fix(flutter): fetch the arm64 macOS archive on Apple Silicon hosts

CHANGELOG.md

@@ -7,6 +7,16 @@ it reaches 1.0.
 
 ## [Unreleased]
 
+### Fixed
+
+- The macOS SDK repository fetches the arm64 release archive on Apple Silicon
+  hosts instead of always fetching the x64 one, whose Dart binaries fail with
+  "Bad CPU type in executable" when Rosetta 2 is not installed. The built-in
+  version table now records a `macos_arm64` integrity per version, the
+  `flutter.toolchain(integrity = {...})` escape hatch accepts a
+  `"macos_arm64"` key, and `flutter_repositories` grew an `integrity_arm64`
+  attribute to carry it.
+
 ## [0.3.0] - 2026-08-23
 
 ### Changed

flutter/extensions.bzl

@@ -31,8 +31,10 @@ registrations of the same toolchain name.
 """, default = []),
     "integrity": attr.string_dict(doc = """\
 Escape hatch for Flutter versions not in the built-in version table: a map
-from platform (macos, linux, windows) to the SRI integrity of that platform's
-stable release archive, e.g. {"macos": "sha256-...", "linux": "sha256-..."}.
+from platform (macos, macos_arm64, linux, windows) to the SRI integrity of
+that platform's stable release archive, e.g. {"macos": "sha256-...",
+"macos_arm64": "sha256-...", "linux": "sha256-..."}. macOS ships separate x64
+and arm64 archives; "macos_arm64" is the one fetched on Apple Silicon hosts.
 Only the platforms you actually build on need an entry (the per-platform SDK
 repositories are fetched lazily). When flutter_version is in the built-in
 table this may be omitted. Merged across registrations of the same name.