[codex] narrow unused skills intro export

[aibrahim-oai]

Summary

• stop publicly re-exporting the internally used SKILLS_INTRO_WITH_ALIASES constant
• keep the constant and all skills rendering behavior unchanged
• preserve every integration helper, API, fixture, assertion, and module used by tests

Scope guardrails

This revision keeps all remote/network-facing functionality and every line introduced by jif <jif@openai.com>.

Following the test-preservation audit, it also restores the in-process RMCP test transport, the original codex-mcp fixture, PluginLoadOutcome::effective_skill_roots and its assertions, the EffectiveSkillRoots API family, the test-only apps renderer, and the TUI dead-code annotation. Those files now match the PR base exactly.

No test imports or directly references the remaining public skills export being narrowed.

Validation

• repository-wide test-reference audit: no test-used code remains deleted or narrowed
• deleted-line git blame audit: zero Jif-authored deletions
• cargo test -p codex-core-plugins -p codex-mcp -p codex-rmcp-client --lib: 467 passed
• cargo test -p codex-core --lib apps::render: 2 passed
• cargo test -p codex-core-skills --lib render::tests: 19 passed
• cargo check -p codex-core-skills --all-targets: passed
• just fix -p codex-core-skills: passed
• just fmt: passed
• git diff --check: passed

The full local codex-core-skills suite passed 106/108 tests; two loader tests detected an ambient repository skills root outside the package and failed their isolation assertions. The scoped renderer suite and all-target compile pass, and CI runs in an isolated environment.

Final code delta: 1 insertion, 2 deletions across 2 files.

[aibrahim-oai]

@codex review this

[chatgpt-codex-connector]

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