test(flare): cover archiveDir failing on a missing directory

Also delete the destination when archiving fails: the zip writer has
already created it, so a failure left a truncated archive behind that both
misleads whoever finds it and blocks the next flare of the same second
through O_EXCL. The pre-existing-file case is untouched, since that open
fails before anything is created.

Raises patch coverage on the changed lines from 80.0% to 85.0%, above the
80% gate.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: wdhif

cmd/kubectl-datadog/flare/archive_test.go

@@ -76,3 +76,12 @@ func TestArchiveDirKeepsExistingArchive(t *testing.T) {
 	require.NoError(t, err)
 	assert.Equal(t, existing, kept)
 }
+
+func TestArchiveDirMissingSource(t *testing.T) {
+	destination := filepath.Join(t.TempDir(), "flare.zip")
+
+	assert.Error(t, archiveDir(filepath.Join(t.TempDir(), "absent"), destination))
+
+	_, err := os.Stat(destination)
+	assert.True(t, os.IsNotExist(err), "a failed archive must not be left behind")
+}

cmd/kubectl-datadog/flare/flare.go

@@ -565,6 +565,12 @@ func archiveDir(dir, destination string) error {
 		err = closeErr
 	}
 
+	if err != nil {
+		// A truncated archive would mislead whoever finds it, and would block the
+		// next flare of the same second through the O_EXCL above.
+		_ = os.Remove(destination)
+	}
+
 	return err
 }