[SDK] Gemini CLI provider for .harness()

[santoshkumarradha]

Overview

Implement the Gemini CLI provider using subprocess (gemini CLI). No native SDK exists — CLI-only for both Python and TypeScript.

Branch: feat/harness-v2
Design doc: docs/design/harness-v2-design.md (Sections 4, 10.3)

Scope

Python (sdk/python/agentfield/harness/providers/)

• gemini.py — GeminiProvider implementing HarnessProvider:
  • CLI: gemini --output-format json [--model model] [--approval-mode yolo] prompt
  • Parse JSON/JSONL output from stdout
  • Extract final result, messages, metrics
  • cwd passed as subprocess working directory
  • Binary path via gemini_bin
• Register in _factory.py for "gemini"
• Tests with mocked subprocess

TypeScript (sdk/typescript/src/harness/providers/)

• gemini.ts — GeminiProvider implementing HarnessProvider
  • Uses shared CLI subprocess utility from cli.ts
• Register in factory.ts
• Tests

Key Details

• --output-format json or --output-format stream-json for JSONL output
• --approval-mode yolo maps to permission_mode: "auto"
• --model <model> for model selection
• No native schema support — relies entirely on file-write strategy
• Binary path configurable via HarnessConfig.gemini_bin

Acceptance Criteria

• CLI command constructed correctly
• Output parsing works for Gemini's JSON format
• Handles binary not found
• Handles non-zero exit codes
• Reuses shared CLI utilities from Codex issue
• All tests pass

Dependencies

• Depends on: [SDK] Core types & provider interface for .harness() #199 (types), [SDK] HarnessRunner with retry & schema orchestration for .harness() #201 (runner), [SDK] Codex provider for .harness() #203 (codex — for shared CLI utils), [SDK] Wire .harness() into Agent class #204 (agent wiring)

[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 #205 in the description

Happy coding! 🚀