From 98bf1454d216bca5bfd10c9e33ac520c38fa1be3 Mon Sep 17 00:00:00 2001
From: Hanbin Noh <282618027+hanbinnoh@users.noreply.github.com>
Date: Tue, 11 Aug 2026 17:29:39 +0900
Subject: [PATCH] fix(openai-chat): tolerate null tool-call padding

---
 src/adapters/openai-chat.ts         |  9 +++++----
 tests/openai-chat-hardening.test.ts | 28 ++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/src/adapters/openai-chat.ts b/src/adapters/openai-chat.ts
index 383544fb40..94cddca397 100644
--- a/src/adapters/openai-chat.ts
+++ b/src/adapters/openai-chat.ts
@@ -975,10 +975,11 @@ export function createOpenAIChatAdapter(provider: OcxProviderConfig): ProviderAd
           }
 
           const rawToolCalls = delta.tool_calls;
-          if (rawToolCalls !== undefined) {
-            // A claimed tool-call payload is not benign padding. Dropping it can leave the
+          if (rawToolCalls !== undefined && rawToolCalls !== null) {
+            // A non-null claimed tool-call payload is not benign padding. Dropping it can leave the
             // matching result permanently orphaned, so malformed nested shapes fail closed
-            // through the adapter error channel instead of escaping as TypeError (#1325).
+            // through the adapter error channel instead of escaping as TypeError (#1325). Null is
+            // tolerated as absent because OpenAI-compatible providers may emit it as stream padding.
             if (!Array.isArray(rawToolCalls)) {
               return yield* terminateWithError(invalidToolCallsEvent(pendingUsage));
             }
@@ -1146,7 +1147,7 @@ export function createOpenAIChatAdapter(provider: OcxProviderConfig): ProviderAd
         if (reasoningText !== undefined) events.push({ type: "reasoning_raw_delta", text: reasoningText });
         if (typeof msg.content === "string") events.push({ type: "text_delta", text: msg.content });
         const rawToolCalls = msg.tool_calls;
-        if (rawToolCalls !== undefined) {
+        if (rawToolCalls !== undefined && rawToolCalls !== null) {
           if (!Array.isArray(rawToolCalls)) return [invalidToolCallsEvent(usage)];
           for (const rawToolCall of rawToolCalls) {
             if (!isRecord(rawToolCall) || !isRecord(rawToolCall.function)) {
diff --git a/tests/openai-chat-hardening.test.ts b/tests/openai-chat-hardening.test.ts
index 95900b3e11..b78c3102b8 100644
--- a/tests/openai-chat-hardening.test.ts
+++ b/tests/openai-chat-hardening.test.ts
@@ -117,6 +117,19 @@ describe("openai-chat non-stream response hardening", () => {
     expect(events).toEqual([{ type: "error", message: "upstream response contained invalid choices" }]);
   });
 
+  test("treats null tool calls as absent", async () => {
+    const adapter = createOpenAIChatAdapter(provider());
+    const events = await adapter.parseResponse!(new Response(JSON.stringify({
+      choices: [{ message: { role: "assistant", content: "ok", tool_calls: null } }],
+      usage: { prompt_tokens: 7, completion_tokens: 2 },
+    })));
+
+    expect(events).toEqual([
+      { type: "text_delta", text: "ok" },
+      { type: "done", usage: { inputTokens: 7, outputTokens: 2 } },
+    ]);
+  });
+
   test("rejects malformed nested tool calls without throwing", async () => {
     const adapter = createOpenAIChatAdapter(provider());
     for (const toolCalls of [
@@ -180,6 +193,21 @@ describe("openai-chat stream response hardening", () => {
     expect(events.some(event => event.type === "done")).toBe(false);
   });
 
+  test("treats null streaming tool calls as padding", async () => {
+    const adapter = createOpenAIChatAdapter(provider());
+    const response = new Response([
+      'data: {"choices":[{"delta":{"content":"ok","tool_calls":null}}]}\n\n',
+      'data: {"choices":[{"delta":{},"finish_reason":"stop"}],"usage":{"prompt_tokens":7,"completion_tokens":2}}\n\n',
+      "data: [DONE]\n\n",
+    ].join(""));
+
+    const events = await collect(adapter.parseStream(response));
+    expect(events).toEqual([
+      { type: "text_delta", text: "ok" },
+      { type: "done", usage: { inputTokens: 7, outputTokens: 2 } },
+    ]);
+  });
+
   test("malformed nested streaming tool calls are terminal errors", async () => {
     const adapter = createOpenAIChatAdapter(provider());
     for (const toolCalls of [{ unexpected: true }, [null]]) {