Add pi (badlogic/pi-mono) support with documented LiteLLM gateway configuration

[srid]

Summary

Please add first-class support (or documented configuration) for running pi (@earendil-works/pi-coding-agent) against the Juspay LiteLLM gateway (https://grid.ai.juspay.net).

Background

opencode works against the gateway today via the @ai-sdk/openai-compatible provider, so running e.g. kimi-k3 needs only:

"litellm": {
  "models": { "kimi-k3": { "name": "kimi-k3", "limit": { "context": 256000, "output": 32000 }, ... } },
  "npm": "@ai-sdk/openai-compatible",
  "options": { "apiKey": "{env:JUSPAY_API_KEY}", "baseURL": "https://grid.ai.juspay.net" }
}

pi has no litellm provider, but it does support arbitrary OpenAI-compatible endpoints via ~/.pi/agent/models.json, so the equivalent configuration is:

{
  "providers": {
    "litellm": {
      "baseUrl": "https://grid.ai.juspay.net",
      "api": "openai-completions",
      "apiKey": "$JUSPAY_API_KEY",
      "models": [
        {
          "id": "kimi-k3",
          "name": "kimi-k3",
          "reasoning": false,
          "input": ["text", "image"],
          "contextWindow": 256000,
          "maxTokens": 32000
        }
      ]
    }
  }
}

then:

pi --model litellm/kimi-k3
# or via nixpkgs:
nix run nixpkgs#pi-coding-agent -- --model litellm/kimi-k3

Request

• Document (or generate) the pi models.json mapping for the gateway, the same way opencode config is already handled.
• Ideally keep the model IDs, context windows, and output limits in sync with the opencode config so the two agents agree on each model's limits.

Open questions / things worth verifying on the pi side

• Whether grid.ai.juspay.net accepts pi's default developer role / reasoning_effort for reasoning models, or whether per-provider "compat": { "supportsDeveloperRole": false, "supportsReasoningEffort": false } is required.
• Whether reasoning: true models map onto any gateway-supported thinking-level parameter, or whether reasoning must be left off.

This is analogous to #22 (Claude Code) and #70 (Codex) — filling in the pi story would round out the supported-agent matrix.