π-DAX — Dual Active eXtension

DAX is a symbiont for the Pi coding agent.

In Star Trek: Deep Space Nine, the Dax symbiont joins with a host, carrying the memories and wisdom of past lifetimes. π-DAX brings that same spirit to LLM-assisted development: a lightweight secondary model joins with the primary worker model, offering real-time peer review, loop detection, and oversight — not as a command-and-control watchdog, but as an active partner that helps the host produce better code.

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How It Works

Example: Two local models communicate via llama.cpp (or any OpenAI-compatible server):

Role	Model	Port	Responsibility
Host (Worker)	Gemma 4 12B	:8080	Drives the conversation, writes code, executes tools
DAX (Symbiont)	Qwen 3.5 4B	:8081	Reviews every edit, detects loops, prunes repeating context

DAX hooks into three Pi lifecycle events:

• tool_call — Tracks tool repetition for loop detection; intercepts write/edit and sends the proposed change to DAX for peer review. If DAX finds bugs, the edit is blocked and feedback is returned to the host.
• message_end — Heuristic loop detection via Jaccard similarity of consecutive assistant messages.
• context — Queries the DAX LLM for semantic loop verification; prunes looping turns and injects a steering warning when a loop is confirmed.

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Project Structure

pi-dax/
├── src/
│   ├── index.ts          # Extension entry point (default export, event handlers)
│   ├── config.ts         # DAX provider configuration (models.json, API keys)
│   ├── peer-review.ts    # Code review logic (reviewCodeChange)
│   └── loops.ts          # Loop detection & pruning utilities
├── tests/                # Test files
├── package.json          # Package manifest with pi.extensions registration
├── tsconfig.json         # TypeScript configuration
├── README.md             # You are here
└── LICENSE               # MIT

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Setup

Prerequisites

• Pi coding agent installed
• Two llama.cpp server instances (or any OpenAI-compatible API)

Step 1: Start the llama.cpp Servers

Host (Worker, port 8080):

./llama-server -m models/gemma-4-12b.gguf --port 8080

DAX (Symbiont / Reviewer, port 8081):

./llama-server -m models/qwen-4b.gguf --port 8081

Step 2: Configure Pi Models (models.json)

Edit ~/.pi/agent/models.json to register the models. You can either run both models locally (Option A), or route the DAX symbiont to a remote API provider like OpenRouter or OpenAI (Option B).

[!IMPORTANT] The provider key in the providers object must be exactly named "local-dax", as the extension explicitly looks up this identifier under the hood—even when it resolves to a remote endpoint.

Option A: Fully Local Setup (Gemma + Qwen)

For a fully offline setup using two local llama.cpp servers:

{
  "providers": {
    "local-worker": {
      "baseUrl": "http://localhost:8080/v1",
      "api": "openai-completions",
      "apiKey": "local",
      "compat": {
        "supportsDeveloperRole": false,
        "supportsReasoningEffort": false
      },
      "models": [
        {
          "id": "gemma-4-12b",
          "name": "Gemma 4 12B (Host)",
          "contextWindow": 262144
        }
      ]
    },
    "local-dax": {
      "baseUrl": "http://localhost:8081/v1",
      "api": "openai-completions",
      "apiKey": "local",
      "compat": {
        "supportsDeveloperRole": false,
        "supportsReasoningEffort": false
      },
      "models": [
        {
          "id": "qwen-4b",
          "name": "Qwen 3.5 4B (DAX)",
          "contextWindow": 262144
        }
      ]
    }
  }
}

Note: For local llama-servers, the apiKey can be any placeholder string.

Option B: Remote Setup (e.g., OpenRouter / any OpenAI-compatible API)

If you prefer not to run a local server for the symbiont, configure the "local-dax" provider to point to a remote endpoint by supplying their base URL, model ID, and API key environment variable (which the extension will resolve in real time):

{
  "providers": {
    "local-dax": {
      "baseUrl": "https://openrouter.ai/api/v1",
      "api": "openai-completions",
      "apiKey": "$OPENROUTER_API_KEY",
      "models": [
        {
          "id": "qwen/qwen-2.5-7b-instruct",
          "name": "Qwen 2.5 7B (DAX)",
          "contextWindow": 32768
        }
      ]
    }
  }
}

Step 3: Configure Default Session Model

Create a project-local .pi/settings.json:

{
  "defaultModel": "local-worker/gemma-4-12b",
  "defaultProjectTrust": "trust"
}

Step 4: Load DAX

Option A — Install from npm (once):

pi install npm:pi-dax

Option B — Load from path (for local development):

pi -e /path/to/pi-dax/src/index.ts

Look for the startup notification:

DAX symbiont active — peer review & loop prevention on port 8081

Commands

• /dax — Show current DAX status
• /dax review on / /dax review off — Toggle peer code review

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Development

npm install
npm run typecheck   # TypeScript type checking
npm test            # Run tests

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The Symbiont Philosophy

DAX is not a supervisor. It is a symbiont — a partner that enhances the host without replacing it. The host makes the decisions and drives the work; DAX offers its accumulated wisdom in two critical moments:

• Before a file is written — reviewing code with fresh eyes
• When the host stalls — recognizing the loop and clearing the path forward

This symbiotic relationship gives the host the benefit of a second model's perspective without the overhead of explicit hand-offs, context switching, or multi-agent orchestration.

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License

MIT