fix: Attachments on public share links broken when using AWS Accelerate

fix: Attachments broken when using non-collab and AWS bucket on the same host
(https://github.com/outline/outline/discussions/3274\)

shared/editor/rules/attachments.ts

@@ -21,8 +21,12 @@ function isLinkClose(token: Token) {
 function isAttachment(token: Token) {
   const href = token.attrGet("href");
   return (
-    href?.includes("attachments.redirect") ||
-    href?.startsWith(env.AWS_S3_UPLOAD_BUCKET_URL)
+    // internal
+    href?.startsWith("/api/attachments.redirect") ||
+    // external (public share are pre-signed and this is a reasonable way of detecting them)
+    ((href?.startsWith(env.AWS_S3_UPLOAD_BUCKET_URL) ||
+      href?.startsWith(env.AWS_S3_ACCELERATE_URL)) &&
+      href?.includes("X-Amz-Signature"))
   );
 }