fix(web): rich text previews keep paragraphs that end with a backslash

apps/web/src/components/files/FilePreviewPanel.test.ts

@@ -189,6 +189,24 @@ describe("document preview contents", () => {
     expect(html).not.toContain("https:");
   });
 
+  it("treats a backslash before a line break as a paragraph break, as TextEdit writes them", () => {
+    const html = (rtf: string) => {
+      const result = openRtf(bytes(rtf));
+      if (result.type !== "document") throw new Error("Expected document");
+      return result.pages.map((page) => page.html);
+    };
+    const textEdit = String.raw`{\rtf1\ansi{\fonttbl\f0\fswiss Helvetica;}
+\pard\f0\fs24 \cf0 First\
+Second\
+\
+Third}`;
+    const expected = html(
+      String.raw`{\rtf1\ansi{\fonttbl\f0\fswiss Helvetica;}\pard\f0\fs24 \cf0 First\par Second\par \par Third}`,
+    );
+    expect(html(textEdit)).toEqual(expected);
+    expect(html(textEdit.replaceAll("\n", "\r\n"))).toEqual(expected);
+  });
+
   it("preserves rich text page breaks and formatting without splitting hidden destinations", () => {
     const result = openRtf(
       bytes(String.raw`{\rtf1\b First\page Second\b0{\*\unknown \page hidden}\page Third\page}`),

apps/web/src/components/files/extendedDocumentPreview.ts

@@ -565,6 +565,8 @@ export function openRtf(bytes: ArrayBuffer): OfficeWorkerResult {
       const match = /^([a-z]+)(-?\d+)? ?/i.exec(source.slice(i));
       if (!match) {
         if (next === "~") emit("\u00a0");
+        // A backslash before a line break is \par; TextEdit ends paragraphs this way.
+        else if ((next === "\n" || next === "\r") && !state.skip) html += "<br>";
         i++;
         continue;
       }