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, 27 insertions, 0 deletions

diff --git a/tests/e2e/test_helpers.go b/tests/e2e/test_helpers.go
index 0ae83aa..6d65011 100644
--- a/tests/e2e/test_helpers.go
+++ b/tests/e2e/test_helpers.go
@@ -3,6 +3,7 @@ package e2e
 import (
 	"fmt"
 	"os"
+	"strings"
 )
 
 // GetBinaryPath resolves the path to the wg-wrap binary.
@@ -19,3 +20,29 @@ func GetBinaryPath() (string, error) {
 
 	return path, nil
 }
+
+// SetEnvOverrides returns a new slice of environment variables with the provided overrides applied.
+// It ensures that overriding an existing variable replaces it rather than appending it.
+func SetEnvOverrides(overrides map[string]string) []string {
+	env := os.Environ()
+	newEnv := make([]string, 0, len(env)+len(overrides))
+
+	for _, e := range env {
+		matched := false
+		for k := range overrides {
+			if strings.HasPrefix(e, k+"=") {
+				matched = true
+				break
+			}
+		}
+		if !matched {
+			newEnv = append(newEnv, e)
+		}
+	}
+
+	for k, v := range overrides {
+		newEnv = append(newEnv, fmt.Sprintf("%s=%s", k, v))
+	}
+
+	return newEnv
+}