refactor: optimize file cleanups, propagate exit codes, and fix Makefile

- Unlink the temporary bootstrap launcher binary immediately after opening a read-only descriptor to it, then execute via `/proc/self/fd/<fd>` to ensure zero-disk footprint on execution.
- Unlink temporary `/tmp/resolvconf*` files immediately after successful bind-mounting over `/etc/resolv.conf`.
- Prune parent ephemeral profile directories when unpinning a namespace, leaving zero directories behind once empty.
- Propagate the exact exit status of the wrapped command to the host process using `errors.As` and `*exec.ExitError` instead of defaulting to exit code 1.
- Added E2E automated test `TestExitCodePropagation` to verify exit status delivery.
- Added the `$(BINARY)` target to `.PHONY` in the Makefile to delegate dependency tracking to Go's compiler cache, ensuring modified Go files are rebuilt during `make test`.

1 files changed, 23 insertions, 0 deletions

diff --git a/tests/e2e/e2e_test.go b/tests/e2e/e2e_test.go
index e37810a..939d231 100644
--- a/tests/e2e/e2e_test.go
+++ b/tests/e2e/e2e_test.go
@@ -286,3 +286,26 @@ func TestMTUFragmentation(t *testing.T) {
 		t.Errorf("expected command to pass, got: %v", err)
 	}
 }
+
+func TestExitCodePropagation(t *testing.T) {
+	binaryPath, err := GetBinaryPath()
+	if err != nil {
+		t.Skipf("Skipping test: %v", err)
+	}
+
+	// Run a command that exits with code 42
+	cmd := exec.Command(binaryPath, "--profile", "default", "--", "sh", "-c", "exit 42")
+	err = cmd.Run()
+	if err == nil {
+		t.Fatalf("expected command to fail with exit status 42, but it succeeded")
+	}
+
+	exitErr, ok := err.(*exec.ExitError)
+	if !ok {
+		t.Fatalf("expected error of type *exec.ExitError, got %T: %v", err, err)
+	}
+
+	if exitErr.ExitCode() != 42 {
+		t.Errorf("expected exit code 42, got %d", exitErr.ExitCode())
+	}
+}