python-sdk: align pinned runtime bootstrap and drop sample image (2026-03-16)

- bump the repo-managed runtime bootstrap to rust-v0.116.0-alpha.1 so example and integration paths match the current SDK thread/start schema
- make release artifact download more robust by retrying metadata lookups without stale auth and preferring deterministic release asset URLs
- refresh generated Python artifacts and signature expectations so artifact drift tests pass on the current branch shape
- replace the checked-in local image asset with a generated temporary PNG used by the examples and notebook local-image flow
- add lightweight tests for pinned runtime doc drift and invalid-auth fallback in runtime metadata resolution

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

sdk/python/examples/_bootstrap.py

@@ -1,10 +1,13 @@
 from __future__ import annotations
 
+import contextlib
 import importlib.util
 import os
 import sys
+import tempfile
+import zlib
 from pathlib import Path
-from typing import Iterable
+from typing import Iterable, Iterator
 
 _SDK_PYTHON_DIR = Path(__file__).resolve().parents[1]
 _SDK_PYTHON_STR = str(_SDK_PYTHON_DIR)
@@ -52,6 +55,55 @@ def runtime_config():
     return AppServerConfig()
 
 
+def _png_chunk(chunk_type: bytes, data: bytes) -> bytes:
+    import struct
+
+    payload = chunk_type + data
+    checksum = zlib.crc32(payload) & 0xFFFFFFFF
+    return struct.pack(">I", len(data)) + payload + struct.pack(">I", checksum)
+
+
+def _generated_sample_png_bytes() -> bytes:
+    import struct
+
+    width = 96
+    height = 96
+    top_left = (120, 180, 255)
+    top_right = (255, 220, 90)
+    bottom_left = (90, 180, 95)
+    bottom_right = (180, 85, 85)
+
+    rows = bytearray()
+    for y in range(height):
+        rows.append(0)
+        for x in range(width):
+            if y < height // 2 and x < width // 2:
+                color = top_left
+            elif y < height // 2:
+                color = top_right
+            elif x < width // 2:
+                color = bottom_left
+            else:
+                color = bottom_right
+            rows.extend(color)
+
+    header = struct.pack(">IIBBBBB", width, height, 8, 2, 0, 0, 0)
+    return (
+        b"\x89PNG\r\n\x1a\n"
+        + _png_chunk(b"IHDR", header)
+        + _png_chunk(b"IDAT", zlib.compress(bytes(rows)))
+        + _png_chunk(b"IEND", b"")
+    )
+
+
+@contextlib.contextmanager
+def temporary_sample_image_path() -> Iterator[Path]:
+    with tempfile.TemporaryDirectory(prefix="codex-python-example-image-") as temp_root:
+        image_path = Path(temp_root) / "generated_sample.png"
+        image_path.write_bytes(_generated_sample_png_bytes())
+        yield image_path
+
+
 def server_label(metadata: object) -> str:
     server = getattr(metadata, "serverInfo", None)
     server_name = ((getattr(server, "name", None) or "") if server is not None else "").strip()