fix: replay refusals in conversation history instead of throwing

src/protocol/body.ts

@@ -24,6 +24,7 @@ const RESPONSES_TOOL_NAME_LIMIT: ToolNameLimit = {
 type ResponsesContentPart =
   | { type: "input_text"; text: string }
   | { type: "output_text"; text: string }
+  | { type: "refusal"; refusal: string }
   | { type: "input_image"; image_url: string }
   | { type: "input_image"; file_id: string }
   | { type: "input_file"; filename: string; file_data: string }
@@ -127,9 +128,11 @@ function toResponsesContentPart(
         `@corbits/openai-responses: adapter does not handle ${block.type} content blocks.`,
       );
     case "refusal":
-      throw new Error(
-        "@corbits/openai-responses: adapter does not handle refusal content blocks.",
-      );
+      // Only a typed assistant message takes output parts; everywhere else
+      // the reason is replayed as plain text.
+      return textKind === "output_text"
+        ? { type: "refusal", refusal: block.reason }
+        : { type: textKind, text: block.reason };
     case "thinking":
     case "tool_call":
     case "tool_result":

src/responses.test.ts

@@ -271,6 +271,48 @@ describe("Responses request builder — quirk matrix", () => {
       { type: "output_text", text: "hi" },
     ]);
   });
+
+  const refusalHistory: ConversationTurn[] = [
+    { role: "user", timestamp: 0, content: [{ type: "text", text: "hi" }] },
+    {
+      role: "assistant",
+      timestamp: 0,
+      content: [{ type: "refusal", reason: "I can't help with that." }],
+    },
+    {
+      role: "user",
+      timestamp: 0,
+      content: [{ type: "refusal", reason: "quoted refusal" }],
+    },
+  ];
+
+  test.each([
+    {
+      shape: "typed",
+      assistant: [{ type: "refusal", refusal: "I can't help with that." }],
+      user: [{ type: "input_text", text: "quoted refusal" }],
+    },
+    {
+      shape: "flat",
+      assistant: "I can't help with that.",
+      user: "quoted refusal",
+    },
+  ] as const)(
+    "$shape shape replays a refusal in history instead of throwing",
+    ({ shape, assistant, user }) => {
+      const adapter = createOpenAIResponsesAdapter(source, {
+        contentShape: shape,
+      });
+      const request = adapter.buildRequest(refusalHistory, "model", {});
+      const items = inputItemsOf(request);
+      expect(items[1]).toEqual({
+        type: "message",
+        role: "assistant",
+        content: assistant,
+      });
+      expect(items[2]?.["content"]).toEqual(user);
+    },
+  );
 });
 
 describe("Responses parser — event schema validation", () => {