## Why
We have some large gaps in our thread start, resume, and pre-sampling
traces that make it hard to tell where latency is coming from.
## What Changed
- Added coarse spans around thread start/resume, turn context
construction, rollout reconstruction, skill/plugin loading, and tool
preparation.
- Added a breakdown of discoverable-tool preparation across connector
loading, plugin discovery, and local plugin details.
## Testing
- `cargo check -p codex-app-server -p codex-core -p codex-core-skills -p
codex-core-plugins`
- Built the app-server locally and exercised thread start, first turn,
follow-up turn, server restart, thread resume, and a resumed turn.
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