feat: add corepack packageManager field support

runner/cmd_npm_test.go

@@ -206,6 +206,44 @@ func TestResolvePM_FromUserSettings(t *testing.T) {
 	}
 }
 
+// --- package.json packageManager field ---
+
+func TestResolvePM_FromPackageJSON(t *testing.T) {
+	isolatePMDetectionToDefault(t)
+
+	ws := t.TempDir()
+	// No .vscode/settings.json, but package.json has packageManager
+	writeFile(t, filepath.Join(ws, "package.json"), `{"packageManager":"pnpm@8.15.0"}`)
+
+	tk := tasks.Task{Type: "npm", Script: "build"}
+	cmd, _, err := buildCmd(tk, ws, os.Environ())
+	if err != nil {
+		t.Fatalf("buildCmd err: %v", err)
+	}
+	if got, want := filepath.Base(cmd.Args[0]), "pnpm"; got != want {
+		t.Fatalf("exe=%q, want %q (packageManager field)", got, want)
+	}
+}
+
+func TestResolvePM_SettingsOverridesPackageJSON(t *testing.T) {
+	isolatePMDetectionToDefault(t)
+
+	ws := t.TempDir()
+	// VS Code settings say yarn, but package.json says pnpm
+	writeFile(t, filepath.Join(ws, ".vscode", "settings.json"), `{"npm.packageManager":"yarn"}`)
+	writeFile(t, filepath.Join(ws, "package.json"), `{"packageManager":"pnpm@8.15.0"}`)
+
+	tk := tasks.Task{Type: "npm", Script: "build"}
+	cmd, _, err := buildCmd(tk, ws, os.Environ())
+	if err != nil {
+		t.Fatalf("buildCmd err: %v", err)
+	}
+	// VS Code settings should win
+	if got, want := filepath.Base(cmd.Args[0]), "yarn"; got != want {
+		t.Fatalf("exe=%q, want %q (settings should override packageManager)", got, want)
+	}
+}
+
 // --- builtin detector ---
 
 func TestIsNpmBuiltin(t *testing.T) {

tasks/settings.go

@@ -150,10 +150,38 @@ func normalizePM(v string) (string, bool) {
 	}
 }
 
+// detectPackageManagerFromPackageJSON reads the "packageManager" field from
+// package.json (the corepack standard, e.g. "pnpm@8.15.0") and returns the
+// executable name if recognized.
+func detectPackageManagerFromPackageJSON(cwd string) (string, bool) {
+	path := filepath.Join(cwd, "package.json")
+	b, err := os.ReadFile(path)
+	if err != nil {
+		return "", false
+	}
+	var pkg struct {
+		PackageManager string `json:"packageManager"`
+	}
+	if err := json.Unmarshal(b, &pkg); err != nil {
+		return "", false
+	}
+	// The field value is "name@version", e.g. "pnpm@8.15.0" or just "pnpm".
+	name := strings.TrimSpace(pkg.PackageManager)
+	if i := strings.IndexByte(name, '@'); i > 0 {
+		name = name[:i]
+	}
+	return normalizePM(name)
+}
+
 func ResolvePackageManagerExecutable(cwd string, defaultExe string) string {
+	// 1) VS Code settings take highest priority (explicit user preference).
 	if exe, ok := detectPackageManagerFromSettings(cwd); ok {
 		return exe
 	}
+	// 2) package.json "packageManager" field (corepack standard).
+	if exe, ok := detectPackageManagerFromPackageJSON(cwd); ok {
+		return exe
+	}
 	if defaultExe == "" {
 		defaultExe = "npm"
 	}