fix(richtext): blank lines survive into PDFs and read-only previews

Quill 2's semantic HTML saves a blank line as a truly empty <p></p> (no
<br> placeholder) — verified in the DB (invoice_sections hold <p></p>,
zero <p><br>) — which collapses to nothing outside the editor.
cleanQuillHtml (PDF path) and the new restoreQuillBlankLines (order/
invoice read-only previews) restore the placeholder at render time, so
existing stored content is covered retroactively.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/__tests__/pdf-shared.test.ts

@@ -32,6 +32,17 @@ describe("cleanQuillHtml — inline-style whitelist", () => {
     );
   });
 
+  it("restores Quill 2's empty <p></p> blank lines to <p><br></p>", () => {
+    // Quill 2's semantic HTML drops the <br> placeholder from blank lines.
+    expect(cleanQuillHtml("<p>A</p><p></p><p>B</p>")).toBe(
+      "<p>A</p><p><br></p><p>B</p>",
+    );
+    // Attribute-carrying and whitespace-only empties too.
+    expect(cleanQuillHtml('<p class="ql-align-center"> </p>')).toBe(
+      '<p class="ql-align-center"><br></p>',
+    );
+  });
+
   it("keeps stripping scripts, event handlers and js: URLs", () => {
     const out = cleanQuillHtml(
       '<p onclick="alert(1)"><script>alert(1)</script>' +

src/admin/pages/InvoiceDetail.tsx

@@ -58,6 +58,7 @@ import {
   formatCurrency,
   formatDate,
   numberOr,
+  restoreQuillBlankLines,
   todayLocalStr,
 } from "../utils/formatters";
 import { normalizeDateStr } from "../utils/attendanceHelpers";
@@ -1670,7 +1671,9 @@ export default function InvoiceDetail() {
                   {(s.content || "").replace(/<[^>]*>/g, "").trim() && (
                     <RichTextView
                       dangerouslySetInnerHTML={{
-                        __html: DOMPurify.sanitize(s.content || ""),
+                        __html: DOMPurify.sanitize(
+                          restoreQuillBlankLines(s.content),
+                        ),
                       }}
                     />
                   )}
@@ -1690,7 +1693,9 @@ export default function InvoiceDetail() {
           invoice.internal_notes !== "<p><br></p>" ? (
             <RichTextView
               dangerouslySetInnerHTML={{
-                __html: DOMPurify.sanitize(invoice.internal_notes),
+                __html: DOMPurify.sanitize(
+                  restoreQuillBlankLines(invoice.internal_notes),
+                ),
               }}
             />
           ) : (

src/admin/pages/OrderDetail.tsx

@@ -18,7 +18,11 @@ import Typography from "@mui/material/Typography";
 import OrderConfirmationModal from "../components/OrderConfirmationModal";
 import Forbidden from "../components/Forbidden";
 import apiFetch from "../utils/api";
-import { formatCurrency, formatDate } from "../utils/formatters";
+import {
+  formatCurrency,
+  formatDate,
+  restoreQuillBlankLines,
+} from "../utils/formatters";
 import { ORDER_STATUS, statusLabel, statusColor } from "../lib/documentStatus";
 import {
   Button,
@@ -713,7 +717,9 @@ export default function OrderDetail() {
                   <RichTextView
                     sx={{ p: 2 }}
                     dangerouslySetInnerHTML={{
-                      __html: DOMPurify.sanitize(section.content),
+                      __html: DOMPurify.sanitize(
+                        restoreQuillBlankLines(section.content),
+                      ),
                     }}
                   />
                 )}

src/admin/utils/formatters.ts

@@ -76,3 +76,15 @@ export function czechPlural(
   if (n >= 2 && n <= 4) return few;
   return many;
 }
+
+/**
+ * Quill 2's semantic HTML saves blank lines as truly empty <p></p>, which
+ * collapse to zero height outside the editor — restore the <br> placeholder
+ * before rendering stored rich text read-only. (The PDF path does the same
+ * in cleanQuillHtml.)
+ */
+export function restoreQuillBlankLines(
+  html: string | null | undefined,
+): string {
+  return (html || "").replace(/<p([^>]*)>\s*<\/p>/gi, "<p$1><br></p>");
+}

src/utils/pdf-shared.ts

@@ -141,6 +141,10 @@ export function cleanQuillHtml(html: string | null | undefined): string {
   );
   // Replace   with regular space (outside of tags)
   s = s.replace(/( )/g, " ");
+  // Quill 2's semantic HTML saves blank lines as truly empty <p></p>, which
+  // collapse to zero height in the PDF — restore the <br> placeholder so an
+  // editor blank line stays a blank line.
+  s = s.replace(/<p([^>]*)>\s*<\/p>/gi, "<p$1><br></p>");
   // Inline styles: Quill writes text/background colors as style attributes.
   // Keep ONLY color/background-color with literal color values — everything
   // else (url(), expression(), positioning…) must never reach Puppeteer.