diff --git a/extensions/README.md b/extensions/README.md
index 4e03bdd..b5af262 100644
--- a/extensions/README.md
+++ b/extensions/README.md
@@ -79,4 +79,4 @@ It tests A, broken B, changed C, an old call across reload, a retained service h
 It also tests the revert command, file operations, and exec environment options.
 The world git and helper components use the executor's shared `CARGO_TARGET_DIR`.
 The API and hook fixtures use that directory too.
-The Nix shell overrides `CARGO_HOME`. Unset that variable before Cargo commands to preserve the configured kache wrapper.
+The Nix shell preserves the user's Cargo configuration and its kache wrapper.
diff --git a/host/tests/extensions.rs b/host/tests/extensions.rs
index 066a550..d6ae8eb 100644
--- a/host/tests/extensions.rs
+++ b/host/tests/extensions.rs
@@ -28,9 +28,7 @@ impl Exec for Author {
 #[tokio::test(flavor = "current_thread")]
 async fn commits_and_restart() -> anyhow::Result<()> {
     let userland = Path::new(env!("CARGO_MANIFEST_DIR")).join("../userland");
-    let target = std::env::var_os("CARGO_TARGET_DIR")
-        .map(std::path::PathBuf::from)
-        .expect("CARGO_TARGET_DIR must name the executor's shared target directory");
+    let target = Path::new(env!("CARGO_TARGET_TMPDIR")).parent().unwrap();
     if !userland.join("cwd-init/init.o").is_file() {
         assert!(
             std::process::Command::new("nu")
@@ -53,7 +51,7 @@ async fn commits_and_restart() -> anyhow::Result<()> {
             ])
             .arg(userland.join("Cargo.toml"))
             .args(["--target", "wasm32-wasip2", "--target-dir"])
-            .arg(&target)
+            .arg(target)
             .args(["-j", "2", "--locked"])
             .current_dir(&userland)
             .status()?
diff --git a/host/tests/hook_git.rs b/host/tests/hook_git.rs
index 1a1365c..f987076 100644
--- a/host/tests/hook_git.rs
+++ b/host/tests/hook_git.rs
@@ -24,10 +24,7 @@ fn git(cwd: &Path, args: &[&str]) {
 async fn several_mb_git_push() {
     static BUILT: OnceLock<std::path::PathBuf> = OnceLock::new();
     let component = BUILT.get_or_init(|| {
-        let target = std::path::PathBuf::from(
-            std::env::var_os("CARGO_TARGET_DIR")
-                .expect("CARGO_TARGET_DIR must name the executor's shared target directory"),
-        );
+        let target = Path::new(env!("CARGO_TARGET_TMPDIR")).parent().unwrap();
         let userland = Path::new(env!("CARGO_MANIFEST_DIR")).join("../userland");
         if !userland.join("cwd-init/init.o").is_file() {
             assert!(
@@ -46,7 +43,7 @@ async fn several_mb_git_push() {
                 .arg(manifest)
                 .current_dir(&userland)
                 .args(["--target", "wasm32-wasip2", "--target-dir"])
-                .arg(&target)
+                .arg(target)
                 .args(["-j", "2", "--locked"])
                 .status()
                 .unwrap()
diff --git a/host/tests/hook_guest.rs b/host/tests/hook_guest.rs
index c56615f..3644367 100644
--- a/host/tests/hook_guest.rs
+++ b/host/tests/hook_guest.rs
@@ -12,7 +12,7 @@ fn write(path: PathBuf, text: &str) -> std::io::Result<()> {
 pub fn component() -> &'static Path {
     static PATH: OnceLock<PathBuf> = OnceLock::new();
     PATH.get_or_init(|| {
-        let target = PathBuf::from(std::env::var_os("CARGO_TARGET_DIR").expect("CARGO_TARGET_DIR must name the executor's shared target directory"));
+        let target = Path::new(env!("CARGO_TARGET_TMPDIR")).parent().unwrap();
         let directory = Path::new(env!("CARGO_TARGET_TMPDIR")).join("hook-guest");
         std::fs::create_dir_all(directory.join("src")).unwrap();
         std::fs::create_dir_all(directory.join("wit/deps")).unwrap();
@@ -68,7 +68,7 @@ async fn main() -> anyhow::Result<()> {
  Ok(())
 }
 "#).unwrap();
-        assert!(std::process::Command::new("cargo").args(["build", "--manifest-path"]).arg(directory.join("Cargo.toml")).args(["--target", "wasm32-wasip2", "--release", "-j", "2"]).env("CARGO_TARGET_DIR", &target).status().unwrap().success(), "test guest build failed");
+        assert!(std::process::Command::new("cargo").args(["build", "--manifest-path"]).arg(directory.join("Cargo.toml")).args(["--target", "wasm32-wasip2", "--release", "-j", "2"]).env("CARGO_TARGET_DIR", target).status().unwrap().success(), "test guest build failed");
         target.join("wasm32-wasip2/release/hook-guest.wasm")
     })
 }