Building SoloAgent to understand AI harnesses

To understand how the harness layer in modern AI workflows actually works, I built one myself.

I was not trying to sell anything. This was a practical experiment to measure how much work it takes to wire a usable local AI coding harness end to end.

The result is SoloAgent: a local desktop app for per-project workspaces, scoped chat context, terminal execution, and live git visibility.

Why I built this harness

I wanted first-hand constraints instead of abstract takes:

• what state needs to persist between prompts, tools, and spaces
• how tool calls should stream and render without killing UX
• where terminal and git integration create real complexity
• what a practical local AI harness looks like without cloud lock-in

What I mean by an AI harness

For this project, an AI harness is the runtime shell around the model:

• input and context shaping
• tool execution and trace visibility
• local command/terminal integration
• persistence for history, settings, and state
• iteration loops so prompts can be tested and refined quickly

What SoloAgent currently does as a harness

• Project + space-scoped chat context
• Streaming assistant responses with tool trace rendering
• PTY terminal workspace with tabs/splits
• Git Diff and file-tree insight panels
• SQLite-backed persistence for projects/settings/history

Core app/runtime

• Electron 39
• React 19
• TypeScript 5
• Node.js 22+
• SQLite via node:sqlite

AI harness + chat runtime

• @tanstack/ai
• @tanstack/ai-react
• @tanstack/ai-openai
• @tanstack/ai-client
• zod (typing/validation support)

Terminal + git workflow

• node-pty (PTY shell sessions)
• ghostty-web (terminal renderer)
• @pierre/diffs (diff rendering)
• Git + GitHub CLI (gh) integration
• codex CLI integration

UI + state

• Tailwind CSS 4
• Radix primitives (@radix-ui/react-*)
• lucide-react
• motion
• zustand
• react-markdown + remark-gfm
• react-syntax-highlighter

Build and quality tooling

• electron-vite
• Vite
• electron-builder
• ESLint
• Prettier
• Vitest

What this experiment gave me

The value was not a framework pitch. The value was implementation clarity.

I now have a better mental model for where harness complexity really lives: state boundaries, tool-call UX, terminal lifecycle, and git operations under real user behavior.

Related updates

• Project page: SoloAgent
• Layoff log: Week 3: SoloAgent AI harness experiment