feat: add SHA256 verification for direct downloads (#2873)

* feat: add SHA256 verification for direct downloads

Store SHA256 hashes when running update scripts and verify them
when downloading files at build time. This improves security by
detecting unexpected changes to downloaded artifacts.

Platforms covered: macOS (CPython, PyPy, GraalPy), iOS, Android,
virtualenv, and python-build-standalone. Windows (nuget) and
Linux (Docker) are excluded.

SHA256 sources per platform:
- macOS/iOS/Android CPython (python.org): sha256_sum from API
- GraalPy: .sha256 sidecar assets from GitHub releases
- python-build-standalone: SHA256SUMS file in release
- PyPy, BeeWare iOS, Maven (Chaquopy): stream-download and compute

Changes:
- cibuildwheel/util/file.py: add sha256 param to download()
- cibuildwheel/platforms/{macos,ios,android}.py: add sha256 to
  PythonConfiguration and pass to download()
- cibuildwheel/venv.py: read sha256 from toml and pass to download()
- cibuildwheel/util/python_build_standalone.py: add sha256 to
  PythonBuildStandaloneAsset and pass to download()
- cibuildwheel/resources/build-platforms.toml: add sha256 fields
- cibuildwheel/resources/virtualenv.toml: add sha256 field
- cibuildwheel/resources/python-build-standalone-releases.json: add sha256
- bin/update_pythons.py: compute/store sha256 per source strategy
- bin/update_virtualenv.py: compute sha256 by streaming download
- bin/update_python_build_standalone.py: parse SHA256SUMS file

Closes #908

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Assisted-by: copilot-cli:claude-sonnet-4.6

* fix: populate sha256 in resource files and fix Windows PythonConfiguration

- Add sha256 field to Windows PythonConfiguration (PyPy/GraalPy have
  direct download URLs on Windows too)
- Pass sha256 to install_pypy() and install_graalpy() in windows.py
- Fix update_pythons.py: handle empty sha256 from CPython API (older
  versions) by streaming download to compute it; fix condition to
  check 'not sha256' rather than 'not in dict'
- Fix update_virtualenv.py: compute sha256 even when version unchanged
  but sha256 is empty (first-time population)
- Fix update_python_build_standalone.py: resolve file path relative to
  the script itself (not the installed package) so writes go to source
  checkout, not the uv cache
- Populate actual sha256 values by running all three update scripts

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Assisted-by: copilot-cli:claude-sonnet-4.6

* fix: also include pyodide

Assisted-by: CopilotCLI:gpt-5.3-codex
Signed-off-by: Henry Schreiner <henryfs@princeton.edu>

* fix: PR review comments for cache verification and docs wording

Co-authored-by: henryiii <4616906+henryiii@users.noreply.github.com>
Signed-off-by: Henry Schreiner <henryfs@princeton.edu>

* fix: require sha256 for download configs

Require sha256 for URL-backed Python and virtualenv download configs. Update the GraalPy updater to refresh macOS x86_64 entries by selecting the latest release that still has a matching asset, and fill the two missing GraalPy checksums in build-platforms.toml.

Assisted-by: CopilotCLI:gpt-5.4

* ci: remove unit test for bin item

Signed-off-by: Henry Schreiner <henryfs@princeton.edu>

* refactor: combine sha256 unit tests into test_sha256.py

Merge pyodide_test.py and python_build_standalone_test.py into a
single unit_test/test_sha256.py since both test sha256-related
behaviour.

Assisted-by: opencode:glm-5

---------

Signed-off-by: Henry Schreiner <henryfs@princeton.edu>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: henryiii <4616906+henryiii@users.noreply.github.com>

cibuildwheel/platforms/ios.py

@@ -46,6 +46,8 @@ class PythonConfiguration:
     identifier: str
     url: str
     build_url: str
+    build_sha256: str
+    sha256: str
 
     @property
     def sdk(self) -> str:
@@ -78,7 +80,7 @@ def all_python_configurations() -> list[PythonConfiguration]:
     # configuration.
     macos_python_configs = resources.read_python_configs("macos")
 
-    def build_url(config_dict: dict[str, str]) -> str:
+    def build_python_config(config_dict: dict[str, str]) -> dict[str, str]:
         # The iOS identifier will be something like cp313-ios_arm64_iphoneos.
         # Drop the iphoneos suffix, then replace ios with macosx to yield
         # cp313-macosx_arm64, which will be a macOS build identifier.
@@ -87,18 +89,22 @@ def all_python_configurations() -> list[PythonConfiguration]:
         matching = [
             config for config in macos_python_configs if config["identifier"] == macos_identifier
         ]
-        return matching[0]["url"]
+        return matching[0]
 
     # Load the platform configuration
     full_python_configs = resources.read_python_configs("ios")
     # Build the configurations, annotating with macOS URL details.
-    return [
-        PythonConfiguration(
-            **item,
-            build_url=build_url(item),
+    python_configurations = []
+    for item in full_python_configs:
+        build_config = build_python_config(item)
+        python_configurations.append(
+            PythonConfiguration(
+                **item,
+                build_url=build_config["url"],
+                build_sha256=build_config["sha256"],
+            )
         )
-        for item in full_python_configs
-    ]
+    return python_configurations
 
 
 def get_python_configurations(
@@ -133,7 +139,7 @@ def install_target_cpython(tmp: Path, config: PythonConfiguration, free_threadin
     with FileLock(str(installation_path) + ".lock"):
         if not installation_path.exists():
             downloaded_tar_gz = tmp / ios_python_tar_gz
-            download(config.url, downloaded_tar_gz)
+            download(config.url, downloaded_tar_gz, sha256=config.sha256)
             installation_path.mkdir(parents=True, exist_ok=True)
             call("tar", "-C", installation_path, "-xf", downloaded_tar_gz)
             downloaded_tar_gz.unlink()
@@ -319,6 +325,7 @@ def setup_python(
             python_configuration.version,
             python_configuration.build_url,
             free_threading,
+            python_configuration.build_sha256,
         )
     else:
         msg = f"Unknown Python implementation: {implementation_id}"