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/src/index.ts

@@ -1,10 +1,36 @@
 /**
- * Connection plugin, node half. The package IS a dshClient plugin: the wire
- * consumer layer lives in its client half in full (src/client/ — contract:
- * api-contracts v3 section 3, inventory §3.2); consumers import the /client
- * subpath. The empty apply exists so the plugin appears in the host Loader
- * (lifecycle governance + dshClient discovery).
+ * Connection plugin, node half: the host end of the web transport. Registers
+ * the /api prefix route on the web server and bridges node:http requests to
+ * the transport-agnostic fetch-shaped api handler. The wire consumer layer
+ * lives in the client half (src/client/ — contract: api-contracts v3
+ * section 3); consumers import the /client subpath.
  */
+import type { Context } from 'cordis'
+// Type-only route import; it also carries the httpServer Context merge.
+import type { WebRoute } from '@deepseek-ai/dsh-host-webserver'
+import { toFetchHandler } from '@deepseek-ai/dsh-host-apiproxy'
+import { API_PATH } from './api-path.ts'
+import { bridge } from './http-bridge.ts'
 
-/** Host plugin body — no host-side behavior for the connection plugin. */
-export function apply(_ctx: unknown): void {}
+export { API_PATH } from './api-path.ts'
+
+/** Cordis plugin name. */
+export const name = 'client-connection'
+
+/** Required services: the route registry and the api gateway. */
+export const inject = ['httpServer', 'apiProxy']
+
+/**
+ * Mount the /api transport: wrap the api gateway into a fetch handler and
+ * serve it under the /api prefix.
+ * @param ctx - host plugin context carrying httpServer and apiProxy.
+ */
+export function apply(ctx: Context): void {
+  const apiHandler = toFetchHandler(ctx.apiProxy)
+  const route: WebRoute = {
+    kind: 'prefix',
+    path: API_PATH,
+    handler: (req, res) => bridge(req, res, apiHandler),
+  }
+  ctx.effect(() => ctx.httpServer.register(route), 'client-connection: /api route')
+}