fix: resolve resource leaks and improve namespace lifecycle management

- Fix DNS resolver leaks by creating temporary resolv.conf files within the profile's runtime directory and ensuring robust cleanup.
- Fix isolation block directory leaks by explicitly removing the block directory during namespace unpinning.
- Improve namespace lifecycle management:
    - Register processes before joining an active namespace to prevent race conditions in reference counting.
    - Update `IsLastProcess` and corresponding tests to reflect the unregister-then-check cleanup flow.
- Improve test reliability and correctness:
    - Convert `TestAppRun_ProfileDirInjection` to use separate binary execution, preventing process replacement and ensuring `t.TempDir()` cleanup.
    - Replace hardcoded test configuration paths with `t.TempDir()` in `mount_leak_test.go`.
    - Implement `SetEnvOverrides` helper for cleaner environment variable management in E2E tests.
    - Improve E2E lifecycle tests with better environment handling and output redirection.

1 files changed, 5 insertions, 4 deletions

diff --git a/tests/e2e/mount_leak_test.go b/tests/e2e/mount_leak_test.go
index bdc9d75..428675f 100644
--- a/tests/e2e/mount_leak_test.go
+++ b/tests/e2e/mount_leak_test.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"strings"
 	"testing"
 )
@@ -21,11 +22,11 @@ func TestDNSMountLeak(t *testing.T) {
 	dnsServer := "8.8.8.8"
 
 	// Pre-create a dummy config for the profile
-	configDir := "/tmp/wg-wrap-test-configs"
-	if err := os.MkdirAll(configDir, 0755); err != nil {
-		t.Fatalf("failed to create config dir: %v", err)
+	configDir := t.TempDir()
+	if err := os.MkdirAll(filepath.Join(configDir, "profiles"), 0755); err != nil {
+		t.Fatalf("failed to create profiles dir: %v", err)
 	}
-	configPath := fmt.Sprintf("%s/%s.conf", configDir, profile)
+	configPath := filepath.Join(configDir, "profiles", profile+".conf")
 	if err := os.WriteFile(configPath, []byte("[Interface]\nAddress = 10.0.0.1/24\nPrivateKey = aAAA\n"), 0644); err != nil {
 		t.Fatalf("failed to write config file: %v", err)
 	}