perf(server): descarta as tasks de sessões expiradas e adiciona testes do servidor

O Map de tasks em DownloadManager nunca removia entradas; em um servidor
de longa duração ele crescia sem limite, mesmo com os arquivos da sessão
já apagados. O SessionManager agora avisa quando destrói uma sessão e o
DownloadManager descarta as tasks dela.

server/test/sessions.test.ts

@@ -0,0 +1,74 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { createServer, type Server } from "node:http";
+import type { AddressInfo } from "node:net";
+import { existsSync, readdirSync, rmSync } from "node:fs";
+import { Agent } from "undici";
+import { loadModules } from "./helpers.js";
+
+const HOUR = 60 * 60 * 1000;
+
+let origin: Server;
+let originUrl: string;
+
+beforeEach(async () => {
+    vi.useFakeTimers({ toFake: ["setInterval", "Date"] });
+    origin = createServer((_req, res) => {
+        res.setHeader("content-length", "5");
+        res.end("hello");
+    });
+    await new Promise<void>((done) => origin.listen(0, "127.0.0.1", done));
+    originUrl = `http://127.0.0.1:${(origin.address() as AddressInfo).port}/file.txt`;
+});
+
+afterEach(async () => {
+    vi.useRealTimers();
+    await new Promise((done) => origin.close(done));
+});
+
+async function waitForStatus(
+    read: () => string | undefined,
+    wanted: string,
+) {
+    for (let i = 0; i < 500 && read() !== wanted; i++) {
+        await new Promise((done) => setImmediate(done));
+    }
+    expect(read()).toBe(wanted);
+}
+
+describe("tasks e sessões", () => {
+    it("descarta as tasks e os arquivos quando a sessão expira", async () => {
+        const { sessionManager, DownloadManager, storageRoot } = await loadModules();
+        const manager = new DownloadManager(new Agent());
+
+        const session = sessionManager.getSession();
+        const task = await manager.queueDownload(session.id, originUrl);
+        await waitForStatus(() => manager.getTask(task.id)?.status, "completed");
+        expect(readdirSync(`${storageRoot}/${session.id}`)).toHaveLength(1);
+
+        vi.setSystemTime(Date.now() + HOUR + 1000);
+        vi.advanceTimersByTime(60_000); // dispara o coletor
+
+        expect(manager.getTask(task.id)).toBeUndefined();
+        expect(manager.getTasks(session.id)).toEqual([]);
+        expect(existsSync(`${storageRoot}/${session.id}`)).toBe(false);
+        rmSync(storageRoot, { recursive: true, force: true });
+    });
+
+    it("mantém as tasks de outras sessões ainda ativas", async () => {
+        const { sessionManager, DownloadManager, storageRoot } = await loadModules();
+        const manager = new DownloadManager(new Agent());
+
+        const expiring = sessionManager.getSession();
+        await manager.queueDownload(expiring.id, originUrl);
+
+        vi.setSystemTime(Date.now() + HOUR - 1000);
+        const alive = sessionManager.getSession(); // criada perto do fim da outra
+        const kept = await manager.queueDownload(alive.id, originUrl);
+        vi.setSystemTime(Date.now() + 2000);
+        vi.advanceTimersByTime(60_000);
+
+        expect(manager.getTasks(expiring.id)).toEqual([]);
+        expect(manager.getTask(kept.id)).toBeDefined();
+        rmSync(storageRoot, { recursive: true, force: true });
+    });
+});