From b77dbb511ed8af1117dcc744eed05b2472145a3e Mon Sep 17 00:00:00 2001
From: Simon Klee <hello@simonklee.dk>
Date: Wed, 15 Jul 2026 23:31:58 +0200
Subject: [PATCH] ix(ai): reject incomplete pending tool calls

Only finalize pending Responses tool calls after response.completed.
Reject incomplete responses with pending calls so partial input cannot be dispatched.
---
 packages/ai/src/protocols/openai-responses.ts |  7 ++++-
 .../ai/test/provider/openai-responses.test.ts | 31 ++++++++++++++++++-
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/packages/ai/src/protocols/openai-responses.ts b/packages/ai/src/protocols/openai-responses.ts
index cc8727d55b..c50d1693ba 100644
--- a/packages/ai/src/protocols/openai-responses.ts
+++ b/packages/ai/src/protocols/openai-responses.ts
@@ -882,7 +882,10 @@ const onResponseFinish = Effect.fn("OpenAIResponses.onResponseFinish")(function*
   state: ParserState,
   event: OpenAIResponsesEvent,
 ) {
-  const pending = yield* ToolStream.finishAll(ADAPTER, state.tools)
+  const pending =
+    event.type === "response.completed"
+      ? yield* ToolStream.finishAll(ADAPTER, state.tools)
+      : { tools: state.tools, events: NO_EVENTS }
   const events = [...pending.events]
   const hasFunctionCall = state.hasFunctionCall || pending.events.some(LLMEvent.is.toolCall)
   const lifecycle = Lifecycle.finish(state.lifecycle, events, {
@@ -944,6 +947,8 @@ const step = (state: ParserState, event: OpenAIResponsesEvent) => {
   if (event.type === "response.output_item.added") return Effect.succeed(onOutputItemAdded(state, event))
   if (event.type === "response.function_call_arguments.delta") return onFunctionCallArgumentsDelta(state, event)
   if (event.type === "response.output_item.done") return onOutputItemDone(state, event)
+  if (event.type === "response.incomplete" && Object.keys(state.tools).length > 0)
+    return ProviderShared.eventError(ADAPTER, "OpenAI Responses response incomplete with pending tool calls")
   if (event.type === "response.completed" || event.type === "response.incomplete") return onResponseFinish(state, event)
   if (event.type === "response.failed") return providerError(event, "OpenAI Responses response failed")
   if (event.type === "error") return providerError(event, "OpenAI Responses stream error")
diff --git a/packages/ai/test/provider/openai-responses.test.ts b/packages/ai/test/provider/openai-responses.test.ts
index aac348db51..dc8cdf217e 100644
--- a/packages/ai/test/provider/openai-responses.test.ts
+++ b/packages/ai/test/provider/openai-responses.test.ts
@@ -1,7 +1,7 @@
 import { describe, expect } from "bun:test"
 import { ConfigProvider, Effect, Layer, Stream } from "effect"
 import { Headers, HttpClientRequest } from "effect/unstable/http"
-import { LLM, LLMError, Message, Model, ToolCallPart, Usage } from "../../src"
+import { LLM, LLMError, LLMEvent, Message, Model, ToolCallPart, Usage } from "../../src"
 import { Auth, LLMClient, RequestExecutor, WebSocketExecutor } from "../../src/route"
 import * as Azure from "../../src/providers/azure"
 import * as OpenAI from "../../src/providers/openai"
@@ -1286,6 +1286,35 @@ describe("OpenAI Responses route", () => {
     }),
   )
 
+  it.effect("rejects an incomplete pending function call", () =>
+    Effect.gen(function* () {
+      const body = sseEvents(
+        {
+          type: "response.output_item.added",
+          item: { type: "function_call", id: "item_1", call_id: "call_1", name: "patch", arguments: "" },
+        },
+        {
+          type: "response.incomplete",
+          response: { incomplete_details: { reason: "max_output_tokens" } },
+        },
+      )
+      const events: LLMEvent[] = []
+      const error = yield* LLMClient.stream(
+        LLM.updateRequest(request, {
+          tools: [{ name: "patch", description: "Apply a patch", inputSchema: { type: "object" } }],
+        }),
+      ).pipe(
+        Stream.runForEach((event) => Effect.sync(() => events.push(event))),
+        Effect.flip,
+        Effect.provide(fixedResponse(body)),
+      )
+
+      expect(events.filter(LLMEvent.is.toolCall)).toEqual([])
+      expect(error.reason).toMatchObject({ _tag: "InvalidProviderOutput" })
+      expect(error.message).toContain("OpenAI Responses response incomplete with pending tool calls")
+    }),
+  )
+
   it.effect("decodes web_search_call as provider-executed tool-call + tool-result", () =>
     Effect.gen(function* () {
       const item = {