Add Python app-server SDK (#14435)

## 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>

sdk/python/docs/faq.md

@@ -0,0 +1,77 @@
+# FAQ
+
+## Thread vs turn
+
+- A `Thread` is conversation state.
+- A `Turn` is one model execution inside that thread.
+- Multi-turn chat means multiple turns on the same `Thread`.
+
+## `run()` vs `stream()`
+
+- `Turn.run()` is the easiest path. It consumes events until completion and returns `TurnResult`.
+- `Turn.stream()` yields raw notifications (`Notification`) so you can react event-by-event.
+
+Choose `run()` for most apps. Choose `stream()` for progress UIs, custom timeout logic, or custom parsing.
+
+## Sync vs async clients
+
+- `Codex` is the minimal sync SDK and best default.
+- `AsyncAppServerClient` wraps the sync transport with `asyncio.to_thread(...)` for async-friendly call sites.
+
+If your app is not already async, stay with `Codex`.
+
+## `thread(...)` vs `thread_resume(...)`
+
+- `codex.thread(thread_id)` only binds a local helper to an existing thread ID.
+- `codex.thread_resume(thread_id, ...)` performs a `thread/resume` RPC and can apply overrides (model, instructions, sandbox, etc.).
+
+Use `thread(...)` for simple continuation. Use `thread_resume(...)` when you need explicit resume semantics or override fields.
+
+## Why does constructor fail?
+
+`Codex()` is eager: it starts transport and calls `initialize` in `__init__`.
+
+Common causes:
+
+- published runtime package (`codex-cli-bin`) is not installed
+- local `codex_bin` override points to a missing file
+- local auth/session is missing
+- incompatible/old app-server
+
+Maintainers stage releases by building the SDK once and the runtime once per
+platform with the same pinned runtime version. Publish `codex-cli-bin` as
+platform wheels only; do not publish an sdist:
+
+```bash
+cd sdk/python
+python scripts/update_sdk_artifacts.py generate-types
+python scripts/update_sdk_artifacts.py \
+  stage-sdk \
+  /tmp/codex-python-release/codex-app-server-sdk \
+  --runtime-version 1.2.3
+python scripts/update_sdk_artifacts.py \
+  stage-runtime \
+  /tmp/codex-python-release/codex-cli-bin \
+  /path/to/codex \
+  --runtime-version 1.2.3
+```
+
+## Why does a turn "hang"?
+
+A turn is complete only when `turn/completed` arrives for that turn ID.
+
+- `run()` waits for this automatically.
+- With `stream()`, make sure you keep consuming notifications until completion.
+
+## How do I retry safely?
+
+Use `retry_on_overload(...)` for transient overload failures (`ServerBusyError`).
+
+Do not blindly retry all errors. For `InvalidParamsError` or `MethodNotFoundError`, fix inputs/version compatibility instead.
+
+## Common pitfalls
+
+- Starting a new thread for every prompt when you wanted continuity.
+- Forgetting to `close()` (or not using `with Codex() as codex:`).
+- Ignoring `TurnResult.status` and `TurnResult.error`.
+- Mixing SDK input classes with raw dicts incorrectly in minimal API paths.