Fixes from PR review

Author: tom-andersen

.changeset/small-geckos-mix.md

@@ -0,0 +1,5 @@
+---
+'@firebase/firestore': patch
+---
+
+Refactor Firestore client instantiation. This prepares for future features that require client to restart.

packages/firestore/src/core/firestore_client.ts

@@ -656,11 +656,9 @@ function readDocumentViaSnapshotListener(
 ): Promise<void> {
   const wrappedObserver = new AsyncObserver({
     next: (snap: ViewSnapshot) => {
-      // No further messages should be processed.
-      wrappedObserver.mute();
-
-      // Remove query first before passing event to user to avoid
+      // Mute and remove query first before passing event to user to avoid
       // user actions affecting the now stale query.
+      wrappedObserver.mute();
       asyncQueue.enqueueAndForget(() =>
         eventManagerUnlisten(eventManager, listener)
       );
@@ -757,11 +755,9 @@ function executeQueryViaSnapshotListener(
 ): Promise<void> {
   const wrappedObserver = new AsyncObserver<ViewSnapshot>({
     next: snapshot => {
-      // No further messages should be processed.
-      wrappedObserver.mute();
-
-      // Remove query first before passing event to user to avoid
+      // Mute and remove query first before passing event to user to avoid
       // user actions affecting the now stale query.
+      wrappedObserver.mute();
       asyncQueue.enqueueAndForget(() =>
         eventManagerUnlisten(eventManager, listener)
       );

packages/firestore/src/lite-api/database.ts

@@ -134,13 +134,18 @@ export class Firestore implements FirestoreService {
   }
 
   _delete(): Promise<void> {
+    // The `_terminateTask` must be assigned future that completes when
+    // terminate is complete. The existence of this future puts SDK in state
+    // that will not accept further API interaction.
     if (this._terminateTask === 'notTerminated') {
       this._terminateTask = this._terminate();
     }
     return this._terminateTask;
   }
 
   async _restart(): Promise<void> {
+    // The `_terminateTask` must equal 'notTerminated' after restart to
+    // signal that client is in a state that accepts API calls.
     if (this._terminateTask === 'notTerminated') {
       await this._terminate();
     } else {