Implemented Markdown escaping for render output

internal/render/markdown_test.go

@@ -108,6 +108,48 @@ func TestMarkdownRendererMetadataOnlyWhenRequested(t *testing.T) {
 	}
 }
 
+func TestMarkdownRendererEscapesUserProvidedMarkdown(t *testing.T) {
+	transcript := Transcript{
+		Schema: "seriatim-intermediate",
+		Metadata: Metadata{
+			Application: "seriatim *cli*",
+			Version:     "v[test]",
+		},
+		Segments: []Segment{
+			{
+				ID:      1,
+				Start:   1,
+				End:     2,
+				Speaker: "Dr. *A_[1]",
+				Text:    "Use *literal* [link](target) and `code` \\ slash!",
+			},
+			{
+				ID:         2,
+				Start:      2,
+				End:        3,
+				Speaker:    "Narrator",
+				Text:       "_aside_ with | pipe",
+				Categories: []string{"background"},
+			},
+		},
+	}
+
+	output, err := MarkdownRenderer{}.Render(transcript, Options{
+		Title:             "# Planning [notes]",
+		IncludeTimestamps: false,
+		IncludeMetadata:   true,
+	})
+	if err != nil {
+		t.Fatalf("render markdown: %v", err)
+	}
+
+	assertContains(t, output, "# \\# Planning \\[notes\\]")
+	assertContains(t, output, "- Application: seriatim \\*cli\\*")
+	assertContains(t, output, "- Version: v\\[test\\]")
+	assertContains(t, output, "**Dr. \\*A\\_\\[1\\]:** Use \\*literal\\* \\[link\\]\\(target\\) and \\`code\\` \\\\ slash\\!")
+	assertContains(t, output, "**Narrator:** *\\_aside\\_ with \\| pipe*")
+}
+
 func TestMarkdownRendererCategoryHintItalicsAndUnknownCategories(t *testing.T) {
 	transcript := Transcript{
 		Segments: []Segment{
@@ -176,3 +218,10 @@ func TestMarkdownRendererIsDeterministic(t *testing.T) {
 		t.Fatalf("expected HH:MM:SS timestamp formatting:\n%s", first)
 	}
 }
+
+func assertContains(t *testing.T, value string, want string) {
+	t.Helper()
+	if !strings.Contains(value, want) {
+		t.Fatalf("expected output to contain %q:\n%s", want, value)
+	}
+}