Support an opt-in authoritative external skill provider

Summary

Support an opt-in authoritative external skill provider that can be used directly by Codex CLI.

Motivation

Organizations may store and manage skills in databases or internal services instead of the local filesystem. They may also need custom routing based on permissions, metadata, availability, or organization-specific policies.

Currently, there is no supported way for Codex CLI to delegate automatic skill discovery and selection to such an external system.

Expected behavior

When an external skill provider is configured:

• The provider becomes authoritative for automatic skill discovery and selection.
• Codex does not expose its native skill catalog to the model for implicit selection.
• The provider decides which skills, if any, apply to each user turn.
• Codex loads and injects the context for the selected skills.
• Returning no skill is a valid result.
• Native skills remain available through explicit user invocation.

When no external provider is configured, Codex keeps its existing skill behavior unchanged.

Use cases

• Store and manage skills in a database.
• Apply organization-specific access control and routing policies.
• Select skills using external metadata, search, or ranking systems.
• Keep skill management consistent across machines and CLI sessions.

Compatibility

This feature should be opt-in and should not change the default Codex experience. Existing sandbox, approval, and permission boundaries should continue to apply.