One Codex UI to rule eighteen coding agents

What it does

Harness Mix is a local kernel that connects official Codex Desktop’s native interface to a crowd of coding agents — Claude Code, OpenCode, Grok, Cursor CLI, Cline, Kimi Code, DeepSeek, and more (18 registered in total). Default Codex sessions still go straight to the official app-server; only when you explicitly pick another harness does the separate Harness Mix Host step in. Sub-agents spawned by each harness show up as native cards in the Codex content stream, so you never bounce back to each vendor’s client.

The interesting bit

The handoff system: four relay modes (continue, execute plan, independent review, re-analyze) let a task pass between harnesses with sanitized checkpoints and evidence trails. It’s honest about capabilities too — adapters declare what they support in a manifest, and the UI renders only what’s real rather than guessing from names. Credentials, models, and tool approvals stay with each harness.

Key highlights

• Cross-harness task relay via /switch with persisted, sanitized checkpoints
• Multi-agent orchestration: any harness can be team lead; six preset team templates (bug review, feature dev, refactoring, etc.)
• Native sub-agent panel — 16 of 18 harnesses wired in (Trae and Kiro CLI pending)
• History import from Pi / Claude / Codex / CodeBuddy with # reference injection and read-only MCP tools for paging
• Usage center aggregating ~90 days of tokens, cost, and report counts across harnesses
• Failure classification (connection / login / quota / rejected / service) with suggested recovery actions

Caveats

• macOS/Linux support is source-build only; full desktop acceptance hasn’t been run on those machines per the README
• The README is dense and mostly Chinese; the English section is thin
• A skin marketplace (Miku, Genshin Night themes) is a curious feature for a developer tool — harmless, but tells you where some energy went

Verdict

Worth a look if you juggle multiple coding agents and want one native-feeling cockpit with real handoffs. If you’re a one-harness person, this is a lot of machinery for a problem you don’t have.