Add optimisticReplyCount to post shadow

src/state/cache/post-shadow.ts

@@ -24,12 +24,13 @@ export interface PostShadow {
   isDeleted: boolean
   embed: AppBskyEmbedRecord.View | AppBskyEmbedRecordWithMedia.View | undefined
   pinned: boolean
+  optimisticReplyCount: number | undefined
 }
 
 export const POST_TOMBSTONE = Symbol('PostTombstone')
 
 const emitter = new EventEmitter()
-const shadows: WeakMap<
+export const shadows: WeakMap<
   AppBskyFeedDefs.PostView,
   Partial<PostShadow>
 > = new WeakMap()
@@ -95,6 +96,11 @@ function mergeShadow(
     repostCount = Math.max(0, repostCount)
   }
 
+  let replyCount = post.replyCount ?? 0
+  if ('optimisticReplyCount' in shadow) {
+    replyCount = shadow.optimisticReplyCount ?? replyCount
+  }
+
   let embed: typeof post.embed
   if ('embed' in shadow) {
     if (
@@ -112,6 +118,7 @@ function mergeShadow(
     embed: embed || post.embed,
     likeCount: likeCount,
     repostCount: repostCount,
+    replyCount: replyCount,
     viewer: {
       ...(post.viewer || {}),
       like: 'likeUri' in shadow ? shadow.likeUri : post.viewer?.like,

src/state/queries/usePostThread/queryCache.ts

@@ -9,6 +9,7 @@ import {
 } from '@atproto/api'
 import {type QueryClient} from '@tanstack/react-query'
 
+import {shadows, updatePostShadow} from '#/state/cache/post-shadow'
 import {findAllPostsInQueryData as findAllPostsInExploreFeedPreviewsQueryData} from '#/state/queries/explore-feed-previews'
 import {findAllPostsInQueryData as findAllPostsInNotifsQueryData} from '#/state/queries/notifications/feed'
 import {findAllPostsInQueryData as findAllPostsInFeedQueryData} from '#/state/queries/post-feed'
@@ -85,10 +86,13 @@ export function createCacheMutator({
           /*
            * Update parent data
            */
-          parent.value.post = {
-            ...parent.value.post,
-            replyCount: (parent.value.post.replyCount || 0) + 1,
-          }
+          const shadow = shadows.get(parent.value.post)
+          const prevOptimisticCount = shadow?.optimisticReplyCount || 0
+          const prevReplyCount = parent.value.post.replyCount || 0
+          updatePostShadow(queryClient, parent.value.post.uri, {
+            // prefer optimistic count, if we already have some
+            optimisticReplyCount: (prevOptimisticCount || prevReplyCount) + 1,
+          })
 
           const opDid = getRootPostAtUri(parent.value.post)?.host
           const nextPreexistingItem = thread.at(i + 1)