Add deterministic Markdown render coverage for renderer behavior

internal/render/markdown_test.go

@@ -138,3 +138,41 @@ func TestMarkdownRendererCategoryHintItalicsAndUnknownCategories(t *testing.T) {
 		t.Fatalf("expected unknown category to be ignored:\n%s", output)
 	}
 }
+
+func TestMarkdownRendererIsDeterministic(t *testing.T) {
+	transcript := Transcript{
+		Schema: "seriatim-intermediate",
+		Metadata: Metadata{
+			Application: "seriatim",
+			Version:     "v-test",
+		},
+		Segments: []Segment{
+			{ID: 1, Start: 1.2, End: 4.4, Speaker: "Eric", Text: "Hello there.", Categories: []string{"unknown-tag"}},
+			{ID: 2, Start: 65.1, End: 68.8, Speaker: "Mike", Text: "Yeah.", Categories: []string{"backchannel"}},
+		},
+	}
+	opts := Options{
+		Title:             "Transcript",
+		IncludeTimestamps: true,
+		IncludeSegmentIDs: true,
+		IncludeMetadata:   true,
+	}
+
+	first, err := MarkdownRenderer{}.Render(transcript, opts)
+	if err != nil {
+		t.Fatalf("first render failed: %v", err)
+	}
+	second, err := MarkdownRenderer{}.Render(transcript, opts)
+	if err != nil {
+		t.Fatalf("second render failed: %v", err)
+	}
+	if first != second {
+		t.Fatalf("render output is not deterministic:\nfirst:\n%s\nsecond:\n%s", first, second)
+	}
+	if !strings.Contains(first, "[00:00:01–00:00:04] [#1] **Eric:** Hello there.") {
+		t.Fatalf("expected HH:MM:SS timestamp formatting:\n%s", first)
+	}
+	if !strings.Contains(first, "[00:01:05–00:01:09] [#2] **Mike:** *Yeah.*") {
+		t.Fatalf("expected HH:MM:SS timestamp formatting:\n%s", first)
+	}
+}