test(langgraph-ts): fix prepare-regenerate-stream fixture to match newest-first getHistory order

`threads.getHistory` returns checkpoints newest-first;
`getCheckpointByMessage` reverses to walk oldest-first and finds the
first checkpoint containing the target message. The previous fixture
ordered ck-old before ck-new, so after reverse the search found ck-new
(which had both u1 and a1), saw `messagesAfter` non-empty, and
recursed on the parent — but the mock returned the same list every
time, so the search never terminated and the worker timed out.

Swap to newest-first so the reversed walk lands on ck-old (only u1, no
messagesAfter) and returns immediately.

Author: ranst91

integrations/langgraph/typescript/src/prepare-regenerate-stream.test.ts

@@ -48,31 +48,36 @@ function makeThreadStream() {
 
 function makeConfig(opts: { useTransformer: boolean }) {
   const threadStreams = new Map<string, ReturnType<typeof makeThreadStream>>();
+  // LangGraph's `threads.getHistory` returns checkpoints newest-first.
+  // `getCheckpointByMessage` reverses to walk oldest→newest and finds
+  // the FIRST checkpoint containing the target message — that's the
+  // one we regenerate from. Order this fixture the same way.
   const history = [
     {
-      // Older checkpoint — includes the message we'll regenerate from.
+      // Newer checkpoint with a follow-up assistant message.
       values: {
         messages: [
           { id: "u1", type: "human", content: "first" } as LangGraphMessage,
+          { id: "a1", type: "ai", content: "answer" } as LangGraphMessage,
         ],
       },
-      checkpoint: { checkpoint_id: "ck-old" },
-      parent_checkpoint: null,
-      next: ["model"],
+      checkpoint: { checkpoint_id: "ck-new" },
+      parent_checkpoint: { checkpoint_id: "ck-old", checkpoint_ns: "" },
+      next: [],
       tasks: [],
       metadata: {},
     },
     {
-      // Newer checkpoint with a follow-up assistant message.
+      // Older checkpoint — contains only the message we'll regenerate
+      // from; no `messagesAfter`, so the search terminates here.
       values: {
         messages: [
           { id: "u1", type: "human", content: "first" } as LangGraphMessage,
-          { id: "a1", type: "ai", content: "answer" } as LangGraphMessage,
         ],
       },
-      checkpoint: { checkpoint_id: "ck-new" },
-      parent_checkpoint: { checkpoint_id: "ck-old", checkpoint_ns: "" },
-      next: [],
+      checkpoint: { checkpoint_id: "ck-old" },
+      parent_checkpoint: null,
+      next: ["model"],
       tasks: [],
       metadata: {},
     },