cli: emit JSONL run trace when CODEX_TRACE_PATH is set

[OS-DevSource]

This adds a small, best-effort JSONL trace for codex-cli when CODEX_TRACE_PATH is set.

• Feature-gated in codex-common (trace feature)
• CLI wrapper writes run_started and run_finished events
• Includes cwd and run_id; never fails the CLI if trace IO fails

Manual test:

export CODEX_TRACE_PATH=/tmp/codex-trace.jsonl
rm -f /tmp/codex-trace.jsonl
just codex # then type: quit
tail -n 5 /tmp/codex-trace.jsonl

Additional note:

• Writes a best-effort JSONL trace only when CODEX_TRACE_PATH is set (no behavior change by default);
• Trace support is feature-gated behind codex-common's "trace" feature.
• Output is JSONL (one JSON object per line), which makes it easy to stream, grep, or ingest in other tooling.

[github-actions]

All contributors have signed the CLA ✍️ ✅
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[OS-DevSource]

I have read the CLA Document and I hereby sign the CLA

[etraut-openai]

Thanks for the contribution. We've updated our contribution guidelines to clarify that we're currently accepting contributions for bugs and security fixes, but we're not generally accepting new features at this time. We need to make sure that all new features compose well with both existing and upcoming features and fit into our roadmap. If you would like to propose a new feature, please file or upvote an enhancement request in the issue tracker. We will generally prioritize new features based on community feedback.

[OS-DevSource]

Thanks for the quick response and the clarity (and for updating the guidelines).

I opened a feature request to track this properly: #8027
PR #8017 was a working prototype for the idea; happy to rework/re-submit in whatever shape (schema/tests/placement) fits the roadmap if the team decides to take it.

Appreciate it!