Short-circuit heartbeat when alive

src/node/heart.ts

@@ -21,7 +21,10 @@ export class Heart {
    * activity. Failures are logged as warnings.
    */
   public beat(): void {
-    if (!this.alive()) {
+    if (this.alive()) {
+      return
+    }
+
     logger.trace("heartbeat")
     fs.writeFile(this.heartbeatPath, "").catch((error) => {
       logger.warn(error.message)
@@ -43,4 +46,3 @@ export class Heart {
     }, this.heartbeatInterval)
   }
 }
-}