Support for Codex via Plano (#808)

* Add Codex CLI support; xAI response improvements

* Add native Plano running check and update CLI agent error handling

* adding PR suggestions for transformations and code quality

* message extraction logic in ResponsesAPIRequest

* xAI support for Responses API by routing to native endpoint + refactor code

demos/llm_routing/codex_router/config.yaml

@@ -0,0 +1,38 @@
+version: v0.3.0
+
+listeners:
+  - type: model
+    name: model_listener
+    port: 12000
+
+model_providers:
+  # OpenAI models used by Codex defaults and preference routing
+  - model: openai/gpt-5.3-codex
+    default: true
+    access_key: $OPENAI_API_KEY
+    routing_preferences:
+      - name: code generation
+        description: generating new code snippets, functions, or boilerplate based on user prompts or requirements
+
+  - model: xai/grok-4-1-fast-non-reasoning
+    access_key: $GROK_API_KEY
+    routing_preferences:
+      - name: project understanding
+        description: understand repository structure, codebase, and code files, readmes, and other documentation
+
+  # Additional providers (optional): Codex can route to any configured model
+  # - model: anthropic/claude-sonnet-4-5
+  #   access_key: $ANTHROPIC_API_KEY
+
+  # - model: xai/grok-4-1-fast-non-reasoning
+  #   access_key: $GROK_API_KEY
+
+  - model: ollama/llama3.1
+    base_url: http://localhost:11434
+
+model_aliases:
+  arch.codex.default:
+    target: gpt-5.3-codex
+
+tracing:
+  random_sampling: 100