This PR depends on [#31296](https://github.com/openai/codex/pull/31296)
for the canonical-to-legacy event mappings.
## Description
This PR makes command execution emit canonical
`TurnItem::CommandExecution` lifecycle from both the shell tool path and
user `/shell` commands.
App-server v2 consumes the canonical command items directly and ignores
the mapped `ExecCommandBegin` / `ExecCommandEnd` compatibility events,
so clients still receive one command item lifecycle.
`UnifiedExecInteraction` stays on the legacy path because
`TerminalInteraction` is still the v2 surface for stdin and poll events.
Emitting a command item there would render the same wait twice.
## Why
This is the first live producer migration after the compatibility
mappings in #31296. Keeping command execution separate makes the unified
exec exception reviewable without mixing in dynamic tools or multi-agent
behavior.
## What changed
- Emit canonical command execution items from shell tool events and user
shell commands.
- Preserve the existing unified exec interaction carveout.
- Move app-server command deduplication and completion bookkeeping onto
canonical item events.
- Update unified exec coverage to assert the completed command item.
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