Clarify the uv layer's use of arch in comments

src/layers/uv.rs

@@ -86,6 +86,9 @@ pub(crate) fn install_uv(
             // There's also a statically compiled musl uv binary archive, but:
             // 1. It's currently slower than the glibc variant: https://github.com/astral-sh/uv/issues/10610
             // 2. At the moment this buildpack only supports Ubuntu anyway (we only compile Python runtimes for Ubuntu).
+            //
+            // Note: We use `ARCH` instead of `context.target.arch` since we need the uname-style arch (e.g. `x86_64`)
+            // rather than the Go-style arch (e.g. `amd64`) used by the OCI/CNB specification and APIs.
             let archive_url = format!(
                 "https://releases.astral.sh/github/uv/releases/download/{UV_VERSION}/uv-{ARCH}-unknown-linux-gnu.tar.gz"
             );
@@ -105,6 +108,8 @@ pub(crate) fn install_uv(
     Ok(())
 }
 
+// uv is a standalone prebuilt binary (rather than a Python package like pip or Poetry), so unlike the
+// other tool layers the uv layer doesn't need invalidating on distro or Python version changes.
 #[derive(Deserialize, PartialEq, Serialize)]
 #[serde(deny_unknown_fields)]
 struct UvLayerMetadata {

tests/mod.rs

@@ -23,7 +23,7 @@ fn default_build_config(fixture_path: impl AsRef<Path>) -> BuildConfig {
     let mut config = BuildConfig::new(&builder, fixture_path);
 
     // TODO: Once Pack build supports `--platform` and libcnb-test is adjusted accordingly, change
-    // this to allow configuring the target arch independently of the builder name (eg via env var).
+    // this to allow configuring the target arch independently of the builder name (e.g. via env var).
     let target_triple = match builder.as_str() {
         // Compile the buildpack for ARM64 iff the builder supports multi-arch and the host is ARM64.
         "heroku/builder:24" | "heroku/builder:26" if cfg!(target_arch = "aarch64") => {