[codex] update multi-agent v2 prompts

[jif-oai]

Summary

• align the default multi-agent v2 root and subagent hints with the evaluated prompt guidance for direct collaboration-tool calls, parallel delegation, and shared workspaces
• keep the current interrupt_agent tool name and existing concurrency-hint placement, with the explicit no-spawn instruction last
• document the context tradeoff between fork_turns="none" and fork_turns="all" in the v2 spawn_agent description
• extend the focused prompt and tool-surface tests

Why

The evaluated multi-agent prompt includes operational guidance that is missing from the current Codex defaults. This applies that guidance to the current tool surface without restoring stale close_agent or duplicated concurrency wording.

User impact

Multi-agent v2 receives clearer instructions about when and how to parallelize work, how agent workspaces interact, and how fork_turns affects subagent context. The existing default opt-out behavior remains in place.

Testing

• just fmt
• just test -p codex-core multi_agent_v2_default_usage_hints_use_configured_thread_cap
• just test -p codex-core multi_agent_feature_selects_one_agent_tool_family

[chatgpt-codex-connector]

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[jif-oai]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 888be7d90b

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".