fix: Skip corepack setup for package managers it doesn't support

Corepack only manages yarn and pnpm. Running corepack enable/prepare
for bun or npm fails since corepack doesn't support them. Guard both
setup_package_manager and prepare_corepack_from_package_json to only
invoke corepack for supported PMs.

Fixes test_lockfile_aware_caching_bun failure.

Author: anthonyshew

crates/turborepo/tests/common/setup.rs

@@ -128,8 +128,13 @@ pub fn setup_package_manager(
         &format!("Updated package manager to {package_manager}"),
     )?;
 
-    // Enable corepack for this package manager
+    // Corepack only manages yarn and pnpm. npm ships with node and bun is
+    // its own runtime — neither needs corepack setup.
     let pm_name = package_manager.split('@').next().unwrap_or(package_manager);
+    if !corepack_supports(pm_name) {
+        return Ok(());
+    }
+
     fs::create_dir_all(corepack_dir)?;
 
     let status = cmd("corepack")
@@ -185,9 +190,14 @@ pub fn prepare_corepack_from_package_json(dir: &Path) {
 
     let pm = match pkg.get("packageManager").and_then(|v| v.as_str()) {
         Some(pm) => pm.to_string(),
-        None => return, // No packageManager field, nothing to prepare
+        None => return,
     };
 
+    let pm_name = pm.split('@').next().unwrap_or(&pm);
+    if !corepack_supports(pm_name) {
+        return;
+    }
+
     let status = cmd("corepack")
         .arg("prepare")
         .arg(&pm)
@@ -338,6 +348,10 @@ fn git_commit_if_changed(dir: &Path, message: &str) -> Result<(), anyhow::Error>
     Ok(())
 }
 
+fn corepack_supports(pm_name: &str) -> bool {
+    matches!(pm_name, "yarn" | "pnpm" | "berry")
+}
+
 fn prepend_to_path(dir: &Path) -> String {
     let current = std::env::var("PATH").unwrap_or_default();
     let sep = if cfg!(windows) { ";" } else { ":" };