fix(message-parser): Merge blockquotes separated by empty > lines into a single block (#39062)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: ggazzo <5263975+ggazzo@users.noreply.github.com>

Author: Copilot

.changeset/fix-blockquote-empty-lines.md

@@ -0,0 +1,5 @@
+---
+'@rocket.chat/message-parser': patch
+---
+
+Fixed blockquotes with empty lines between paragraphs not rendering as a single blockquote. Lines like `> ` or `>` (empty quote lines) are now treated as part of the surrounding blockquote rather than breaking it into separate quotes.

packages/message-parser/src/grammar.pegjs

@@ -76,7 +76,9 @@ Blocks
  */
 Blockquote = b:BlockquoteLine+ { return quote(b); }
 
-BlockquoteLine = ">" [ \t]* @Paragraph
+BlockquoteLine
+  = ">" [ \t]* EndOfLine { return paragraph([plain('')]); }
+  / ">" [ \t]* @Paragraph
 
 /**
  * Block Spoiler

packages/message-parser/tests/blockquotes.test.ts

@@ -26,6 +26,22 @@ As Rocket Cat said:
 `.trim(),
 		[paragraph([plain('As Rocket Cat said:')]), quote([paragraph([plain('meowww')]), paragraph([plain('grr.')])])],
 	],
+	[
+		`
+> meowww
+>
+> grr.
+`.trim(),
+		[quote([paragraph([plain('meowww')]), paragraph([plain('')]), paragraph([plain('grr.')])])],
+	],
+	[
+		`
+> meowww
+> 
+> grr.
+`.trim(),
+		[quote([paragraph([plain('meowww')]), paragraph([plain('')]), paragraph([plain('grr.')])])],
+	],
 ])('parses %p', (input, output) => {
 	expect(parse(input)).toMatchObject(output);
 });