Refresh the Codex runtime docs

Refresh the Codex runtime docs and cross-link the Codex harness, OpenAI provider, agent runtime, plugin hook, ACP agent, and status pages.

docs/concepts/agent-runtimes.md

@@ -46,6 +46,10 @@ That means OpenClaw selects an OpenAI model ref, then asks the Codex app-server
 runtime to run the embedded agent turn. It does not mean the channel, model
 provider catalog, or OpenClaw session store becomes Codex.
 
+For the OpenAI-family prefix split, see [OpenAI](/providers/openai) and
+[Model providers](/concepts/model-providers). For the Codex runtime support
+contract, see [Codex harness](/plugins/codex-harness#v1-support-contract).
+
 ## Runtime ownership
 
 Different runtimes own different amounts of the loop.
@@ -84,7 +88,9 @@ OpenClaw chooses an embedded runtime after provider and model resolution:
 
 Explicit plugin runtimes fail closed by default. For example,
 `runtime: "codex"` means Codex or a clear selection error unless you set
-`fallback: "pi"` in the same override scope.
+`fallback: "pi"` in the same override scope. A runtime override does not inherit
+a broader fallback setting, so an agent-level `runtime: "codex"` is not silently
+routed back to PI just because defaults used `fallback: "pi"`.
 
 ## Compatibility contract
 
@@ -122,6 +128,8 @@ session systems.
 ## Related
 
 - [Codex harness](/plugins/codex-harness)
+- [OpenAI](/providers/openai)
 - [Agent harness plugins](/plugins/sdk-agent-harness)
 - [Agent loop](/concepts/agent-loop)
 - [Models](/concepts/models)
+- [Status](/cli/status)

docs/concepts/model-providers.md

@@ -20,7 +20,8 @@ For model selection rules, see [/concepts/models](/concepts/models).
   OpenAI API-key provider in PI, `openai-codex/<model>` uses Codex OAuth in PI,
   and `openai/<model>` plus `agents.defaults.embeddedHarness.runtime: "codex"`
   uses the native Codex app-server harness. See [OpenAI](/providers/openai)
-  and [Codex harness](/plugins/codex-harness).
+  and [Codex harness](/plugins/codex-harness). If the provider/runtime split is
+  confusing, read [Agent runtimes](/concepts/agent-runtimes) first.
 - Plugin auto-enable follows that same boundary: `openai-codex/<model>` belongs
   to the OpenAI plugin, while the Codex plugin is enabled by
   `embeddedHarness.runtime: "codex"` or legacy `codex/<model>` refs.
@@ -75,6 +76,8 @@ OpenClaw ships with the pi‑ai catalog. These providers require **no**
 - Optional rotation: `OPENAI_API_KEYS`, `OPENAI_API_KEY_1`, `OPENAI_API_KEY_2`, plus `OPENCLAW_LIVE_OPENAI_KEY` (single override)
 - Example models: `openai/gpt-5.4`, `openai/gpt-5.4-mini`
 - GPT-5.5 direct API support is future-ready here once OpenAI exposes GPT-5.5 on the API
+- Verify direct API availability with `openclaw models list --provider openai`
+  before using `openai/gpt-5.5` without the Codex app-server runtime
 - CLI: `openclaw onboard --auth-choice openai-api-key`
 - Default transport is `auto` (WebSocket-first, SSE fallback)
 - Override per model via `agents.defaults.models["openai/<model>"].params.transport` (`"sse"`, `"websocket"`, or `"auto"`)
@@ -118,6 +121,7 @@ OpenClaw ships with the pi‑ai catalog. These providers require **no**
 - Auth: OAuth (ChatGPT)
 - PI model ref: `openai-codex/gpt-5.5`
 - Native Codex app-server harness ref: `openai/gpt-5.5` with `agents.defaults.embeddedHarness.runtime: "codex"`
+- Native Codex app-server harness docs: [Codex harness](/plugins/codex-harness)
 - Legacy model refs: `codex/gpt-*`
 - Plugin boundary: `openai-codex/*` loads the OpenAI plugin; the native Codex
   app-server plugin is selected only by the Codex harness runtime or legacy