[lib] use v2 relevant followers API to find farcaster friends

Summary: this API returns what we want -- farcaster mutuals. and it seems to work pretty consistently, unlike the paginated v1 followers API.

Test Plan: successfully got back farcaster mutuals for dwr.eth (fid 3), who has a ton of followers

Reviewers: ashoat, will

Reviewed By: ashoat, will

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D13530

lib/utils/neynar-client.js

@@ -3,19 +3,17 @@
 import invariant from 'invariant';
 
 import { getMessageForException } from './errors.js';
-import type {
-  NeynarChannel,
-  NeynarUser,
-  NeynarUserWithViewerContext,
-} from '../types/farcaster-types.js';
-
-type FetchFollowersResponse = {
-  +result: {
-    +users: $ReadOnlyArray<NeynarUserWithViewerContext>,
-    +next: {
-      +cursor: ?string,
+import type { NeynarChannel, NeynarUser } from '../types/farcaster-types.js';
+
+type FetchRelevantFollowersResponse = {
+  +all_relevant_followers_dehydrated: $ReadOnlyArray<{
+    +user: {
+      +fid: number,
+      ...
     },
-  },
+    ...
+  }>,
+  ...
 };
 
 type FetchFarcasterChannelsResponse = {
@@ -60,7 +58,6 @@ function getNeynarURL(
   return `${neynarURL}${apiCall}?${new URLSearchParams(params).toString()}`;
 }
 
-const fetchFollowerLimit = 150;
 const fetchFollowedChannelsLimit = 100;
 const fetchChannelsLimit = 50;
 
@@ -73,48 +70,35 @@ class NeynarClient {
 
   // We're using the term "friend" for a bidirectional follow
   async fetchFriendFIDs(fid: string): Promise<string[]> {
-    const fids = [];
-    let paginationCursor = null;
-
-    do {
-      const params: { [string]: string } = {
-        fid,
-        viewerFid: fid,
-        limit: fetchFollowerLimit.toString(),
-        ...(paginationCursor ? { cursor: paginationCursor } : null),
-      };
-
-      const url = getNeynarURL('1', 'followers', params);
-
-      try {
-        const response = await fetch(url, {
-          method: 'GET',
-          headers: {
-            Accept: 'application/json',
-            api_key: this.apiKey,
-          },
-        });
+    const params: { [string]: string } = {
+      target_fid: fid,
+      viewer_fid: fid,
+    };
 
-        const json: FetchFollowersResponse = await response.json();
-        const { users } = json.result;
+    const url = getNeynarURL('2', 'followers/relevant', params);
 
-        for (const user of users) {
-          if (user.viewerContext.following) {
-            fids.push(user.fid.toString());
-          }
-        }
+    try {
+      const response = await fetch(url, {
+        method: 'GET',
+        headers: {
+          Accept: 'application/json',
+          api_key: this.apiKey,
+        },
+      });
 
-        paginationCursor = json.result.next.cursor;
-      } catch (error) {
-        console.log(
-          'Failed to fetch friend FIDs:',
-          getMessageForException(error) ?? 'unknown',
-        );
-        throw error;
-      }
-    } while (paginationCursor);
+      const json: FetchRelevantFollowersResponse = await response.json();
+      const { all_relevant_followers_dehydrated } = json;
 
-    return fids;
+      return all_relevant_followers_dehydrated.map(follower =>
+        follower.user.fid.toString(),
+      );
+    } catch (error) {
+      console.log(
+        'Failed to fetch friend FIDs:',
+        getMessageForException(error) ?? 'unknown',
+      );
+      throw error;
+    }
   }
 
   async fetchFollowedFarcasterChannelsWithFilter(