feat(web): move connection downlinks to WebSocket

packages/host/apiproxy/src/api/events.ts

@@ -1,5 +1,5 @@
 /**
- * events domain contract: signatures and frame unions for the two SSE
+ * events domain contract: signatures and frame unions for the two logical
  * streams. Four-quadrant: streams yield the narrow form `RpcRequest<Frame>` (server-request
  * view) — rpcId must be exposed to the business layer, because responses to answerable frames
  * (approval/question requested) echo it; for pure pushes it identifies that one push.
@@ -42,7 +42,7 @@ export interface QueuedInboxItem {
   message: Message
 }
 
-/** Streaming face of the contract: the two SSE stream openers (mux + host). */
+/** Streaming face of the contract: the two logical stream openers (mux + host). */
 export interface EventsApi {
   /**
    * All-session aggregated mux stream. On open, emits a subscribed control frame for every

packages/host/apiproxy/src/api/index.ts

@@ -1,7 +1,7 @@
 /**
  * apiproxy contract-layer barrel. api/ has zero Node dependencies and is
- * importable from the browser; the TS interfaces are the authoritative contract, HTTP/SSE are
- * merely physical channels (four-quadrant message model).
+ * importable from the browser; the TS interfaces are the authoritative contract, while HTTP,
+ * WebSocket, and in-process SSE are merely physical channels (four-quadrant message model).
  */
 
 import type { SessionsApi } from './sessions.ts'

packages/host/apiproxy/src/api/rpc.ts

@@ -1,7 +1,7 @@
 /**
- * Four-quadrant RPC message model. Channels and messages are
- * decoupled: HTTP is the client→server physical channel, SSE the server→client one; logical
- * messages are channel-independent, and the wire full form is a four-member discriminated union.
+ * Four-quadrant RPC message model. Channels and messages are decoupled: HTTP,
+ * WebSocket, and in-process SSE are physical carriers, while logical messages
+ * are channel-independent and form a four-member discriminated union.
  * api/ contract layer: zero Node dependencies, importable from the browser.
  */
 
@@ -147,7 +147,7 @@ export interface ServerResponse {
 }
 
 /**
- * Message initiated by the server (wire carrier: SSE frame). Answerable interactions
+ * Message initiated by the server (wire carrier: downstream stream frame). Answerable interactions
  * (approval/question requested — stable rpcId, reused on replay) and pure pushes
  * (session/event etc. — rpcId identifies that one push) share this shape; whether a
  * response is expected is determined statically by method (a strict dichotomy, no third kind).

packages/host/apiproxy/src/fetch/client.ts

@@ -1,6 +1,6 @@
 /**
  * Client side of the fetch carrier. AbstractApiClient holds every protocol invariant: rpcId minting,
- * four-quadrant envelope wrap/unwrap, zod parsing, SSE frame decoding, and the payload-direct
+ * four-quadrant envelope wrap/unwrap, zod parsing, in-process SSE frame decoding, and the payload-direct
  * IApiClient domain methods (business code never mints). Platform differences ride two aspects:
  * abstract doFetch (transport) + overridable onEnvelope (tap). ApiProxy (the impl face) is untouched.
  */
@@ -69,8 +69,8 @@ import {
  * Bounded calls merge it with the instance timeout via AbortSignal.any; user-paced calls
  * carry only that external signal. In both cases the signal rides beside the request, never
  * on the wire, like the stream signatures.
- * Stream methods accept an optional onOpen callback: it fires once the SSE transport is
- * readable (response headers received, before any frame) — the "stream established" signal
+ * Stream methods accept an optional onOpen callback: it fires once the physical transport is
+ * readable (before any frame) — the "stream established" signal
  * connection controllers need for the readiness handshake. Generators are lazy, so the
  * underlying fetch (and therefore onOpen) only happens once iteration starts.
  * Relationship: ApiProxy is the narrow-form signature contract the impl side implements;

packages/host/apiproxy/src/index.ts

@@ -5,7 +5,7 @@
  * platform subclasses on the client side), and the host-side implementation
  * (api-proxy.ts: createApiProxy + the ApiProxyService gateway plugin providing
  * `ctx.apiProxy`). Transport-agnostic by design: this package registers no
- * routes — carriers (HTTP today, IPC later) wrap `ctx.apiProxy` themselves.
+ * routes — physical carriers wrap `ctx.apiProxy` themselves.
  */
 
 import { resolve } from 'node:path'

packages/host/webserver/README.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/host/webserver/README.md
-README.md: c3c7b222683bc7731a6c21f2fffd325225099bab
-README.zh.md: 99c0560eb74dc8076772ba1deef3034000f5f0db
+README.md: f01c1a66b19e4f49b9cad31a6d41555aecb28168
+README.zh.md: 980bc3dbac4dac2e758e0043ead292fb5a42e674

packages/host/webserver/README.md

@@ -2,17 +2,17 @@
 
 English | [中文](README.zh.md)
 
-Plain HTTP route-registration plugin (default-exported `HttpServerService`, config `{host, port, distIndex}`): a `node:http` server that listens on activation and provides `ctx.httpServer` — `register(route)` adds a named `exact`/`prefix` route (duplicate `(kind, path)` throws: route patterns are a composition-level contract, so a collision is a misconfiguration; the returned disposer removes the route), `tapIndex(transform)` adds an index.html transform applied in registration order, `port` reads the listening port (the OS-assigned value when `port` is 0), and `host` reads the configured bind host (composition-time facts other plugins adapt to, e.g. the directory-picker chooser). The match order is fixed — exact over the whole table, then longest prefix, then the static dist fallback with the locked semantics: traversal outside the dist root is 403, any miss falls back to `index.html` with HTTP 200 (SPA routing), unknown extensions ship as octet-stream, non-GET/HEAD is 405. Registration order carries no request-facing semantics.
+Web HTTP and upgrade-route registration plugin (default-exported `HttpServerService`, config `{host, port, distIndex}`): a `node:http` server that listens on activation and provides `ctx.httpServer`. `register(route)` adds a named `exact`/`prefix` HTTP route; `registerUpgrade(route)` adds an upgrade route for an exact pathname. A duplicate path within either table throws because route patterns are a composition-level contract and a collision is a misconfiguration; both methods return a disposer that removes the registration. `tapIndex(transform)` adds an index.html transform applied in registration order, `port` reads the listening port (the OS-assigned value when `port` is 0), and `host` reads the configured bind host (composition-time facts other plugins adapt to, e.g. the directory-picker chooser). HTTP match order is fixed: exact over the whole table, then longest prefix, then the static dist fallback with the locked semantics: traversal outside the dist root is 403, any miss falls back to `index.html` with HTTP 200 (SPA routing), unknown extensions ship as octet-stream, and non-GET/HEAD is 405. Upgrades match exactly and unmatched connections are closed; registration order carries no request-facing semantics.
 
-The package knows no harness concepts: the `/api` bridge is the connection plugin's route, plugin bundles and the HMR event stream are the modules/hmr plugins' routes. `host` accepts only `127.0.0.1` (default posture) and `0.0.0.0` (deliberate network exposure); `distIndex` is an assembly fact the composing app resolves and injects, never self-resolved (dist location is workspace knowledge of the app). Web (browser) shape only — Electron loads dist over `file://` and carries fetch over an IPC bridge, not this server. This package never prints; the URL line belongs to the shell.
+The package knows no harness concepts: the `/api` HTTP bridge and downlink WebSockets are routes owned by the connection plugin, while plugin bundles and the HMR event stream are routes owned by the modules/hmr plugins. The upgrade handler owns the protocol handshake and connection contents; the webserver only delivers the raw socket and request. `host` accepts only `127.0.0.1` (default posture) and `0.0.0.0` (deliberate network exposure); `distIndex` is an assembly fact the composing app resolves and injects, never self-resolved (dist location is workspace knowledge of the app). Web (browser) shape only — Electron loads dist over `file://` and carries fetch over an IPC bridge, not this server. This package never prints; the URL line belongs to the shell.
 
-A listen failure (EADDRINUSE…) throws out of activation and rejects Loader composition with the bind diagnostic; the failed candidate fiber is disposed. A request whose handling throws (a malformed %-escape hitting `decodeURIComponent`, a client dropping mid-body) is answered 400 — or the socket destroyed when headers are already out — and logged as a warning; it never exits the process. Disposal pairs `close()` with `closeAllConnections()` because held-open responses (SSE) never end on their own.
+A listen failure (EADDRINUSE…) throws out of activation and rejects Loader composition with the bind diagnostic; the failed candidate fiber is disposed. An HTTP request whose handling throws (a malformed %-escape hitting `decodeURIComponent`, a client dropping mid-body) is answered 400 — or the socket destroyed when headers are already out — and logged as a warning; it never exits the process. An upgrade-handler exception is logged as a warning and destroys its socket. Disposal first calls `close()` and `closeAllConnections()`, then destroys upgraded sockets the webserver still tracks so they cannot hold teardown open.
 
 In development, the client-plugin registry synchronously captures each built bundle's stat baseline before it returns, then polls those baselines and re-hashes changed content. Each rescan stages its candidate table, graph, and watch map before publishing them, so a baseline failure preserves the prior graph. An immediate rebuild therefore cannot disappear into an asynchronously established watch baseline; a rename window marks the path dirty, retains the last successful baseline, and forces a re-hash when the bundle reappears even with identical metadata.
 
 ## Model Experience
 
-None, as the package is a pure HTTP carrier between the browser and the routes other plugins register; nothing here reaches a model request.
+None, as the package is a Web carrier between the browser and the HTTP/upgrade routes other plugins register; nothing here reaches a model request.
 
 #### KV Cache effect
 

packages/host/webserver/README.zh.md

@@ -2,17 +2,17 @@
 
 [English](README.md) | 中文
 
-朴素的 HTTP 路由注册插件（默认导出 `HttpServerService`，配置为 `{host, port, distIndex}`）：一个在激活时开始监听的 `node:http` 服务器，提供 `ctx.httpServer`。`register(route)` 添加具名的 `exact`／`prefix` 路由；重复的 `(kind, path)` 会抛错，因为路由模式是组合层契约，冲突即配置错误；返回的 disposer 会移除该路由。`tapIndex(transform)` 添加按注册顺序应用的 index.html 转换，`port` 读取正在监听的端口（当 `port` 为 0 时读取 OS 分配的值），`host` 读取配置的绑定宿主（这些是其他插件据以自适应的组合期事实，例如 directory-picker 选择器）。匹配顺序固定不变：先在整张表中匹配精确路由，再匹配最长前缀，最后回退到静态 dist，并遵循固定语义：越出 dist 根目录的遍历返回 403，任何未命中项都以 HTTP 200 回退到 `index.html`（SPA 路由），未知扩展名按 octet-stream 提供，GET／HEAD 之外的方法返回 405。注册顺序不承载任何面向请求的语义。
+Web HTTP 与 upgrade route 注册插件（默认导出 `HttpServerService`，配置为 `{host, port, distIndex}`）：一个在激活时开始监听的 `node:http` 服务器，提供 `ctx.httpServer`。`register(route)` 添加具名的 `exact`／`prefix` HTTP route；`registerUpgrade(route)` 添加精确 pathname 的 upgrade route；同一张表内的重复路径会抛错，因为 route 模式是组合层契约，冲突即配置错误；两者返回的 disposer 都会移除注册。`tapIndex(transform)` 添加按注册顺序应用的 index.html 转换，`port` 读取正在监听的端口（当 `port` 为 0 时读取 OS 分配的值），`host` 读取配置的绑定宿主（这些是其他插件据以自适应的组合期事实，例如 directory-picker 选择器）。HTTP 匹配顺序固定不变：先在整张表中匹配精确 route，再匹配最长前缀，最后回退到静态 dist，并遵循固定语义：越出 dist 根目录的遍历返回 403，任何未命中项都以 HTTP 200 回退到 `index.html`（SPA 路由），未知扩展名按 octet-stream 提供，GET／HEAD 之外的方法返回 405。upgrade 只做精确匹配，未命中连接直接关闭；注册顺序不承载任何面向请求的语义。
 
-该包不了解任何 harness 概念：`/api` 桥接是 connection 插件的路由，插件 bundle 与 HMR（热模块替换）事件流则是 modules／hmr 插件的路由。`host` 只接受 `127.0.0.1`（默认姿态）和 `0.0.0.0`（有意向网络开放）；`distIndex` 是由组合应用解析并注入的组装事实，绝不会自行解析，因为 dist 位置属于应用的工作区知识。该服务器只服务 Web（浏览器）形态；Electron 通过 `file://` 加载 dist，并经 IPC 桥接承载 fetch，而不使用本服务器。该包从不打印内容；URL 行属于 shell。
+该包不了解任何 harness 概念：`/api` HTTP 桥接与下行 WebSocket 是 connection 插件的 route，插件 bundle 与 HMR（热模块替换）事件流则是 modules／hmr 插件的 route。upgrade handler 拥有协议握手与连接内容；webserver 只交付原始 socket 与 request。`host` 只接受 `127.0.0.1`（默认姿态）和 `0.0.0.0`（有意向网络开放）；`distIndex` 是由组合应用解析并注入的组装事实，绝不会自行解析，因为 dist 位置属于应用的工作区知识。该服务器只服务 Web（浏览器）形态；Electron 通过 `file://` 加载 dist，并经 IPC 桥接承载 fetch，而不使用本服务器。该包从不打印内容；URL 行属于 shell。
 
-监听失败（EADDRINUSE……）会从激活过程抛出，以 bind 诊断使 Loader 组合 reject；失败的候选 fiber 会被 dispose（资源释放）。处理请求时抛错（例如格式错误的百分号转义传入 `decodeURIComponent`，或客户端在请求体传输中途断开）时，服务器会响应 400；若响应头已经发出，则销毁 socket，并记录 warning，但绝不会退出进程。资源释放会把 `close()` 与 `closeAllConnections()` 配对，因为一直保持打开的 SSE（Server-Sent Events）响应不会自行结束。
+监听失败（EADDRINUSE……）会从激活过程抛出，以 bind 诊断使 Loader 组合 reject；失败的候选 fiber 会被 dispose（资源释放）。处理 HTTP 请求时抛错（例如格式错误的百分号转义传入 `decodeURIComponent`，或客户端在请求体传输中途断开）时，服务器会响应 400；若响应头已经发出，则销毁 socket，并记录 warning，但绝不会退出进程。upgrade handler 抛错会记录 warning 并销毁其 socket。资源释放会先调用 `close()` 与 `closeAllConnections()`，再销毁 webserver 仍跟踪的升级 socket，确保升级连接不会悬住 teardown。
 
 在开发环境中，客户端插件注册表会在返回前同步捕获每个已构建 bundle 的 stat 基线，随后轮询这些基线，并在内容变化后重新计算哈希。每次重新扫描都会先暂存候选表、图和监听 map，再统一发布，因此基线失败会保留先前的图。这样，即时重建不会消失在异步建立的监听基线中；重命名窗口会把路径标记为脏，保留最近一次成功基线，并在 bundle 重新出现时强制重新计算哈希，即使其元数据完全相同也不例外。
 
 ## 模型体验
 
-无。该包只是浏览器与其他插件所注册路由之间的纯 HTTP 载体，其中没有任何内容会进入模型请求。
+无。该包只是浏览器与其他插件所注册 HTTP／upgrade route 之间的 Web 载体，其中没有任何内容会进入模型请求。
 
 #### KV 缓存影响
 

packages/host/webserver/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@deepseek-ai/dsh-host-webserver",
-  "description": "Plain HTTP route-registration plugin: named-route registry (webServer service) + index transform taps + static dist fallback; knows no harness concepts",
+  "description": "Web route-registration plugin: HTTP and upgrade routes, index transform taps, and static dist fallback; knows no harness concepts",
   "version": "0.0.1",
   "private": true,
   "type": "module",

packages/host/webserver/src/index.ts

@@ -1,10 +1,9 @@
 /**
- * @deepseek-ai/dsh-host-webserver — plain HTTP route-registration plugin: a
- * node:http server plus the `httpServer` service (named-route registry + index
- * transform taps + static dist fallback). Knows no harness concepts — every
- * feature surface (API bridge, plugin bundles, SSE) is a route some other
- * plugin registers. Web (browser) shape only — Electron loads dist over
- * file:// and carries fetch over an IPC bridge, not this server. This package
+ * @deepseek-ai/dsh-host-webserver — Web route-registration plugin: a node:http
+ * server plus the `httpServer` service (HTTP and upgrade route registries,
+ * index transform taps, and static dist fallback). Knows no harness concepts;
+ * feature plugins own every registered protocol. Web shape only — Electron
+ * loads dist over file:// and carries fetch over an IPC bridge. This package
  * never prints: the URL line belongs to the shell.
  */
 
@@ -12,6 +11,7 @@ import { createServer } from 'node:http'
 import type { IncomingMessage, ServerResponse, Server } from 'node:http'
 import { readFile } from 'node:fs/promises'
 import type { AddressInfo } from 'node:net'
+import type { Duplex } from 'node:stream'
 import { dirname } from 'node:path'
 import { Context, Service } from 'cordis'
 import z from 'schemastery'
@@ -35,6 +35,14 @@ export interface WebRoute {
   handler: (req: IncomingMessage, res: ServerResponse) => void | Promise<void>
 }
 
+/** One exact-path HTTP upgrade registration. */
+export interface WebUpgradeRoute {
+  /** Absolute pathname, no trailing slash. */
+  path: string
+  /** Owns protocol negotiation and the upgraded socket after dispatch. */
+  handler: (req: IncomingMessage, socket: Duplex, head: Buffer) => void | Promise<void>
+}
+
 /** Gateway config: listen address plus the static dist anchor (injected by the composing app, never self-resolved). */
 export interface Config {
   /** Listen host; the two supported values are loopback and all-interfaces. */
@@ -61,6 +69,8 @@ export class HttpServerService extends Service {
 
   private readonly exact = new Map<string, WebRoute>()
   private readonly prefixes = new Map<string, WebRoute>()
+  private readonly upgrades = new Map<string, WebUpgradeRoute>()
+  private readonly upgradedSockets = new Set<Duplex>()
   private readonly indexTaps: ((html: string) => string)[] = []
   private readonly distRoot: string
   private readonly distIndex: string
@@ -98,6 +108,20 @@ export class HttpServerService extends Service {
     return () => { table.delete(route.path) }
   }
 
+  /**
+   * Register an exact-path HTTP upgrade route. Duplicate paths throw because
+   * one socket can have only one protocol owner.
+   * @param route - pathname and handler owning negotiation plus socket use.
+   * @returns the disposer removing the route.
+   */
+  registerUpgrade(route: WebUpgradeRoute): () => void {
+    if (this.upgrades.has(route.path)) {
+      throw new Error(`webserver: duplicate upgrade route "${route.path}"`)
+    }
+    this.upgrades.set(route.path, route)
+    return () => { this.upgrades.delete(route.path) }
+  }
+
   /**
    * Register an index.html transform, applied to every index response in
    * registration order.
@@ -147,6 +171,32 @@ export class HttpServerService extends Service {
         res.end()
       })
     })
+    this.server.on('upgrade', (req, socket, head) => {
+      let route: WebUpgradeRoute | undefined
+      try {
+        /* v8 ignore next -- node:http always sets url on server requests. */
+        route = this.upgrades.get(new URL(req.url ?? '/', 'http://x').pathname)
+      } catch (error) {
+        this.ctx.logger.warn(error instanceof Error ? error : new Error(String(error)))
+        socket.destroy()
+        return
+      }
+      if (route === undefined) {
+        socket.destroy()
+        return
+      }
+      this.upgradedSockets.add(socket)
+      socket.once('close', () => { this.upgradedSockets.delete(socket) })
+      try {
+        Promise.resolve(route.handler(req, socket, head)).catch((error: unknown) => {
+          this.ctx.logger.warn(error instanceof Error ? error : new Error(String(error)))
+          socket.destroy()
+        })
+      } catch (error) {
+        this.ctx.logger.warn(error instanceof Error ? error : new Error(String(error)))
+        socket.destroy()
+      }
+    })
 
     await new Promise<void>((resolve, reject) => {
       this.server.once('error', reject)
@@ -158,11 +208,12 @@ export class HttpServerService extends Service {
       })
     })
 
-    // close + closeAllConnections: held-open responses (SSE) never end on
-    // their own; without the force-close, close() would hang teardown.
+    // Node does not include upgraded sockets in closeAllConnections(), so the
+    // service tracks and destroys them as part of the same ownership boundary.
     this.ctx.effect(() => () => new Promise<void>((resolve) => {
       this.server.close(() => { resolve() })
       this.server.closeAllConnections()
+      for (const socket of this.upgradedSockets) socket.destroy()
     }), 'httpServer.listen')
   }
 

packages/host/webserver/src/invariant.ts

@@ -15,7 +15,7 @@ export const name = 'host-webserver-invariant'
 export const inject = ['invariants']
 
 /**
- * Owned relation: route registrations and their disposers must stay
+ * Owned relation: HTTP and upgrade route registrations and their disposers must stay
  * symmetric — after the owning fiber of a registered route unloads, the
  * route table must no longer answer for its path (a stale route would keep
  * serving a disposed plugin's handler). Checked on every fiber teardown
@@ -26,7 +26,10 @@ export const inject = ['invariants']
 const install: InvariantInstaller = (ctx, fail) => {
   ctx.on('internal/plugin', () => {
     const server = ctx.get('httpServer') as
-      | { register(route: { kind: 'exact'; path: string; handler: () => void }): () => void }
+      | {
+        register(route: { kind: 'exact'; path: string; handler: () => void }): () => void
+        registerUpgrade(route: { path: string; handler: () => void }): () => void
+      }
       | undefined
     if (server === undefined) return // no webserver row in this composition
     // Register/dispose probe on a reserved path: if dispose leaves the route
@@ -37,8 +40,11 @@ const install: InvariantInstaller = (ctx, fail) => {
     try {
       server.register(probe)()
       server.register(probe)()
+      const upgradeProbe = { path: '/__dsh_invariant_upgrade_probe__', handler: () => {} }
+      server.registerUpgrade(upgradeProbe)()
+      server.registerUpgrade(upgradeProbe)()
     } catch {
-      fail('httpServer.register() disposer left the route registered — route table and fiber lifecycles diverged')
+      fail('httpServer route disposer left a route registered — route tables and fiber lifecycles diverged')
     }
   }, { global: true })
 }

packages/host/webserver/tests/webserver.spec.ts

@@ -7,6 +7,8 @@
 
 import { mkdtemp, rm, writeFile } from 'node:fs/promises'
 import { mkdir } from 'node:fs/promises'
+import { once } from 'node:events'
+import { connect } from 'node:net'
 import { tmpdir } from 'node:os'
 import { join } from 'node:path'
 import { pathToFileURL } from 'node:url'
@@ -72,6 +74,24 @@ async function request(port: number, path: string, init?: RequestInit): Promise<
   return { status: response.status, body: (await response.text()).slice(0, 80) }
 }
 
+/** Open one raw upgrade request and return after the handler writes its response. */
+async function upgrade(port: number, path: string): Promise<ReturnType<typeof connect>> {
+  const socket = connect(port, '127.0.0.1')
+  await once(socket, 'connect')
+  const response = once(socket, 'data')
+  socket.write([
+    `GET ${path} HTTP/1.1`,
+    `Host: 127.0.0.1:${String(port)}`,
+    'Connection: Upgrade',
+    'Upgrade: dsh-test',
+    '',
+    '',
+  ].join('\r\n'))
+  const [data] = await response
+  expect(String(data)).toContain('101 Switching Protocols')
+  return socket
+}
+
 describe('real Loader composition', () => {
   // Real-Loader composition resolves workspace packages through tsx at test
   // time; first resolution after the host/client program split is slow enough
@@ -131,8 +151,25 @@ describe('real Loader composition', () => {
     expect((await request(port, '/once')).body).toContain('shell') // back to the SPA fallback
     expect(() => server.register({ kind: 'exact', path: '/once', handler: () => {} })).not.toThrow()
 
-    // Teardown: fiber dispose closes the socket and severs held connections.
+    // Upgrade routes match exact pathnames, reject duplicate ownership, and
+    // become registrable again after disposal. The accepted socket stays open
+    // so the teardown assertion also covers upgraded-connection ownership.
+    const disposeUpgrade = server.registerUpgrade({
+      path: '/events',
+      handler: (_req, socket) => {
+        socket.write('HTTP/1.1 101 Switching Protocols\r\nConnection: Upgrade\r\nUpgrade: dsh-test\r\n\r\n')
+      },
+    })
+    expect(() => server.registerUpgrade({ path: '/events', handler: () => {} }))
+      .toThrow(/duplicate upgrade route/)
+    const upgraded = await upgrade(port, '/events?stream=mux')
+    disposeUpgrade()
+    expect(() => server.registerUpgrade({ path: '/events', handler: () => {} })).not.toThrow()
+
+    // Teardown closes both ordinary and upgraded sockets before it resolves.
+    const upgradedClosed = once(upgraded, 'close')
     await loaded.fiber.dispose()
+    await upgradedClosed
     await expect(request(port, '/probe')).rejects.toThrow()
   })