Add Python SDK public API and examples

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

sdk/python/examples/03_turn_stream_events/sync.py

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+import sys
+from pathlib import Path
+
+_EXAMPLES_ROOT = Path(__file__).resolve().parents[1]
+if str(_EXAMPLES_ROOT) not in sys.path:
+    sys.path.insert(0, str(_EXAMPLES_ROOT))
+
+from _bootstrap import ensure_local_sdk_src, runtime_config
+
+ensure_local_sdk_src()
+
+from codex_app_server import Codex, TextInput
+
+with Codex(config=runtime_config()) as codex:
+    thread = codex.thread_start(model="gpt-5", config={"model_reasoning_effort": "high"})
+    turn = thread.turn(TextInput("Count from 1 to 200 with commas, then one summary sentence."))
+
+    # Best effort controls: models can finish quickly, so races are expected.
+    try:
+        _ = turn.steer(TextInput("Keep it brief and stop after 20 numbers."))
+        print("steer: sent")
+    except Exception as exc:
+        print("steer: skipped", type(exc).__name__)
+
+    try:
+        _ = turn.interrupt()
+        print("interrupt: sent")
+    except Exception as exc:
+        print("interrupt: skipped", type(exc).__name__)
+
+    event_count = 0
+    for event in turn.stream():
+        event_count += 1
+        print(event.method, event.payload)
+
+    print("events.count:", event_count)