build: align build script execution platforms

patches/rules_rust_windows_exec_bin_target.patch

@@ -1,11 +1,10 @@
-# What: compile exec-side Rust binaries against the exec Windows triple instead
-# of the lint target triple.
+# What: compile exec-side Rust binaries against the exec Windows triple and
+# keep build-script wrappers on the matching Rust execution platform.
 # Why: Windows native argument-comment-lint keeps the repo target platform on
 # `windows-gnullvm` to preserve cfg coverage, but exec-side helper binaries
-# (build.rs, runners, bootstrap tools) must link as host tools. With
-# `toolchain_linker_preference=rust`, rules_rust was still feeding those exec
-# binaries the `windows-gnullvm` target/std path, which broke linking under the
-# native Bazel lint lane.
+# (build.rs, runners, bootstrap tools) must link as host tools. Without a Rust
+# toolchain on the runfiles wrapper, its `cfg=exec` build-script dependency can
+# drift onto Linux RBE even though the consuming action runs on Windows.
 
 diff --git a/rust/private/rustc.bzl b/rust/private/rustc.bzl
 --- a/rust/private/rustc.bzl
@@ -69,3 +68,16 @@ diff --git a/rust/private/rustc.bzl b/rust/private/rustc.bzl
 -    rustc_flags.add_all(toolchain.rust_std_paths, before_each = "-L", format_each = "%s")
 +    rustc_flags.add_all(_effective_rust_std_paths(toolchain, use_exec_target), before_each = "-L", format_each = "%s")
      rustc_flags.add_all(rust_flags, map_each = map_flag)
+
+diff --git a/cargo/private/cargo_build_script.bzl b/cargo/private/cargo_build_script.bzl
+--- a/cargo/private/cargo_build_script.bzl
++++ b/cargo/private/cargo_build_script.bzl
+@@ -117,5 +117,8 @@ cargo_build_script_runfiles = rule(
+             default = Label("//cargo/private:copy_file"),
+         ),
+     },
+     executable = True,
++    # Keep the cfg=exec build-script binary on the same Rust-capable execution
++    # platform as the wrapper action that consumes it.
++    toolchains = [str(Label("//rust:toolchain_type"))],
+ )