diff --git a/src/common/stores/chat/chat.fragments.ts b/src/common/stores/chat/chat.fragments.ts
index a96181d21..0afdf9e53 100644
--- a/src/common/stores/chat/chat.fragments.ts
+++ b/src/common/stores/chat/chat.fragments.ts
@@ -440,7 +440,8 @@ function _create_Sentinel_Part(): _SentinelPart {
 }
 
 function _duplicate_Part<TPart extends (DMessageContentFragment | DMessageAttachmentFragment | DMessageVoidFragment)['part']>(part: TPart): TPart {
-  switch (part.pt) {
+  const pt = part.pt;
+  switch (pt) {
     case 'doc':
       const newDocVersion = Number(part.version ?? 1); // we don't increase the version on duplication (not sure we should?)
       return _create_Doc_Part(part.vdt, _duplicate_InlineData(part.data), part.ref, part.l1Title, newDocVersion, part.meta ? { ...part.meta } : undefined) as TPart;
@@ -481,6 +482,16 @@ function _duplicate_Part<TPart extends (DMessageContentFragment | DMessageAttach
 
     case '_pt_sentinel':
       return _create_Sentinel_Part() as TPart;
+
+    default:
+      const _exhaustiveCheck: never = pt;
+
+      // console.warn('[DEV] _duplicate_Part: Unknown part type, will duplicate as Error', { part });
+      // return _create_Error_Part(`Unknown part type '${(part as any)?.pt || '(undefined)'}'`) as TPart;
+
+      // unexpected case: if we are here, the best to do is probably to return a clone of the part, as returning
+      // nothing would corrupt the Fragment
+      return structuredClone(part) as TPart; // fallback to structured clone for unknown parts
   }
 }