[SDK] Core types & provider interface for .harness()

[santoshkumarradha]

Overview

Define all foundational types for the .harness() feature: HarnessConfig, HarnessOptions, HarnessResult, RawResult, Metrics, Message, and the HarnessProvider protocol/interface. Also implement the provider factory skeleton.

Branch: feat/harness-v2
Design doc: docs/design/harness-v2-design.md (Sections 6, 7, 4.4)

Scope

Python (sdk/python/agentfield/harness/)

• __init__.py — public API exports
• _result.py — HarnessResult, RawResult, Metrics, Message dataclasses
• providers/_base.py — HarnessProvider Protocol class
• providers/_factory.py — build_provider() skeleton (raises for unknown providers)
• providers/__init__.py — exports
• Add HarnessConfig to sdk/python/agentfield/types.py (alongside AIConfig)
• Unit tests for all types (construction, defaults, validation)
• Unit tests for config resolution (constructor defaults + per-call overrides)

TypeScript (sdk/typescript/src/harness/)

• types.ts — all type/interface definitions
• providers/base.ts — HarnessProvider interface
• providers/factory.ts — buildProvider() skeleton
• providers/index.ts — exports
• index.ts — public API exports
• Unit tests for types and factory

Acceptance Criteria

• All types match the design doc
• HarnessConfig.provider is required (no default)
• Config resolution: per-call overrides > constructor defaults
• Factory raises/throws for unknown provider names
• All tests pass, no lint errors

Dependencies

• None (foundation issue)
• Blocks: [SDK] Schema handling with universal file-write strategy for .harness() #200, [SDK] HarnessRunner with retry & schema orchestration for .harness() #201, all provider issues

TDD Approach

Write tests for type construction, validation, and config resolution BEFORE implementing the types.

[github-actions]

Thanks for picking this up, @santoshkumarradha! 🎉

Here's what to expect:

• We'll check in after 7 days if we haven't heard an update
• After 14 days, we'll send a second reminder
• After 21 days without activity, we'll unassign to let others contribute

Tips for success:

• Drop a comment when you start working on it
• Share any blockers - we're here to help!
• Link your PR with Fixes #199 in the description

Happy coding! 🚀