## Why
Streamed message deltas can be dropped when the transport is saturated, leaving
clients with a truncated final response.
## What changed
- Include the last non-empty final agent message in successful `turn/completed`
notifications and mark the items as a summary.
- Treat completed message content as authoritative in the TUI, repairing an
incomplete stream while avoiding duplicate messages when `item/completed` was
already received.
- Continue backfilling full turn items for persisted `codex exec` threads when a
completion contains only the summary view.
## Testing
Added coverage for completion summaries, dropped stream deltas, duplicate item
handling, and directive-only responses.
GitOrigin-RevId: ffe9d36d683d6b6690e4a468ff68aa9189fe6ab7