feat: ship host metrics as a first-party in-process plugin

plugins/host-metrics/backend/index.mjs

@@ -0,0 +1,66 @@
+/**
+ * Host Metrics - first-party, in-process plugin.
+ *
+ * This plugin runs on the main thread rather than in a worker for the same
+ * reason ssh-terminal and docker do (see src/backend/plugins/first-party.ts):
+ * its polling manager holds long-lived ssh2.Client connections across a
+ * whole fleet of hosts, reused between polling ticks, and its connect flow
+ * implements the same jump-host/SOCKS5/TOTP/Warpgate/OPKSSH/Vault
+ * keyboard-interactive handshakes the terminal does. None of that can cross
+ * the structured-clone postMessage boundary a worker plugin talks over, and
+ * the worker ctx.ssh primitive (connect + single exec-and-collect) has no
+ * hook for a session that outlives one request.
+ *
+ * routes.ts is what used to be src/backend/hosts/metrics/index.ts, moved
+ * here and rewritten from a module-scope SIGINT/SIGTERM + listenOnServicePort
+ * call into startHostMetricsService()/shutdown(), called from
+ * activate()/deactivate() below.
+ *
+ * Proxmox-related code (metrics/proxmox/*, proxmox-stats-*) stays in core at
+ * src/backend/hosts/metrics/ rather than moving here -- it is planned as its
+ * own future plugin, so this move does not touch it.
+ */
+
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+
+/**
+ * Loads a module by its path relative to this file's own directory.
+ *
+ * The plugin ships beside dist/backend, so in a built server the compiled
+ * .js for the moved host-metrics files (routes.js, ...) sits right next to
+ * this .mjs, and core modules resolve via ../../../backend/backend/... from
+ * there (dist/plugins/host-metrics/backend -> dist/backend/backend). Under
+ * vitest/dev nothing imports this plugin directly (the loader loads
+ * in-process plugins with a plain dynamic import, no tsx loader involved),
+ * so the only layout that needs to resolve here is the built one.
+ */
+async function loadRelative(relativePath) {
+  const here = path.dirname(fileURLToPath(import.meta.url));
+  const target = path.join(here, `${relativePath}.js`);
+  return import(new URL(`file://${target.replace(/\\/g, "/")}`).href);
+}
+
+let routesModule = null;
+let httpServer = null;
+
+export async function activate(ctx) {
+  routesModule = await loadRelative("routes");
+
+  httpServer = routesModule.startHostMetricsService();
+
+  ctx.log.info(`Host Metrics listening on ${routesModule.PORT ?? 30005}`);
+}
+
+export async function deactivate() {
+  if (routesModule) {
+    routesModule.shutdown();
+    routesModule = null;
+  }
+
+  if (httpServer) {
+    const server = httpServer;
+    httpServer = null;
+    await new Promise((resolve) => server.close(() => resolve()));
+  }
+}