## Why
App-server command output deltas populate an exec cell before the command
finishes. Treating the presence of output as completion can therefore mark a
streaming command inactive too early and mishandle it when the turn is
interrupted.
## What changed
- Use the recorded duration, which is set when a command ends, as the exec
call's completion marker.
- Preserve streamed output when marking unfinished calls as failed and render
status lines only after completion.
- Keep a single aggregated output representation and render truncated output
without collecting every line first.
- Append grouped exploration calls in place and coalesce adjacent reads while
rendering without cloning the calls.
## Testing
- Add snapshots covering active streamed output, transcript output, and the
resulting history entry after interruption.
- Add coverage for truncating newline-dense output.
GitOrigin-RevId: 420ac1e5fe1b9fcdbdaa5a8998f3e43a5b720254
Charlie Marsh
854a82dbfd