[codex] Accept string input for Python turns (#23162)

## Summary
- Allow thread.turn and turn.steer, including async variants, to accept
RunInput so plain strings work alongside typed input objects.
- Export RunInput and update the SDK artifact generator so regenerated
turn methods keep the same signature and normalization.
- Update docs, examples, notebook cells, and tests to use string
shorthand for text-only turns while keeping typed inputs for multimodal
input.

## Validation
- uv run --extra dev ruff format .
- uv run --extra dev ruff check --output-format=github .
- python3 -m py_compile sdk/python/src/openai_codex/__init__.py
sdk/python/src/openai_codex/api.py
sdk/python/src/openai_codex/_inputs.py
sdk/python/scripts/update_sdk_artifacts.py
sdk/python/tests/test_public_api_signatures.py
sdk/python/tests/test_app_server_streaming.py
sdk/python/tests/test_app_server_turn_controls.py
sdk/python/tests/test_real_app_server_integration.py
- python3 -c "import json;
json.load(open('sdk/python/notebooks/sdk_walkthrough.ipynb'))"
- sdk/python/.venv/bin/python -c "import inspect, openai_codex; from
openai_codex import Thread, AsyncThread, TurnHandle, AsyncTurnHandle,
RunInput; funcs=[Thread.run, Thread.turn, AsyncThread.run,
AsyncThread.turn, TurnHandle.steer, AsyncTurnHandle.steer]; assert
all(inspect.signature(fn).parameters['input'].annotation == 'RunInput'
for fn in funcs); assert RunInput is openai_codex.RunInput"

sdk/python/src/openai_codex/__init__.py

@@ -14,6 +14,7 @@ from .api import (
     InputItem,
     LocalImageInput,
     MentionInput,
+    RunInput,
     SkillInput,
     TextInput,
     Thread,
@@ -54,6 +55,7 @@ __all__ = [
     "TurnResult",
     "Input",
     "InputItem",
+    "RunInput",
     "TextInput",
     "ImageInput",
     "LocalImageInput",

sdk/python/src/openai_codex/api.py

@@ -12,7 +12,7 @@ from ._approval_mode import (
 from ._initialize_metadata import validate_initialize_metadata
 from ._inputs import (
     ImageInput as ImageInput,
-    Input,
+    Input as Input,
     InputItem as InputItem,
     LocalImageInput as LocalImageInput,
     MentionInput as MentionInput,
@@ -534,7 +534,7 @@ class Thread:
         summary: ReasoningSummary | None = None,
     ) -> TurnResult:
         turn = self.turn(
-            _normalize_run_input(input),
+            input,
             approval_mode=approval_mode,
             cwd=cwd,
             effort=effort,
@@ -554,7 +554,7 @@ class Thread:
     # BEGIN GENERATED: Thread.flat_methods
     def turn(
         self,
-        input: Input,
+        input: RunInput,
         *,
         approval_mode: ApprovalMode | None = None,
         cwd: str | None = None,
@@ -566,7 +566,7 @@ class Thread:
         service_tier: str | None = None,
         summary: ReasoningSummary | None = None,
     ) -> TurnHandle:
-        wire_input = _to_wire_input(input)
+        wire_input = _to_wire_input(_normalize_run_input(input))
         approval_policy, approvals_reviewer = _approval_mode_override_settings(approval_mode)
         params = TurnStartParams(
             thread_id=self.id,
@@ -617,7 +617,7 @@ class AsyncThread:
         summary: ReasoningSummary | None = None,
     ) -> TurnResult:
         turn = await self.turn(
-            _normalize_run_input(input),
+            input,
             approval_mode=approval_mode,
             cwd=cwd,
             effort=effort,
@@ -637,7 +637,7 @@ class AsyncThread:
     # BEGIN GENERATED: AsyncThread.flat_methods
     async def turn(
         self,
-        input: Input,
+        input: RunInput,
         *,
         approval_mode: ApprovalMode | None = None,
         cwd: str | None = None,
@@ -650,7 +650,7 @@ class AsyncThread:
         summary: ReasoningSummary | None = None,
     ) -> AsyncTurnHandle:
         await self._codex._ensure_initialized()
-        wire_input = _to_wire_input(input)
+        wire_input = _to_wire_input(_normalize_run_input(input))
         approval_policy, approvals_reviewer = _approval_mode_override_settings(approval_mode)
         params = TurnStartParams(
             thread_id=self.id,
@@ -694,8 +694,12 @@ class TurnHandle:
     thread_id: str
     id: str
 
-    def steer(self, input: Input) -> TurnSteerResponse:
-        return self._client.turn_steer(self.thread_id, self.id, _to_wire_input(input))
+    def steer(self, input: RunInput) -> TurnSteerResponse:
+        return self._client.turn_steer(
+            self.thread_id,
+            self.id,
+            _to_wire_input(_normalize_run_input(input)),
+        )
 
     def interrupt(self) -> TurnInterruptResponse:
         return self._client.turn_interrupt(self.thread_id, self.id)
@@ -730,12 +734,12 @@ class AsyncTurnHandle:
     thread_id: str
     id: str
 
-    async def steer(self, input: Input) -> TurnSteerResponse:
+    async def steer(self, input: RunInput) -> TurnSteerResponse:
         await self._codex._ensure_initialized()
         return await self._codex._client.turn_steer(
             self.thread_id,
             self.id,
-            _to_wire_input(input),
+            _to_wire_input(_normalize_run_input(input)),
         )
 
     async def interrupt(self) -> TurnInterruptResponse: