Add device agent library

Provide enrollment, elevated install, posture checks, keystore, and
system-tray helpers shared by the probo-agent binary.

Signed-off-by: Ludovic Vielle <ludovic@probo.com>

pkg/deviceagent/enrollment_state.go

@@ -0,0 +1,112 @@
+// Copyright (c) 2026 Probo Inc <hello@probo.com>.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+package deviceagent
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+const (
+	// EnrollmentRunDirMode is searchable by the user-session tray helper so
+	// IsEnrolled can stat the marker without access to the secrets directory.
+	EnrollmentRunDirMode = 0o755
+
+	// EnrollmentMarkerMode is owner-only; tray detection uses os.Stat via
+	// the searchable run directory, not read access to the marker contents.
+	EnrollmentMarkerMode = 0o600
+
+	// EnrollmentMarkerName is the runtime enrollment flag filename.
+	EnrollmentMarkerName = "enrolled"
+)
+
+// EnrollmentRunDir returns the runtime directory for the public enrollment
+// marker. Production installs use DefaultEnrollmentRunDir(); custom --dir
+// values get an isolated sibling run tree for dev and tests.
+func EnrollmentRunDir(configDir string) string {
+	if configDir == "" {
+		configDir = DefaultConfigDir()
+	}
+
+	if configDir == DefaultConfigDir() {
+		return DefaultEnrollmentRunDir()
+	}
+
+	return filepath.Join(filepath.Dir(configDir), "run", filepath.Base(configDir))
+}
+
+func enrollmentMarkerPath(runDir string) string {
+	if runDir == "" {
+		runDir = DefaultEnrollmentRunDir()
+	}
+
+	return filepath.Join(runDir, EnrollmentMarkerName)
+}
+
+// IsEnrolled reports whether the enrollment marker exists in runDir.
+func IsEnrolled(runDir string) (bool, error) {
+	_, err := os.Stat(enrollmentMarkerPath(runDir))
+	if err == nil {
+		return true, nil
+	}
+
+	if os.IsNotExist(err) {
+		return false, nil
+	}
+
+	return false, fmt.Errorf("cannot stat enrollment marker: %w", err)
+}
+
+// MarkEnrolled writes the enrollment marker under runDir.
+func MarkEnrolled(runDir string) error {
+	if runDir == "" {
+		runDir = DefaultEnrollmentRunDir()
+	}
+
+	if err := os.MkdirAll(runDir, EnrollmentRunDirMode); err != nil {
+		return fmt.Errorf("cannot create enrollment run dir: %w", err)
+	}
+
+	if err := os.Chmod(runDir, EnrollmentRunDirMode); err != nil {
+		return fmt.Errorf("cannot set enrollment run dir permissions: %w", err)
+	}
+
+	path := enrollmentMarkerPath(runDir)
+	if err := os.WriteFile(path, []byte("ok\n"), EnrollmentMarkerMode); err != nil {
+		return fmt.Errorf("cannot write enrollment marker: %w", err)
+	}
+
+	if err := os.Chmod(path, EnrollmentMarkerMode); err != nil {
+		return fmt.Errorf("cannot set enrollment marker permissions: %w", err)
+	}
+
+	return nil
+}
+
+// ClearEnrollmentMarker removes the public enrollment marker from runDir.
+func ClearEnrollmentMarker(runDir string) error {
+	if err := os.Remove(enrollmentMarkerPath(runDir)); err != nil && !os.IsNotExist(err) {
+		return fmt.Errorf("cannot remove enrollment marker: %w", err)
+	}
+
+	return nil
+}