[1/8] Pin Python SDK runtime dependency (#21891)

## Why

The Python SDK depends on the app-server runtime package for the bundled
`codex` binary and schema source of truth. That relationship should be
explicit in package metadata instead of inferred from matching version
numbers, so installers, lockfiles, and reviewers can see exactly which
runtime the SDK expects.

## What

- Declare `openai-codex-cli-bin==0.131.0a4` as a Python SDK dependency.
- Update runtime setup helpers to resolve the runtime version from the
declared dependency pin.
- Refresh the SDK lockfile for the pinned runtime wheel.
- Update package/runtime tests and docs that describe where the runtime
version comes from.

## Stack

1. This PR `[1/8]` Pin Python SDK runtime dependency
2. #21893 `[2/8]` Generate Python SDK types from pinned runtime
3. #21895 `[3/8]` Run Python SDK tests in CI
4. #21896 `[4/8]` Define Python SDK public API surface
5. #21905 `[5/8]` Rename Python SDK package to `openai-codex`
6. #21910 `[6/8]` Add high-level Python SDK approval mode
7. #22014 `[7/8]` Add Python SDK app-server integration harness
8. #22021 `[8/8]` Add Python SDK Ruff formatting

## Verification

- Added coverage for the SDK runtime dependency pin and runtime
distribution naming.

---------

Co-authored-by: Codex <noreply@openai.com>

sdk/python/scripts/update_sdk_artifacts.py

@@ -61,6 +61,7 @@ def staged_runtime_bin_path(root: Path) -> Path:
 
 
 def staged_runtime_resource_path(root: Path, resource: Path) -> Path:
+    """Stage runtime helper binaries beside the main bundled Codex binary."""
     # Runtime wheels include the whole bin/ directory, so helper executables
     # should be staged beside the main Codex binary instead of changing the
     # package template for each platform.
@@ -588,6 +589,7 @@ def _notification_specs() -> list[tuple[str, str]]:
 def _notification_turn_id_specs(
     specs: list[tuple[str, str]],
 ) -> tuple[list[str], list[str]]:
+    """Classify generated notification payloads by where the turn id lives."""
     server_notifications = json.loads(
         (schema_root_dir() / "ServerNotification.json").read_text()
     )
@@ -615,6 +617,7 @@ def _notification_turn_id_specs(
 
 
 def _type_tuple_source(class_names: list[str]) -> str:
+    """Render a generated tuple literal for notification payload classes."""
     if not class_names:
         return "()"
     if len(class_names) == 1:
@@ -623,6 +626,7 @@ def _type_tuple_source(class_names: list[str]) -> str:
 
 
 def generate_notification_registry() -> None:
+    """Regenerate notification models and routing metadata from generated schemas."""
     out = (
         sdk_root()
         / "src"
@@ -666,6 +670,7 @@ def generate_notification_registry() -> None:
             "",
             "",
             "def notification_turn_id(payload: BaseModel) -> str | None:",
+            '    """Return the turn id carried by generated notification payload metadata."""',
             "    if isinstance(payload, DIRECT_TURN_ID_NOTIFICATION_TYPES):",
             "        return payload.turn_id if isinstance(payload.turn_id, str) else None",
             "    if isinstance(payload, NESTED_TURN_NOTIFICATION_TYPES):",