docs: PZERO custom model_providers example

What is the type of issue?

• Documentation is missing

What is the issue?

Codex already supports custom model_providers in ~/.codex/config.toml. People looking for prepaid, privacy-first inference still have to guess base_url, wire_api, and whether the key goes in experimental_bearer_token or a ChatGPT login.

A named PZERO example on the custom-provider docs (or docs/example-config.md) would let users copy this and launch. No bundled Codex plugin required.

Append to ~/.codex/config.toml. Do not pin model or model_provider in the file. Pick those at launch.

[model_providers.pzero]
name = "PZERO"
base_url = "https://api.pzero.studio/v1"
experimental_bearer_token = "pzero_YOUR_KEY"
wire_api = "responses"
requires_openai_auth = false

codex -c model_provider="pzero" -c model="deepseek-v4-flash"

Get a key: https://pzero.studio/agents (sign-in free; min top-up 1 USDC on Base; no starter credits). Live text ids: GET https://api.pzero.studio/v1/models (public). A pzero/ model prefix is optional.

PZERO POST /v1/responses exists (401 without a key). That is why wire_api = "responses". Chat completions also exist at POST /v1/chat/completions if a later Codex path needs them.

I am not asking for a first-party provider next to OpenAI. Custom model_providers is the existing seam.

Every AI Credit is at least 20% off $1 list. Usage is paid. Do not start implementation on my behalf until the board says Ready; the config is for users today.

Where did you find it?

• https://developers.openai.com/codex/config-advanced
• https://github.com/openai/codex/blob/main/docs/config.md
• PZERO side (already shipping): https://docs.pzero.studio/integrations/codex

Start with docs/config.md and the custom model_providers section linked in the issue; compare whether docs/example-config.md is the better location. Add the PZERO TOML example and launch command without pinning model or model_provider, then verify the documentation clearly explains the provider settings and key setup.