🛠️ HarnessRouter: Unified API for Agent Harnesses

As various coding agents like Claude Code, Codex, and DeepSeek Harness emerge, managing and routing them becomes a new challenge. HarnessRouter addresses this by providing a self-hosted, Apache-2.0 licensed gateway that unifies different agent engines under a single API. The hard part is not simply forwarding requests, but managing complex interaction states. It implements the open standard UHP (Unified Harness Protocol), handling sessions, streaming, file operations, task cancellation, and failure recovery. The direction here is clear: developers want to maintain control over their infrastructure while avoiding vendor lock-in with any single agent framework.