feat: introduce registry for tool handlers and schemas

[joerucci]

What

This PR refactors tool dispatch to use a centralized, registry-based system.

• Introduces a shared tool registry (registerTool, getToolHandler)
• Supports OpenAI-compatible tool schemas (FunctionTool)
• Enables alias resolution for legacy tool names (e.g. container.exec)
• Moves shell tool definition and handler into standalone modules
• Adds registerDefaultTools() to cleanly register built-in tools
• Replaces hardcoded tool dispatch logic in AgentLoop with dynamic lookup

Why

Previously, tool execution was hardcoded inside agent-loop.ts, limiting extensibility. This change lays the foundation for modular and plugin-based tooling, while preserving existing behavior.

How

• Built a minimal tool-registry.ts to track tool schemas and handlers
• Aliases are resolved internally, but not sent to the model
• shell is now first-class tool registered by default
• Updated AgentLoop to call getToolHandler() instead of matching on tool name

This prepares Codex CLI for easier tool extension while preserving existing functionality.

[joerucci]

I have read the CLA Document and I hereby sign the CLA

[github-actions]

All contributors have signed the CLA ✍️ ✅
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[ottojung]

Please make it possible to disable the built-in shell tool. Codex is often very inefficient with generic shell commands + it's difficult to make them unavailable otherwise (ex: by removing them from $PATH).

[joerucci]

Please make it possible to disable the built-in shell tool. Codex is often very inefficient with generic shell commands + it's difficult to make them unavailable otherwise (ex: by removing them from $PATH).

Thanks, that’s a great point. I’ll follow up with a separate PR to make the default tool registration optional — possibly via an env var or config hook.