fix: scrolling on suggestions

suggestions_test.go

@@ -85,6 +85,27 @@ func TestDetailRendersSuggestionAsRemovalAndAddition(t *testing.T) {
 	}
 }
 
+func TestRenderedSuggestionsAreCachedWithoutSharingMutableLines(t *testing.T) {
+	renderedSuggestions.clear()
+	reviewed := []string{"old_value = compute()", "return old_value"}
+	first := renderSuggestion(
+		"example.py", reviewed, "new_value = compute()\nreturn new_value", 50,
+	)
+	if len(renderedSuggestions.entries) != 1 {
+		t.Fatalf("suggestion cache entries = %d, want 1", len(renderedSuggestions.entries))
+	}
+	first.removed[0].rail = "mutated"
+	second := renderSuggestion(
+		"example.py", reviewed, "new_value = compute()\nreturn new_value", 50,
+	)
+	if second.removed[0].rail != "" {
+		t.Fatal("caller mutation changed cached suggestion lines")
+	}
+	if len(renderedSuggestions.entries) != 1 {
+		t.Fatalf("cache miss for unchanged suggestion: %d entries", len(renderedSuggestions.entries))
+	}
+}
+
 func TestSuggestionBackgroundIsDirectionalWithoutTextUnderline(t *testing.T) {
 	removed := suggestionHighlight("  - ", "old", 12, '-')
 	added := suggestionHighlight("  + ", "new", 12, '+')