Add custom agent reasoning effort across SDKs

[roji]

Summary

• add optional per-agent reasoning effort to every SDK binding
• serialize the wire field as reasoningEffort without adding an SDK default
• document finalized omission semantics: when per-agent effort is omitted, the SDK sends no override and the backend chooses its default; the parent/session effort is not inherited
• add focused serialization, cloning, builder, and DTO tests

This is SDK-side changes to support https://github.com/github/copilot-agent-runtime/pull/11166 (runtime PR).

Closes github/copilot-sdk-internal#195.

Validation

• Node.js: Prettier, ESLint, TypeScript typecheck, targeted Vitest (3 passed)
• Python: Ruff, ty, targeted pytest (4 passed)
• Go: gofmt, go vet, targeted go test
• .NET: dotnet format, targeted tests (34 passed)
• Java: Spotless, Checkstyle, targeted Maven verify (27 passed; integration tests skipped)
• Rust: rustfmt, Clippy library target, targeted tests (7 passed)

[Copilot]

Pull request overview

Adds optional per-agent reasoning effort across all SDKs while preserving wire omission semantics.

Changes:

• Adds language-specific custom-agent reasoning effort APIs.
• Serializes the field as reasoningEffort.
• Adds tests and documentation.

Show a summary per file

File	Description
rust/src/types.rs	Adds Rust field, builder, and tests.
python/test_client.py	Tests Python wire conversion.
python/copilot/session.py	Adds Python typed configuration.
python/copilot/client.py	Converts the field to camel case.
nodejs/test/client.test.ts	Tests Node.js request payloads.
nodejs/src/types.ts	Adds the TypeScript property.
java/src/test/java/com/github/copilot/DataObjectCoverageTest.java	Tests Java DTO behavior.
java/src/main/java/com/github/copilot/rpc/CustomAgentConfig.java	Adds Java getter and setter.
go/types.go	Adds the Go JSON field.
go/types_test.go	Tests Go serialization and omission.
dotnet/test/Unit/SerializationTests.cs	Tests .NET serialization.
dotnet/test/Unit/CloneTests.cs	Covers cloning the new property.
dotnet/src/Types.cs	Adds the .NET property.
docs/features/custom-agents.md	Documents model and reasoning overrides.

Review details

• Files reviewed: 14/14 changed files
• Comments generated: 2
• Review effort level: Medium

[github-actions]

Cross-SDK Consistency Review ✅

This PR adds reasoningEffort to CustomAgentConfig consistently across all six SDK implementations. The changes are well-aligned:

SDK	Field name	Wire name	Type
Node.js	reasoningEffort	reasoningEffort	ReasoningEffort (typed)
Python	reasoning_effort	reasoningEffort	ReasoningEffort (typed)
Go	ReasoningEffort	reasoningEffort	string
.NET	ReasoningEffort	reasoningEffort	string?
Java	reasoningEffort / setReasoningEffort	reasoningEffort	String
Rust	reasoning_effort	reasoningEffort	Option<String>

All SDKs:

• Omit the field when unset (no default injected)
• Document the same omission semantics (backend chooses default; parent effort not inherited)
• Include serialization tests verifying both presence and absence

The naming conventions (camelCase for TS/Java, snake_case for Python/Rust, PascalCase for Go/.NET) match each language's established patterns and are consistent with how the existing model field is handled in the same struct.

No consistency issues found.

Generated by SDK Consistency Review Agent for issue #1981 · sonnet46 430.9K · ◷