Add Python SDK public API and examples

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

sdk/python/examples/05_existing_thread/sync.py

@@ -0,0 +1,23 @@
+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:
+    # Create an initial thread and turn so we have a real thread to resume.
+    original = codex.thread_start(model="gpt-5", config={"model_reasoning_effort": "high"})
+    first = original.turn(TextInput("Tell me one fact about Saturn.")).run()
+    print("Created thread:", first.thread_id)
+
+    # Resume the existing thread by ID.
+    resumed = codex.thread_resume(first.thread_id)
+    second = resumed.turn(TextInput("Continue with one more fact.")).run()
+    print(second.text)