simplify fetcher's fetchPromise assignment

packages/client/src/sync/fetcher/fetcher.ts

@@ -481,42 +481,43 @@ export abstract class Fetcher<JobTask, JobResult, StorageItem> extends Readable
   /**
    * Run the fetcher. Returns a promise that resolves once all tasks are completed.
    */
+  async _fetch() {
+    try {
+      this.write()
+      this.running = true
+      this.nextTasks()
+
+      while (this.running) {
+        if (this.next() === false) {
+          if (this.finished === this.total && this.destroyWhenDone) {
+            this.push(null)
+          }
+          await this.wait()
+        }
+      }
+      this.running = false
+      if (this.destroyWhenDone) {
+        this.destroy()
+        this.writer = null
+      }
+      if (this.syncErrored) throw this.syncErrored
+      return true
+    } finally {
+      this.fetchPromise = null
+    }
+  }
+
+  /**
+   * Wraps the internal fetcher to track its promise
+   */
   async fetch() {
     if (this.running) {
       return false
     }
 
-    this.fetchPromise = new Promise(
-      // wrapped in try catch to make sure no unhandled exception is thrown so we can
-      // ignore eslint error
-      // eslint-disable-next-line no-async-promise-executor
-      async (resolve, reject) => {
-        try {
-          this.write()
-          this.running = true
-          this.nextTasks()
-
-          while (this.running) {
-            if (this.next() === false) {
-              if (this.finished === this.total && this.destroyWhenDone) {
-                this.push(null)
-              }
-              await this.wait()
-            }
-          }
-          this.running = false
-          if (this.destroyWhenDone) {
-            this.destroy()
-            this.writer = null
-          }
-          if (this.syncErrored) throw this.syncErrored
-          this.fetchPromise = null
-          resolve(true)
-        } catch (e) {
-          reject(e)
-        }
-      }
-    )
+    if (this.fetchPromise === null) {
+      this.fetchPromise = this._fetch()
+    }
     return this.fetchPromise
   }