diff --git a/src/from_openapi.ts b/src/from_openapi.ts
index cac3cf0..207d2a6 100644
--- a/src/from_openapi.ts
+++ b/src/from_openapi.ts
@@ -1,6 +1,8 @@
 import * as Type from "@alkdev/typebox";
 import { FromSchema } from "./from_schema.js";
 import { OperationType, type OperationSpec, type OperationHandler, type OperationContext } from "./types.js";
+import { CallError } from "./error.js";
+import { httpEnvelope } from "./response-envelope.js";
 
 export interface OpenAPIFS {
   readFile(path: string): Promise<string>;
@@ -265,18 +267,24 @@ function createHTTPOperation(
     });
 
     if (!response.ok) {
-      throw new Error(`HTTP ${response.status}: ${response.statusText}`);
+      throw new CallError("EXECUTION_ERROR", `HTTP ${response.status}: ${response.statusText}`);
     }
 
     const contentType = response.headers.get("Content-Type") || "";
-    
+    let data: unknown;
     if (contentType.includes("application/json")) {
-      return response.json();
+      data = await response.json();
     } else if (contentType.includes("text/")) {
-      return response.text();
+      data = await response.text();
     } else {
-      return response.arrayBuffer();
+      data = await response.arrayBuffer();
     }
+
+    return httpEnvelope(data, {
+      statusCode: response.status,
+      headers: Object.fromEntries(response.headers.entries()),
+      contentType,
+    });
   };
 
   return {
diff --git a/test/from_openapi.test.ts b/test/from_openapi.test.ts
index d24fe65..f320e2a 100644
--- a/test/from_openapi.test.ts
+++ b/test/from_openapi.test.ts
@@ -1,6 +1,8 @@
-import { describe, it, expect } from "vitest";
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
 import { FromOpenAPI } from "../src/from_openapi.js";
 import { OperationType } from "../src/types.js";
+import { CallError } from "../src/error.js";
+import { isResponseEnvelope } from "../src/response-envelope.js";
 import { Value } from "@alkdev/typebox/value";
 
 const simpleSpec = {
@@ -191,4 +193,206 @@ describe("FromOpenAPI", () => {
     const ops = FromOpenAPI(specWithRef as any, config);
     expect(ops.length).toBe(1);
   });
+});
+
+describe("FromOpenAPI handler envelope behavior", () => {
+  const config = {
+    namespace: "api",
+    baseUrl: "https://api.example.com",
+  };
+
+  let originalFetch: typeof globalThis.fetch;
+
+  beforeEach(() => {
+    originalFetch = globalThis.fetch;
+  });
+
+  afterEach(() => {
+    globalThis.fetch = originalFetch;
+  });
+
+  it("returns httpEnvelope with JSON response data", async () => {
+    globalThis.fetch = vi.fn().mockResolvedValue({
+      ok: true,
+      status: 200,
+      statusText: "OK",
+      headers: new Headers({ "Content-Type": "application/json", "X-Custom": "value" }),
+      json: async () => ({ users: ["alice", "bob"] }),
+      text: async () => "",
+      arrayBuffer: async () => new ArrayBuffer(0),
+    });
+
+    const ops = FromOpenAPI(simpleSpec as any, config);
+    const listUsers = ops.find((o) => o.name === "listUsers")!;
+    const result = await listUsers.handler({}, {} as any);
+
+    expect(isResponseEnvelope(result)).toBe(true);
+    if (isResponseEnvelope(result)) {
+      expect(result.meta.source).toBe("http");
+      expect(result.data).toEqual({ users: ["alice", "bob"] });
+      const meta = result.meta as { statusCode: number; headers: Record<string, string>; contentType: string };
+      expect(meta.statusCode).toBe(200);
+      expect(meta.contentType).toBe("application/json");
+      expect(meta.headers).toHaveProperty("x-custom", "value");
+    }
+  });
+
+  it("returns httpEnvelope with text response data", async () => {
+    const textSpec = {
+      openapi: "3.0.0",
+      info: { title: "Test", version: "1.0.0" },
+      paths: {
+        "/readme": {
+          get: {
+            operationId: "getReadme",
+            responses: {
+              "200": {
+                content: { "text/plain": { schema: { type: "string" } } },
+              },
+            },
+          },
+        },
+      },
+    };
+
+    globalThis.fetch = vi.fn().mockResolvedValue({
+      ok: true,
+      status: 200,
+      statusText: "OK",
+      headers: new Headers({ "Content-Type": "text/plain" }),
+      json: async () => ({}),
+      text: async () => "Hello, world!",
+      arrayBuffer: async () => new ArrayBuffer(0),
+    });
+
+    const ops = FromOpenAPI(textSpec as any, config);
+    const getReadme = ops.find((o) => o.name === "getReadme")!;
+    const result = await getReadme.handler({}, {} as any);
+
+    expect(isResponseEnvelope(result)).toBe(true);
+    if (isResponseEnvelope(result)) {
+      expect(result.meta.source).toBe("http");
+      expect(result.data).toBe("Hello, world!");
+      const meta = result.meta as { statusCode: number; headers: Record<string, string>; contentType: string };
+      expect(meta.statusCode).toBe(200);
+      expect(meta.contentType).toBe("text/plain");
+    }
+  });
+
+  it("returns httpEnvelope with arrayBuffer for binary responses", async () => {
+    const binaryData = new Uint8Array([1, 2, 3, 4]).buffer;
+
+    globalThis.fetch = vi.fn().mockResolvedValue({
+      ok: true,
+      status: 200,
+      statusText: "OK",
+      headers: new Headers({ "Content-Type": "application/octet-stream" }),
+      json: async () => ({}),
+      text: async () => "",
+      arrayBuffer: async () => binaryData,
+    });
+
+    const ops = FromOpenAPI(simpleSpec as any, config);
+    const listUsers = ops.find((o) => o.name === "listUsers")!;
+    const result = await listUsers.handler({}, {} as any);
+
+    expect(isResponseEnvelope(result)).toBe(true);
+    if (isResponseEnvelope(result)) {
+      expect(result.meta.source).toBe("http");
+      expect(result.data).toBe(binaryData);
+      const meta = result.meta as { statusCode: number; headers: Record<string, string>; contentType: string };
+      expect(meta.contentType).toBe("application/octet-stream");
+    }
+  });
+
+  it("throws CallError on HTTP error status", async () => {
+    globalThis.fetch = vi.fn().mockResolvedValue({
+      ok: false,
+      status: 404,
+      statusText: "Not Found",
+      headers: new Headers(),
+    });
+
+    const ops = FromOpenAPI(simpleSpec as any, config);
+    const getUser = ops.find((o) => o.name === "getUser")!;
+
+    try {
+      await getUser.handler({ id: "123" }, {} as any);
+      expect.fail("Expected CallError to be thrown");
+    } catch (error) {
+      expect(error).toBeInstanceOf(CallError);
+      expect((error as CallError).code).toBe("EXECUTION_ERROR");
+      expect((error as CallError).message).toContain("HTTP 404");
+    }
+  });
+
+  it("throws CallError on 500 status", async () => {
+    globalThis.fetch = vi.fn().mockResolvedValue({
+      ok: false,
+      status: 500,
+      statusText: "Internal Server Error",
+      headers: new Headers(),
+    });
+
+    const ops = FromOpenAPI(simpleSpec as any, config);
+    const listUsers = ops.find((o) => o.name === "listUsers")!;
+
+    try {
+      await listUsers.handler({}, {} as any);
+      expect.fail("Expected CallError to be thrown");
+    } catch (error) {
+      expect(error).toBeInstanceOf(CallError);
+      expect((error as CallError).code).toBe("EXECUTION_ERROR");
+      expect((error as CallError).message).toContain("HTTP 500");
+    }
+  });
+
+  it("includes statusCode from response in envelope", async () => {
+    globalThis.fetch = vi.fn().mockResolvedValue({
+      ok: true,
+      status: 201,
+      statusText: "Created",
+      headers: new Headers({ "Content-Type": "application/json" }),
+      json: async () => ({ id: "abc" }),
+      text: async () => "",
+      arrayBuffer: async () => new ArrayBuffer(0),
+    });
+
+    const ops = FromOpenAPI(simpleSpec as any, config);
+    const createUser = ops.find((o) => o.name === "createUser")!;
+    const result = await createUser.handler({ body: { name: "Alice" } }, {} as any);
+
+    expect(isResponseEnvelope(result)).toBe(true);
+    if (isResponseEnvelope(result)) {
+      const meta = result.meta as { statusCode: number };
+      expect(meta.statusCode).toBe(201);
+    }
+  });
+
+  it("converts response headers to Record<string, string>", async () => {
+    const headers = new Headers();
+    headers.set("Content-Type", "application/json");
+    headers.set("X-Request-Id", "req-123");
+
+    globalThis.fetch = vi.fn().mockResolvedValue({
+      ok: true,
+      status: 200,
+      statusText: "OK",
+      headers,
+      json: async () => ({ result: "ok" }),
+      text: async () => "",
+      arrayBuffer: async () => new ArrayBuffer(0),
+    });
+
+    const ops = FromOpenAPI(simpleSpec as any, config);
+    const listUsers = ops.find((o) => o.name === "listUsers")!;
+    const result = await listUsers.handler({}, {} as any);
+
+    expect(isResponseEnvelope(result)).toBe(true);
+    if (isResponseEnvelope(result)) {
+      const meta = result.meta as { headers: Record<string, string> };
+      expect(meta.headers["content-type"]).toBe("application/json");
+      expect(meta.headers["x-request-id"]).toBe("req-123");
+    }
+  });
 });
\ No newline at end of file