docs(examples): add codex_with_skill_and_mcp example

[yaozheng-fang]

What

A runnable example (examples/codex_with_skill_and_mcp/) of a runtime="codex" agent that uses both a local skill and an MCP tool on a chat backend (Ark) — tying together #640 (skill passthrough) and #641 (MCP/function tool passthrough).

codex_with_skill_and_mcp/
├── main.py                     # the agent + a sample run
├── mcp_server.py               # a tiny stdio MCP server (get_weather)
├── skills/weather-style/SKILL.md
└── README.md / README.zh.md

The agent wires them the ordinary way — SkillToolset(skills=[load_skill_from_dir(...)]) + MCPToolset(StdioServerParameters(...)) — and the codex runtime routes each: the skill is materialized into $CODEX_HOME/skills/, the MCP tool is executed by the Responses shim.

Small code change

tools_bridge now skips skill toolsets (SkillToolset / SkillsToolset) so their internal tools (list_skills / load_skill / …) aren't also shim-executed — skills are handled by the materialization path (#640). Without this, an agent with both a skill and an MCP tool would double-expose the skill machinery.

Validation

Ran end to end on the bundled Codex binary + Ark (deepseek):

skills.py: materialized 1 skill(s) into .../skills
tools_bridge: bridging 1 agent tool(s): ['get_weather']   # guard: only the MCP tool, not the skill toolset's tools
Agent: Beijing is currently sunny and 28°C ☀️              # MCP tool data flowed into the answer

Skill materialized + discovered, MCP tool bridged + executed + used, and the two coexist.

🤖 Generated with Claude Code