## Why
Tool results can be ready before the sampling loop collects them, and code-mode cells can outlive a turn. Separate trace milestones make these timings visible and link nested calls to the turn that dispatches them.
## What changed
- Emit `codex.tool_call_received` and `codex.tool_result_ready` events for direct and code-mode calls, using identifiers and tool names without arguments or output. Record readiness before result encoding or collection, including ordinary errors and aborted responses, but excluding fatal errors.
- Assign nested call IDs at broker receipt and carry them through dispatch. Trace dispatch and interruptions caused by cancellation, cell closure, or abandonment.
- Add code-mode execute and wait handler spans with conversation, turn, call, and cell identifiers and `completed`, `failed`, or `interrupted` outcomes.
GitOrigin-RevId: b098a29d8ee030c823665e4b1031a0d67cc09502
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