diff --git a/keyserver/src/fetchers/message-fetchers.js b/keyserver/src/fetchers/message-fetchers.js
index c61f20fcb..dd29cc0d8 100644
--- a/keyserver/src/fetchers/message-fetchers.js
+++ b/keyserver/src/fetchers/message-fetchers.js
@@ -1,997 +1,1013 @@
 // @flow
 
 import invariant from 'invariant';
 
 import {
   sortMessageInfoList,
   shimUnsupportedRawMessageInfos,
   isInvalidSidebarSource,
   isUnableToBeRenderedIndependently,
+  isInvalidPinSource,
 } from 'lib/shared/message-utils.js';
 import { messageSpecs } from 'lib/shared/messages/message-specs.js';
 import { getNotifCollapseKey } from 'lib/shared/notif-utils.js';
 import { hasMinCodeVersion } from 'lib/shared/version-utils.js';
 import {
   messageTypes,
   type MessageType,
   assertMessageType,
 } from 'lib/types/message-types-enum.js';
 import {
   type RawMessageInfo,
   type RawComposableMessageInfo,
   type RawRobotextMessageInfo,
   type EditMessageContent,
   type MessageSelectionCriteria,
   type MessageTruncationStatus,
   messageTruncationStatus,
   type FetchMessageInfosResult,
   defaultMaxMessageAge,
   type FetchPinnedMessagesRequest,
   type FetchPinnedMessagesResult,
   type SearchMessagesResponse,
 } from 'lib/types/message-types.js';
 import { defaultNumberPerThread } from 'lib/types/message-types.js';
 import { threadPermissions } from 'lib/types/thread-permission-types.js';
 import { ServerError } from 'lib/utils/errors.js';
 
 import {
   constructMediaFromMediaMessageContentsAndUploadRows,
   imagesFromRow,
 } from './upload-fetchers.js';
 import {
   dbQuery,
   SQL,
   mergeOrConditions,
   mergeAndConditions,
 } from '../database/database.js';
 import { processQueryForSearch } from '../database/search-utils.js';
 import type { SQLStatementType } from '../database/types.js';
 import type { PushInfo } from '../push/send.js';
 import type { Viewer } from '../session/viewer.js';
 import {
   creationString,
   localIDFromCreationString,
 } from '../utils/idempotent.js';
 
 export type CollapsableNotifInfo = {
   collapseKey: ?string,
   existingMessageInfos: RawMessageInfo[],
   newMessageInfos: RawMessageInfo[],
 };
 export type FetchCollapsableNotifsResult = {
   [userID: string]: CollapsableNotifInfo[],
 };
 
 const visibleExtractString = `$.${threadPermissions.VISIBLE}.value`;
 
 // 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 (const userID in pushInfo) {
     usersToCollapseKeysToInfo[userID] = {};
     usersToCollapsableNotifInfo[userID] = [];
     for (let i = 0; i < pushInfo[userID].messageInfos.length; i++) {
       const rawMessageInfo = pushInfo[userID].messageInfos[i];
       const messageData = pushInfo[userID].messageDatas[i];
       const collapseKey = getNotifCollapseKey(rawMessageInfo, messageData);
       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 (const userID in usersToCollapseKeysToInfo) {
     const collapseKeysToInfo = usersToCollapseKeysToInfo[userID];
     for (const collapseKey in collapseKeysToInfo) {
       sqlTuples.push(
         SQL`(n.user = ${userID} AND n.collapse_key = ${collapseKey})`,
       );
     }
   }
 
   if (sqlTuples.length === 0) {
     return usersToCollapsableNotifInfo;
   }
 
   const collapseQuery = SQL`
     SELECT m.id, m.thread AS threadID, m.content, m.time, m.type,
       m.user AS creatorID, m.target_message as targetMessageID,
       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 up.container = m.id
     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, ${visibleExtractString}) IS TRUE AND
   `;
   collapseQuery.append(mergeOrConditions(sqlTuples));
   collapseQuery.append(SQL`ORDER BY m.time DESC, m.id 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 (const userID in usersToCollapseKeysToInfo) {
     const collapseKeysToInfo = usersToCollapseKeysToInfo[userID];
     for (const 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,
     RawComposableMessageInfo | RawRobotextMessageInfo,
   >,
   viewer?: Viewer,
 ): MessageSQLResult {
   const rowsByID = new Map();
   for (const 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 (const 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(
   rawRows: $ReadOnlyArray<Object>,
   viewer?: Viewer,
   derivedMessages: $ReadOnlyMap<
     string,
     RawComposableMessageInfo | RawRobotextMessageInfo,
   >,
 ): ?RawMessageInfo {
   const rows = rawRows.map(row => ({
     ...row,
     subthread_permissions: JSON.parse(row.subthread_permissions),
   }));
 
   const type = mostRecentRowType(rows);
   const messageSpec = messageSpecs[type];
 
   if (type === messageTypes.IMAGES || type === messageTypes.MULTIMEDIA) {
     let media;
     if (type === messageTypes.MULTIMEDIA) {
       const mediaMessageContents = JSON.parse(rows[0].content);
       media = constructMediaFromMediaMessageContentsAndUploadRows(
         mediaMessageContents,
         rows,
       );
     } else {
       media = rows.filter(row => row.uploadID).map(imagesFromRow);
     }
     const [row] = rows;
     const localID = localIDFromCreationString(viewer, row.creation);
     invariant(
       messageSpec.rawMessageInfoFromServerDBRow,
       `multimedia message spec should have rawMessageInfoFromServerDBRow`,
     );
     return messageSpec.rawMessageInfoFromServerDBRow(row, {
       media,
       derivedMessages,
       localID,
     });
   }
 
   const row = assertSingleRow(rows);
   const localID = localIDFromCreationString(viewer, row.creation);
   invariant(
     messageSpec.rawMessageInfoFromServerDBRow,
     `message spec ${type} should have rawMessageInfoFromServerDBRow`,
   );
   return messageSpec.rawMessageInfoFromServerDBRow(row, {
     derivedMessages,
     localID,
   });
 }
 
 async function fetchMessageInfos(
   viewer: Viewer,
   criteria: MessageSelectionCriteria,
   numberPerThread: number,
 ): Promise<FetchMessageInfosResult> {
   const { sqlClause: selectionClause, timeFilterData } =
     parseMessageSelectionCriteria(viewer, criteria);
   const truncationStatuses = {};
 
   const viewerID = viewer.id;
   const query = SQL`
     WITH thread_window AS (
       SELECT m.id, m.thread AS threadID, m.user AS creatorID,
         m.target_message as targetMessageID, m.content, m.time, m.type,
         m.creation, stm.permissions AS subthread_permissions,
         ROW_NUMBER() OVER (
           PARTITION BY threadID ORDER BY m.time DESC, m.id DESC
         ) n
       FROM messages m
       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(selectionClause);
   query.append(SQL`
     )
     SELECT tw.*,
       up.id AS uploadID, up.type AS uploadType, up.secret AS uploadSecret,
       up.extra AS uploadExtra
     FROM thread_window tw
     LEFT JOIN uploads up ON up.container = tw.id
     WHERE tw.n <= ${numberPerThread}
     ORDER BY tw.threadID, tw.time DESC, tw.id DESC
   `);
 
   const [result] = await dbQuery(query);
   const derivedMessages = await fetchDerivedMessages(result, viewer);
   const messages = await parseMessageSQLResult(result, derivedMessages, viewer);
 
   const rawMessageInfos = [];
   const threadToMessageCount = new Map();
   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 (const [threadID, messageCount] of threadToMessageCount) {
     // If we matched the exact amount we limited to, we're probably truncating
     // our result set. By setting TRUNCATED here, we tell the client that the
     // result set might not be continguous with what's already in their
     // MessageStore. More details about TRUNCATED can be found in
     // lib/types/message-types.js
     if (messageCount >= numberPerThread) {
       // We won't set TRUNCATED if a cursor was specified for a given thread,
       // since then the result is guaranteed to be contiguous with what the
       // client has
       if (criteria.threadCursors && criteria.threadCursors[threadID]) {
         truncationStatuses[threadID] = messageTruncationStatus.UNCHANGED;
       } else {
         truncationStatuses[threadID] = messageTruncationStatus.TRUNCATED;
       }
       continue;
     }
     const hasTimeFilter = hasTimeFilterForThread(timeFilterData, threadID);
     if (!hasTimeFilter) {
       // If there is no time filter for a given thread, and there are fewer
       // messages returned than the max we queried for a given thread, we can
       // conclude that our result set includes all messages for that thread
       truncationStatuses[threadID] = messageTruncationStatus.EXHAUSTIVE;
     }
   }
 
   for (const rawMessageInfo of rawMessageInfos) {
     if (messageSpecs[rawMessageInfo.type].startsThread) {
       truncationStatuses[rawMessageInfo.threadID] =
         messageTruncationStatus.EXHAUSTIVE;
     }
   }
 
   for (const threadID in criteria.threadCursors) {
     const truncationStatus = truncationStatuses[threadID];
     if (truncationStatus !== null && truncationStatus !== undefined) {
       continue;
     }
     const hasTimeFilter = hasTimeFilterForThread(timeFilterData, threadID);
     if (!hasTimeFilter) {
       // If there is no time filter for a given thread, and zero messages were
       // returned, we can conclude that this thread has zero messages. This is
       // a case of database corruption that should not be possible, but likely
       // we have some threads like this on prod (either due to some transient
       // issues or due to old buggy code)
       truncationStatuses[threadID] = messageTruncationStatus.EXHAUSTIVE;
     } else {
       // If this thread was explicitly queried for, and we got no results, but
       // we can't conclude that it's EXHAUSTIVE, then we'll set to UNCHANGED.
       truncationStatuses[threadID] = messageTruncationStatus.UNCHANGED;
     }
   }
 
   const shimmedRawMessageInfos = shimUnsupportedRawMessageInfos(
     rawMessageInfos,
     viewer.platformDetails,
   );
 
   return {
     rawMessageInfos: shimmedRawMessageInfos,
     truncationStatuses,
   };
 }
 
 // ESLint doesn't recognize that invariant always throws
 // eslint-disable-next-line consistent-return
 function hasTimeFilterForThread(
   timeFilterData: TimeFilterData,
   threadID: string,
 ) {
   if (timeFilterData.timeFilter === 'ALL') {
     return true;
   } else if (timeFilterData.timeFilter === 'NONE') {
     return false;
   } else if (timeFilterData.timeFilter === 'ALL_EXCEPT_EXCLUDED') {
     return !timeFilterData.excludedFromTimeFilter.has(threadID);
   } else {
     invariant(
       false,
       `unrecognized timeFilter type ${timeFilterData.timeFilter}`,
     );
   }
 }
 
 type TimeFilterData =
   | { +timeFilter: 'ALL' | 'NONE' }
   | {
       +timeFilter: 'ALL_EXCEPT_EXCLUDED',
       +excludedFromTimeFilter: $ReadOnlySet<string>,
     };
 type ParsedMessageSelectionCriteria = {
   +sqlClause: SQLStatementType,
   +timeFilterData: TimeFilterData,
 };
 function parseMessageSelectionCriteria(
   viewer: Viewer,
   criteria: MessageSelectionCriteria,
 ): ParsedMessageSelectionCriteria {
   const minMessageTime = Date.now() - defaultMaxMessageAge;
   const shouldApplyTimeFilter = hasMinCodeVersion(viewer.platformDetails, {
     native: 130,
   });
 
   let globalTimeFilter;
   if (criteria.newerThan) {
     globalTimeFilter = SQL`m.time > ${criteria.newerThan}`;
   } else if (!criteria.threadCursors && shouldApplyTimeFilter) {
     globalTimeFilter = SQL`m.time > ${minMessageTime}`;
   }
 
   const threadConditions = [];
   if (
     criteria.joinedThreads === true &&
     shouldApplyTimeFilter &&
     !globalTimeFilter
   ) {
     threadConditions.push(SQL`(mm.role > 0 AND m.time > ${minMessageTime})`);
   } else if (criteria.joinedThreads === true) {
     threadConditions.push(SQL`mm.role > 0`);
   }
   if (criteria.threadCursors) {
     for (const threadID in criteria.threadCursors) {
       const cursor = criteria.threadCursors[threadID];
       if (cursor) {
         threadConditions.push(
           SQL`(m.thread = ${threadID} AND m.id < ${cursor})`,
         );
       } else {
         threadConditions.push(SQL`m.thread = ${threadID}`);
       }
     }
   }
   if (threadConditions.length === 0) {
     throw new ServerError('internal_error');
   }
   const threadClause = mergeOrConditions(threadConditions);
 
   let timeFilterData;
   if (globalTimeFilter) {
     timeFilterData = { timeFilter: 'ALL' };
   } else if (!shouldApplyTimeFilter) {
     timeFilterData = { timeFilter: 'NONE' };
   } else {
     invariant(
       criteria.threadCursors,
       'ALL_EXCEPT_EXCLUDED should correspond to threadCursors being set',
     );
     const excludedFromTimeFilter = new Set(Object.keys(criteria.threadCursors));
     timeFilterData = {
       timeFilter: 'ALL_EXCEPT_EXCLUDED',
       excludedFromTimeFilter,
     };
   }
 
   const conditions = [globalTimeFilter, threadClause].filter(Boolean);
   const sqlClause = mergeAndConditions(conditions);
 
   return { sqlClause, timeFilterData };
 }
 
 function messageSelectionCriteriaToInitialTruncationStatuses(
   criteria: MessageSelectionCriteria,
   defaultTruncationStatus: MessageTruncationStatus,
 ) {
   const truncationStatuses = {};
   if (criteria.threadCursors) {
     for (const threadID in criteria.threadCursors) {
       truncationStatuses[threadID] = defaultTruncationStatus;
     }
   }
   return truncationStatuses;
 }
 
 async function fetchMessageInfosSince(
   viewer: Viewer,
   criteria: MessageSelectionCriteria,
   maxNumberPerThread: number,
 ): Promise<FetchMessageInfosResult> {
   const { sqlClause: selectionClause } = parseMessageSelectionCriteria(
     viewer,
     criteria,
   );
   const truncationStatuses =
     messageSelectionCriteriaToInitialTruncationStatuses(
       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, m.target_message as targetMessageID,
       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 up.container = m.id
     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(selectionClause);
   query.append(SQL`
     ORDER BY m.thread, m.time DESC, m.id DESC
   `);
   const [result] = await dbQuery(query);
   const derivedMessages = await fetchDerivedMessages(result, viewer);
   const messages = await parseMessageSQLResult(result, derivedMessages, viewer);
 
   const rawMessageInfos = [];
   let currentThreadID = null;
   let numMessagesForCurrentThreadID = 0;
   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 (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 (const 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, m.target_message as targetMessageID,
       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 up.container = m.id
     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, m.target_message as targetMessageID,
       up.id AS uploadID, up.type AS uploadType, up.secret AS uploadSecret,
       up.extra AS uploadExtra
     FROM messages m
     LEFT JOIN uploads up ON up.container = m.id
     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, m.target_message as targetMessageID,
       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 up.container = m.id
     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 fetchPinnedMessageInfos(
   viewer: Viewer,
   request: FetchPinnedMessagesRequest,
 ): Promise<FetchPinnedMessagesResult> {
   // The only message types that can be pinned are 0, 14, and 15
   // (text, images, and multimedia), so we don't need to worry about
   // an admin pinning a message about creating a secret subchannel. This is
   // why we don't check subthread permissions (as opposed to other queries).
   const messageRowsQuery = SQL`
     SELECT m.id, m.thread AS threadID, m.content, m.time, m.type, m.creation,
       m.user AS creatorID, m.target_message as targetMessageID,
       NULL AS subthread_permissions, u.id AS uploadID,
       u.type AS uploadType, u.secret AS uploadSecret, u.extra AS uploadExtra
     FROM messages m
     LEFT JOIN uploads u ON u.container = m.id
     LEFT JOIN memberships mm ON mm.thread = m.thread AND mm.user = ${viewer.id}
     WHERE m.thread = ${request.threadID} 
       AND m.pinned = 1
       AND JSON_EXTRACT(mm.permissions, ${visibleExtractString}) IS TRUE
     ORDER BY m.pin_time DESC
   `;
   const [messageRows] = await dbQuery(messageRowsQuery);
   if (messageRows.length === 0) {
     return { pinnedMessages: [] };
   }
 
   const pinnedAndRelatedMessages =
     await rawMessageInfoForRowsAndRelatedMessages(messageRows, viewer);
 
   const shimmedPinnedRawMessageInfos = shimUnsupportedRawMessageInfos(
     pinnedAndRelatedMessages,
     viewer.platformDetails,
   );
 
   return {
     pinnedMessages: shimmedPinnedRawMessageInfos,
   };
 }
 
 async function fetchDerivedMessages(
   rows: $ReadOnlyArray<Object>,
   viewer?: Viewer,
 ): Promise<
   $ReadOnlyMap<string, RawComposableMessageInfo | RawRobotextMessageInfo>,
 > {
   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);
     } else if (row.type === messageTypes.TOGGLE_PIN) {
       const content = JSON.parse(row.content);
       requiredIDs.add(content.targetMessageID);
     }
   }
 
   const messagesByID = new Map<
     string,
     RawComposableMessageInfo | RawRobotextMessageInfo,
   >();
   if (requiredIDs.size === 0) {
     return messagesByID;
   }
 
   const [result, edits] = await Promise.all([
     fetchMessageRowsByIDs([...requiredIDs]),
     fetchLatestEditMessageContentByIDs([...requiredIDs]),
   ]);
   const messages = await parseMessageSQLResult(result, new Map(), viewer);
 
   for (const message of messages) {
     let { rawMessageInfo } = message;
-    invariant(
-      !isInvalidSidebarSource(rawMessageInfo),
-      'SIDEBAR_SOURCE or TOGGLE_PIN should not point to a ' +
-        'SIDEBAR_SOURCE, REACTION, EDIT_MESSAGE or TOGGLE_PIN',
-    );
+
+    if (rawMessageInfo.type === messageTypes.SIDEBAR_SOURCE) {
+      invariant(
+        !isInvalidSidebarSource(rawMessageInfo),
+        'SIDEBAR_SOURCE should not point to a ' +
+          'SIDEBAR_SOURCE, REACTION, EDIT_MESSAGE or TOGGLE_PIN',
+      );
+    }
+    if (rawMessageInfo.type === messageTypes.TOGGLE_PIN) {
+      invariant(
+        !isInvalidPinSource(rawMessageInfo),
+        'TOGGLE_PIN should not point to a non-composable message type',
+      );
+    }
+
     if (rawMessageInfo.id) {
       const editedContent = edits.get(rawMessageInfo.id);
       if (editedContent && rawMessageInfo.type === messageTypes.TEXT) {
         rawMessageInfo = {
           ...rawMessageInfo,
           text: editedContent.text,
         };
       }
       invariant(rawMessageInfo.id, 'rawMessageInfo.id should not be null');
+      // Flow doesn't refine the types if we don't explicitly invariant on
+      // or check against all of the unexpected message types, and that list
+      // can both get long and generally defeats the purpose of moving the
+      // logic into message specs to have one 'single source of truth'.
+      // $FlowFixMe
       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);
 }
 
 async function fetchThreadMessagesCount(threadID: string): Promise<number> {
   const query = SQL`
     SELECT COUNT(*) AS count
     FROM messages
     WHERE thread = ${threadID}
   `;
   const [result] = await dbQuery(query);
   return result[0].count;
 }
 
 async function fetchLatestEditMessageContentByIDs(
   messageIDs: $ReadOnlyArray<string>,
 ): Promise<$ReadOnlyMap<string, EditMessageContent>> {
   const latestEditedMessageQuery = SQL`
     SELECT m.id, (
       SELECT m2.content
       FROM messages m2
       WHERE m.id = m2.target_message
         AND m.thread = m2.thread
         AND m2.type = ${messageTypes.EDIT_MESSAGE}
       ORDER BY time DESC, id DESC
       LIMIT 1
     ) content
     FROM messages m
     WHERE m.id IN(${messageIDs})
   `;
 
   const [result] = await dbQuery(latestEditedMessageQuery);
   const latestContentByID = new Map();
   for (const row of result) {
     if (!row.content) {
       continue;
     }
     const content = JSON.parse(row.content);
     latestContentByID.set(row.id.toString(), content);
   }
 
   return latestContentByID;
 }
 
 async function fetchLatestEditMessageContentByID(
   messageID: string,
 ): Promise<?EditMessageContent> {
   const result = await fetchLatestEditMessageContentByIDs([messageID]);
   const content = result.get(messageID);
   return content;
 }
 
 async function fetchRelatedMessages(
   viewer?: Viewer,
   messages: $ReadOnlyMap<
     string,
     RawComposableMessageInfo | RawRobotextMessageInfo,
   >,
 ): Promise<$ReadOnlyArray<RawMessageInfo>> {
   if (messages.size === 0) {
     return [];
   }
   const originalMessageIDs = [...messages.keys()];
 
   const query = SQL`
     SELECT m.id, m.thread AS threadID, m.content, m.time, m.type, m.creation,
       m.user AS creatorID, m.target_message as targetMessageID,
       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 up.container = m.id
     LEFT JOIN memberships stm ON m.type = ${messageTypes.CREATE_SUB_THREAD}
       AND stm.thread = m.content AND stm.user = m.user
     WHERE m.target_message IN (${originalMessageIDs})
       AND (
         m.type = ${messageTypes.SIDEBAR_SOURCE}
         OR m.type = ${messageTypes.REACTION}
         OR m.type = ${messageTypes.TOGGLE_PIN}
       )
     UNION SELECT m.id, m.thread AS threadID, m.content, m.time, m.type, 
       m.creation, m.user AS creatorID, m.target_message as targetMessageID,
       stm.permissions AS subthread_permissions, up.id AS uploadID,
       up.type AS uploadType, up.secret AS uploadSecret, up.extra AS uploadExtra
     FROM messages m2
     INNER JOIN messages m ON m.id = (
       SELECT m3.id FROM messages m3
       WHERE m3.target_message = m2.id
         AND m3.thread = m2.thread
         AND m3.type = ${messageTypes.EDIT_MESSAGE}
       ORDER BY time DESC, id DESC
       LIMIT 1
     )
     LEFT JOIN uploads up ON up.container = m2.id
     LEFT JOIN memberships stm ON m2.type = ${messageTypes.CREATE_SUB_THREAD}
       AND stm.thread = m2.content AND stm.user = m2.user
     WHERE m2.id IN (${originalMessageIDs})
   `;
 
   const [resultRows] = await dbQuery(query);
 
   if (resultRows.length === 0) {
     return [];
   }
   const SQLResult = await parseMessageSQLResult(resultRows, messages, viewer);
   return SQLResult.map(item => item.rawMessageInfo);
 }
 
 async function rawMessageInfoForRowsAndRelatedMessages(
   rows: $ReadOnlyArray<Object>,
   viewer?: Viewer,
 ): Promise<$ReadOnlyArray<RawMessageInfo>> {
   const parsedResults = await parseMessageSQLResult(rows, new Map(), viewer);
   const rawMessageInfoMap = new Map<
     string,
     RawComposableMessageInfo | RawRobotextMessageInfo,
   >();
   for (const message of parsedResults) {
     const { rawMessageInfo } = message;
     if (isUnableToBeRenderedIndependently(rawMessageInfo)) {
       continue;
     }
     invariant(rawMessageInfo.id, 'rawMessageInfo.id should not be null');
     // Flow fails to refine types correctly since
     // isUnableToBeRenderedIndependently introspects into a message spec
     // instead of directly checking message types. We use "continue" to avoid
     // invalid messages, but Flow doesn't recognize this. The
     // alternative is to check against every message type, but that defeats
     // the purpose of a 'single source of truth.'
     // $FlowFixMe
     rawMessageInfoMap.set(rawMessageInfo.id, rawMessageInfo);
   }
 
   const rawMessageInfos = parsedResults.map(item => item.rawMessageInfo);
   const rawRelatedMessageInfos = await fetchRelatedMessages(
     viewer,
     rawMessageInfoMap,
   );
 
   return [...rawMessageInfos, ...rawRelatedMessageInfos];
 }
 
 const searchMessagesPageSize = defaultNumberPerThread + 1;
 
 async function searchMessagesInSingleChat(
   inputQuery: string,
   threadID: string,
   viewer?: Viewer,
   cursor?: string,
 ): Promise<SearchMessagesResponse> {
   if (inputQuery === '') {
     console.warn('received empty search query');
     return { messages: [], endReached: true };
   }
   const pattern = processQueryForSearch(inputQuery);
 
   if (pattern === '') {
     return {
       endReached: true,
       messages: [],
     };
   }
 
   const query = SQL`
     SELECT m.id, m.thread AS threadID, m.content, m.time, m.type, m.creation,
     m.user AS creatorID, m.target_message as targetMessageID,
     stm.permissions AS subthread_permissions, up.id AS uploadID,
     up.type AS uploadType, up.secret AS uploadSecret, up.extra AS uploadExtra
     FROM message_search s
     LEFT JOIN messages m ON m.id = s.original_message_id
     LEFT JOIN memberships stm ON m.type = ${messageTypes.CREATE_SUB_THREAD}
       AND stm.thread = m.content AND stm.user = m.user
     LEFT JOIN uploads up ON up.container = m.id
     LEFT JOIN messages m2 ON m2.target_message = m.id 
       AND m2.type = ${messageTypes.SIDEBAR_SOURCE} AND m2.thread = ${threadID}
     WHERE MATCH(s.processed_content) AGAINST(${pattern} IN BOOLEAN MODE)
       AND (m.thread = ${threadID} OR m2.id IS NOT NULL)
   `;
 
   if (cursor) {
     query.append(SQL`AND m.id < ${cursor} `);
   }
   query.append(SQL`   
     ORDER BY m.time DESC, m.id DESC
     LIMIT ${searchMessagesPageSize}
   `);
 
   const [results] = await dbQuery(query);
   if (results.length === 0) {
     return { messages: [], endReached: true };
   }
 
   const endReached = results.length < searchMessagesPageSize;
 
   const resultsPage = endReached ? results : results.slice(0, -1);
 
   const rawMessageInfos = await rawMessageInfoForRowsAndRelatedMessages(
     resultsPage,
     viewer,
   );
 
   return {
     messages: shimUnsupportedRawMessageInfos(
       rawMessageInfos,
       viewer?.platformDetails,
     ),
     endReached: endReached,
   };
 }
 
 export {
   fetchCollapsableNotifs,
   fetchMessageInfos,
   fetchMessageInfosSince,
   getMessageFetchResultFromRedisMessages,
   fetchMessageInfoForLocalID,
   fetchMessageInfoForEntryAction,
   fetchMessageInfoByID,
   fetchThreadMessagesCount,
   fetchLatestEditMessageContentByID,
   fetchPinnedMessageInfos,
   searchMessagesInSingleChat,
 };