feat: finish the host-metrics plugin, move host status into core (B16)

src/backend/plugins/schedule.ts

@@ -0,0 +1,81 @@
+/**
+ * ctx.schedule: timers a plugin owns. They live in the plugin's disposable
+ * bag, so deactivate clears every one of them.
+ */
+
+import type { PluginSchedule } from "@termix/plugin-sdk/backend";
+import type { DisposableBag } from "./disposables.js";
+
+type Log = (message: string, error: unknown) => void;
+
+export function createPluginSchedule(
+  bag: DisposableBag,
+  logError: Log,
+): PluginSchedule {
+  const run = async (fn: () => void | Promise<void>) => {
+    try {
+      await fn();
+    } catch (error) {
+      logError("Scheduled job failed", error);
+    }
+  };
+
+  return {
+    every: (intervalMs, fn, options) => {
+      let running = false;
+      let stopped = false;
+      let interval: NodeJS.Timeout | undefined;
+
+      const tick = () => {
+        if (running || stopped) return;
+        running = true;
+        void run(fn).finally(() => {
+          running = false;
+        });
+      };
+
+      const jitter = Math.max(0, Math.floor(options?.jitterMs ?? 0));
+      const start = setTimeout(
+        () => {
+          if (stopped) return;
+          interval = setInterval(tick, Math.max(1, intervalMs));
+          if (jitter > 0) tick();
+        },
+        jitter > 0 ? Math.floor(Math.random() * jitter) : 0,
+      );
+      if (options?.runNow) tick();
+
+      let drop = () => {};
+      const stop = () => {
+        if (stopped) return;
+        stopped = true;
+        clearTimeout(start);
+        if (interval) clearInterval(interval);
+        drop();
+      };
+      drop = bag.add(stop, "scheduled job");
+      return stop;
+    },
+
+    after: (delayMs, fn) => {
+      let done = false;
+      let drop = () => {};
+      const timer = setTimeout(
+        () => {
+          done = true;
+          drop();
+          void run(fn);
+        },
+        Math.max(0, delayMs),
+      );
+      const cancel = () => {
+        if (done) return;
+        done = true;
+        clearTimeout(timer);
+        drop();
+      };
+      drop = bag.add(cancel, "scheduled job");
+      return cancel;
+    },
+  };
+}