diff --git a/lib/shared/message-utils.js b/lib/shared/message-utils.js
index 7a1f84e63..20b49cf22 100644
--- a/lib/shared/message-utils.js
+++ b/lib/shared/message-utils.js
@@ -1,564 +1,578 @@
 // @flow
 
 import invariant from 'invariant';
 import _maxBy from 'lodash/fp/maxBy.js';
 import _orderBy from 'lodash/fp/orderBy.js';
 import * as React from 'react';
 
 import { codeBlockRegex, type ParserRules } from './markdown.js';
+import type { CreationSideEffectsFunc } from './messages/message-spec.js';
 import { messageSpecs } from './messages/message-specs.js';
 import { threadIsGroupChat } from './thread-utils.js';
 import { useStringForUser } from '../hooks/ens-cache.js';
 import { userIDsToRelativeUserInfos } from '../selectors/user-selectors.js';
 import type { PlatformDetails } from '../types/device-types.js';
 import type { Media } from '../types/media-types.js';
 import {
   type MessageInfo,
   type RawMessageInfo,
   type RobotextMessageInfo,
   type RawMultimediaMessageInfo,
   type MessageData,
   type MessageTruncationStatus,
   type MultimediaMessageData,
   type MessageStore,
   type ComposableMessageInfo,
   messageTypes,
   messageTruncationStatus,
   type RawComposableMessageInfo,
   type ThreadMessageInfo,
 } from '../types/message-types.js';
 import type { ImagesMessageData } from '../types/messages/images.js';
 import type { MediaMessageData } from '../types/messages/media.js';
 import type {
   RawReactionMessageInfo,
   ReactionMessageInfo,
 } from '../types/messages/reaction.js';
 import { type ThreadInfo } from '../types/thread-types.js';
 import type { UserInfos } from '../types/user-types.js';
 import {
   type EntityText,
   useEntityTextAsString,
 } from '../utils/entity-text.js';
 
 const localIDPrefix = 'local';
 
 // Prefers localID
 function messageKey(messageInfo: MessageInfo | RawMessageInfo): string {
   if (messageInfo.localID) {
     return messageInfo.localID;
   }
   invariant(messageInfo.id, 'localID should exist if ID does not');
   return messageInfo.id;
 }
 
 // Prefers serverID
 function messageID(messageInfo: MessageInfo | RawMessageInfo): string {
   if (messageInfo.id) {
     return messageInfo.id;
   }
   invariant(messageInfo.localID, 'localID should exist if ID does not');
   return messageInfo.localID;
 }
 
 function robotextForMessageInfo(
   messageInfo: RobotextMessageInfo,
   threadInfo: ?ThreadInfo,
 ): EntityText {
   const messageSpec = messageSpecs[messageInfo.type];
   invariant(
     messageSpec.robotext,
     `we're not aware of messageType ${messageInfo.type}`,
   );
   return messageSpec.robotext(messageInfo, { threadInfo });
 }
 
 function createMessageInfo(
   rawMessageInfo: RawMessageInfo,
   viewerID: ?string,
   userInfos: UserInfos,
   threadInfos: { +[id: string]: ThreadInfo },
 ): ?MessageInfo {
   const creatorInfo = userInfos[rawMessageInfo.creatorID];
   const creator = {
     id: rawMessageInfo.creatorID,
     username: creatorInfo ? creatorInfo.username : 'anonymous',
     isViewer: rawMessageInfo.creatorID === viewerID,
   };
 
   const createRelativeUserInfos = (userIDs: $ReadOnlyArray<string>) =>
     userIDsToRelativeUserInfos(userIDs, viewerID, userInfos);
   const createMessageInfoFromRaw = (rawInfo: RawMessageInfo) =>
     createMessageInfo(rawInfo, viewerID, userInfos, threadInfos);
 
   const messageSpec = messageSpecs[rawMessageInfo.type];
 
   return messageSpec.createMessageInfo(rawMessageInfo, creator, {
     threadInfos,
     createMessageInfoFromRaw,
     createRelativeUserInfos,
   });
 }
 
 type LengthResult = {
   +local: number,
   +realized: number,
 };
 function findMessageIDMaxLengths(
   messageIDs: $ReadOnlyArray<?string>,
 ): LengthResult {
   const result = {
     local: 0,
     realized: 0,
   };
   for (const id of messageIDs) {
     if (!id) {
       continue;
     }
     if (id.startsWith(localIDPrefix)) {
       result.local = Math.max(result.local, id.length - localIDPrefix.length);
     } else {
       result.realized = Math.max(result.realized, id.length);
     }
   }
   return result;
 }
 
 function extendMessageID(id: ?string, lengths: LengthResult): ?string {
   if (!id) {
     return id;
   }
   if (id.startsWith(localIDPrefix)) {
     const zeroPaddedID = id
       .substr(localIDPrefix.length)
       .padStart(lengths.local, '0');
     return `${localIDPrefix}${zeroPaddedID}`;
   }
   return id.padStart(lengths.realized, '0');
 }
 
 function sortMessageInfoList<T: MessageInfo | RawMessageInfo>(
   messageInfos: $ReadOnlyArray<T>,
 ): T[] {
   const lengths = findMessageIDMaxLengths(
     messageInfos.map(message => message?.id),
   );
   return _orderBy([
     'time',
     (message: T) => extendMessageID(message?.id, lengths),
   ])(['desc', 'desc'])(messageInfos);
 }
 
 const sortMessageIDs: (messages: { +[id: string]: RawMessageInfo }) => (
   messageIDs: $ReadOnlyArray<string>,
 ) => string[] = messages => messageIDs => {
   const lengths = findMessageIDMaxLengths(messageIDs);
   return _orderBy([
     (id: string) => messages[id].time,
     (id: string) => extendMessageID(id, lengths),
   ])(['desc', 'desc'])(messageIDs);
 };
 
 function rawMessageInfoFromMessageData(
   messageData: MessageData,
   id: ?string,
 ): RawMessageInfo {
   const messageSpec = messageSpecs[messageData.type];
   invariant(
     messageSpec.rawMessageInfoFromMessageData,
     `we're not aware of messageType ${messageData.type}`,
   );
   return messageSpec.rawMessageInfoFromMessageData(messageData, id);
 }
 
 function mostRecentMessageTimestamp(
   messageInfos: $ReadOnlyArray<RawMessageInfo>,
   previousTimestamp: number,
 ): number {
   if (messageInfos.length === 0) {
     return previousTimestamp;
   }
   return _maxBy('time')(messageInfos).time;
 }
 
 function usersInMessageInfos(
   messageInfos: $ReadOnlyArray<MessageInfo | RawMessageInfo>,
 ): string[] {
   const userIDs = new Set();
   for (const messageInfo of messageInfos) {
     if (messageInfo.creatorID) {
       userIDs.add(messageInfo.creatorID);
     } else if (messageInfo.creator) {
       userIDs.add(messageInfo.creator.id);
     }
   }
   return [...userIDs];
 }
 
 function combineTruncationStatuses(
   first: MessageTruncationStatus,
   second: ?MessageTruncationStatus,
 ): MessageTruncationStatus {
   if (
     first === messageTruncationStatus.EXHAUSTIVE ||
     second === messageTruncationStatus.EXHAUSTIVE
   ) {
     return messageTruncationStatus.EXHAUSTIVE;
   } else if (
     first === messageTruncationStatus.UNCHANGED &&
     second !== null &&
     second !== undefined
   ) {
     return second;
   } else {
     return first;
   }
 }
 
 function shimUnsupportedRawMessageInfos(
   rawMessageInfos: $ReadOnlyArray<RawMessageInfo>,
   platformDetails: ?PlatformDetails,
 ): RawMessageInfo[] {
   if (platformDetails && platformDetails.platform === 'web') {
     return [...rawMessageInfos];
   }
   return rawMessageInfos.map(rawMessageInfo => {
     const { shimUnsupportedMessageInfo } = messageSpecs[rawMessageInfo.type];
     if (shimUnsupportedMessageInfo) {
       return shimUnsupportedMessageInfo(rawMessageInfo, platformDetails);
     }
     return rawMessageInfo;
   });
 }
 
 type MediaMessageDataCreationInput = {
   +threadID: string,
   +creatorID: string,
   +media: $ReadOnlyArray<Media>,
   +localID?: ?string,
   +time?: ?number,
   +sidebarCreation?: ?boolean,
   ...
 };
 function createMediaMessageData(
   input: MediaMessageDataCreationInput,
 ): MultimediaMessageData {
   let allMediaArePhotos = true;
   const photoMedia = [];
   for (const singleMedia of input.media) {
     if (singleMedia.type === 'video') {
       allMediaArePhotos = false;
       break;
     } else {
       photoMedia.push(singleMedia);
     }
   }
 
   const { localID, threadID, creatorID, sidebarCreation } = input;
   const time = input.time ? input.time : Date.now();
   let messageData;
   if (allMediaArePhotos) {
     messageData = ({
       type: messageTypes.IMAGES,
       threadID,
       creatorID,
       time,
       media: photoMedia,
     }: ImagesMessageData);
     if (localID) {
       messageData = { ...messageData, localID };
     }
     if (sidebarCreation) {
       messageData = { ...messageData, sidebarCreation };
     }
   } else {
     messageData = ({
       type: messageTypes.MULTIMEDIA,
       threadID,
       creatorID,
       time,
       media: input.media,
     }: MediaMessageData);
     if (localID) {
       messageData = { ...messageData, localID };
     }
     if (sidebarCreation) {
       messageData = { ...messageData, sidebarCreation };
     }
   }
   return messageData;
 }
 
 type MediaMessageInfoCreationInput = {
   ...$Exact<MediaMessageDataCreationInput>,
   +id?: ?string,
 };
 function createMediaMessageInfo(
   input: MediaMessageInfoCreationInput,
 ): RawMultimediaMessageInfo {
   const messageData = createMediaMessageData(input);
   const createRawMessageInfo =
     messageSpecs[messageData.type].rawMessageInfoFromMessageData;
   invariant(
     createRawMessageInfo,
     'multimedia message spec should have rawMessageInfoFromMessageData',
   );
   const result = createRawMessageInfo(messageData, input.id);
   invariant(
     result.type === messageTypes.MULTIMEDIA ||
       result.type === messageTypes.IMAGES,
     `media messageSpec returned MessageType ${result.type}`,
   );
   return result;
 }
 
 function stripLocalID(
   rawMessageInfo: RawComposableMessageInfo | RawReactionMessageInfo,
 ) {
   const { localID, ...rest } = rawMessageInfo;
   return rest;
 }
 
 function stripLocalIDs(
   input: $ReadOnlyArray<RawMessageInfo>,
 ): RawMessageInfo[] {
   const output = [];
   for (const rawMessageInfo of input) {
     if (rawMessageInfo.localID) {
       invariant(
         rawMessageInfo.id,
         'serverID should be set if localID is being stripped',
       );
       output.push(stripLocalID(rawMessageInfo));
     } else {
       output.push(rawMessageInfo);
     }
   }
   return output;
 }
 
 // Normally we call trim() to remove whitespace at the beginning and end of each
 // message. However, our Markdown parser supports a "codeBlock" format where the
 // user can indent each line to indicate a code block. If we match the
 // corresponding RegEx, we'll only trim whitespace off the end.
 function trimMessage(message: string): string {
   message = message.replace(/^\n*/, '');
   return codeBlockRegex.exec(message) ? message.trimEnd() : message.trim();
 }
 
 function createMessageQuote(message: string): string {
   // add `>` to each line to include empty lines in the quote
   return message.replace(/^/gm, '> ');
 }
 
 function createMessageReply(message: string): string {
   return createMessageQuote(message) + '\n\n';
 }
 
 function getMostRecentNonLocalMessageID(
   threadID: string,
   messageStore: MessageStore,
 ): ?string {
   const thread = messageStore.threads[threadID];
   return thread?.messageIDs.find(id => !id.startsWith(localIDPrefix));
 }
 
 function getMessageTitle(
   messageInfo:
     | ComposableMessageInfo
     | RobotextMessageInfo
     | ReactionMessageInfo,
   threadInfo: ThreadInfo,
   markdownRules: ParserRules,
 ): EntityText {
   const { messageTitle } = messageSpecs[messageInfo.type];
   if (messageTitle) {
     return messageTitle({ messageInfo, threadInfo, markdownRules });
   }
 
   invariant(
     messageInfo.type !== messageTypes.TEXT &&
       messageInfo.type !== messageTypes.IMAGES &&
       messageInfo.type !== messageTypes.MULTIMEDIA &&
       messageInfo.type !== messageTypes.REACTION,
     'messageTitle can only be auto-generated for RobotextMessageInfo',
   );
   return robotextForMessageInfo(messageInfo, threadInfo);
 }
 
 function mergeThreadMessageInfos(
   first: ThreadMessageInfo,
   second: ThreadMessageInfo,
   messages: { +[id: string]: RawMessageInfo },
 ): ThreadMessageInfo {
   let firstPointer = 0;
   let secondPointer = 0;
   const mergedMessageIDs = [];
   let firstCandidate = first.messageIDs[firstPointer];
   let secondCandidate = second.messageIDs[secondPointer];
   while (firstCandidate !== undefined || secondCandidate !== undefined) {
     if (firstCandidate === undefined) {
       mergedMessageIDs.push(secondCandidate);
       secondPointer++;
     } else if (secondCandidate === undefined) {
       mergedMessageIDs.push(firstCandidate);
       firstPointer++;
     } else if (firstCandidate === secondCandidate) {
       mergedMessageIDs.push(firstCandidate);
       firstPointer++;
       secondPointer++;
     } else {
       const firstMessage = messages[firstCandidate];
       const secondMessage = messages[secondCandidate];
       invariant(
         firstMessage && secondMessage,
         'message in messageIDs not present in MessageStore',
       );
       if (
         (firstMessage.id &&
           secondMessage.id &&
           firstMessage.id === secondMessage.id) ||
         (firstMessage.localID &&
           secondMessage.localID &&
           firstMessage.localID === secondMessage.localID)
       ) {
         mergedMessageIDs.push(firstCandidate);
         firstPointer++;
         secondPointer++;
       } else if (firstMessage.time < secondMessage.time) {
         mergedMessageIDs.push(secondCandidate);
         secondPointer++;
       } else {
         mergedMessageIDs.push(firstCandidate);
         firstPointer++;
       }
     }
     firstCandidate = first.messageIDs[firstPointer];
     secondCandidate = second.messageIDs[secondPointer];
   }
   return {
     messageIDs: mergedMessageIDs,
     startReached: first.startReached && second.startReached,
     lastNavigatedTo: Math.max(first.lastNavigatedTo, second.lastNavigatedTo),
     lastPruned: Math.max(first.lastPruned, second.lastPruned),
   };
 }
 
 type MessagePreviewPart = {
   +text: string,
   // unread has highest contrast, followed by primary, followed by secondary
   +style: 'unread' | 'primary' | 'secondary',
 };
 type MessagePreviewResult = {
   +message: MessagePreviewPart,
   +username: ?MessagePreviewPart,
 };
 function useMessagePreview(
   originalMessageInfo: ?MessageInfo,
   threadInfo: ThreadInfo,
   markdownRules: ParserRules,
 ): ?MessagePreviewResult {
   let messageInfo;
   if (
     originalMessageInfo &&
     originalMessageInfo.type === messageTypes.SIDEBAR_SOURCE
   ) {
     messageInfo = originalMessageInfo.sourceMessage;
   } else {
     messageInfo = originalMessageInfo;
   }
 
   const hasUsername =
     threadIsGroupChat(threadInfo) ||
     threadInfo.name !== '' ||
     messageInfo?.creator.isViewer;
   const shouldDisplayUser =
     messageInfo?.type === messageTypes.TEXT && hasUsername;
 
   const stringForUser = useStringForUser(
     shouldDisplayUser ? messageInfo?.creator : null,
   );
 
   const { unread } = threadInfo.currentUser;
   const username = React.useMemo(() => {
     if (!shouldDisplayUser) {
       return null;
     }
     invariant(
       stringForUser,
       'useStringForUser should only return falsey if pass null or undefined',
     );
     return {
       text: stringForUser,
       style: unread ? 'unread' : 'secondary',
     };
   }, [shouldDisplayUser, stringForUser, unread]);
 
   const messageTitleEntityText = React.useMemo(() => {
     if (!messageInfo) {
       return messageInfo;
     }
     return getMessageTitle(messageInfo, threadInfo, markdownRules);
   }, [messageInfo, threadInfo, markdownRules]);
 
   const threadID = threadInfo.id;
   const entityTextToStringParams = React.useMemo(
     () => ({
       threadID,
     }),
     [threadID],
   );
   const messageTitle = useEntityTextAsString(
     messageTitleEntityText,
     entityTextToStringParams,
   );
 
   const isTextMessage = messageInfo?.type === messageTypes.TEXT;
   const message = React.useMemo(() => {
     if (messageTitle === null || messageTitle === undefined) {
       return messageTitle;
     }
 
     let style;
     if (unread) {
       style = 'unread';
     } else if (isTextMessage) {
       style = 'primary';
     } else {
       style = 'secondary';
     }
 
     return { text: messageTitle, style };
   }, [messageTitle, unread, isTextMessage]);
 
   return React.useMemo(() => {
     if (!message) {
       return message;
     }
     return { message, username };
   }, [message, username]);
 }
 
+function useMessageCreationSideEffectsFunc<Info: RawMessageInfo>(
+  messageType: $PropertyType<Info, 'type'>,
+): CreationSideEffectsFunc<Info> {
+  const messageSpec = messageSpecs[messageType];
+  invariant(messageSpec, `we're not aware of messageType ${messageType}`);
+  invariant(
+    messageSpec.useCreationSideEffectsFunc,
+    `no useCreationSideEffectsFunc in message spec for ${messageType}`,
+  );
+  return messageSpec.useCreationSideEffectsFunc();
+}
+
 export {
   localIDPrefix,
   messageKey,
   messageID,
   robotextForMessageInfo,
   createMessageInfo,
   sortMessageInfoList,
   sortMessageIDs,
   rawMessageInfoFromMessageData,
   mostRecentMessageTimestamp,
   usersInMessageInfos,
   combineTruncationStatuses,
   shimUnsupportedRawMessageInfos,
   createMediaMessageData,
   createMediaMessageInfo,
   stripLocalIDs,
   trimMessage,
   createMessageQuote,
   createMessageReply,
   getMostRecentNonLocalMessageID,
   getMessageTitle,
   mergeThreadMessageInfos,
   useMessagePreview,
+  useMessageCreationSideEffectsFunc,
 };
diff --git a/lib/shared/messages/message-spec.js b/lib/shared/messages/message-spec.js
index bf2066948..6b611e7b7 100644
--- a/lib/shared/messages/message-spec.js
+++ b/lib/shared/messages/message-spec.js
@@ -1,106 +1,113 @@
 // @flow
 
 import type { PlatformDetails } from '../../types/device-types.js';
 import type { Media } from '../../types/media-types.js';
 import type {
   MessageInfo,
   ClientDBMessageInfo,
   RawComposableMessageInfo,
   RawMessageInfo,
   RawRobotextMessageInfo,
 } from '../../types/message-types.js';
 import type { RawUnsupportedMessageInfo } from '../../types/messages/unsupported.js';
 import type { NotifTexts } from '../../types/notif-types.js';
 import type { ThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import type { EntityText } from '../../utils/entity-text.js';
 import { type ParserRules } from '../markdown.js';
 
 export type MessageTitleParam<Info> = {
   +messageInfo: Info,
   +threadInfo: ThreadInfo,
   +markdownRules: ParserRules,
 };
 
 export type RawMessageInfoFromServerDBRowParams = {
   +localID: ?string,
   +media?: $ReadOnlyArray<Media>,
   +derivedMessages: $ReadOnlyMap<
     string,
     RawComposableMessageInfo | RawRobotextMessageInfo,
   >,
 };
 
 export type CreateMessageInfoParams = {
   +threadInfos: { +[id: string]: ThreadInfo },
   +createMessageInfoFromRaw: (rawInfo: RawMessageInfo) => ?MessageInfo,
   +createRelativeUserInfos: (
     userIDs: $ReadOnlyArray<string>,
   ) => RelativeUserInfo[],
 };
 
 export type RobotextParams = {
   +threadInfo: ?ThreadInfo,
 };
 
 export type NotificationTextsParams = {
   +notificationTexts: (
     messageInfos: $ReadOnlyArray<MessageInfo>,
     threadInfo: ThreadInfo,
   ) => Promise<NotifTexts>,
 };
 
 export type GeneratesNotifsParams = {
   +notifTargetUserID: string,
   +userNotMemberOfSubthreads: Set<string>,
   +fetchMessageInfoByID: (messageID: string) => Promise<?RawMessageInfo>,
 };
 
 export const pushTypes = Object.freeze({
   NOTIF: 'notif',
   RESCIND: 'rescind',
 });
 export type PushType = $Values<typeof pushTypes>;
 
+export type CreationSideEffectsFunc<RawInfo> = (
+  messageInfo: RawInfo,
+  threadInfo: ThreadInfo,
+  parentThreadInfo: ?ThreadInfo,
+) => Promise<mixed>;
+
 export type MessageSpec<Data, RawInfo, Info> = {
   +messageContentForServerDB?: (data: Data | RawInfo) => string,
   +messageContentForClientDB?: (data: RawInfo) => string,
   +messageTitle?: (param: MessageTitleParam<Info>) => EntityText,
   +rawMessageInfoFromServerDBRow?: (
     row: Object,
     params: RawMessageInfoFromServerDBRowParams,
   ) => ?RawInfo,
   +rawMessageInfoFromClientDB: (
     clientDBMessageInfo: ClientDBMessageInfo,
   ) => RawInfo,
   +createMessageInfo: (
     rawMessageInfo: RawInfo,
     creator: RelativeUserInfo,
     params: CreateMessageInfoParams,
   ) => ?Info,
   +rawMessageInfoFromMessageData?: (messageData: Data, id: ?string) => RawInfo,
   +robotext?: (messageInfo: Info, params: RobotextParams) => EntityText,
   +shimUnsupportedMessageInfo?: (
     rawMessageInfo: RawInfo,
     platformDetails: ?PlatformDetails,
   ) => RawInfo | RawUnsupportedMessageInfo,
   +unshimMessageInfo?: (
     unwrapped: RawInfo,
     messageInfo: RawMessageInfo,
   ) => ?RawMessageInfo,
   +notificationTexts?: (
     messageInfos: $ReadOnlyArray<MessageInfo>,
     threadInfo: ThreadInfo,
     params: NotificationTextsParams,
   ) => Promise<NotifTexts>,
   +notificationCollapseKey?: (rawMessageInfo: RawInfo) => string,
   +generatesNotifs: (
     rawMessageInfo: RawInfo,
     messageData: Data,
     params: GeneratesNotifsParams,
   ) => Promise<?PushType>,
   +userIDs?: (rawMessageInfo: RawInfo) => $ReadOnlyArray<string>,
   +startsThread?: boolean,
   +threadIDs?: (rawMessageInfo: RawInfo) => $ReadOnlyArray<string>,
   +includedInRepliesCount?: boolean,
+  +useCreationSideEffectsFunc?: () => CreationSideEffectsFunc<RawInfo>,
 };