Rathor

[github-actions]

Cross-SDK Consistency Review

The PR successfully adds strongly-typed CopilotExpAssignmentResponse, ExpConfigEntry, and ExpFlagValue across all six SDKs (Node.js, Python, Go, .NET, Java, Rust) in a consistent and well-documented way. The wire contract (PascalCase JSON keys, required collection fields default to empty arrays/objects rather than null) is faithfully mirrored in every language.

One minor inconsistency found: Python ExpConfigEntry.id has no default

All other SDKs default ExpConfigEntry.Id / id to an empty string:

• Go: ID string — zero-value is ""
• .NET: public string Id { get; set; } = string.Empty;
• Java: private String id = ""; (explicitly fixed in a follow-up commit in this very PR — commit 69ab40f)
• Rust: #[derive(Default)] pub id: String — zero value is ""
• Node.js/TypeScript: interface Id: string — no default needed at declaration

But in Python (python/copilot/client.py line 160), id has no default value:

`@dataclass`
class ExpConfigEntry:
    id: str          # no default — required positional argument
    parameters: dict[str, ExpFlagValue] = field(default_factory=dict)

Because id has no default but parameters does, Python dataclass rules force callers to always supply id — ExpConfigEntry() raises TypeError. The Java id field was explicitly defaulted to "" for exactly this reason. Suggest the same fix in Python:

    id: str = ""
    """Identifier of the configuration entry."""

This is minor since ExpConfigEntry is an internal/trusted-integrator type, but keeping zero-value construction consistent across all SDKs matches the stated goal of this PR.

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