fix(core): allow input_json_delta aggregation for anthropic tool_use …

.changeset/soft-monkeys-jump.md

@@ -0,0 +1,5 @@
+---
+"@langchain/core": patch
+---
+
+fix(core): support input_json_delta aggregation for anthropic tool streams

libs/langchain-core/src/messages/base.ts

@@ -566,7 +566,14 @@ function hasMergeableId(value: unknown): value is { id: string | number } {
 }
 
 function getMergeableTypeBase(type: string): string {
-  return type.endsWith("_delta") ? type.slice(0, -"_delta".length) : type;
+  if (type === "input_json_delta" || type === "input_json") {
+    return "tool_use";
+  }
+
+  if (type.endsWith("_delta")) {
+    return type.replace("_delta", "");
+  }
+  return type;
 }
 
 function hasMismatchedMergeableType(left: unknown, right: unknown): boolean {

libs/langchain-core/src/messages/tests/messages.test.ts

@@ -1,4 +1,5 @@
 import { isMessage } from "../message.js";
+import { AIMessageChunk } from "../index.js";
 
 describe("isMessage", () => {
   describe("valid cases", () => {
@@ -73,3 +74,50 @@ describe("isMessage", () => {
     });
   });
 });
+
+describe("AIMessageChunk", () => {
+  describe(".concat()", () => {
+    test("should successfully aggregate tool_use and input_json_delta chunks", async () => {
+      const chunk1 = new AIMessageChunk({
+        content: [
+          {
+            type: "tool_use",
+            index: 0,
+            id: "toolu_01Xyz",
+            name: "my_tool",
+          },
+        ],
+      });
+
+      const chunk2 = new AIMessageChunk({
+        content: [
+          {
+            type: "input_json_delta",
+            index: 0,
+            partial_json: '{"prompt":',
+          },
+        ],
+      });
+
+      const chunk3 = new AIMessageChunk({
+        content: [
+          {
+            type: "input_json_delta",
+            index: 0,
+            partial_json: '"hello"}',
+          },
+        ],
+      });
+
+      const merged = chunk1.concat(chunk2).concat(chunk3);
+
+      expect(merged.content[0]).toEqual({
+        type: "tool_use",
+        index: 0,
+        id: "toolu_01Xyz",
+        name: "my_tool",
+        partial_json: '{"prompt":"hello"}',
+      });
+    });
+  });
+});