Fix Azure 40 character limit on tool_call_id (#5575)

Author: colegottdank

packages/__tests__/llm-mapper/openai-chat-to-responses-converters.test.ts

@@ -373,6 +373,51 @@ describe("OpenAI Chat -> Responses converters", () => {
       expect(assistant2.tool_calls?.[0].id).toBe("call_c");
     });
 
+    it("truncates long tool_call_ids to 40 characters for Azure compatibility", () => {
+      const longId = "call_1234567890abcdefghij1234567890abcdefghij1234567890"; // 54 chars
+      const req = {
+        model: "gpt-4o-mini",
+        input: [
+          { role: "user", content: "Hello" },
+          { type: "function_call", call_id: longId, name: "my_func", arguments: "{}" },
+          { type: "function_call_output", call_id: longId, output: "result" },
+        ],
+      } as unknown as ResponsesRequestBody;
+
+      const oai = toChatCompletions(req);
+
+      // Check assistant message tool_call id is truncated
+      const assistant = oai.messages?.[1] as any;
+      expect(assistant.tool_calls?.[0].id.length).toBeLessThanOrEqual(40);
+
+      // Check tool response tool_call_id is truncated
+      const toolResponse = oai.messages?.[2] as any;
+      expect(toolResponse.tool_call_id.length).toBeLessThanOrEqual(40);
+
+      // Both should have the same truncated ID (deterministic)
+      expect(assistant.tool_calls?.[0].id).toBe(toolResponse.tool_call_id);
+    });
+
+    it("preserves short tool_call_ids unchanged", () => {
+      const shortId = "call_abc123"; // < 40 chars
+      const req = {
+        model: "gpt-4o-mini",
+        input: [
+          { role: "user", content: "Hello" },
+          { type: "function_call", call_id: shortId, name: "my_func", arguments: "{}" },
+          { type: "function_call_output", call_id: shortId, output: "result" },
+        ],
+      } as unknown as ResponsesRequestBody;
+
+      const oai = toChatCompletions(req);
+
+      const assistant = oai.messages?.[1] as any;
+      expect(assistant.tool_calls?.[0].id).toBe(shortId);
+
+      const toolResponse = oai.messages?.[2] as any;
+      expect(toolResponse.tool_call_id).toBe(shortId);
+    });
+
     it("maps Responses tools (flattened) to Chat tools (nested)", () => {
       const req = {
         model: "gpt-4o-mini",

packages/llm-mapper/transform/providers/responses/request/toChatCompletions.ts

@@ -11,6 +11,33 @@ import {
 } from "@helicone-package/prompts/types";
 import { ResponsesToolDefinition } from "../../../types/responses";
 
+/**
+ * Azure has a 40 character limit on tool_call_id.
+ * This function truncates long IDs deterministically so that:
+ * 1. IDs <= 40 chars are unchanged
+ * 2. IDs > 40 chars are shortened to prefix + hash suffix
+ * The same input always produces the same output, ensuring tool_calls
+ * and their corresponding tool responses match.
+ */
+const AZURE_TOOL_CALL_ID_LIMIT = 40;
+
+function truncateToolCallId(id: string): string {
+  if (id.length <= AZURE_TOOL_CALL_ID_LIMIT) {
+    return id;
+  }
+  // Use a simple deterministic hash for the suffix
+  let hash = 0;
+  for (let i = 0; i < id.length; i++) {
+    const char = id.charCodeAt(i);
+    hash = ((hash << 5) - hash) + char;
+    hash = hash & hash; // Convert to 32-bit integer
+  }
+  const hashStr = Math.abs(hash).toString(36);
+  // Keep prefix + underscore + hash, ensuring total <= 40 chars
+  const prefixLength = AZURE_TOOL_CALL_ID_LIMIT - hashStr.length - 1;
+  return `${id.substring(0, prefixLength)}_${hashStr}`;
+}
+
 function mapRole(role: string): "system" | "user" | "assistant" | "tool" | "function" {
   if (role === "developer") return "system";
   if (role === "system" || role === "user" || role === "assistant") return role;
@@ -88,7 +115,7 @@ function convertInputToMessages(input: ResponsesRequestBody["input"]) {
       >(input, i, "function_call");
 
       const toolCalls = functionCalls.map((fc, idx) => ({
-        id: fc.id || fc.call_id || `call_${i + idx}`,
+        id: truncateToolCallId(fc.id || fc.call_id || `call_${i + idx}`),
         type: "function" as const,
         function: {
           name: fc.name,
@@ -110,7 +137,7 @@ function convertInputToMessages(input: ResponsesRequestBody["input"]) {
       const fco = item;
       messages.push({
         role: "tool",
-        tool_call_id: fco.call_id,
+        tool_call_id: truncateToolCallId(fco.call_id),
         content: fco.output ?? "",
       });
       continue;