diff --git a/lib/shared/thread-utils.js b/lib/shared/thread-utils.js
index 7a0a6548e..715d8f9d8 100644
--- a/lib/shared/thread-utils.js
+++ b/lib/shared/thread-utils.js
@@ -1,1928 +1,1974 @@
 // @flow
 
 import invariant from 'invariant';
 import _find from 'lodash/fp/find.js';
 import _mapValues from 'lodash/fp/mapValues.js';
 import _omitBy from 'lodash/fp/omitBy.js';
 import * as React from 'react';
 
 import { generatePendingThreadColor } from './color-utils.js';
 import { type ParserRules } from './markdown.js';
 import { extractUserMentionsFromText } from './mention-utils.js';
 import { getMessageTitle, isInvalidSidebarSource } from './message-utils.js';
 import { relationshipBlockedInEitherDirection } from './relationship-utils.js';
 import threadWatcher from './thread-watcher.js';
 import {
   fetchMostRecentMessagesActionTypes,
   fetchMostRecentMessages,
 } from '../actions/message-actions.js';
 import {
   changeThreadMemberRolesActionTypes,
   newThreadActionTypes,
   removeUsersFromThreadActionTypes,
 } from '../actions/thread-actions.js';
 import { searchUsers as searchUserCall } from '../actions/user-actions.js';
 import ashoat from '../facts/ashoat.js';
 import genesis from '../facts/genesis.js';
 import { useLoggedInUserInfo } from '../hooks/account-hooks.js';
 import {
   permissionLookup,
   getAllThreadPermissions,
   makePermissionsBlob,
 } from '../permissions/thread-permissions.js';
 import type {
   ChatThreadItem,
   ChatMessageInfoItem,
 } from '../selectors/chat-selectors.js';
 import { useGlobalThreadSearchIndex } from '../selectors/nav-selectors.js';
 import {
   threadInfoSelector,
   pendingToRealizedThreadIDsSelector,
   threadInfosSelectorForThreadType,
 } from '../selectors/thread-selectors.js';
 import {
   getRelativeMemberInfos,
   usersWithPersonalThreadSelector,
 } from '../selectors/user-selectors.js';
 import { getUserAvatarForThread } from '../shared/avatar-utils.js';
+import SentencePrefixSearchIndex from '../shared/sentence-prefix-search-index.js';
 import type { CalendarQuery } from '../types/entry-types.js';
 import { messageTypes } from '../types/message-types-enum.js';
 import {
   type RobotextMessageInfo,
   type ComposableMessageInfo,
 } from '../types/message-types.js';
 import { userRelationshipStatus } from '../types/relationship-types.js';
 import {
   threadPermissionPropagationPrefixes,
   threadPermissions,
   configurableCommunityPermissions,
   type ThreadPermission,
   type ThreadPermissionsInfo,
   type UserSurfacedPermission,
 } from '../types/thread-permission-types.js';
 import {
   type ThreadType,
   threadTypes,
   threadTypeIsCommunityRoot,
   assertThreadType,
 } from '../types/thread-types-enum.js';
 import {
   type RawThreadInfo,
   type ThreadInfo,
   type MemberInfo,
   type ServerThreadInfo,
   type RelativeMemberInfo,
   type ThreadCurrentUserInfo,
   type RoleInfo,
   type ServerMemberInfo,
   type ClientNewThreadRequest,
   type NewThreadResult,
   type ChangeThreadSettingsPayload,
   type ResolvedThreadInfo,
   type ChatMentionCandidatesObj,
   type ChatMentionCandidates,
   type UserProfileThreadInfo,
 } from '../types/thread-types.js';
 import { updateTypes } from '../types/update-types-enum.js';
 import { type ClientUpdateInfo } from '../types/update-types.js';
 import type {
   GlobalAccountUserInfo,
   UserInfos,
   AccountUserInfo,
   LoggedInUserInfo,
   UserInfo,
 } from '../types/user-types.js';
 import {
   useDispatchActionPromise,
   useServerCall,
 } from '../utils/action-utils.js';
 import type { DispatchActionPromise } from '../utils/action-utils.js';
 import type { GetENSNames } from '../utils/ens-helpers.js';
 import { useResolvedThreadInfosObj } from '../utils/entity-helpers.js';
 import {
   ET,
   entityTextToRawString,
   getEntityTextAsString,
   type ThreadEntity,
 } from '../utils/entity-text.js';
 import { useSelector } from '../utils/redux-utils.js';
 import { firstLine } from '../utils/string-utils.js';
 import { trimText } from '../utils/text-utils.js';
 import { pendingThreadIDRegex } from '../utils/validation-utils.js';
 
 const chatNameMaxLength = 191;
 const chatNameMinLength = 0;
 const secondCharRange = `{${chatNameMinLength},${chatNameMaxLength}}`;
 const validChatNameRegexString = `^.${secondCharRange}$`;
 const validChatNameRegex: RegExp = new RegExp(validChatNameRegexString);
 
 function threadHasPermission(
   threadInfo: ?(ThreadInfo | RawThreadInfo),
   permission: ThreadPermission,
 ): boolean {
   if (!threadInfo) {
     return false;
   }
   invariant(
     !permissionsDisabledByBlock.has(permission) || threadInfo?.uiName,
     `${permission} can be disabled by a block, but threadHasPermission can't ` +
       'check for a block on RawThreadInfo. Please pass in ThreadInfo instead!',
   );
   if (!threadInfo.currentUser.permissions[permission]) {
     return false;
   }
   return threadInfo.currentUser.permissions[permission].value;
 }
 
 function viewerIsMember(threadInfo: ?(ThreadInfo | RawThreadInfo)): boolean {
   return !!(
     threadInfo &&
     threadInfo.currentUser.role !== null &&
     threadInfo.currentUser.role !== undefined
   );
 }
 
 function threadIsInHome(threadInfo: ?(ThreadInfo | RawThreadInfo)): boolean {
   return !!(threadInfo && threadInfo.currentUser.subscription.home);
 }
 
 // Can have messages
 function threadInChatList(threadInfo: ?(ThreadInfo | RawThreadInfo)): boolean {
   return (
     viewerIsMember(threadInfo) &&
     threadHasPermission(threadInfo, threadPermissions.VISIBLE)
   );
 }
 
 function threadIsTopLevel(threadInfo: ?(ThreadInfo | RawThreadInfo)): boolean {
   return threadInChatList(threadInfo) && threadIsChannel(threadInfo);
 }
 
 function threadIsChannel(threadInfo: ?(ThreadInfo | RawThreadInfo)): boolean {
   return !!(threadInfo && threadInfo.type !== threadTypes.SIDEBAR);
 }
 
 function threadIsSidebar(threadInfo: ?(ThreadInfo | RawThreadInfo)): boolean {
   return threadInfo?.type === threadTypes.SIDEBAR;
 }
 
 function threadInBackgroundChatList(
   threadInfo: ?(ThreadInfo | RawThreadInfo),
 ): boolean {
   return threadInChatList(threadInfo) && !threadIsInHome(threadInfo);
 }
 
 function threadInHomeChatList(
   threadInfo: ?(ThreadInfo | RawThreadInfo),
 ): boolean {
   return threadInChatList(threadInfo) && threadIsInHome(threadInfo);
 }
 
 // Can have Calendar entries,
 // does appear as a top-level entity in the thread list
 function threadInFilterList(
   threadInfo: ?(ThreadInfo | RawThreadInfo),
 ): boolean {
   return (
     threadInChatList(threadInfo) &&
     !!threadInfo &&
     threadInfo.type !== threadTypes.SIDEBAR
   );
 }
 
 function userIsMember(
   threadInfo: ?(ThreadInfo | RawThreadInfo),
   userID: string,
 ): boolean {
   if (!threadInfo) {
     return false;
   }
   if (threadInfo.id === genesis.id) {
     return true;
   }
   return threadInfo.members.some(member => member.id === userID && member.role);
 }
 
 function threadActualMembers(
   memberInfos: $ReadOnlyArray<MemberInfo | RelativeMemberInfo>,
 ): $ReadOnlyArray<string> {
   return memberInfos
     .filter(memberInfo => memberInfo.role)
     .map(memberInfo => memberInfo.id);
 }
 
 function threadOtherMembers<T: MemberInfo | RelativeMemberInfo>(
   memberInfos: $ReadOnlyArray<T>,
   viewerID: ?string,
 ): $ReadOnlyArray<T> {
   return memberInfos.filter(
     memberInfo => memberInfo.role && memberInfo.id !== viewerID,
   );
 }
 
 function threadMembersWithoutAddedAshoat<T: ThreadInfo | RawThreadInfo>(
   threadInfo: T,
 ): $PropertyType<T, 'members'> {
   if (threadInfo.community !== genesis.id) {
     return threadInfo.members;
   }
   return threadInfo.members.filter(
     member => member.id !== ashoat.id || member.role,
   );
 }
 
 function threadIsGroupChat(threadInfo: ThreadInfo | RawThreadInfo): boolean {
   return (
     threadMembersWithoutAddedAshoat(threadInfo).filter(
       member =>
         member.role || member.permissions[threadPermissions.VOICED]?.value,
     ).length > 2
   );
 }
 
 function threadOrParentThreadIsGroupChat(
   threadInfo: RawThreadInfo | ThreadInfo,
 ) {
   return threadMembersWithoutAddedAshoat(threadInfo).length > 2;
 }
 
 function threadIsPending(threadID: ?string): boolean {
   return !!threadID?.startsWith('pending');
 }
 
 function threadIsPendingSidebar(threadID: ?string): boolean {
   return !!threadID?.startsWith('pending/sidebar/');
 }
 
 function getSingleOtherUser(
   threadInfo: ThreadInfo | RawThreadInfo,
   viewerID: ?string,
 ): ?string {
   if (!viewerID) {
     return undefined;
   }
   const otherMembers = threadOtherMembers(threadInfo.members, viewerID);
   if (otherMembers.length !== 1) {
     return undefined;
   }
   return otherMembers[0].id;
 }
 
 function getPendingThreadID(
   threadType: ThreadType,
   memberIDs: $ReadOnlyArray<string>,
   sourceMessageID: ?string,
 ): string {
   const pendingThreadKey = sourceMessageID
     ? `sidebar/${sourceMessageID}`
     : [...memberIDs].sort().join('+');
   const pendingThreadTypeString = sourceMessageID ? '' : `type${threadType}/`;
   return `pending/${pendingThreadTypeString}${pendingThreadKey}`;
 }
 
 type PendingThreadIDContents = {
   +threadType: ThreadType,
   +memberIDs: $ReadOnlyArray<string>,
   +sourceMessageID: ?string,
 };
 
 function parsePendingThreadID(
   pendingThreadID: string,
 ): ?PendingThreadIDContents {
   const pendingRegex = new RegExp(`^${pendingThreadIDRegex}$`);
   const pendingThreadIDMatches = pendingRegex.exec(pendingThreadID);
   if (!pendingThreadIDMatches) {
     return null;
   }
   const [threadTypeString, threadKey] = pendingThreadIDMatches[1].split('/');
   const threadType =
     threadTypeString === 'sidebar'
       ? threadTypes.SIDEBAR
       : assertThreadType(Number(threadTypeString.replace('type', '')));
   const memberIDs = threadTypeString === 'sidebar' ? [] : threadKey.split('+');
   const sourceMessageID = threadTypeString === 'sidebar' ? threadKey : null;
   return {
     threadType,
     memberIDs,
     sourceMessageID,
   };
 }
 
 type UserIDAndUsername = {
   +id: string,
   +username: string,
   ...
 };
 type CreatePendingThreadArgs = {
   +viewerID: string,
   +threadType: ThreadType,
   +members: $ReadOnlyArray<UserIDAndUsername>,
   +parentThreadInfo?: ?ThreadInfo,
   +threadColor?: ?string,
   +name?: ?string,
   +sourceMessageID?: string,
 };
 
 function createPendingThread({
   viewerID,
   threadType,
   members,
   parentThreadInfo,
   threadColor,
   name,
   sourceMessageID,
 }: CreatePendingThreadArgs): ThreadInfo {
   const now = Date.now();
   if (!members.some(member => member.id === viewerID)) {
     throw new Error(
       'createPendingThread should be called with the viewer as a member',
     );
   }
 
   const memberIDs = members.map(member => member.id);
   const threadID = getPendingThreadID(threadType, memberIDs, sourceMessageID);
 
   const permissions = {
     [threadPermissions.KNOW_OF]: true,
     [threadPermissions.VISIBLE]: true,
     [threadPermissions.VOICED]: true,
   };
 
   const membershipPermissions = getAllThreadPermissions(
     makePermissionsBlob(permissions, null, threadID, threadType),
     threadID,
   );
   const role = {
     id: `${threadID}/role`,
     name: 'Members',
     permissions,
     isDefault: true,
   };
 
   const rawThreadInfo = {
     id: threadID,
     type: threadType,
     name: name ?? null,
     description: null,
     color: threadColor ?? generatePendingThreadColor(memberIDs),
     creationTime: now,
     parentThreadID: parentThreadInfo?.id ?? null,
     containingThreadID: getContainingThreadID(parentThreadInfo, threadType),
     community: getCommunity(parentThreadInfo),
     members: members.map(member => ({
       id: member.id,
       role: role.id,
       permissions: membershipPermissions,
       isSender: false,
     })),
     roles: {
       [role.id]: role,
     },
     currentUser: {
       role: role.id,
       permissions: membershipPermissions,
       subscription: {
         pushNotifs: false,
         home: false,
       },
       unread: false,
     },
     repliesCount: 0,
     sourceMessageID,
     pinnedCount: 0,
   };
 
   const userInfos = {};
   for (const member of members) {
     const { id, username } = member;
     userInfos[id] = { id, username };
   }
 
   return threadInfoFromRawThreadInfo(rawThreadInfo, viewerID, userInfos);
 }
 
 type PendingPersonalThread = {
   +threadInfo: ThreadInfo,
   +pendingPersonalThreadUserInfo: UserInfo,
 };
 
 function createPendingPersonalThread(
   loggedInUserInfo: LoggedInUserInfo,
   userID: string,
   username: string,
 ): PendingPersonalThread {
   const pendingPersonalThreadUserInfo = {
     id: userID,
     username: username,
   };
 
   const threadInfo = createPendingThread({
     viewerID: loggedInUserInfo.id,
     threadType: threadTypes.PERSONAL,
     members: [loggedInUserInfo, pendingPersonalThreadUserInfo],
   });
 
   return { threadInfo, pendingPersonalThreadUserInfo };
 }
 
 function createPendingThreadItem(
   loggedInUserInfo: LoggedInUserInfo,
   user: UserIDAndUsername,
 ): ChatThreadItem {
   const { threadInfo, pendingPersonalThreadUserInfo } =
     createPendingPersonalThread(loggedInUserInfo, user.id, user.username);
 
   return {
     type: 'chatThreadItem',
     threadInfo,
     mostRecentMessageInfo: null,
     mostRecentNonLocalMessage: null,
     lastUpdatedTime: threadInfo.creationTime,
     lastUpdatedTimeIncludingSidebars: threadInfo.creationTime,
     sidebars: [],
     pendingPersonalThreadUserInfo,
   };
 }
 
 // Returns map from lowercase username to AccountUserInfo
 function memberLowercaseUsernameMap(
   members: $ReadOnlyArray<RelativeMemberInfo>,
 ): Map<string, AccountUserInfo> {
   const memberMap = new Map();
   for (const member of members) {
     const { id, role, username } = member;
     if (!role || !username) {
       continue;
     }
     memberMap.set(username.toLowerCase(), { id, username });
   }
   return memberMap;
 }
 
 // Returns map from user ID to AccountUserInfo
 function extractMentionedMembers(
   text: string,
   threadInfo: ThreadInfo,
 ): Map<string, AccountUserInfo> {
   const memberMap = memberLowercaseUsernameMap(threadInfo.members);
   const mentions = extractUserMentionsFromText(text);
 
   const mentionedMembers = new Map();
   for (const mention of mentions) {
     const userInfo = memberMap.get(mention.toLowerCase());
     if (userInfo) {
       mentionedMembers.set(userInfo.id, userInfo);
     }
   }
   return mentionedMembers;
 }
 
 // When a member of the parent is mentioned in a sidebar,
 // they will be automatically added to that sidebar
 function extractNewMentionedParentMembers(
   messageText: string,
   threadInfo: ThreadInfo,
   parentThreadInfo: ThreadInfo,
 ): AccountUserInfo[] {
   const mentionedMembersOfParent = extractMentionedMembers(
     messageText,
     parentThreadInfo,
   );
   for (const member of threadInfo.members) {
     if (member.role) {
       mentionedMembersOfParent.delete(member.id);
     }
   }
   return [...mentionedMembersOfParent.values()];
 }
 
 type SharedCreatePendingSidebarInput = {
   +sourceMessageInfo: ComposableMessageInfo | RobotextMessageInfo,
   +parentThreadInfo: ThreadInfo,
   +loggedInUserInfo: LoggedInUserInfo,
 };
 
 type BaseCreatePendingSidebarInput = {
   ...SharedCreatePendingSidebarInput,
   +messageTitle: string,
 };
 function baseCreatePendingSidebar(
   input: BaseCreatePendingSidebarInput,
 ): ThreadInfo {
   const {
     sourceMessageInfo,
     parentThreadInfo,
     loggedInUserInfo,
     messageTitle,
   } = input;
   const { color, type: parentThreadType } = parentThreadInfo;
   const threadName = trimText(messageTitle, 30);
 
   const initialMembers = new Map();
 
   const { id: viewerID, username: viewerUsername } = loggedInUserInfo;
   initialMembers.set(viewerID, { id: viewerID, username: viewerUsername });
 
   if (userIsMember(parentThreadInfo, sourceMessageInfo.creator.id)) {
     const { id: sourceAuthorID, username: sourceAuthorUsername } =
       sourceMessageInfo.creator;
     invariant(
       sourceAuthorUsername,
       'sourceAuthorUsername should be set in createPendingSidebar',
     );
     const initialMemberUserInfo = {
       id: sourceAuthorID,
       username: sourceAuthorUsername,
     };
     initialMembers.set(sourceAuthorID, initialMemberUserInfo);
   }
 
   const singleOtherUser = getSingleOtherUser(parentThreadInfo, viewerID);
   if (parentThreadType === threadTypes.PERSONAL && singleOtherUser) {
     const singleOtherUsername = parentThreadInfo.members.find(
       member => member.id === singleOtherUser,
     )?.username;
     invariant(
       singleOtherUsername,
       'singleOtherUsername should be set in createPendingSidebar',
     );
     const singleOtherUserInfo = {
       id: singleOtherUser,
       username: singleOtherUsername,
     };
     initialMembers.set(singleOtherUser, singleOtherUserInfo);
   }
 
   if (sourceMessageInfo.type === messageTypes.TEXT) {
     const mentionedMembersOfParent = extractMentionedMembers(
       sourceMessageInfo.text,
       parentThreadInfo,
     );
     for (const [memberID, member] of mentionedMembersOfParent) {
       initialMembers.set(memberID, member);
     }
   }
 
   return createPendingThread({
     viewerID,
     threadType: threadTypes.SIDEBAR,
     members: [...initialMembers.values()],
     parentThreadInfo,
     threadColor: color,
     name: threadName,
     sourceMessageID: sourceMessageInfo.id,
   });
 }
 
 // The message title here may have ETH addresses that aren't resolved to ENS
 // names. This function should only be used in cases where we're sure that we
 // don't care about the thread title. We should prefer createPendingSidebar
 // wherever possible
 type CreateUnresolvedPendingSidebarInput = {
   ...SharedCreatePendingSidebarInput,
   +markdownRules: ParserRules,
 };
 function createUnresolvedPendingSidebar(
   input: CreateUnresolvedPendingSidebarInput,
 ): ThreadInfo {
   const {
     sourceMessageInfo,
     parentThreadInfo,
     loggedInUserInfo,
     markdownRules,
   } = input;
 
   const messageTitleEntityText = getMessageTitle(
     sourceMessageInfo,
     parentThreadInfo,
     parentThreadInfo,
     markdownRules,
   );
   const messageTitle = entityTextToRawString(messageTitleEntityText, {
     ignoreViewer: true,
   });
 
   return baseCreatePendingSidebar({
     sourceMessageInfo,
     parentThreadInfo,
     messageTitle,
     loggedInUserInfo,
   });
 }
 
 type CreatePendingSidebarInput = {
   ...SharedCreatePendingSidebarInput,
   +markdownRules: ParserRules,
   +getENSNames: ?GetENSNames,
 };
 async function createPendingSidebar(
   input: CreatePendingSidebarInput,
 ): Promise<ThreadInfo> {
   const {
     sourceMessageInfo,
     parentThreadInfo,
     loggedInUserInfo,
     markdownRules,
     getENSNames,
   } = input;
 
   const messageTitleEntityText = getMessageTitle(
     sourceMessageInfo,
     parentThreadInfo,
     parentThreadInfo,
     markdownRules,
   );
   const messageTitle = await getEntityTextAsString(
     messageTitleEntityText,
     getENSNames,
     { ignoreViewer: true },
   );
   invariant(
     messageTitle !== null && messageTitle !== undefined,
     'getEntityTextAsString only returns falsey when passed falsey',
   );
 
   return baseCreatePendingSidebar({
     sourceMessageInfo,
     parentThreadInfo,
     messageTitle,
     loggedInUserInfo,
   });
 }
 
 function pendingThreadType(numberOfOtherMembers: number): 4 | 6 | 7 {
   if (numberOfOtherMembers === 0) {
     return threadTypes.PRIVATE;
   } else if (numberOfOtherMembers === 1) {
     return threadTypes.PERSONAL;
   } else {
     return threadTypes.LOCAL;
   }
 }
 
 function threadTypeCanBePending(threadType: ThreadType): boolean {
   return (
     threadType === threadTypes.PERSONAL ||
     threadType === threadTypes.LOCAL ||
     threadType === threadTypes.SIDEBAR ||
     threadType === threadTypes.PRIVATE
   );
 }
 
 type CreateRealThreadParameters = {
   +threadInfo: ThreadInfo,
   +dispatchActionPromise: DispatchActionPromise,
   +createNewThread: ClientNewThreadRequest => Promise<NewThreadResult>,
   +sourceMessageID: ?string,
   +viewerID: ?string,
   +handleError?: () => mixed,
   +calendarQuery: CalendarQuery,
 };
 async function createRealThreadFromPendingThread({
   threadInfo,
   dispatchActionPromise,
   createNewThread,
   sourceMessageID,
   viewerID,
   calendarQuery,
 }: CreateRealThreadParameters): Promise<string> {
   if (!threadIsPending(threadInfo.id)) {
     return threadInfo.id;
   }
 
   const otherMemberIDs = threadOtherMembers(threadInfo.members, viewerID).map(
     member => member.id,
   );
   let resultPromise;
   if (threadInfo.type !== threadTypes.SIDEBAR) {
     invariant(
       otherMemberIDs.length > 0,
       'otherMemberIDs should not be empty for threads',
     );
     resultPromise = createNewThread({
       type: pendingThreadType(otherMemberIDs.length),
       initialMemberIDs: otherMemberIDs,
       color: threadInfo.color,
       calendarQuery,
     });
   } else {
     invariant(
       sourceMessageID,
       'sourceMessageID should be set when creating a sidebar',
     );
     resultPromise = createNewThread({
       type: threadTypes.SIDEBAR,
       initialMemberIDs: otherMemberIDs,
       color: threadInfo.color,
       sourceMessageID,
       parentThreadID: threadInfo.parentThreadID,
       name: threadInfo.name,
       calendarQuery,
     });
   }
   dispatchActionPromise(newThreadActionTypes, resultPromise);
   const { newThreadID } = await resultPromise;
   return newThreadID;
 }
 
 type RawThreadInfoOptions = {
   +filterThreadEditAvatarPermission?: boolean,
   +excludePinInfo?: boolean,
   +filterManageInviteLinksPermission?: boolean,
 };
 function rawThreadInfoFromServerThreadInfo(
   serverThreadInfo: ServerThreadInfo,
   viewerID: string,
   options?: RawThreadInfoOptions,
 ): ?RawThreadInfo {
   const filterThreadEditAvatarPermission =
     options?.filterThreadEditAvatarPermission;
   const excludePinInfo = options?.excludePinInfo;
   const filterManageInviteLinksPermission =
     options?.filterManageInviteLinksPermission;
 
   const filterThreadPermissions = _omitBy(
     (v, k) =>
       (filterThreadEditAvatarPermission &&
         [
           threadPermissions.EDIT_THREAD_AVATAR,
           threadPermissionPropagationPrefixes.DESCENDANT +
             threadPermissions.EDIT_THREAD_AVATAR,
         ].includes(k)) ||
       (excludePinInfo &&
         [
           threadPermissions.MANAGE_PINS,
           threadPermissionPropagationPrefixes.DESCENDANT +
             threadPermissions.MANAGE_PINS,
         ].includes(k)) ||
       (filterManageInviteLinksPermission &&
         [threadPermissions.MANAGE_INVITE_LINKS].includes(k)),
   );
 
   const members = [];
   let currentUser;
   for (const serverMember of serverThreadInfo.members) {
     if (
       serverThreadInfo.id === genesis.id &&
       serverMember.id !== viewerID &&
       serverMember.id !== ashoat.id
     ) {
       continue;
     }
 
     const memberPermissions = filterThreadPermissions(serverMember.permissions);
 
     members.push({
       id: serverMember.id,
       role: serverMember.role,
       permissions: memberPermissions,
       isSender: serverMember.isSender,
     });
     if (serverMember.id === viewerID) {
       currentUser = {
         role: serverMember.role,
         permissions: memberPermissions,
         subscription: serverMember.subscription,
         unread: serverMember.unread,
       };
     }
   }
 
   let currentUserPermissions;
   if (currentUser) {
     currentUserPermissions = currentUser.permissions;
   } else {
     currentUserPermissions = filterThreadPermissions(
       getAllThreadPermissions(null, serverThreadInfo.id),
     );
     currentUser = {
       role: null,
       permissions: currentUserPermissions,
       subscription: {
         home: false,
         pushNotifs: false,
       },
       unread: null,
     };
   }
   if (!permissionLookup(currentUserPermissions, threadPermissions.KNOW_OF)) {
     return null;
   }
 
   const rolesWithFilteredThreadPermissions = _mapValues(role => ({
     ...role,
     permissions: filterThreadPermissions(role.permissions),
   }))(serverThreadInfo.roles);
 
   let rawThreadInfo: any = {
     id: serverThreadInfo.id,
     type: serverThreadInfo.type,
     name: serverThreadInfo.name,
     description: serverThreadInfo.description,
     color: serverThreadInfo.color,
     creationTime: serverThreadInfo.creationTime,
     parentThreadID: serverThreadInfo.parentThreadID,
     members,
     roles: rolesWithFilteredThreadPermissions,
     currentUser,
     repliesCount: serverThreadInfo.repliesCount,
     containingThreadID: serverThreadInfo.containingThreadID,
     community: serverThreadInfo.community,
   };
   const sourceMessageID = serverThreadInfo.sourceMessageID;
   if (sourceMessageID) {
     rawThreadInfo = { ...rawThreadInfo, sourceMessageID };
   }
   if (serverThreadInfo.avatar) {
     rawThreadInfo = { ...rawThreadInfo, avatar: serverThreadInfo.avatar };
   }
   if (!excludePinInfo) {
     return {
       ...rawThreadInfo,
       pinnedCount: serverThreadInfo.pinnedCount,
     };
   }
   return rawThreadInfo;
 }
 
 function threadUIName(threadInfo: ThreadInfo): string | ThreadEntity {
   if (threadInfo.name) {
     return firstLine(threadInfo.name);
   }
   const threadMembers = threadInfo.members.filter(
     memberInfo => memberInfo.role,
   );
   const memberEntities = threadMembers.map(member =>
     ET.user({ userInfo: member }),
   );
   return {
     type: 'thread',
     id: threadInfo.id,
     name: threadInfo.name,
     display: 'uiName',
     uiName: memberEntities,
     ifJustViewer:
       threadInfo.type === threadTypes.PRIVATE
         ? 'viewer_username'
         : 'just_you_string',
   };
 }
 
 function threadInfoFromRawThreadInfo(
   rawThreadInfo: RawThreadInfo,
   viewerID: ?string,
   userInfos: UserInfos,
 ): ThreadInfo {
   let threadInfo: ThreadInfo = {
     id: rawThreadInfo.id,
     type: rawThreadInfo.type,
     name: rawThreadInfo.name,
     uiName: '',
     description: rawThreadInfo.description,
     color: rawThreadInfo.color,
     creationTime: rawThreadInfo.creationTime,
     parentThreadID: rawThreadInfo.parentThreadID,
     containingThreadID: rawThreadInfo.containingThreadID,
     community: rawThreadInfo.community,
     members: getRelativeMemberInfos(rawThreadInfo, viewerID, userInfos),
     roles: rawThreadInfo.roles,
     currentUser: getCurrentUser(rawThreadInfo, viewerID, userInfos),
     repliesCount: rawThreadInfo.repliesCount,
   };
   threadInfo = {
     ...threadInfo,
     uiName: threadUIName(threadInfo),
   };
   const { sourceMessageID, avatar, pinnedCount } = rawThreadInfo;
   if (sourceMessageID) {
     threadInfo = { ...threadInfo, sourceMessageID };
   }
 
   if (avatar) {
     threadInfo = { ...threadInfo, avatar };
   } else if (
     rawThreadInfo.type === threadTypes.PERSONAL ||
     rawThreadInfo.type === threadTypes.PRIVATE
   ) {
     threadInfo = {
       ...threadInfo,
       avatar: getUserAvatarForThread(rawThreadInfo, viewerID, userInfos),
     };
   }
 
   if (pinnedCount) {
     threadInfo = { ...threadInfo, pinnedCount };
   }
 
   return threadInfo;
 }
 
 function getCurrentUser(
   threadInfo: RawThreadInfo | ThreadInfo,
   viewerID: ?string,
   userInfos: UserInfos,
 ): ThreadCurrentUserInfo {
   if (!threadFrozenDueToBlock(threadInfo, viewerID, userInfos)) {
     return threadInfo.currentUser;
   }
 
   return {
     ...threadInfo.currentUser,
     permissions: {
       ...threadInfo.currentUser.permissions,
       ...disabledPermissions,
     },
   };
 }
 
 function threadIsWithBlockedUserOnly(
   threadInfo: RawThreadInfo | ThreadInfo,
   viewerID: ?string,
   userInfos: UserInfos,
   checkOnlyViewerBlock?: boolean,
 ): boolean {
   if (
     threadOrParentThreadIsGroupChat(threadInfo) ||
     threadOrParentThreadHasAdminRole(threadInfo)
   ) {
     return false;
   }
 
   const otherUserID = getSingleOtherUser(threadInfo, viewerID);
   if (!otherUserID) {
     return false;
   }
   const otherUserRelationshipStatus =
     userInfos[otherUserID]?.relationshipStatus;
 
   if (checkOnlyViewerBlock) {
     return (
       otherUserRelationshipStatus === userRelationshipStatus.BLOCKED_BY_VIEWER
     );
   }
 
   return (
     !!otherUserRelationshipStatus &&
     relationshipBlockedInEitherDirection(otherUserRelationshipStatus)
   );
 }
 
 function threadFrozenDueToBlock(
   threadInfo: RawThreadInfo | ThreadInfo,
   viewerID: ?string,
   userInfos: UserInfos,
 ): boolean {
   return threadIsWithBlockedUserOnly(threadInfo, viewerID, userInfos);
 }
 
 function threadFrozenDueToViewerBlock(
   threadInfo: RawThreadInfo | ThreadInfo,
   viewerID: ?string,
   userInfos: UserInfos,
 ): boolean {
   return threadIsWithBlockedUserOnly(threadInfo, viewerID, userInfos, true);
 }
 
 const threadTypeDescriptions: { [ThreadType]: string } = {
   [threadTypes.COMMUNITY_OPEN_SUBTHREAD]:
     'Anybody in the parent channel can see an open subchannel.',
   [threadTypes.COMMUNITY_SECRET_SUBTHREAD]:
     'Only visible to its members and admins of ancestor channels.',
 };
 
 function memberIsAdmin(
   memberInfo: RelativeMemberInfo | MemberInfo,
   threadInfo: ThreadInfo | RawThreadInfo,
 ): boolean {
   return !!(
     memberInfo.role && roleIsAdminRole(threadInfo.roles[memberInfo.role])
   );
 }
 
 // Since we don't have access to all of the ancestor ThreadInfos, we approximate
 // "parent admin" as anybody with CHANGE_ROLE permissions.
 function memberHasAdminPowers(
   memberInfo: RelativeMemberInfo | MemberInfo | ServerMemberInfo,
 ): boolean {
   return !!memberInfo.permissions[threadPermissions.CHANGE_ROLE]?.value;
 }
 
 function roleIsAdminRole(roleInfo: ?RoleInfo): boolean {
   return !!(roleInfo && !roleInfo.isDefault && roleInfo.name === 'Admins');
 }
 
 function threadHasAdminRole(
   threadInfo: ?(RawThreadInfo | ThreadInfo | ServerThreadInfo),
 ): boolean {
   if (!threadInfo) {
     return false;
   }
   return !!_find({ name: 'Admins' })(threadInfo.roles);
 }
 
 function threadOrParentThreadHasAdminRole(
   threadInfo: RawThreadInfo | ThreadInfo,
 ) {
   return (
     threadMembersWithoutAddedAshoat(threadInfo).filter(member =>
       memberHasAdminPowers(member),
     ).length > 0
   );
 }
 
 function identifyInvalidatedThreads(
   updateInfos: $ReadOnlyArray<ClientUpdateInfo>,
 ): Set<string> {
   const invalidated = new Set();
   for (const updateInfo of updateInfos) {
     if (updateInfo.type === updateTypes.DELETE_THREAD) {
       invalidated.add(updateInfo.threadID);
     }
   }
   return invalidated;
 }
 
 const permissionsDisabledByBlockArray = [
   threadPermissions.VOICED,
   threadPermissions.EDIT_ENTRIES,
   threadPermissions.EDIT_THREAD_NAME,
   threadPermissions.EDIT_THREAD_COLOR,
   threadPermissions.EDIT_THREAD_DESCRIPTION,
   threadPermissions.CREATE_SUBCHANNELS,
   threadPermissions.CREATE_SIDEBARS,
   threadPermissions.JOIN_THREAD,
   threadPermissions.EDIT_PERMISSIONS,
   threadPermissions.ADD_MEMBERS,
   threadPermissions.REMOVE_MEMBERS,
 ];
 
 const permissionsDisabledByBlock: Set<ThreadPermission> = new Set(
   permissionsDisabledByBlockArray,
 );
 
 const disabledPermissions: ThreadPermissionsInfo =
   permissionsDisabledByBlockArray.reduce(
     (permissions: ThreadPermissionsInfo, permission: string) => ({
       ...permissions,
       [permission]: { value: false, source: null },
     }),
     {},
   );
 
 // Consider updating itemHeight in native/chat/chat-thread-list.react.js
 // if you change this
 const emptyItemText: string =
   `Background chats are just like normal chats, except they don't ` +
   `contribute to your unread count.\n\n` +
   `To move a chat over here, switch the “Background” option in its settings.`;
 
 function threadNoun(threadType: ThreadType, parentThreadID: ?string): string {
   if (threadType === threadTypes.SIDEBAR) {
     return 'thread';
   } else if (
     threadType === threadTypes.COMMUNITY_SECRET_SUBTHREAD &&
     parentThreadID === genesis.id
   ) {
     return 'chat';
   } else if (
     threadType === threadTypes.COMMUNITY_ROOT ||
     threadType === threadTypes.COMMUNITY_ANNOUNCEMENT_ROOT ||
     threadType === threadTypes.COMMUNITY_OPEN_SUBTHREAD ||
     threadType === threadTypes.COMMUNITY_OPEN_ANNOUNCEMENT_SUBTHREAD ||
     threadType === threadTypes.COMMUNITY_SECRET_SUBTHREAD ||
     threadType === threadTypes.COMMUNITY_SECRET_ANNOUNCEMENT_SUBTHREAD ||
     threadType === threadTypes.GENESIS
   ) {
     return 'channel';
   } else {
     return 'chat';
   }
 }
 
 function threadLabel(threadType: ThreadType): string {
   if (
     threadType === threadTypes.COMMUNITY_OPEN_SUBTHREAD ||
     threadType === threadTypes.COMMUNITY_OPEN_ANNOUNCEMENT_SUBTHREAD
   ) {
     return 'Open';
   } else if (threadType === threadTypes.PERSONAL) {
     return 'Personal';
   } else if (threadType === threadTypes.SIDEBAR) {
     return 'Thread';
   } else if (threadType === threadTypes.PRIVATE) {
     return 'Private';
   } else if (
     threadType === threadTypes.COMMUNITY_ROOT ||
     threadType === threadTypes.COMMUNITY_ANNOUNCEMENT_ROOT ||
     threadType === threadTypes.GENESIS
   ) {
     return 'Community';
   } else {
     return 'Secret';
   }
 }
 
 function useWatchThread(threadInfo: ?ThreadInfo) {
   const dispatchActionPromise = useDispatchActionPromise();
   const callFetchMostRecentMessages = useServerCall(fetchMostRecentMessages);
 
   const threadID = threadInfo?.id;
   const threadNotInChatList = !threadInChatList(threadInfo);
   React.useEffect(() => {
     if (threadID && threadNotInChatList) {
       threadWatcher.watchID(threadID);
       dispatchActionPromise(
         fetchMostRecentMessagesActionTypes,
         callFetchMostRecentMessages(threadID),
       );
     }
     return () => {
       if (threadID && threadNotInChatList) {
         threadWatcher.removeID(threadID);
       }
     };
   }, [
     callFetchMostRecentMessages,
     dispatchActionPromise,
     threadNotInChatList,
     threadID,
   ]);
 }
 
 type ExistingThreadInfoFinderParams = {
   +searching: boolean,
   +userInfoInputArray: $ReadOnlyArray<AccountUserInfo>,
 };
 type ExistingThreadInfoFinder = (
   params: ExistingThreadInfoFinderParams,
 ) => ?ThreadInfo;
 function useExistingThreadInfoFinder(
   baseThreadInfo: ?ThreadInfo,
 ): ExistingThreadInfoFinder {
   const threadInfos = useSelector(threadInfoSelector);
   const loggedInUserInfo = useLoggedInUserInfo();
   const userInfos = useSelector(state => state.userStore.userInfos);
 
   const pendingToRealizedThreadIDs = useSelector(state =>
     pendingToRealizedThreadIDsSelector(state.threadStore.threadInfos),
   );
   return React.useCallback(
     (params: ExistingThreadInfoFinderParams): ?ThreadInfo => {
       if (!baseThreadInfo) {
         return null;
       }
 
       const realizedThreadInfo = threadInfos[baseThreadInfo.id];
       if (realizedThreadInfo) {
         return realizedThreadInfo;
       }
 
       if (!loggedInUserInfo || !threadIsPending(baseThreadInfo.id)) {
         return baseThreadInfo;
       }
       const viewerID = loggedInUserInfo?.id;
 
       invariant(
         threadTypeCanBePending(baseThreadInfo.type),
         `ThreadInfo has pending ID ${baseThreadInfo.id}, but type that ` +
           `should not be pending ${baseThreadInfo.type}`,
       );
 
       const { searching, userInfoInputArray } = params;
 
       const { sourceMessageID } = baseThreadInfo;
       const pendingThreadID = searching
         ? getPendingThreadID(
             pendingThreadType(userInfoInputArray.length),
             [...userInfoInputArray.map(user => user.id), viewerID],
             sourceMessageID,
           )
         : getPendingThreadID(
             baseThreadInfo.type,
             baseThreadInfo.members.map(member => member.id),
             sourceMessageID,
           );
 
       const realizedThreadID = pendingToRealizedThreadIDs.get(pendingThreadID);
       if (realizedThreadID && threadInfos[realizedThreadID]) {
         return threadInfos[realizedThreadID];
       }
 
       const updatedThread = searching
         ? createPendingThread({
             viewerID,
             threadType: pendingThreadType(userInfoInputArray.length),
             members: [loggedInUserInfo, ...userInfoInputArray],
           })
         : baseThreadInfo;
       return {
         ...updatedThread,
         currentUser: getCurrentUser(updatedThread, viewerID, userInfos),
       };
     },
     [
       baseThreadInfo,
       threadInfos,
       loggedInUserInfo,
       pendingToRealizedThreadIDs,
       userInfos,
     ],
   );
 }
 
 type ThreadTypeParentRequirement = 'optional' | 'required' | 'disabled';
 function getThreadTypeParentRequirement(
   threadType: ThreadType,
 ): ThreadTypeParentRequirement {
   if (
     threadType === threadTypes.COMMUNITY_OPEN_SUBTHREAD ||
     threadType === threadTypes.COMMUNITY_OPEN_ANNOUNCEMENT_SUBTHREAD ||
     //threadType === threadTypes.COMMUNITY_SECRET_SUBTHREAD ||
     threadType === threadTypes.COMMUNITY_SECRET_ANNOUNCEMENT_SUBTHREAD ||
     threadType === threadTypes.SIDEBAR
   ) {
     return 'required';
   } else if (
     threadType === threadTypes.COMMUNITY_ROOT ||
     threadType === threadTypes.COMMUNITY_ANNOUNCEMENT_ROOT ||
     threadType === threadTypes.GENESIS ||
     threadType === threadTypes.PERSONAL ||
     threadType === threadTypes.PRIVATE
   ) {
     return 'disabled';
   } else {
     return 'optional';
   }
 }
 
 function threadMemberHasPermission(
   threadInfo: ServerThreadInfo | RawThreadInfo | ThreadInfo,
   memberID: string,
   permission: ThreadPermission,
 ): boolean {
   for (const member of threadInfo.members) {
     if (member.id !== memberID) {
       continue;
     }
     return permissionLookup(member.permissions, permission);
   }
   return false;
 }
 
 function useCanCreateSidebarFromMessage(
   threadInfo: ThreadInfo,
   messageInfo: ComposableMessageInfo | RobotextMessageInfo,
 ): boolean {
   const messageCreatorUserInfo = useSelector(
     state => state.userStore.userInfos[messageInfo.creator.id],
   );
 
   if (
     !messageInfo.id ||
     threadInfo.sourceMessageID === messageInfo.id ||
     isInvalidSidebarSource(messageInfo.type)
   ) {
     return false;
   }
 
   const messageCreatorRelationship = messageCreatorUserInfo?.relationshipStatus;
   const creatorRelationshipHasBlock =
     messageCreatorRelationship &&
     relationshipBlockedInEitherDirection(messageCreatorRelationship);
 
   const hasPermission = threadHasPermission(
     threadInfo,
     threadPermissions.CREATE_SIDEBARS,
   );
 
   return hasPermission && !creatorRelationshipHasBlock;
 }
 
 function useSidebarExistsOrCanBeCreated(
   threadInfo: ThreadInfo,
   messageItem: ChatMessageInfoItem,
 ): boolean {
   const canCreateSidebarFromMessage = useCanCreateSidebarFromMessage(
     threadInfo,
     messageItem.messageInfo,
   );
   return !!messageItem.threadCreatedFromMessage || canCreateSidebarFromMessage;
 }
 
 function checkIfDefaultMembersAreVoiced(threadInfo: ThreadInfo): boolean {
   const defaultRoleID = Object.keys(threadInfo.roles).find(
     roleID => threadInfo.roles[roleID].isDefault,
   );
   invariant(
     defaultRoleID !== undefined,
     'all threads should have a default role',
   );
   const defaultRole = threadInfo.roles[defaultRoleID];
   return !!defaultRole.permissions[threadPermissions.VOICED];
 }
 
 const draftKeySuffix = '/message_composer';
 
 function draftKeyFromThreadID(threadID: string): string {
   return `${threadID}${draftKeySuffix}`;
 }
 
 function getContainingThreadID(
   parentThreadInfo: ?ServerThreadInfo | RawThreadInfo | ThreadInfo,
   threadType: ThreadType,
 ): ?string {
   if (!parentThreadInfo) {
     return null;
   }
   if (threadType === threadTypes.SIDEBAR) {
     return parentThreadInfo.id;
   }
   if (!parentThreadInfo.containingThreadID) {
     return parentThreadInfo.id;
   }
   return parentThreadInfo.containingThreadID;
 }
 
 function getCommunity(
   parentThreadInfo: ?ServerThreadInfo | RawThreadInfo | ThreadInfo,
 ): ?string {
   if (!parentThreadInfo) {
     return null;
   }
   const { id, community, type } = parentThreadInfo;
   if (community !== null && community !== undefined) {
     return community;
   }
   if (threadTypeIsCommunityRoot(type)) {
     return id;
   }
   return null;
 }
 
 function getThreadListSearchResults(
   chatListData: $ReadOnlyArray<ChatThreadItem>,
   searchText: string,
   threadFilter: ThreadInfo => boolean,
   threadSearchResults: $ReadOnlySet<string>,
   usersSearchResults: $ReadOnlyArray<GlobalAccountUserInfo>,
   loggedInUserInfo: ?LoggedInUserInfo,
 ): $ReadOnlyArray<ChatThreadItem> {
   if (!searchText) {
     return chatListData.filter(
       item =>
         threadIsTopLevel(item.threadInfo) && threadFilter(item.threadInfo),
     );
   }
 
   const privateThreads = [];
   const personalThreads = [];
   const otherThreads = [];
   for (const item of chatListData) {
     if (!threadSearchResults.has(item.threadInfo.id)) {
       continue;
     }
     if (item.threadInfo.type === threadTypes.PRIVATE) {
       privateThreads.push({ ...item, sidebars: [] });
     } else if (item.threadInfo.type === threadTypes.PERSONAL) {
       personalThreads.push({ ...item, sidebars: [] });
     } else {
       otherThreads.push({ ...item, sidebars: [] });
     }
   }
 
   const chatItems = [...privateThreads, ...personalThreads, ...otherThreads];
   if (loggedInUserInfo) {
     chatItems.push(
       ...usersSearchResults.map(user =>
         createPendingThreadItem(loggedInUserInfo, user),
       ),
     );
   }
   return chatItems;
 }
 
 type ThreadListSearchResult = {
   +threadSearchResults: $ReadOnlySet<string>,
   +usersSearchResults: $ReadOnlyArray<GlobalAccountUserInfo>,
 };
 function useThreadListSearch(
   searchText: string,
   viewerID: ?string,
 ): ThreadListSearchResult {
   const callSearchUsers = useServerCall(searchUserCall);
   const usersWithPersonalThread = useSelector(usersWithPersonalThreadSelector);
   const searchUsers = React.useCallback(
     async (usernamePrefix: string) => {
       if (usernamePrefix.length === 0) {
         return [];
       }
 
       const { userInfos } = await callSearchUsers(usernamePrefix);
       return userInfos.filter(
         info => !usersWithPersonalThread.has(info.id) && info.id !== viewerID,
       );
     },
     [callSearchUsers, usersWithPersonalThread, viewerID],
   );
 
   const [threadSearchResults, setThreadSearchResults] = React.useState(
     new Set(),
   );
   const [usersSearchResults, setUsersSearchResults] = React.useState([]);
   const threadSearchIndex = useGlobalThreadSearchIndex();
   React.useEffect(() => {
     (async () => {
       const results = threadSearchIndex.getSearchResults(searchText);
       setThreadSearchResults(new Set(results));
       const usersResults = await searchUsers(searchText);
       setUsersSearchResults(usersResults);
     })();
   }, [searchText, threadSearchIndex, searchUsers]);
 
   return { threadSearchResults, usersSearchResults };
 }
 
 function removeMemberFromThread(
   threadInfo: ThreadInfo,
   memberInfo: RelativeMemberInfo,
   dispatchActionPromise: DispatchActionPromise,
   removeUserFromThreadServerCall: (
     threadID: string,
     memberIDs: $ReadOnlyArray<string>,
   ) => Promise<ChangeThreadSettingsPayload>,
 ) {
   const customKeyName = `${removeUsersFromThreadActionTypes.started}:${memberInfo.id}`;
   dispatchActionPromise(
     removeUsersFromThreadActionTypes,
     removeUserFromThreadServerCall(threadInfo.id, [memberInfo.id]),
     { customKeyName },
   );
 }
 
 function switchMemberAdminRoleInThread(
   threadInfo: ThreadInfo,
   memberInfo: RelativeMemberInfo,
   isCurrentlyAdmin: boolean,
   dispatchActionPromise: DispatchActionPromise,
   changeUserRoleServerCall: (
     threadID: string,
     memberIDs: $ReadOnlyArray<string>,
     newRole: string,
   ) => Promise<ChangeThreadSettingsPayload>,
 ) {
   let newRole = null;
   for (const roleID in threadInfo.roles) {
     const role = threadInfo.roles[roleID];
     if (isCurrentlyAdmin && role.isDefault) {
       newRole = role.id;
       break;
     } else if (!isCurrentlyAdmin && roleIsAdminRole(role)) {
       newRole = role.id;
       break;
     }
   }
   invariant(newRole !== null, 'Could not find new role');
 
   const customKeyName = `${changeThreadMemberRolesActionTypes.started}:${memberInfo.id}`;
   dispatchActionPromise(
     changeThreadMemberRolesActionTypes,
     changeUserRoleServerCall(threadInfo.id, [memberInfo.id], newRole),
     { customKeyName },
   );
 }
 
 function getAvailableThreadMemberActions(
   memberInfo: RelativeMemberInfo,
   threadInfo: ThreadInfo,
   canEdit: ?boolean = true,
 ): $ReadOnlyArray<'change_role' | 'remove_user'> {
   const role = memberInfo.role;
   if (!canEdit || !role) {
     return [];
   }
 
   const canRemoveMembers = threadHasPermission(
     threadInfo,
     threadPermissions.REMOVE_MEMBERS,
   );
   const canChangeRoles = threadHasPermission(
     threadInfo,
     threadPermissions.CHANGE_ROLE,
   );
 
   const result = [];
 
   if (canChangeRoles && memberInfo.username && threadHasAdminRole(threadInfo)) {
     result.push('change_role');
   }
 
   if (
     canRemoveMembers &&
     !memberInfo.isViewer &&
     (canChangeRoles || threadInfo.roles[role]?.isDefault)
   ) {
     result.push('remove_user');
   }
 
   return result;
 }
 
 function patchThreadInfoToIncludeMentionedMembersOfParent(
   threadInfo: ThreadInfo,
   parentThreadInfo: ThreadInfo,
   messageText: string,
   viewerID: string,
 ): ThreadInfo {
   const members: UserIDAndUsername[] = threadInfo.members
     .map(({ id, username }) => (username ? { id, username } : null))
     .filter(Boolean);
   const mentionedNewMembers = extractNewMentionedParentMembers(
     messageText,
     threadInfo,
     parentThreadInfo,
   );
   if (mentionedNewMembers.length === 0) {
     return threadInfo;
   }
   members.push(...mentionedNewMembers);
   return createPendingThread({
     viewerID,
     threadType: threadTypes.SIDEBAR,
     members,
     parentThreadInfo,
     threadColor: threadInfo.color,
     name: threadInfo.name,
     sourceMessageID: threadInfo.sourceMessageID,
   });
 }
 
 function threadInfoInsideCommunity(
   threadInfo: RawThreadInfo | ThreadInfo,
   communityID: string,
 ): boolean {
   return threadInfo.community === communityID || threadInfo.id === communityID;
 }
 
 type RoleAndMemberCount = {
   [roleName: string]: number,
 };
 
 function useRoleMemberCountsForCommunity(
   threadInfo: ThreadInfo,
 ): RoleAndMemberCount {
   return React.useMemo(() => {
     const roleIDsToNames = {};
 
     Object.keys(threadInfo.roles).forEach(roleID => {
       roleIDsToNames[roleID] = threadInfo.roles[roleID].name;
     });
 
     const roleNamesToMemberCount: RoleAndMemberCount = {};
 
     threadInfo.members.forEach(({ role: roleID }) => {
       invariant(roleID, 'Community member should have a role');
       const roleName = roleIDsToNames[roleID];
 
       roleNamesToMemberCount[roleName] =
         (roleNamesToMemberCount[roleName] ?? 0) + 1;
     });
 
     // For all community roles with no members, add them to the list with 0
     Object.keys(roleIDsToNames).forEach(roleName => {
       if (roleNamesToMemberCount[roleIDsToNames[roleName]] === undefined) {
         roleNamesToMemberCount[roleIDsToNames[roleName]] = 0;
       }
     });
 
     return roleNamesToMemberCount;
   }, [threadInfo]);
 }
 
 type RoleUserSurfacedPermissions = {
   +[roleName: string]: $ReadOnlySet<UserSurfacedPermission>,
 };
 // Iterates through the existing roles in the community and 'reverse maps'
 // the set of permission literals for each role to user-facing permission enums
 // to help pre-populate the permission checkboxes when editing roles.
 function useRoleUserSurfacedPermissions(
   threadInfo: ThreadInfo,
 ): RoleUserSurfacedPermissions {
   return React.useMemo(() => {
     const roleNamesToPermissions = {};
 
     Object.keys(threadInfo.roles).forEach(roleID => {
       const roleName = threadInfo.roles[roleID].name;
       const rolePermissions = Object.keys(threadInfo.roles[roleID].permissions);
       const setOfUserSurfacedPermissions = new Set();
 
       rolePermissions.forEach(rolePermission => {
         const userSurfacedPermission = Object.keys(
           configurableCommunityPermissions,
         ).find(key =>
           configurableCommunityPermissions[key].has(rolePermission),
         );
 
         if (userSurfacedPermission) {
           setOfUserSurfacedPermissions.add(userSurfacedPermission);
         }
       });
       roleNamesToPermissions[roleName] = setOfUserSurfacedPermissions;
     });
 
     return roleNamesToPermissions;
   }, [threadInfo]);
 }
 
 function communityOrThreadNoun(threadInfo: RawThreadInfo | ThreadInfo): string {
   return threadTypeIsCommunityRoot(threadInfo.type)
     ? 'community'
     : threadNoun(threadInfo.type, threadInfo.parentThreadID);
 }
 
 function getThreadsToDeleteText(
   threadInfo: RawThreadInfo | ThreadInfo,
 ): string {
   return `${
     threadTypeIsCommunityRoot(threadInfo.type)
       ? 'Subchannels and threads'
       : 'Threads'
   } within this ${communityOrThreadNoun(threadInfo)}`;
 }
 
 function getChatMentionCandidates(threadInfos: {
   +[id: string]: ResolvedThreadInfo,
 }): {
   chatMentionCandidatesObj: ChatMentionCandidatesObj,
   communityThreadIDForGenesisThreads: { +[id: string]: string },
 } {
   const result = {};
   const visitedGenesisThreads = new Set();
   const communityThreadIDForGenesisThreads = {};
   for (const currentThreadID in threadInfos) {
     const currentThreadInfo = threadInfos[currentThreadID];
     const { community: currentThreadCommunity } = currentThreadInfo;
     if (!currentThreadCommunity) {
       if (!result[currentThreadID]) {
         result[currentThreadID] = { [currentThreadID]: currentThreadInfo };
       }
       continue;
     }
     if (!result[currentThreadCommunity]) {
       result[currentThreadCommunity] = {
         [currentThreadCommunity]: threadInfos[currentThreadCommunity],
       };
     }
     // Handle GENESIS community case: mentioning inside GENESIS should only
     // show chats and threads inside the top level that is below GENESIS.
     if (threadInfos[currentThreadCommunity].type === threadTypes.GENESIS) {
       if (visitedGenesisThreads.has(currentThreadID)) {
         continue;
       }
       const threadTraversePath = [currentThreadInfo];
       visitedGenesisThreads.add(currentThreadID);
       let currentlySelectedThreadID = currentThreadInfo.parentThreadID;
       while (currentlySelectedThreadID) {
         const currentlySelectedThreadInfo =
           threadInfos[currentlySelectedThreadID];
         if (
           visitedGenesisThreads.has(currentlySelectedThreadID) ||
           !currentlySelectedThreadInfo ||
           currentlySelectedThreadInfo.type === threadTypes.GENESIS
         ) {
           break;
         }
         threadTraversePath.push(currentlySelectedThreadInfo);
         visitedGenesisThreads.add(currentlySelectedThreadID);
         currentlySelectedThreadID = currentlySelectedThreadInfo.parentThreadID;
       }
       const lastThreadInTraversePath =
         threadTraversePath[threadTraversePath.length - 1];
       let lastThreadInTraversePathParentID;
       if (lastThreadInTraversePath.parentThreadID) {
         lastThreadInTraversePathParentID = threadInfos[
           lastThreadInTraversePath.parentThreadID
         ]
           ? lastThreadInTraversePath.parentThreadID
           : lastThreadInTraversePath.id;
       } else {
         lastThreadInTraversePathParentID = lastThreadInTraversePath.id;
       }
       if (
         threadInfos[lastThreadInTraversePathParentID].type ===
         threadTypes.GENESIS
       ) {
         if (!result[lastThreadInTraversePath.id]) {
           result[lastThreadInTraversePath.id] = {};
         }
         for (const threadInfo of threadTraversePath) {
           result[lastThreadInTraversePath.id][threadInfo.id] = threadInfo;
           communityThreadIDForGenesisThreads[threadInfo.id] =
             lastThreadInTraversePath.id;
         }
       } else {
         if (
           !communityThreadIDForGenesisThreads[lastThreadInTraversePathParentID]
         ) {
           result[lastThreadInTraversePathParentID] = {};
           communityThreadIDForGenesisThreads[lastThreadInTraversePathParentID] =
             lastThreadInTraversePathParentID;
         }
         const lastThreadInTraversePathParentCommunityThreadID =
           communityThreadIDForGenesisThreads[lastThreadInTraversePathParentID];
         for (const threadInfo of threadTraversePath) {
           result[lastThreadInTraversePathParentCommunityThreadID][
             threadInfo.id
           ] = threadInfo;
           communityThreadIDForGenesisThreads[threadInfo.id] =
             lastThreadInTraversePathParentCommunityThreadID;
         }
       }
       continue;
     }
     result[currentThreadCommunity][currentThreadID] = currentThreadInfo;
   }
   return {
     chatMentionCandidatesObj: result,
     communityThreadIDForGenesisThreads,
   };
 }
 
 function useChatMentionCandidatesObjAndUtils(): {
   chatMentionCandidatesObj: ChatMentionCandidatesObj,
   resolvedThreadInfos: ChatMentionCandidates,
   communityThreadIDForGenesisThreads: { +[id: string]: string },
 } {
   const threadInfos = useSelector(threadInfoSelector);
   const resolvedThreadInfos = useResolvedThreadInfosObj(threadInfos);
   const { chatMentionCandidatesObj, communityThreadIDForGenesisThreads } =
     React.useMemo(
       () => getChatMentionCandidates(resolvedThreadInfos),
       [resolvedThreadInfos],
     );
   return {
     chatMentionCandidatesObj,
     resolvedThreadInfos,
     communityThreadIDForGenesisThreads,
   };
 }
 
 function useChatMentionCandidatesObj(): ChatMentionCandidatesObj {
   const { chatMentionCandidatesObj } = useChatMentionCandidatesObjAndUtils();
   return chatMentionCandidatesObj;
 }
 
 function useThreadChatMentionCandidates(
   threadInfo: ThreadInfo,
 ): ChatMentionCandidates {
   const { chatMentionCandidatesObj, communityThreadIDForGenesisThreads } =
     useChatMentionCandidatesObjAndUtils();
   return React.useMemo(() => {
     let communityID,
       result = {};
     if (threadInfo.community === genesis.id) {
       communityID = communityThreadIDForGenesisThreads[threadInfo.id];
     } else {
       communityID = threadInfo.community ?? threadInfo.id;
     }
     if (chatMentionCandidatesObj[communityID]) {
       result = { ...chatMentionCandidatesObj[communityID] };
     }
     delete result[threadInfo.id];
     return result;
   }, [
     chatMentionCandidatesObj,
     communityThreadIDForGenesisThreads,
     threadInfo.community,
     threadInfo.id,
   ]);
 }
 
 function useUserProfileThreadInfo(userInfo: ?UserInfo): ?UserProfileThreadInfo {
   const userID = userInfo?.id;
   const username = userInfo?.username;
 
   const loggedInUserInfo = useLoggedInUserInfo();
   const isViewerProfile = loggedInUserInfo?.id === userID;
 
   const privateThreadInfosSelector = threadInfosSelectorForThreadType(
     threadTypes.PRIVATE,
   );
   const privateThreadInfos = useSelector(privateThreadInfosSelector);
 
   const personalThreadInfosSelector = threadInfosSelectorForThreadType(
     threadTypes.PERSONAL,
   );
 
   const personalThreadInfos = useSelector(personalThreadInfosSelector);
 
   const usersWithPersonalThread = useSelector(usersWithPersonalThreadSelector);
 
   return React.useMemo(() => {
     if (!loggedInUserInfo || !userID || !username) {
       return null;
     }
 
     if (isViewerProfile) {
       const privateThreadInfo: ?ThreadInfo = privateThreadInfos[0];
 
       return privateThreadInfo ? { threadInfo: privateThreadInfo } : null;
     }
 
     if (usersWithPersonalThread.has(userID)) {
       const personalThreadInfo: ?ThreadInfo = personalThreadInfos.find(
         threadInfo =>
           userID === getSingleOtherUser(threadInfo, loggedInUserInfo.id),
       );
 
       return personalThreadInfo ? { threadInfo: personalThreadInfo } : null;
     }
 
     const pendingPersonalThreadInfo = createPendingPersonalThread(
       loggedInUserInfo,
       userID,
       username,
     );
 
     return pendingPersonalThreadInfo;
   }, [
     isViewerProfile,
     loggedInUserInfo,
     personalThreadInfos,
     privateThreadInfos,
     userID,
     username,
     usersWithPersonalThread,
   ]);
 }
 
+function useChatMentionSearchIndex(): {
+  +[id: string]: SentencePrefixSearchIndex,
+} {
+  const { chatMentionCandidatesObj } = useChatMentionCandidatesObjAndUtils();
+  return React.useMemo(() => {
+    const result = {};
+    for (const communityThreadID in chatMentionCandidatesObj) {
+      const searchIndex = new SentencePrefixSearchIndex();
+      const searchIndexEntries = [];
+      for (const threadID in chatMentionCandidatesObj[communityThreadID]) {
+        searchIndexEntries.push({
+          id: threadID,
+          uiName: chatMentionCandidatesObj[communityThreadID][threadID].uiName,
+        });
+      }
+      // Sort the keys so that the order of the search result is consistent
+      searchIndexEntries.sort(({ uiName: uiNameA }, { uiName: uiNameB }) =>
+        uiNameA.localeCompare(uiNameB),
+      );
+      for (const { id, uiName } of searchIndexEntries) {
+        searchIndex.addEntry(id, uiName);
+      }
+      result[communityThreadID] = searchIndex;
+    }
+    return result;
+  }, [chatMentionCandidatesObj]);
+}
+
+function useThreadChatMentionSearchIndex(
+  threadInfo: ThreadInfo,
+): SentencePrefixSearchIndex {
+  const chatMentionCandidatesSearchIndex = useChatMentionSearchIndex();
+  const { communityThreadIDForGenesisThreads } =
+    useChatMentionCandidatesObjAndUtils();
+  if (threadInfo.community === genesis.id) {
+    return chatMentionCandidatesSearchIndex[
+      communityThreadIDForGenesisThreads[threadInfo.id]
+    ];
+  }
+  return chatMentionCandidatesSearchIndex[
+    threadInfo.community ?? threadInfo.id
+  ];
+}
+
 export {
   threadHasPermission,
   viewerIsMember,
   threadInChatList,
   threadIsTopLevel,
   threadIsChannel,
   threadIsSidebar,
   threadInBackgroundChatList,
   threadInHomeChatList,
   threadIsInHome,
   threadInFilterList,
   userIsMember,
   threadActualMembers,
   threadOtherMembers,
   threadIsGroupChat,
   threadIsPending,
   threadIsPendingSidebar,
   getSingleOtherUser,
   getPendingThreadID,
   parsePendingThreadID,
   createPendingThread,
   createUnresolvedPendingSidebar,
   extractNewMentionedParentMembers,
   createPendingSidebar,
   pendingThreadType,
   createRealThreadFromPendingThread,
   getCurrentUser,
   threadFrozenDueToBlock,
   threadFrozenDueToViewerBlock,
   rawThreadInfoFromServerThreadInfo,
   threadUIName,
   threadInfoFromRawThreadInfo,
   threadTypeDescriptions,
   memberIsAdmin,
   memberHasAdminPowers,
   roleIsAdminRole,
   threadHasAdminRole,
   identifyInvalidatedThreads,
   permissionsDisabledByBlock,
   emptyItemText,
   threadNoun,
   threadLabel,
   useWatchThread,
   useExistingThreadInfoFinder,
   getThreadTypeParentRequirement,
   threadMemberHasPermission,
   useCanCreateSidebarFromMessage,
   useSidebarExistsOrCanBeCreated,
   checkIfDefaultMembersAreVoiced,
   draftKeySuffix,
   draftKeyFromThreadID,
   threadTypeCanBePending,
   getContainingThreadID,
   getCommunity,
   getThreadListSearchResults,
   useThreadListSearch,
   removeMemberFromThread,
   switchMemberAdminRoleInThread,
   getAvailableThreadMemberActions,
   threadMembersWithoutAddedAshoat,
   validChatNameRegex,
   chatNameMaxLength,
   patchThreadInfoToIncludeMentionedMembersOfParent,
   threadInfoInsideCommunity,
   useRoleMemberCountsForCommunity,
   useRoleUserSurfacedPermissions,
   getThreadsToDeleteText,
   useChatMentionCandidatesObj,
   useThreadChatMentionCandidates,
   useUserProfileThreadInfo,
+  useThreadChatMentionSearchIndex,
 };