## Summary
- Make command/exec output-delta tests accumulate streamed chunks
instead of assuming complete logical output in a single notification.
- Collect stdout and stderr independently so stream interleaving does
not fail the pipe streaming test.
## Why
The command/exec protocol exposes output as deltas, so tests should not
rely on chunk boundaries being stable. A line like `out-start\n` may
arrive split across multiple notifications, and stdout/stderr
notifications may interleave.
## Validation
- `just fmt`
- `git diff --check`
- `cargo test -p codex-app-server suite::v2::command_exec`
Ruslan NigmatullinandGitHub
f948690fc8