fix(coverage): cover three uncovered diff paths to pass patch gate

- extract executeMetricsGet(w io.Writer, format, path) int from
  runMetricsGet, matching the executeMetricsRank pattern, so the
  writeGetOutput error path is testable with an injected writer
- add TestExecuteMetricsGet_WriteError_ExitsTwo to exercise the new
  function's write-error branch
- add TestExecuteMetricsRank_UnknownFormat_ExitsTwo to exercise the
  validateOutputFormat early-return in executeMetricsRank
- add TestMET008_Readability_PlainTextErrorAfterWordCountSuccess to
  cover the PlainText error path in MET008 when WordCount succeeds
  with a non-zero count (the existing PlainTextError test only hits
  the WordCount error path)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BjaGA7w2gqtcdgMbGjgsh9

Author: claude

cmd/mdsmith/metrics.go

@@ -451,14 +451,18 @@ func runMetricsGet(args []string) int {
 		return 2
 	}
 
+	return executeMetricsGet(os.Stdout, format, path)
+}
+
+func executeMetricsGet(w io.Writer, format, path string) int {
 	defs := metricspkg.ForScope(metricspkg.ScopeFile)
 	rows, err := metricspkg.Collect([]string{path}, defs, bytelimit.DefaultMaxInputBytes)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "mdsmith: %v\n", err)
 		return 2
 	}
 
-	if err := writeGetOutput(os.Stdout, format, rows[0], defs); err != nil {
+	if err := writeGetOutput(w, format, rows[0], defs); err != nil {
 		fmt.Fprintf(os.Stderr, "mdsmith: writing output: %v\n", err)
 		return 2
 	}

cmd/mdsmith/metrics_unit_test.go

@@ -168,6 +168,16 @@ func TestResolveRankSelection_ByNotInDefaultsGetsAppended(t *testing.T) {
 	assert.True(t, containsMetric(defs, byDef.ID))
 }
 
+// --- executeMetricsRank ---
+
+func TestExecuteMetricsRank_UnknownFormat_ExitsTwo(t *testing.T) {
+	captureStderr(func() {
+		opts := metricsRankOptions{format: "toml"}
+		code := executeMetricsRank(opts, nil)
+		assert.Equal(t, 2, code)
+	})
+}
+
 // --- writeRankOutput ---
 
 func TestWriteRankOutput_UnknownFormat_Error(t *testing.T) {
@@ -641,6 +651,14 @@ func TestRunMetricsGet_RealFile_YAMLContainsSentences(t *testing.T) {
 	assert.Contains(t, out, "readability")
 }
 
+func TestExecuteMetricsGet_WriteError_ExitsTwo(t *testing.T) {
+	path := testMetricsFile(t)
+	captureStderr(func() {
+		code := executeMetricsGet(&alwaysErrorWriter{}, "json", path)
+		assert.Equal(t, 2, code)
+	})
+}
+
 func TestRunMetricsGet_RealFile_JSONAndYAMLAgreeOnSentences(t *testing.T) {
 	path := testMetricsFile(t)
 	jsonOut := captureStdout(func() {

internal/metrics/metrics_morecoverage_test.go

@@ -249,6 +249,25 @@ func TestMET008_Readability_PlainTextError(t *testing.T) {
 	assert.False(t, v.Available)
 }
 
+func TestMET008_Readability_PlainTextErrorAfterWordCountSuccess(t *testing.T) {
+	def, ok := Lookup("MET008")
+	require.True(t, ok, "MET008 must be registered")
+
+	doc := NewDocument("test.md", []byte("# Hello\n"))
+	sentinel := errors.New("plain-text failure")
+	// WordCount succeeds with a non-zero result; the subsequent PlainText call fails.
+	doc.wordCountReady = true
+	doc.wordCount = 5
+	doc.wordCountErr = nil
+	doc.plainTextReady = true
+	doc.plainTextErr = sentinel
+
+	v, err := def.Compute(doc)
+	require.Error(t, err)
+	assert.ErrorIs(t, err, sentinel)
+	assert.False(t, v.Available)
+}
+
 func TestMET009_Sentences_PlainTextError(t *testing.T) {
 	def, ok := Lookup("MET009")
 	require.True(t, ok, "MET009 must be registered")