feat(fetch): add Effection-native fetch package

fetch/README.md

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+# fetch
+
+Effection-native fetch with structured concurrency and streaming response support.
+
+---
+
+## Installation
+
+```bash
+npm install @effectionx/fetch effection
+```
+
+## Usage
+
+```ts
+import { main } from "effection";
+import { fetch } from "@effectionx/fetch";
+
+await main(function* () {
+  let users = yield* fetch("https://api.example.com/users").json();
+  console.log(users);
+});
+```
+
+### Fluent API
+
+Chain methods directly on `fetch()` for concise one-liners:
+
+```ts
+// JSON
+let data = yield* fetch("https://api.example.com/users").json();
+
+// Text
+let html = yield* fetch("https://example.com").text();
+
+// With validation - throws HttpError on non-2xx
+let data = yield* fetch("https://api.example.com/users").expect().json();
+```
+
+### Traditional API
+
+You can also get the response first, then consume the body:
+
+```ts
+let response = yield* fetch("https://api.example.com/users");
+let data = yield* response.json();
+```
+
+### Streaming response bodies
+
+```ts
+import { each } from "effection";
+import { fetch } from "@effectionx/fetch";
+
+function* example() {
+  for (let chunk of yield* each(fetch("https://example.com/large-file.bin").body())) {
+    console.log(chunk.length);
+    yield* each.next();
+  }
+}
+```
+
+### Concurrent requests
+
+```ts
+import { all } from "effection";
+import { fetch } from "@effectionx/fetch";
+
+function* fetchMultiple() {
+  let [users, posts, comments] = yield* all([
+    fetch("https://api.example.com/users").json(),
+    fetch("https://api.example.com/posts").json(),
+    fetch("https://api.example.com/comments").json(),
+  ]);
+
+  return { users, posts, comments };
+}
+```
+
+### Validate JSON while parsing
+
+```ts
+import { fetch } from "@effectionx/fetch";
+
+interface User {
+  id: string;
+  name: string;
+}
+
+function parseUser(value: unknown): User {
+  if (
+    typeof value === "object" &&
+    value !== null &&
+    "id" in value &&
+    "name" in value
+  ) {
+    return value as User;
+  }
+
+  throw new Error("invalid user payload");
+}
+
+function* getUser() {
+  return yield* fetch("https://api.example.com/user").json(parseUser);
+}
+```
+
+### Handle non-2xx responses
+
+```ts
+import { HttpError, fetch } from "@effectionx/fetch";
+
+function* getUser(id: string) {
+  try {
+    return yield* fetch(`https://api.example.com/users/${id}`).expect().json();
+  } catch (error) {
+    if (error instanceof HttpError) {
+      console.error(error.status, error.statusText);
+    }
+    throw error;
+  }
+}
+```
+
+## API
+
+### `fetch(input, init?)`
+
+Returns a `FetchOperation` that supports both fluent chaining and traditional usage.
+
+- `input` - URL string, `URL` object, or `Request` object
+- `init` - Optional `FetchInit` options (same as `RequestInit` but without `signal`)
+
+Cancellation is handled automatically via Effection's structured concurrency. When the
+scope exits, the request is aborted. The `signal` option is intentionally omitted since
+Effection manages cancellation for you.
+
+### `FetchOperation`
+
+Chainable fetch operation returned by `fetch()`.
+
+- `json<T>()`, `json<T>(parse)` - parse response as JSON
+- `text()` - get response as text
+- `arrayBuffer()` - get response as ArrayBuffer
+- `blob()` - get response as Blob
+- `formData()` - get response as FormData
+- `body()` - stream response body as `Stream<Uint8Array, void>`
+- `expect()` - returns a new `FetchOperation` that throws `HttpError` on non-2xx
+
+Can also be yielded directly to get a `FetchResponse`:
+
+```ts
+let response = yield* fetch("https://api.example.com/users");
+```
+
+### `FetchResponse`
+
+Effection wrapper around native `Response` with operation-based body readers.
+
+- `json<T>()`, `json<T>(parse)`
+- `text()`
+- `arrayBuffer()`
+- `blob()`
+- `formData()`
+- `body(): Stream<Uint8Array, void>`
+- `expect()` - throws `HttpError` for non-2xx responses
+- `raw` - access the underlying native `Response`

fetch/fetch.test.ts

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+import { beforeEach, describe, it } from "@effectionx/bdd";
+import { expect } from "expect";
+
+import {
+  type IncomingMessage,
+  type ServerResponse,
+  createServer,
+} from "node:http";
+import {
+  Err,
+  Ok,
+  type Operation,
+  type Result,
+  call,
+  each,
+  ensure,
+  withResolvers,
+} from "effection";
+
+import { HttpError, fetch } from "./fetch.ts";
+
+function box<T>(content: () => Operation<T>): Operation<Result<T>> {
+  return {
+    *[Symbol.iterator]() {
+      try {
+        return Ok(yield* content());
+      } catch (error) {
+        return Err(error as Error);
+      }
+    },
+  };
+}
+
+describe("fetch()", () => {
+  let url: string;
+
+  beforeEach(function* () {
+    let server = createServer((req: IncomingMessage, res: ServerResponse) => {
+      if (req.url === "/json") {
+        res.writeHead(200, { "Content-Type": "application/json" });
+        res.end(JSON.stringify({ id: 1, title: "do things" }));
+        return;
+      }
+
+      if (req.url === "/text") {
+        res.writeHead(200, { "Content-Type": "text/plain" });
+        res.end("hello");
+        return;
+      }
+
+      if (req.url === "/stream") {
+        res.writeHead(200, { "Content-Type": "application/octet-stream" });
+        res.write("chunk-1");
+        res.write("chunk-2");
+        res.end("chunk-3");
+        return;
+      }
+
+      res.writeHead(404, { "Content-Type": "text/plain" });
+      res.end("not found");
+    });
+
+    let ready = withResolvers<void>();
+    server.listen(0, () => ready.resolve());
+    yield* ready.operation;
+
+    let addr = server.address();
+    let port = typeof addr === "object" && addr ? addr.port : 0;
+
+    url = `http://localhost:${port}`;
+    yield* ensure(() =>
+      call(() => new Promise<void>((resolve) => server.close(() => resolve()))),
+    );
+  });
+
+  describe("traditional API", () => {
+    it("reads JSON responses", function* () {
+      let response = yield* fetch(`${url}/json`);
+      let data = yield* response.json<{ id: number; title: string }>();
+
+      expect(data).toEqual({ id: 1, title: "do things" });
+    });
+
+    it("supports parser-based json()", function* () {
+      let response = yield* fetch(`${url}/json`);
+      let data = yield* response.json((value) => {
+        if (
+          typeof value !== "object" ||
+          value === null ||
+          !("id" in value) ||
+          !("title" in value)
+        ) {
+          throw new Error("invalid payload");
+        }
+
+        return { id: value.id as number, title: value.title as string };
+      });
+
+      expect(data).toEqual({ id: 1, title: "do things" });
+    });
+
+    it("streams response bodies", function* () {
+      let response = yield* fetch(`${url}/stream`);
+      let body = response.body();
+      let decoder = new TextDecoder();
+      let chunks: string[] = [];
+
+      for (let chunk of yield* each(body)) {
+        chunks.push(decoder.decode(chunk, { stream: true }));
+        yield* each.next();
+      }
+
+      chunks.push(decoder.decode());
+      expect(chunks.join("")).toEqual("chunk-1chunk-2chunk-3");
+    });
+
+    it("throws HttpError for expect() when response is not ok", function* () {
+      let response = yield* fetch(`${url}/missing`);
+      let result = yield* box(() => response.expect());
+
+      expect(result.ok).toBe(false);
+      if (!result.ok) {
+        expect(result.error).toBeInstanceOf(HttpError);
+        expect(result.error).toMatchObject({
+          status: 404,
+          statusText: "Not Found",
+        });
+      }
+    });
+  });
+
+  describe("fluent API", () => {
+    it("reads JSON with fetch().json()", function* () {
+      let data = yield* fetch(`${url}/json`).json<{
+        id: number;
+        title: string;
+      }>();
+
+      expect(data).toEqual({ id: 1, title: "do things" });
+    });
+
+    it("reads text with fetch().text()", function* () {
+      let text = yield* fetch(`${url}/text`).text();
+
+      expect(text).toEqual("hello");
+    });
+
+    it("supports parser with fetch().json(parse)", function* () {
+      let data = yield* fetch(`${url}/json`).json((value) => {
+        if (
+          typeof value !== "object" ||
+          value === null ||
+          !("id" in value) ||
+          !("title" in value)
+        ) {
+          throw new Error("invalid payload");
+        }
+
+        return { id: value.id as number, title: value.title as string };
+      });
+
+      expect(data).toEqual({ id: 1, title: "do things" });
+    });
+
+    it("streams response bodies with fetch().body()", function* () {
+      let body = fetch(`${url}/stream`).body();
+      let decoder = new TextDecoder();
+      let chunks: string[] = [];
+
+      for (let chunk of yield* each(body)) {
+        chunks.push(decoder.decode(chunk, { stream: true }));
+        yield* each.next();
+      }
+
+      chunks.push(decoder.decode());
+      expect(chunks.join("")).toEqual("chunk-1chunk-2chunk-3");
+    });
+
+    it("throws HttpError with fetch().expect().json()", function* () {
+      let result = yield* box(() => fetch(`${url}/missing`).expect().json());
+
+      expect(result.ok).toBe(false);
+      if (!result.ok) {
+        expect(result.error).toBeInstanceOf(HttpError);
+        expect(result.error).toMatchObject({
+          status: 404,
+          statusText: "Not Found",
+        });
+      }
+    });
+
+    it("chains expect() before json() successfully", function* () {
+      let data = yield* fetch(`${url}/json`)
+        .expect()
+        .json<{ id: number; title: string }>();
+
+      expect(data).toEqual({ id: 1, title: "do things" });
+    });
+  });
+});