fix: handle Responses API text.format parameter correctly

The Responses API uses text.format for structured output configuration,
not response_format (which is used in Chat Completions API). This fix:

- Removes response_format from ResponsesRequestBody and OpenAIResponseRequest
- Adds proper text.format type with json_schema support
- Updates toChatCompletions to convert text.format to response_format
- Adds tests for json_schema, json_object, and text format types

Fixes the error: "Unsupported parameter: 'response_format'. In the
Responses API, this parameter has moved to 'text.format'."

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: replicas-connector[bot]

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

@@ -351,6 +351,122 @@ describe("OpenAI Chat -> Responses converters", () => {
         expect(textPart).toMatchObject({ type: "text", text: "Hi there" });
       }
     });
+
+    it("maps text.format json_schema to response_format", () => {
+      const req: ResponsesRequestBody = {
+        model: "gpt-4o-mini",
+        input: "Generate a JSON object with name and age",
+        text: {
+          format: {
+            type: "json_schema",
+            json_schema: {
+              name: "person",
+              description: "A person object",
+              schema: {
+                type: "object",
+                properties: {
+                  name: { type: "string" },
+                  age: { type: "number" },
+                },
+                required: ["name", "age"],
+              },
+              strict: true,
+            },
+          },
+        },
+      };
+      const oai = toChatCompletions(req);
+      expect(oai.response_format).toBeDefined();
+      expect(oai.response_format?.type).toBe("json_schema");
+      expect((oai.response_format as any)?.json_schema).toEqual({
+        name: "person",
+        description: "A person object",
+        schema: {
+          type: "object",
+          properties: {
+            name: { type: "string" },
+            age: { type: "number" },
+          },
+          required: ["name", "age"],
+        },
+        strict: true,
+      });
+    });
+
+    it("maps text.format json_object to response_format", () => {
+      const req: ResponsesRequestBody = {
+        model: "gpt-4o-mini",
+        input: "Generate a JSON response",
+        text: {
+          format: {
+            type: "json_object",
+          },
+        },
+      };
+      const oai = toChatCompletions(req);
+      expect(oai.response_format).toBeDefined();
+      expect(oai.response_format?.type).toBe("json_object");
+      expect((oai.response_format as any)?.json_schema).toBeUndefined();
+    });
+
+    it("maps text.format text type to response_format", () => {
+      const req: ResponsesRequestBody = {
+        model: "gpt-4o-mini",
+        input: "Hello",
+        text: {
+          format: {
+            type: "text",
+          },
+        },
+      };
+      const oai = toChatCompletions(req);
+      expect(oai.response_format).toBeDefined();
+      expect(oai.response_format?.type).toBe("text");
+    });
+
+    it("does not set response_format when text.format is not provided", () => {
+      const req: ResponsesRequestBody = {
+        model: "gpt-4o-mini",
+        input: "Hello",
+        text: {
+          verbosity: "high",
+        },
+      };
+      const oai = toChatCompletions(req);
+      expect(oai.response_format).toBeUndefined();
+    });
+
+    it("does not set response_format when text is not provided", () => {
+      const req: ResponsesRequestBody = {
+        model: "gpt-4o-mini",
+        input: "Hello",
+      };
+      const oai = toChatCompletions(req);
+      expect(oai.response_format).toBeUndefined();
+    });
+
+    it("preserves text.verbosity separately from text.format", () => {
+      const req: ResponsesRequestBody = {
+        model: "gpt-4o-mini",
+        input: "Generate JSON",
+        text: {
+          format: {
+            type: "json_schema",
+            json_schema: {
+              name: "test",
+              schema: { type: "object" },
+            },
+          },
+          verbosity: "medium",
+        },
+      };
+      const oai = toChatCompletions(req);
+      // response_format should be set from text.format
+      expect(oai.response_format).toBeDefined();
+      expect(oai.response_format?.type).toBe("json_schema");
+      // Note: verbosity is not directly mapped to Chat Completions API
+      // but the response_format should still work correctly
+    });
   });
 
   describe("fromChatCompletions (request mapping)", () => {

packages/llm-mapper/mappers/openai/responses.ts

@@ -45,7 +45,20 @@ interface OpenAIResponseRequest {
   reasoning?: {
     effort?: "low" | "medium" | "high" | "minimal";
   };
+  /**
+   * Text output configuration including format for structured output.
+   * In the Responses API, `text.format` replaces `response_format` from Chat Completions.
+   */
   text?: {
+    format?: {
+      type: "text" | "json_schema" | "json_object";
+      json_schema?: {
+        name: string;
+        description?: string;
+        schema: Record<string, any>;
+        strict?: boolean;
+      };
+    };
     verbosity?: "low" | "medium" | "high";
   };
   store?: boolean;
@@ -73,7 +86,6 @@ interface OpenAIResponseRequest {
   logprobs?: boolean;
   top_logprobs?: number;
   n?: number;
-  response_format?: { type: string; json_schema?: any };
   seed?: number;
   service_tier?: string;
   stream_options?: any;

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

@@ -234,7 +234,15 @@ export function toChatCompletions(
     logit_bias: body.logit_bias,
     logprobs: body.logprobs,
     top_logprobs: body.top_logprobs,
-    response_format: body.response_format,
+    // Convert Responses API text.format to Chat Completions response_format
+    response_format: body.text?.format
+      ? {
+          type: body.text.format.type,
+          ...(body.text.format.json_schema && {
+            json_schema: body.text.format.json_schema,
+          }),
+        }
+      : undefined,
     seed: body.seed,
     user: body.user,
     service_tier: body.service_tier,

packages/llm-mapper/transform/types/responses.ts

@@ -120,6 +120,20 @@ export interface ResponsesImageGenerationConfig {
   image_size: string; // e.g "2K"
 }
 
+/**
+ * Text format configuration for structured output in the Responses API.
+ * Maps to response_format in Chat Completions API.
+ */
+export interface ResponsesTextFormat {
+  type: "text" | "json_schema" | "json_object";
+  json_schema?: {
+    name: string;
+    description?: string;
+    schema: Record<string, any>;
+    strict?: boolean;
+  };
+}
+
 export interface ResponsesRequestBody {
   model: string;
   input: string | ResponsesInputItem[];
@@ -136,7 +150,12 @@ export interface ResponsesRequestBody {
   reasoning_options?: {
     budget_tokens?: number;
   };
+  /**
+   * Text output configuration including format for structured output.
+   * In the Responses API, `text.format` replaces `response_format` from Chat Completions.
+   */
   text?: {
+    format?: ResponsesTextFormat;
     verbosity?: "low" | "medium" | "high";
   };
   store?: boolean;
@@ -154,7 +173,6 @@ export interface ResponsesRequestBody {
   logprobs?: boolean;
   top_logprobs?: number;
   n?: number;
-  response_format?: { type: string; json_schema?: any };
   seed?: number;
   service_tier?: string;
   stream_options?: any;