Bug: Apply SELinux context after binary replacement (#1678)

- Move SELinux context handling to internal/ghupdate for reuse
- Make chcon a true fallback (only runs if semanage/restorecon unavailable)
- Handle existing semanage rules with -m (modify) after -a (add) fails
- Apply SELinux handling to both agent and hub updates
- Add tests with proper skip behavior for SELinux systems

---------

Co-authored-by: henrygd <hank@henrygd.me>

internal/ghupdate/selinux.go

@@ -0,0 +1,66 @@
+package ghupdate
+
+import (
+	"fmt"
+	"os/exec"
+	"strings"
+)
+
+// HandleSELinuxContext restores or applies the correct SELinux label to the binary.
+func HandleSELinuxContext(path string) error {
+	out, err := exec.Command("getenforce").Output()
+	if err != nil {
+		// SELinux not enabled or getenforce not available
+		return nil
+	}
+	state := strings.TrimSpace(string(out))
+	if state == "Disabled" {
+		return nil
+	}
+
+	ColorPrint(ColorYellow, "SELinux is enabled; applying context…")
+
+	// Try persistent context via semanage+restorecon
+	if success := trySemanageRestorecon(path); success {
+		return nil
+	}
+
+	// Fallback to temporary context via chcon
+	if chconPath, err := exec.LookPath("chcon"); err == nil {
+		if err := exec.Command(chconPath, "-t", "bin_t", path).Run(); err != nil {
+			return fmt.Errorf("chcon failed: %w", err)
+		}
+		return nil
+	}
+
+	return fmt.Errorf("no SELinux tools available (semanage/restorecon or chcon)")
+}
+
+// trySemanageRestorecon attempts to set persistent SELinux context using semanage and restorecon.
+// Returns true if successful, false otherwise.
+func trySemanageRestorecon(path string) bool {
+	semanagePath, err := exec.LookPath("semanage")
+	if err != nil {
+		return false
+	}
+
+	restoreconPath, err := exec.LookPath("restorecon")
+	if err != nil {
+		return false
+	}
+
+	// Try to add the fcontext rule; if it already exists, try to modify it
+	if err := exec.Command(semanagePath, "fcontext", "-a", "-t", "bin_t", path).Run(); err != nil {
+		// Rule may already exist, try modify instead
+		if err := exec.Command(semanagePath, "fcontext", "-m", "-t", "bin_t", path).Run(); err != nil {
+			return false
+		}
+	}
+
+	// Apply the context with restorecon
+	if err := exec.Command(restoreconPath, "-v", path).Run(); err != nil {
+		return false
+	}
+
+	return true
+}