## What changed
Decode live item start and completion notifications as `TranscriptUpdate::ItemStarted` and `TranscriptUpdate::ItemCompleted`, with turn identity, lifecycle timestamps, and summaries for user messages, agent messages, reasoning, commands, and file changes.
Preserve structured agent questions even when message text is empty, optional command output and exit details, and command or patch status independently of lifecycle completion. Keep unsupported or incomplete items as opaque notifications and redact summary fields in debug output.
## Testing
Add fixtures covering lifecycle ordering alongside deltas, identity and timestamps, status and optional-field preservation, structured questions, opaque fallback, malformed payloads, thread ownership, and debug redaction.
GitOrigin-RevId: d6bf2d25ee85be17d895726c5072850a9851b55f
