[codex] Extract turn skill and plugin injections

[pakrym-oai]

Why

run_turn had accumulated the turn-scoped skill, plugin, app, MCP, connector-selection, and analytics setup inline. That made the orchestration path harder to scan even though the actual turn item injection still needs to stay in run_turn so ordering is explicit.

What changed

This extracts that setup into build_skills_and_plugins, which returns the combined injection ResponseItems and the explicitly enabled connector IDs. run_turn now keeps the required orchestration pieces: context update recording, user input handling, connector selection merge, and the explicit per-item record_conversation_items calls for injection items.

The refactor keeps the change LOC-neutral in core/src/session/turn.rs and preserves the existing response-item based injection path.

Validation

• cargo test -p codex-core collect_explicit_app_ids_from_skill_items
• just fix -p codex-core

[chatgpt-codex-connector]

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