fix(responses): don't close message on empty tool_calls array

Some providers (e.g. codebuddy/cbcn) attach an empty tool_calls array to every streaming chunk. An empty array is truthy in JS, so the guard 'if (delta.tool_calls)' closed the message on the first content token and emitted response.output_text.done early, dropping the remaining deltas. Guard on a non-empty array; finish_reason still closes the message and real tool calls still close it before emitting function_call items.

fixes #3234

open-sse/translator/response/openai-responses.js

@@ -99,8 +99,8 @@ export function openaiToOpenAIResponsesResponse(chunk, state) {
     }
   }
 
-  // Handle tool_calls
-  if (delta.tool_calls) {
+  // Handle tool_calls (empty array is truthy; require a real call)
+  if (delta.tool_calls && delta.tool_calls.length) {
     closeMessage(state, emit, idx);
     for (const tc of delta.tool_calls) {
       emitToolCall(state, emit, tc);

tests/unit/openai-responses-empty-toolcalls.test.js

@@ -0,0 +1,52 @@
+/**
+ * Some providers (e.g. codebuddy / cbcn) attach `tool_calls: []` to every
+ * streaming chunk. An empty array is truthy in JS, so the guard
+ * `if (delta.tool_calls)` closed the message on the first content token,
+ * emitting `output_text.done` early and truncating the answer. This mirrors
+ * the real repro: `codex exec -m cbcn/kimi-k3` answered only "cod" instead
+ * of "codex-ok".
+ */
+import { describe, it, expect } from "vitest";
+import { openaiToOpenAIResponsesResponse } from "../../open-sse/translator/response/openai-responses.js";
+import { initState } from "../../open-sse/translator/index.js";
+import { FORMATS } from "../../open-sse/translator/formats.js";
+
+describe("OpenAI Chat stream → Responses: empty tool_calls arrays", () => {
+  it("does not emit output_text.done early when every chunk carries tool_calls: []", () => {
+    const state = initState(FORMATS.OPENAI_RESPONSES);
+    const chunks = [
+      { id: "cmb-test", choices: [{ index: 0, delta: { role: "assistant", content: "", reasoning_content: "", tool_calls: [] }, finish_reason: null }] },
+      { id: "cmb-test", choices: [{ index: 0, delta: { content: "", reasoning_content: "thinking", tool_calls: [] }, finish_reason: null }] },
+      { id: "cmb-test", choices: [{ index: 0, delta: { content: "cod", reasoning_content: "", tool_calls: [] }, finish_reason: null }] },
+      { id: "cmb-test", choices: [{ index: 0, delta: { content: "ex", reasoning_content: "", tool_calls: [] }, finish_reason: null }] },
+      { id: "cmb-test", choices: [{ index: 0, delta: { content: "-ok", reasoning_content: "", tool_calls: [] }, finish_reason: null }] },
+      { id: "cmb-test", choices: [{ index: 0, delta: { content: "", reasoning_content: "", tool_calls: [] }, finish_reason: "stop" }] },
+    ];
+
+    const events = chunks.flatMap((chunk) => openaiToOpenAIResponsesResponse(chunk, state));
+    const textDone = events.filter((e) => e.event === "response.output_text.done");
+    const textDeltas = events.filter((e) => e.event === "response.output_text.delta");
+
+    expect(textDone).toHaveLength(1);
+    expect(textDone[0].data.text).toBe("codex-ok");
+    expect(textDeltas.map((e) => e.data.delta).join("")).toBe("codex-ok");
+    // done must come after every delta
+    expect(events.indexOf(textDone[0])).toBe(events.indexOf(textDeltas[textDeltas.length - 1]) + 1);
+  });
+
+  it("still closes the message before a real tool call", () => {
+    const state = initState(FORMATS.OPENAI_RESPONSES);
+    const chunks = [
+      { id: "cmb-test", choices: [{ index: 0, delta: { content: "Let me run that.", tool_calls: [] }, finish_reason: null }] },
+      { id: "cmb-test", choices: [{ index: 0, delta: { tool_calls: [{ index: 0, id: "call_1", type: "function", function: { name: "exec", arguments: "" } }] }, finish_reason: null }] },
+      { id: "cmb-test", choices: [{ index: 0, delta: {}, finish_reason: "tool_calls" }] },
+    ];
+
+    const events = chunks.flatMap((chunk) => openaiToOpenAIResponsesResponse(chunk, state));
+    const added = events.find((e) => e.event === "response.output_item.added" && e.data.item?.type === "function_call");
+    const textDone = events.find((e) => e.event === "response.output_text.done");
+
+    expect(added).toBeTruthy();
+    expect(textDone.data.text).toBe("Let me run that.");
+  });
+});