[lib] Invalidate UserIdentityCache when changing FID

Summary:
When we change the current user's FID, we should invalidate their entry in the `UserIdentityCache`. Otherwise, `FarcasterDataHandler` will continue to use the old value, and can end up wiping the FID if `handleCurrentUserFID` is run again before the app is killed (this can happen if the app is backgrounded/foregrounded).

This addresses [ENG-9704](https://linear.app/comm/issue/ENG-9704/farcaster-channel-books-linked-to-deleted-community).

Depends on D13736

Test Plan:
1. Open mobile app when Farcaster account not linked
2. Link Farcaster account
3. Background the app
4. Foreground the app
5. Confirm that the Farcaster account is not unlinked

Reviewers: will

Reviewed By: will

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D13737

lib/components/user-identity-cache.react.js

@@ -51,6 +51,7 @@ type UserIdentityCache = {
     userIDs: $ReadOnlyArray<string>,
   ) => Promise<UserIdentitiesResponse>,
   +getCachedUserIdentity: (userID: string) => ?UserIdentityResult,
+  +invalidateCacheForUser: (userID: string) => void,
 };
 
 type UserIdentityResult =
@@ -225,12 +226,18 @@ function UserIdentityCacheProvider(props: Props): React.Node {
     [getCachedUserIdentityEntry, findUserIdentities],
   );
 
+  const invalidateCacheForUser = React.useCallback((userID: string) => {
+    const cache = userIdentityCacheRef.current;
+    cache.delete(userID);
+  }, []);
+
   const value = React.useMemo(
     () => ({
       getUserIdentities,
       getCachedUserIdentity,
+      invalidateCacheForUser,
     }),
-    [getUserIdentities, getCachedUserIdentity],
+    [getUserIdentities, getCachedUserIdentity, invalidateCacheForUser],
   );
 
   return (

lib/utils/farcaster-utils.js

@@ -4,6 +4,7 @@ import invariant from 'invariant';
 import * as React from 'react';
 
 import { setSyncedMetadataEntryActionType } from '../actions/synced-metadata-actions.js';
+import { useUserIdentityCache } from '../components/user-identity-cache.react.js';
 import { IdentityClientContext } from '../shared/identity-client-context.js';
 import { syncedMetadataNames } from '../types/synced-metadata-types.js';
 import { useSelector, useDispatch } from '../utils/redux-utils.js';
@@ -32,6 +33,8 @@ function useCurrentUserFID(): ?string {
 
 function useSetLocalFID(): (fid: ?string) => void {
   const dispatch = useDispatch();
+  const { invalidateCacheForUser } = useUserIdentityCache();
+  const currentUserID = useSelector(state => state.currentUserInfo?.id);
   return React.useCallback(
     (fid: ?string) => {
       // If we're unsetting the FID, we should set it to NO_FID_METADATA to
@@ -44,8 +47,11 @@ function useSetLocalFID(): (fid: ?string) => void {
           data: fidToSet,
         },
       });
+      if (currentUserID) {
+        invalidateCacheForUser(currentUserID);
+      }
     },
-    [dispatch],
+    [dispatch, currentUserID, invalidateCacheForUser],
   );
 }