Bridge host-loaded skills into the skills extension

[jif-oai]

Why

The skills extension needs to become the path that exposes local host skills without losing the behavior already owned by core skill loading. Host skill discovery is not just $CODEX_HOME/skills: it also includes config layers, bundled-skill settings, plugin roots, runtime extra roots, and the filesystem for the selected primary environment.

Rather than making the extension reload host skills and risk drifting from that authoritative load, this PR bridges the already-loaded per-turn skills outcome into the extension. That lets the extension advertise host skills and inject explicit $skill prompts while preserving the same roots, disabled/hidden state, rendered paths, and environment-backed file reads that the legacy path uses.

What Changed

• Adds HostLoadedSkills in core-skills to wrap the turn's SkillLoadOutcome and read SKILL.md through the filesystem that loaded that skill.
• Stores HostLoadedSkills in turn extension data for normal turns and review turns, so the skills extension can consume the loaded host catalog without reloading it.
• Adds HostSkillProvider under ext/skills/src/provider/host.rs, mapping host-loaded skill metadata into the skills-extension catalog/read contract.
• Registers the host provider by default from codex_skills_extension::install().
• Preserves host skill metadata such as dependencies, disabled state, hidden-from-prompt policy, and slash-normalized display paths.
• Passes host-loaded skills through SkillListQuery and SkillReadRequest so explicit skill invocation reads only resources from the loaded host catalog.
• Adds integration coverage for a real legacy $CODEX_HOME/skills/.../SKILL.md skill being listed and injected through the installed extension.

Testing

• Added installed_extension_loads_host_skills_from_legacy_roots in ext/skills/tests/skills_extension.rs.
• just test -p codex-skills-extension

[chatgpt-codex-connector]

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[jif-oai]

@codex review

[chatgpt-codex-connector]

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@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 37b7939f9e

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[jif-oai]

truncation is not in the scope of this PR