diff --git a/lib/shared/messages/create-thread-message-spec.js b/lib/shared/messages/create-thread-message-spec.js
index 91fc565b5..301fd6ac2 100644
--- a/lib/shared/messages/create-thread-message-spec.js
+++ b/lib/shared/messages/create-thread-message-spec.js
@@ -1,125 +1,127 @@
 // @flow
 
 import invariant from 'invariant';
 
 import { messageTypes } from '../../types/message-types';
 import type {
   CreateThreadMessageData,
   CreateThreadMessageInfo,
   RawCreateThreadMessageInfo,
 } from '../../types/message/create-thread';
 import { stringForUser } from '../user-utils';
 import type { MessageSpec } from './message-spec';
 import { assertSingleMessageInfo } from './utils';
 
 export const createThreadMessageSpec: MessageSpec<
   CreateThreadMessageData,
   RawCreateThreadMessageInfo,
   CreateThreadMessageInfo,
 > = Object.freeze({
   messageContent(data) {
     return JSON.stringify(data.initialThreadState);
   },
 
   rawMessageInfoFromRow(row) {
     return {
       type: messageTypes.CREATE_THREAD,
       id: row.id.toString(),
       threadID: row.threadID.toString(),
       time: row.time,
       creatorID: row.creatorID.toString(),
       initialThreadState: JSON.parse(row.content),
     };
   },
 
   createMessageInfo(rawMessageInfo, creator, params) {
     const initialParentThreadID =
       rawMessageInfo.initialThreadState.parentThreadID;
     const parentThreadInfo = initialParentThreadID
       ? params.threadInfos[initialParentThreadID]
       : null;
 
     return {
       type: messageTypes.CREATE_THREAD,
       id: rawMessageInfo.id,
       threadID: rawMessageInfo.threadID,
       creator,
       time: rawMessageInfo.time,
       initialThreadState: {
         name: rawMessageInfo.initialThreadState.name,
         parentThreadInfo,
         type: rawMessageInfo.initialThreadState.type,
         color: rawMessageInfo.initialThreadState.color,
         otherMembers: params.createRelativeUserInfos(
           rawMessageInfo.initialThreadState.memberIDs.filter(
             (userID: string) => userID !== rawMessageInfo.creatorID,
           ),
         ),
       },
     };
   },
 
   rawMessageInfoFromMessageData(messageData, id) {
     return { ...messageData, id };
   },
 
   robotext(messageInfo, creator, params) {
     let text = `created ${params.encodedThreadEntity(
       messageInfo.threadID,
       `this thread`,
     )}`;
     const parentThread = messageInfo.initialThreadState.parentThreadInfo;
     if (parentThread) {
       text +=
         ' as a child of ' +
         `<${encodeURI(parentThread.uiName)}|t${parentThread.id}>`;
     }
     if (messageInfo.initialThreadState.name) {
       text += ` with the name "${encodeURI(
         messageInfo.initialThreadState.name,
       )}"`;
     }
     const users = messageInfo.initialThreadState.otherMembers;
     if (users.length !== 0) {
       const initialUsersString = params.robotextForUsers(users);
       text += ` and added ${initialUsersString}`;
     }
     return `${creator} ${text}`;
   },
 
   notificationTexts(messageInfos, threadInfo, params) {
     const messageInfo = assertSingleMessageInfo(messageInfos);
     invariant(
       messageInfo.type === messageTypes.CREATE_THREAD,
       'messageInfo should be messageTypes.CREATE_THREAD!',
     );
     const parentThreadInfo = messageInfo.initialThreadState.parentThreadInfo;
     if (parentThreadInfo) {
       return params.notifTextForSubthreadCreation(
         messageInfo.creator,
         messageInfo.initialThreadState.type,
         parentThreadInfo,
         messageInfo.initialThreadState.name,
         threadInfo.uiName,
       );
     }
     const prefix = stringForUser(messageInfo.creator);
     const body = 'created a new thread';
     let merged = `${prefix} ${body}`;
     if (messageInfo.initialThreadState.name) {
       merged += ` called "${messageInfo.initialThreadState.name}"`;
     }
     return {
       merged,
       body,
       title: threadInfo.uiName,
       prefix,
     };
   },
 
   generatesNotifs: true,
 
   userIDs(rawMessageInfo) {
     return rawMessageInfo.initialThreadState.memberIDs;
   },
+
+  startsThread: true,
 });
diff --git a/lib/shared/messages/message-spec.js b/lib/shared/messages/message-spec.js
index df8e95293..2d0ea612d 100644
--- a/lib/shared/messages/message-spec.js
+++ b/lib/shared/messages/message-spec.js
@@ -1,81 +1,82 @@
 // @flow
 
 import type { PlatformDetails } from '../../types/device-types';
 import type { Media } from '../../types/media-types';
 import type {
   MessageInfo,
   RawComposableMessageInfo,
   RawMessageInfo,
   RawRobotextMessageInfo,
   RobotextMessageInfo,
 } from '../../types/message-types';
 import type { RawUnsupportedMessageInfo } from '../../types/message/unsupported';
 import type { NotifTexts } from '../../types/notif-types';
 import type { ThreadInfo, ThreadType } from '../../types/thread-types';
 import type { RelativeUserInfo } from '../../types/user-types';
 
 export type MessageSpec<Data, RawInfo, Info> = {|
   +messageContent?: (data: Data) => string | null,
   +rawMessageInfoFromRow?: (
     row: Object,
     params: {|
       +localID: string,
       +media?: $ReadOnlyArray<Media>,
       +derivedMessages: $ReadOnlyMap<
         string,
         RawComposableMessageInfo | RawRobotextMessageInfo,
       >,
     |},
   ) => ?RawInfo,
   +createMessageInfo: (
     rawMessageInfo: RawInfo,
     creator: RelativeUserInfo,
     params: {|
       +threadInfos: {| [id: string]: ThreadInfo |},
       +createMessageInfoFromRaw: (rawInfo: RawMessageInfo) => MessageInfo,
       +createRelativeUserInfos: (
         userIDs: $ReadOnlyArray<string>,
       ) => RelativeUserInfo[],
     |},
   ) => ?Info,
   +rawMessageInfoFromMessageData?: (messageData: Data, id: string) => RawInfo,
   +robotext?: (
     messageInfo: Info,
     creator: string,
     params: {|
       +encodedThreadEntity: (threadID: string, text: string) => string,
       +robotextForUsers: (users: RelativeUserInfo[]) => string,
       +robotextForUser: (user: RelativeUserInfo) => string,
       +threadInfo: ThreadInfo,
     |},
   ) => string,
   +shimUnsupportedMessageInfo?: (
     rawMessageInfo: RawInfo,
     platformDetails: ?PlatformDetails,
   ) => RawInfo | RawUnsupportedMessageInfo,
   +notificationTexts?: (
     messageInfos: $ReadOnlyArray<MessageInfo>,
     threadInfo: ThreadInfo,
     params: {|
       +notifThreadName: (threadInfo: ThreadInfo) => string,
       +notifTextForSubthreadCreation: (
         creator: RelativeUserInfo,
         threadType: ThreadType,
         parentThreadInfo: ThreadInfo,
         childThreadName: ?string,
         childThreadUIName: string,
       ) => NotifTexts,
       +strippedRobotextForMessageInfo: (
         messageInfo: RobotextMessageInfo,
         threadInfo: ThreadInfo,
       ) => string,
       +notificationTexts: (
         messageInfos: $ReadOnlyArray<MessageInfo>,
         threadInfo: ThreadInfo,
       ) => NotifTexts,
     |},
   ) => NotifTexts,
   +notificationCollapseKey?: (rawMessageInfo: RawInfo) => ?string,
   +generatesNotifs: boolean,
   +userIDs?: (rawMessageInfo: RawInfo) => $ReadOnlyArray<string>,
+  +startsThread?: boolean,
 |};
diff --git a/lib/shared/messages/sidebar-source-message-spec.js b/lib/shared/messages/sidebar-source-message-spec.js
index a8673d473..9f52d1811 100644
--- a/lib/shared/messages/sidebar-source-message-spec.js
+++ b/lib/shared/messages/sidebar-source-message-spec.js
@@ -1,108 +1,110 @@
 // @flow
 
 import invariant from 'invariant';
 
 import type {
   RawSidebarSourceMessageInfo,
   SidebarSourceMessageData,
   SidebarSourceMessageInfo,
 } from '../../types/message-types';
 import { messageTypes } from '../../types/message-types';
 import { hasMinCodeVersion } from '../version-utils';
 import type { MessageSpec } from './message-spec';
 import { assertSingleMessageInfo } from './utils';
 
 export const sidebarSourceMessageSpec: MessageSpec<
   SidebarSourceMessageData,
   RawSidebarSourceMessageInfo,
   SidebarSourceMessageInfo,
 > = Object.freeze({
   messageContent(data) {
     const sourceMessageID = data.sourceMessage?.id;
     invariant(sourceMessageID, 'Source message id should be set');
     return JSON.stringify({
       sourceMessageID,
     });
   },
 
   rawMessageInfoFromRow(row, params) {
     const { derivedMessages } = params;
     invariant(derivedMessages, 'Derived messages should be provided');
 
     const content = JSON.parse(row.content);
     const sourceMessage = derivedMessages.get(content.sourceMessageID);
     if (!sourceMessage) {
       console.warn(
         `Message with id ${row.id} has a derived message ` +
           `${content.sourceMessageID} which is not present in the database`,
       );
     }
     return {
       type: messageTypes.SIDEBAR_SOURCE,
       id: row.id.toString(),
       threadID: row.threadID.toString(),
       time: row.time,
       creatorID: row.creatorID.toString(),
       sourceMessage,
     };
   },
 
   createMessageInfo(rawMessageInfo, creator, params) {
     if (!rawMessageInfo.sourceMessage) {
       return null;
     }
     const sourceMessage = params.createMessageInfoFromRaw(
       rawMessageInfo.sourceMessage,
     );
     invariant(
       sourceMessage && sourceMessage.type !== messageTypes.SIDEBAR_SOURCE,
       'Sidebars can not be created from SIDEBAR SOURCE',
     );
 
     return {
       type: messageTypes.SIDEBAR_SOURCE,
       id: rawMessageInfo.id,
       threadID: rawMessageInfo.threadID,
       creator,
       time: rawMessageInfo.time,
       sourceMessage,
     };
   },
 
   rawMessageInfoFromMessageData(messageData, id) {
     return { ...messageData, id };
   },
 
   shimUnsupportedMessageInfo(rawMessageInfo, platformDetails) {
     // TODO determine min code version
     if (
       hasMinCodeVersion(platformDetails, 75) &&
       rawMessageInfo.sourceMessage
     ) {
       return rawMessageInfo;
     }
     const { id } = rawMessageInfo;
     invariant(id !== null && id !== undefined, 'id should be set on server');
     return {
       type: messageTypes.UNSUPPORTED,
       id,
       threadID: rawMessageInfo.threadID,
       creatorID: rawMessageInfo.creatorID,
       time: rawMessageInfo.time,
       robotext: 'first message in sidebar',
       unsupportedMessageInfo: rawMessageInfo,
     };
   },
 
   notificationTexts(messageInfos, threadInfo, params) {
     const messageInfo = assertSingleMessageInfo(messageInfos);
     invariant(
       messageInfo.type === messageTypes.SIDEBAR_SOURCE,
       'messageInfo should be messageTypes.SIDEBAR_SOURCE!',
     );
     const sourceMessageInfo = messageInfo.sourceMessage;
     return params.notificationTexts([sourceMessageInfo], threadInfo);
   },
 
   generatesNotifs: false,
+
+  startsThread: true,
 });
diff --git a/server/src/fetchers/message-fetchers.js b/server/src/fetchers/message-fetchers.js
index 325d22466..dc0733335 100644
--- a/server/src/fetchers/message-fetchers.js
+++ b/server/src/fetchers/message-fetchers.js
@@ -1,599 +1,588 @@
 // @flow
 
 import invariant from 'invariant';
 
 import {
   sortMessageInfoList,
   shimUnsupportedRawMessageInfos,
 } from 'lib/shared/message-utils';
 import { messageSpecs } from 'lib/shared/messages/message-specs';
 import { notifCollapseKeyForRawMessageInfo } from 'lib/shared/notif-utils';
 import {
   type RawMessageInfo,
   messageTypes,
   type MessageType,
   assertMessageType,
   type ThreadSelectionCriteria,
   type MessageTruncationStatus,
   messageTruncationStatus,
   type FetchMessageInfosResult,
 } from 'lib/types/message-types';
 import { threadPermissions } from 'lib/types/thread-types';
 import { ServerError } from 'lib/utils/errors';
 
 import { dbQuery, SQL, mergeOrConditions } from '../database/database';
 import type { PushInfo } from '../push/send';
 import type { Viewer } from '../session/viewer';
 import { creationString, localIDFromCreationString } from '../utils/idempotent';
 import { mediaFromRow } from './upload-fetchers';
 
 export type CollapsableNotifInfo = {|
   collapseKey: ?string,
   existingMessageInfos: RawMessageInfo[],
   newMessageInfos: RawMessageInfo[],
 |};
 export type FetchCollapsableNotifsResult = {
   [userID: string]: CollapsableNotifInfo[],
 };
 
 // This function doesn't filter RawMessageInfos based on what messageTypes the
 // client supports, since each user can have multiple clients. The caller must
 // handle this filtering.
 async function fetchCollapsableNotifs(
   pushInfo: PushInfo,
 ): Promise<FetchCollapsableNotifsResult> {
   // First, we need to fetch any notifications that should be collapsed
   const usersToCollapseKeysToInfo = {};
   const usersToCollapsableNotifInfo = {};
   for (let userID in pushInfo) {
     usersToCollapseKeysToInfo[userID] = {};
     usersToCollapsableNotifInfo[userID] = [];
     for (let rawMessageInfo of pushInfo[userID].messageInfos) {
       const collapseKey = notifCollapseKeyForRawMessageInfo(rawMessageInfo);
       if (!collapseKey) {
         const collapsableNotifInfo = {
           collapseKey,
           existingMessageInfos: [],
           newMessageInfos: [rawMessageInfo],
         };
         usersToCollapsableNotifInfo[userID].push(collapsableNotifInfo);
         continue;
       }
       if (!usersToCollapseKeysToInfo[userID][collapseKey]) {
         usersToCollapseKeysToInfo[userID][collapseKey] = {
           collapseKey,
           existingMessageInfos: [],
           newMessageInfos: [],
         };
       }
       usersToCollapseKeysToInfo[userID][collapseKey].newMessageInfos.push(
         rawMessageInfo,
       );
     }
   }
 
   const sqlTuples = [];
   for (let userID in usersToCollapseKeysToInfo) {
     const collapseKeysToInfo = usersToCollapseKeysToInfo[userID];
     for (let collapseKey in collapseKeysToInfo) {
       sqlTuples.push(
         SQL`(n.user = ${userID} AND n.collapse_key = ${collapseKey})`,
       );
     }
   }
 
   if (sqlTuples.length === 0) {
     return usersToCollapsableNotifInfo;
   }
 
   const visPermissionExtractString = `$.${threadPermissions.VISIBLE}.value`;
   const collapseQuery = SQL`
     SELECT m.id, m.thread AS threadID, m.content, m.time, m.type,
       m.user AS creatorID, stm.permissions AS subthread_permissions, n.user,
       n.collapse_key, up.id AS uploadID, up.type AS uploadType,
       up.secret AS uploadSecret, up.extra AS uploadExtra
     FROM notifications n
     LEFT JOIN messages m ON m.id = n.message
     LEFT JOIN uploads up
       ON m.type IN (${[messageTypes.IMAGES, messageTypes.MULTIMEDIA]})
         AND JSON_CONTAINS(m.content, CAST(up.id as JSON), '$')
     LEFT JOIN memberships mm ON mm.thread = m.thread AND mm.user = n.user
     LEFT JOIN memberships stm
       ON m.type = ${messageTypes.CREATE_SUB_THREAD}
         AND stm.thread = m.content AND stm.user = n.user
     WHERE n.rescinded = 0 AND
       JSON_EXTRACT(mm.permissions, ${visPermissionExtractString}) IS TRUE AND
   `;
   collapseQuery.append(mergeOrConditions(sqlTuples));
   collapseQuery.append(SQL`ORDER BY m.time DESC`);
   const [collapseResult] = await dbQuery(collapseQuery);
 
   const rowsByUser = new Map();
   for (const row of collapseResult) {
     const user = row.user.toString();
     const currentRowsForUser = rowsByUser.get(user);
     if (currentRowsForUser) {
       currentRowsForUser.push(row);
     } else {
       rowsByUser.set(user, [row]);
     }
   }
 
   const derivedMessages = await fetchDerivedMessages(collapseResult);
   for (const userRows of rowsByUser.values()) {
     const messages = parseMessageSQLResult(userRows, derivedMessages);
     for (const message of messages) {
       const { rawMessageInfo, rows } = message;
       const [row] = rows;
       const info = usersToCollapseKeysToInfo[row.user][row.collapse_key];
       info.existingMessageInfos.push(rawMessageInfo);
     }
   }
 
   for (let userID in usersToCollapseKeysToInfo) {
     const collapseKeysToInfo = usersToCollapseKeysToInfo[userID];
     for (let collapseKey in collapseKeysToInfo) {
       const info = collapseKeysToInfo[collapseKey];
       usersToCollapsableNotifInfo[userID].push({
         collapseKey: info.collapseKey,
         existingMessageInfos: sortMessageInfoList(info.existingMessageInfos),
         newMessageInfos: sortMessageInfoList(info.newMessageInfos),
       });
     }
   }
 
   return usersToCollapsableNotifInfo;
 }
 
 type MessageSQLResult = $ReadOnlyArray<{|
   rawMessageInfo: RawMessageInfo,
   rows: $ReadOnlyArray<Object>,
 |}>;
 function parseMessageSQLResult(
   rows: $ReadOnlyArray<Object>,
   derivedMessages: $ReadOnlyMap<string, RawMessageInfo>,
   viewer?: Viewer,
 ): MessageSQLResult {
   const rowsByID = new Map();
   for (let row of rows) {
     const id = row.id.toString();
     const currentRowsForID = rowsByID.get(id);
     if (currentRowsForID) {
       currentRowsForID.push(row);
     } else {
       rowsByID.set(id, [row]);
     }
   }
 
   const messages = [];
   for (let messageRows of rowsByID.values()) {
     const rawMessageInfo = rawMessageInfoFromRows(
       messageRows,
       viewer,
       derivedMessages,
     );
     if (rawMessageInfo) {
       messages.push({ rawMessageInfo, rows: messageRows });
     }
   }
 
   return messages;
 }
 
 function assertSingleRow(rows: $ReadOnlyArray<Object>): Object {
   if (rows.length === 0) {
     throw new Error('expected single row, but none present!');
   } else if (rows.length !== 1) {
     const messageIDs = rows.map((row) => row.id.toString());
     console.warn(
       `expected single row, but there are multiple! ${messageIDs.join(', ')}`,
     );
   }
   return rows[0];
 }
 
 function mostRecentRowType(rows: $ReadOnlyArray<Object>): MessageType {
   if (rows.length === 0) {
     throw new Error('expected row, but none present!');
   }
   return assertMessageType(rows[0].type);
 }
 
 function rawMessageInfoFromRows(
   rows: $ReadOnlyArray<Object>,
   viewer?: Viewer,
   derivedMessages: $ReadOnlyMap<string, RawMessageInfo>,
 ): ?RawMessageInfo {
   const type = mostRecentRowType(rows);
   const messageSpec = messageSpecs[type];
 
   if (type === messageTypes.IMAGES || type === messageTypes.MULTIMEDIA) {
     const media = rows.filter((row) => row.uploadID).map(mediaFromRow);
     const [row] = rows;
     const localID = localIDFromCreationString(viewer, row.creation);
     return messageSpec.rawMessageInfoFromRow(row, {
       media,
       derivedMessages,
       localID,
     });
   }
 
   const row = assertSingleRow(rows);
   const localID = localIDFromCreationString(viewer, row.creation);
   invariant(
     messageSpec.rawMessageInfoFromRow,
     `unrecognized messageType ${type}`,
   );
   return messageSpec.rawMessageInfoFromRow(row, { derivedMessages, localID });
 }
 
 const visibleExtractString = `$.${threadPermissions.VISIBLE}.value`;
 
 async function fetchMessageInfos(
   viewer: Viewer,
   criteria: ThreadSelectionCriteria,
   numberPerThread: number,
 ): Promise<FetchMessageInfosResult> {
   const threadSelectionClause = threadSelectionCriteriaToSQLClause(criteria);
   const truncationStatuses = {};
 
   const viewerID = viewer.id;
   const query = SQL`
     SELECT * FROM (
       SELECT x.id, x.content, x.time, x.type, x.user AS creatorID,
         x.creation, x.subthread_permissions, x.uploadID, x.uploadType,
         x.uploadSecret, x.uploadExtra,
         @num := if(
           @thread = x.thread,
           if(@message = x.id, @num, @num + 1),
           1
         ) AS number,
         @message := x.id AS messageID,
         @thread := x.thread AS threadID
       FROM (SELECT @num := 0, @thread := '', @message := '') init
       JOIN (
         SELECT m.id, m.thread, m.user, m.content, m.time, m.type,
           m.creation, stm.permissions AS subthread_permissions,
           up.id AS uploadID, up.type AS uploadType, up.secret AS uploadSecret,
           up.extra AS uploadExtra
         FROM messages m
         LEFT JOIN uploads up
           ON m.type IN (${[messageTypes.IMAGES, messageTypes.MULTIMEDIA]})
             AND JSON_CONTAINS(m.content, CAST(up.id as JSON), '$')
         LEFT JOIN memberships mm
           ON mm.thread = m.thread AND mm.user = ${viewerID}
         LEFT JOIN memberships stm ON m.type = ${messageTypes.CREATE_SUB_THREAD}
           AND stm.thread = m.content AND stm.user = ${viewerID}
         WHERE JSON_EXTRACT(mm.permissions, ${visibleExtractString}) IS TRUE AND
   `;
   query.append(threadSelectionClause);
   query.append(SQL`
         ORDER BY m.thread, m.time DESC
       ) x
     ) y
     WHERE y.number <= ${numberPerThread}
   `);
   const [result] = await dbQuery(query);
   const derivedMessages = await fetchDerivedMessages(result, viewer);
   const messages = parseMessageSQLResult(result, derivedMessages, viewer);
 
   const rawMessageInfos = [];
   const threadToMessageCount = new Map();
-  for (let message of messages) {
+  for (const message of messages) {
     const { rawMessageInfo } = message;
     rawMessageInfos.push(rawMessageInfo);
     const { threadID } = rawMessageInfo;
     const currentCountValue = threadToMessageCount.get(threadID);
     const currentCount = currentCountValue ? currentCountValue : 0;
     threadToMessageCount.set(threadID, currentCount + 1);
   }
 
-  for (let [threadID, messageCount] of threadToMessageCount) {
+  for (const [threadID, messageCount] of threadToMessageCount) {
     // If there are fewer messages returned than the max for a given thread,
     // then our result set includes all messages in the query range for that
     // thread
     truncationStatuses[threadID] =
       messageCount < numberPerThread
         ? messageTruncationStatus.EXHAUSTIVE
         : messageTruncationStatus.TRUNCATED;
   }
 
-  for (let rawMessageInfo of rawMessageInfos) {
-    if (
-      rawMessageInfo.type === messageTypes.CREATE_THREAD ||
-      rawMessageInfo.type === messageTypes.SIDEBAR_SOURCE
-    ) {
-      // If a CREATE_THREAD or SIDEBAR_SOURCE message for a given thread is in
-      // the result set, then our result set includes all messages in the query
-      // range for that thread
+  for (const rawMessageInfo of rawMessageInfos) {
+    if (messageSpecs[rawMessageInfo.type].startsThread) {
       truncationStatuses[rawMessageInfo.threadID] =
         messageTruncationStatus.EXHAUSTIVE;
     }
   }
 
-  for (let threadID in criteria.threadCursors) {
+  for (const threadID in criteria.threadCursors) {
     const truncationStatus = truncationStatuses[threadID];
     if (truncationStatus === null || truncationStatus === undefined) {
       // If nothing was returned for a thread that was explicitly queried for,
       // then our result set includes all messages in the query range for that
       // thread
       truncationStatuses[threadID] = messageTruncationStatus.EXHAUSTIVE;
     } else if (truncationStatus === messageTruncationStatus.TRUNCATED) {
       // If a cursor was specified for a given thread, then the result is
       // guaranteed to be contiguous with what the client has, and as such the
       // result should never be TRUNCATED
       truncationStatuses[threadID] = messageTruncationStatus.UNCHANGED;
     }
   }
 
   const shimmedRawMessageInfos = shimUnsupportedRawMessageInfos(
     rawMessageInfos,
     viewer.platformDetails,
   );
 
   return {
     rawMessageInfos: shimmedRawMessageInfos,
     truncationStatuses,
   };
 }
 
 function threadSelectionCriteriaToSQLClause(criteria: ThreadSelectionCriteria) {
   const conditions = [];
   if (criteria.joinedThreads === true) {
     conditions.push(SQL`mm.role > 0`);
   }
   if (criteria.threadCursors) {
     for (let threadID in criteria.threadCursors) {
       const cursor = criteria.threadCursors[threadID];
       if (cursor) {
         conditions.push(SQL`(m.thread = ${threadID} AND m.id < ${cursor})`);
       } else {
         conditions.push(SQL`m.thread = ${threadID}`);
       }
     }
   }
   if (conditions.length === 0) {
     throw new ServerError('internal_error');
   }
   return mergeOrConditions(conditions);
 }
 
 function threadSelectionCriteriaToInitialTruncationStatuses(
   criteria: ThreadSelectionCriteria,
   defaultTruncationStatus: MessageTruncationStatus,
 ) {
   const truncationStatuses = {};
   if (criteria.threadCursors) {
     for (let threadID in criteria.threadCursors) {
       truncationStatuses[threadID] = defaultTruncationStatus;
     }
   }
   return truncationStatuses;
 }
 
 async function fetchMessageInfosSince(
   viewer: Viewer,
   criteria: ThreadSelectionCriteria,
   currentAsOf: number,
   maxNumberPerThread: number,
 ): Promise<FetchMessageInfosResult> {
   const threadSelectionClause = threadSelectionCriteriaToSQLClause(criteria);
   const truncationStatuses = threadSelectionCriteriaToInitialTruncationStatuses(
     criteria,
     messageTruncationStatus.UNCHANGED,
   );
 
   const viewerID = viewer.id;
   const query = SQL`
     SELECT m.id, m.thread AS threadID, m.content, m.time, m.type,
       m.creation, m.user AS creatorID, stm.permissions AS subthread_permissions,
       up.id AS uploadID, up.type AS uploadType, up.secret AS uploadSecret,
       up.extra AS uploadExtra
     FROM messages m
     LEFT JOIN uploads up
       ON m.type IN (${[messageTypes.IMAGES, messageTypes.MULTIMEDIA]})
         AND JSON_CONTAINS(m.content, CAST(up.id as JSON), '$')
     LEFT JOIN memberships mm ON mm.thread = m.thread AND mm.user = ${viewerID}
     LEFT JOIN memberships stm ON m.type = ${messageTypes.CREATE_SUB_THREAD}
       AND stm.thread = m.content AND stm.user = ${viewerID}
     WHERE m.time > ${currentAsOf} AND
       JSON_EXTRACT(mm.permissions, ${visibleExtractString}) IS TRUE AND
   `;
   query.append(threadSelectionClause);
   query.append(SQL`
     ORDER BY m.thread, m.time DESC
   `);
   const [result] = await dbQuery(query);
   const derivedMessages = await fetchDerivedMessages(result, viewer);
   const messages = parseMessageSQLResult(result, derivedMessages, viewer);
 
   const rawMessageInfos = [];
   let currentThreadID = null;
   let numMessagesForCurrentThreadID = 0;
-  for (let message of messages) {
+  for (const message of messages) {
     const { rawMessageInfo } = message;
     const { threadID } = rawMessageInfo;
     if (threadID !== currentThreadID) {
       currentThreadID = threadID;
       numMessagesForCurrentThreadID = 1;
       truncationStatuses[threadID] = messageTruncationStatus.UNCHANGED;
     } else {
       numMessagesForCurrentThreadID++;
     }
     if (numMessagesForCurrentThreadID <= maxNumberPerThread) {
-      if (
-        rawMessageInfo.type === messageTypes.CREATE_THREAD ||
-        rawMessageInfo.type === messageTypes.SIDEBAR_SOURCE
-      ) {
-        // If a CREATE_THREAD or SIDEBAR_SOURCE message is here, then we have
-        // all messages
+      if (messageSpecs[rawMessageInfo.type].startsThread) {
         truncationStatuses[threadID] = messageTruncationStatus.EXHAUSTIVE;
       }
       rawMessageInfos.push(rawMessageInfo);
     } else if (numMessagesForCurrentThreadID === maxNumberPerThread + 1) {
       truncationStatuses[threadID] = messageTruncationStatus.TRUNCATED;
     }
   }
 
   const shimmedRawMessageInfos = shimUnsupportedRawMessageInfos(
     rawMessageInfos,
     viewer.platformDetails,
   );
 
   return {
     rawMessageInfos: shimmedRawMessageInfos,
     truncationStatuses,
   };
 }
 
 function getMessageFetchResultFromRedisMessages(
   viewer: Viewer,
   rawMessageInfos: $ReadOnlyArray<RawMessageInfo>,
 ): FetchMessageInfosResult {
   const truncationStatuses = {};
   for (let rawMessageInfo of rawMessageInfos) {
     truncationStatuses[rawMessageInfo.threadID] =
       messageTruncationStatus.UNCHANGED;
   }
   const shimmedRawMessageInfos = shimUnsupportedRawMessageInfos(
     rawMessageInfos,
     viewer.platformDetails,
   );
   return {
     rawMessageInfos: shimmedRawMessageInfos,
     truncationStatuses,
   };
 }
 
 async function fetchMessageInfoForLocalID(
   viewer: Viewer,
   localID: ?string,
 ): Promise<?RawMessageInfo> {
   if (!localID || !viewer.hasSessionInfo) {
     return null;
   }
   const creation = creationString(viewer, localID);
   const viewerID = viewer.id;
   const query = SQL`
     SELECT m.id, m.thread AS threadID, m.content, m.time, m.type, m.creation,
       m.user AS creatorID, stm.permissions AS subthread_permissions,
       up.id AS uploadID, up.type AS uploadType, up.secret AS uploadSecret,
       up.extra AS uploadExtra
     FROM messages m
     LEFT JOIN uploads up
       ON m.type IN (${[messageTypes.IMAGES, messageTypes.MULTIMEDIA]})
         AND JSON_CONTAINS(m.content, CAST(up.id as JSON), '$')
     LEFT JOIN memberships mm ON mm.thread = m.thread AND mm.user = ${viewerID}
     LEFT JOIN memberships stm ON m.type = ${messageTypes.CREATE_SUB_THREAD}
       AND stm.thread = m.content AND stm.user = ${viewerID}
     WHERE m.user = ${viewerID} AND m.creation = ${creation} AND
       JSON_EXTRACT(mm.permissions, ${visibleExtractString}) IS TRUE
   `;
 
   const [result] = await dbQuery(query);
   if (result.length === 0) {
     return null;
   }
   const derivedMessages = await fetchDerivedMessages(result, viewer);
   return rawMessageInfoFromRows(result, viewer, derivedMessages);
 }
 
 const entryIDExtractString = '$.entryID';
 async function fetchMessageInfoForEntryAction(
   viewer: Viewer,
   messageType: MessageType,
   entryID: string,
   threadID: string,
 ): Promise<?RawMessageInfo> {
   const viewerID = viewer.id;
   const query = SQL`
     SELECT m.id, m.thread AS threadID, m.content, m.time, m.type, m.creation,
       m.user AS creatorID, up.id AS uploadID, up.type AS uploadType,
       up.secret AS uploadSecret, up.extra AS uploadExtra
     FROM messages m
     LEFT JOIN uploads up
       ON m.type IN (${[messageTypes.IMAGES, messageTypes.MULTIMEDIA]})
         AND JSON_CONTAINS(m.content, CAST(up.id as JSON), '$')
     LEFT JOIN memberships mm ON mm.thread = m.thread AND mm.user = ${viewerID}
     WHERE m.user = ${viewerID} AND m.thread = ${threadID} AND
       m.type = ${messageType} AND
       JSON_EXTRACT(m.content, ${entryIDExtractString}) = ${entryID} AND
       JSON_EXTRACT(mm.permissions, ${visibleExtractString}) IS TRUE
   `;
 
   const [result] = await dbQuery(query);
   if (result.length === 0) {
     return null;
   }
   const derivedMessages = await fetchDerivedMessages(result, viewer);
   return rawMessageInfoFromRows(result, viewer, derivedMessages);
 }
 
 async function fetchMessageRowsByIDs(messageIDs: $ReadOnlyArray<string>) {
   const query = SQL`
     SELECT m.id, m.thread AS threadID, m.content, m.time, m.type, m.creation, 
       m.user AS creatorID, stm.permissions AS subthread_permissions,
       up.id AS uploadID, up.type AS uploadType, up.secret AS uploadSecret, 
       up.extra AS uploadExtra
     FROM messages m
     LEFT JOIN uploads up
       ON m.type IN (${[messageTypes.IMAGES, messageTypes.MULTIMEDIA]})
         AND JSON_CONTAINS(m.content, CAST(up.id as JSON), '$')
     LEFT JOIN memberships stm ON m.type = ${messageTypes.CREATE_SUB_THREAD}
       AND stm.thread = m.content AND stm.user = m.user
     WHERE m.id IN (${messageIDs})
   `;
   const [result] = await dbQuery(query);
   return result;
 }
 
 async function fetchDerivedMessages(
   rows: $ReadOnlyArray<Object>,
   viewer?: Viewer,
 ): Promise<$ReadOnlyMap<string, RawMessageInfo>> {
   const requiredIDs = new Set<string>();
   for (const row of rows) {
     if (row.type === messageTypes.SIDEBAR_SOURCE) {
       const content = JSON.parse(row.content);
       requiredIDs.add(content.sourceMessageID);
     }
   }
 
   const messagesByID = new Map<string, RawMessageInfo>();
   if (requiredIDs.size === 0) {
     return messagesByID;
   }
 
   const result = await fetchMessageRowsByIDs([...requiredIDs]);
   const messages = parseMessageSQLResult(result, new Map(), viewer);
 
   for (const message of messages) {
     const { rawMessageInfo } = message;
     if (rawMessageInfo.id) {
       messagesByID.set(rawMessageInfo.id, rawMessageInfo);
     }
   }
   return messagesByID;
 }
 
 async function fetchMessageInfoByID(
   viewer?: Viewer,
   messageID: string,
 ): Promise<?RawMessageInfo> {
   const result = await fetchMessageRowsByIDs([messageID]);
   if (result.length === 0) {
     return null;
   }
   const derivedMessages = await fetchDerivedMessages(result, viewer);
   return rawMessageInfoFromRows(result, viewer, derivedMessages);
 }
 
 export {
   fetchCollapsableNotifs,
   fetchMessageInfos,
   fetchMessageInfosSince,
   getMessageFetchResultFromRedisMessages,
   fetchMessageInfoForLocalID,
   fetchMessageInfoForEntryAction,
   fetchMessageInfoByID,
 };