feat(web): grow real node halves in connection and hmr

connection binds the web transport: it injects httpServer + apiProxy and
registers toFetchHandler(ctx.apiProxy) under the /api prefix (the node:http
to fetch bridge moves in from the webserver, keeping the res-close disconnect
detection and drain/close backpressure waits). hmr owns dev reload: a
stat-poll watch per graph row driven by clientModuleHost.onGraphChanged,
rebuilt(id) on content change, and the /plugins/events SSE route (GET/HEAD
guarded); frame types are single-sourced in events.ts shared by both halves.

packages/client/connection/tests/node-half.spec.ts

@@ -1,10 +1,33 @@
-/** Node half: the empty host apply (Loader governance + dshClient discovery placeholder). */
+/** Node half: registers the /api prefix route bridging to the api gateway. */
+import { Context } from 'cordis'
 import { describe, expect, it } from 'vitest'
-import { apply } from '../src/index.ts'
+import type { ApiProxy } from '@deepseek-ai/dsh-host-apiproxy/api'
+import type { HttpServerService, WebRoute } from '@deepseek-ai/dsh-host-webserver'
+import { API_PATH, apply, inject } from '../src/index.ts'
 
-describe('node half', () => {
-  it('apply is a no-op host placeholder', () => {
-    apply(undefined)
-    expect(true).toBe(true) // reaching here without throw is the contract
+describe('connection node half', () => {
+  it('registers the /api prefix route and removes it with the fiber', async () => {
+    const ctx = new Context()
+    const routes: WebRoute[] = []
+    // Structural fake: the plugin only touches register(); the service class
+    // carries private state a literal cannot (and need not) reproduce.
+    const httpServer: Pick<HttpServerService, 'register' | 'tapIndex' | 'port'> = {
+      register(route) {
+        routes.push(route)
+        return () => { routes.splice(routes.indexOf(route), 1) }
+      },
+      tapIndex: () => () => {},
+      port: 0,
+    }
+    ctx.provide('httpServer', httpServer as HttpServerService)
+    ctx.provide('apiProxy', {} as unknown as ApiProxy)
+
+    const fiber = ctx.plugin({ inject: [...inject], apply })
+    await fiber.await()
+    expect(routes).toHaveLength(1)
+    expect(routes[0]).toMatchObject({ kind: 'prefix', path: API_PATH })
+
+    await fiber.dispose()
+    expect(routes).toHaveLength(0)
   })
 })