## TL;DR
Pin the Python app-server SDK subprocess pipes to UTF-8 so Windows users
on non-UTF-8 locales do not hit `UnicodeDecodeError` when the `codex`
child emits UTF-8 text.
- add `encoding="utf-8"` to the `subprocess.Popen(...)` call in
`AppServerClient.start()`
- add a focused regression test that asserts the client launches the
subprocess with UTF-8 text I/O
- validates with `python -m pytest
sdk/python/tests/test_client_rpc_methods.py
sdk/python/tests/test_client_process_launch.py
sdk/python/tests/test_public_api_runtime_behavior.py`
Fixes#14311.
## TL;DR
Bring the Python app-server SDK from `main-with-prs-13953-and-14232`
onto current `main` as a standalone SDK-only PR.
- adds the new `sdk/python` and `sdk/python-runtime` package trees
- keeps the scope to the SDK payload only, without the unrelated
branch-history or workflow changes from the source branch
- regenerates `sdk/python/src/codex_app_server/generated/v2_all.py`
against current `main` schema so the extracted SDK matches today's
protocol definitions
## Validation
- `PYTHONPATH=sdk/python/src python3 -m pytest sdk/python/tests`
Co-authored-by: Codex <noreply@openai.com>
