Fix BBCode::getSpoilerHeadings()

src/Content/Text/BBCode.php

@@ -2184,9 +2184,9 @@ class BBCode
 	 * Returns a list of the headings of "spoiler" elements
 	 * 
 	 * @param string $text The text containing spoiler elements
-	 * @return array The list of spoiler headings
+	 * @return string The list of spoiler headings
 	 */
-	public static function getSpoilerHeadings(string $text): array
+	public static function getSpoilerHeadings(string $text): string
 	{
 		DI::profiler()->startRecording('rendering');
 		
@@ -2197,7 +2197,7 @@ class BBCode
 					$headings[] = BBCode::toPlaintext($item);
 				}
 			}
-			return $headings;
+			return implode(', ', $headings);
 		});
 		
 		DI::profiler()->stopRecording();

src/Protocol/ActivityPub/Transmitter.php

@@ -1605,7 +1605,7 @@ class Transmitter
 		} else {
 			$warnings = BBCode::getSpoilerHeadings($item['body']);
 			if ($warnings) {
-				$data['summary'] = implode(', ', $warnings);
+				$data['summary'] = $warnings;
 				$data['keithext:summaryFromSpoilers'] = true;
 			}
 		}