diff --git a/keyserver/src/updaters/thread-permission-updaters.js b/keyserver/src/updaters/thread-permission-updaters.js
index a888882d1..78cfc341a 100644
--- a/keyserver/src/updaters/thread-permission-updaters.js
+++ b/keyserver/src/updaters/thread-permission-updaters.js
@@ -1,1380 +1,1382 @@
 // @flow
 
 import invariant from 'invariant';
 import _isEqual from 'lodash/fp/isEqual.js';
 
 import bots from 'lib/facts/bots.js';
 import genesis from 'lib/facts/genesis.js';
+import { specialRoles } from 'lib/permissions/special-roles.js';
 import {
   makePermissionsBlob,
   makePermissionsForChildrenBlob,
   getRoleForPermissions,
 } from 'lib/permissions/thread-permissions.js';
 import type { CalendarQuery } from 'lib/types/entry-types.js';
 import { messageTypes } from 'lib/types/message-types-enum.js';
 import type {
   ThreadPermissionsBlob,
   ThreadRolePermissionsBlob,
 } from 'lib/types/thread-permission-types.js';
 import { threadPermissions } from 'lib/types/thread-permission-types.js';
 import {
   type ThreadType,
   assertThreadType,
 } from 'lib/types/thread-types-enum.js';
 import { updateTypes } from 'lib/types/update-types-enum.js';
 import {
   type ServerUpdateInfo,
   type CreateUpdatesResult,
 } from 'lib/types/update-types.js';
 import { pushAll } from 'lib/utils/array.js';
 import { ServerError } from 'lib/utils/errors.js';
 
 import { updateChangedUndirectedRelationships } from './relationship-updaters.js';
 import {
   createUpdates,
   type UpdatesForCurrentSession,
 } from '../creators/update-creator.js';
 import { dbQuery, SQL } from '../database/database.js';
 import {
   fetchServerThreadInfos,
   rawThreadInfosFromServerThreadInfos,
 } from '../fetchers/thread-fetchers.js';
 import { rescindPushNotifs } from '../push/rescind.js';
 import { createScriptViewer } from '../session/scripts.js';
 import type { Viewer } from '../session/viewer.js';
 import { updateRoles } from '../updaters/role-updaters.js';
 import DepthQueue from '../utils/depth-queue.js';
 import RelationshipChangeset from '../utils/relationship-changeset.js';
 
 export type MembershipRowToSave = {
   +operation: 'save',
   +intent: 'join' | 'leave' | 'none',
   +userID: string,
   +threadID: string,
   +userNeedsFullThreadDetails: boolean,
   +permissions: ?ThreadPermissionsBlob,
   +permissionsForChildren: ?ThreadPermissionsBlob,
   // null role represents by "0"
   +role: string,
   +oldRole: string,
   +unread?: boolean,
 };
 type MembershipRowToDelete = {
   +operation: 'delete',
   +intent: 'join' | 'leave' | 'none',
   +userID: string,
   +threadID: string,
   +oldRole: string,
 };
 type MembershipRow = MembershipRowToSave | MembershipRowToDelete;
 type Changeset = {
   +membershipRows: MembershipRow[],
   +relationshipChangeset: RelationshipChangeset,
 };
 
 // 0 role means to remove the user from the thread
 // null role means to set the user to the default role
 // string role means to set the user to the role with that ID
 // -1 role means to set the user as a "ghost" (former member)
 type ChangeRoleOptions = {
   +setNewMembersToUnread?: boolean,
   +forcePermissionRecalculation?: boolean,
 };
 type ChangeRoleMemberInfo = {
   permissionsFromParent?: ?ThreadPermissionsBlob,
   memberOfContainingThread?: boolean,
 };
 async function changeRole(
   threadID: string,
   userIDs: $ReadOnlyArray<string>,
   role: string | -1 | 0 | null,
   options?: ChangeRoleOptions,
 ): Promise<Changeset> {
   const intent = role === -1 || role === 0 ? 'leave' : 'join';
   const setNewMembersToUnread =
     options?.setNewMembersToUnread && intent === 'join';
   const forcePermissionRecalculation = options?.forcePermissionRecalculation;
 
   if (userIDs.length === 0) {
     return {
       membershipRows: [],
       relationshipChangeset: new RelationshipChangeset(),
     };
   }
 
   const membershipQuery = SQL`
     SELECT user, role, permissions, permissions_for_children
     FROM memberships
     WHERE thread = ${threadID}
   `;
   const parentMembershipQuery = SQL`
     SELECT pm.user, pm.permissions_for_children AS permissions_from_parent
     FROM threads t
     INNER JOIN memberships pm ON pm.thread = t.parent_thread_id
     WHERE t.id = ${threadID} AND
       (pm.user IN (${userIDs}) OR t.parent_thread_id != ${genesis.id})
   `;
   const containingMembershipQuery = SQL`
     SELECT cm.user, cm.role AS containing_role
     FROM threads t
     INNER JOIN memberships cm ON cm.thread = t.containing_thread_id
     WHERE t.id = ${threadID} AND cm.user IN (${userIDs})
   `;
   const [
     [membershipResults],
     [parentMembershipResults],
     containingMembershipResults,
     roleThreadResult,
   ] = await Promise.all([
     dbQuery(membershipQuery),
     dbQuery(parentMembershipQuery),
     (async () => {
       if (intent === 'leave') {
         // Membership in the container only needs to be checked for members
         return [];
       }
       const [result] = await dbQuery(containingMembershipQuery);
       return result;
     })(),
     changeRoleThreadQuery(threadID, role),
   ]);
 
   const {
     roleColumnValue: intendedRole,
     threadType,
     parentThreadID,
     hasContainingThreadID,
     rolePermissions: intendedRolePermissions,
     depth,
   } = roleThreadResult;
 
   const existingMembershipInfo = new Map();
   for (const row of membershipResults) {
     const userID = row.user.toString();
     existingMembershipInfo.set(userID, {
       oldRole: row.role.toString(),
       oldPermissions: JSON.parse(row.permissions),
       oldPermissionsForChildren: JSON.parse(row.permissions_for_children),
     });
   }
 
   const ancestorMembershipInfo: Map<string, ChangeRoleMemberInfo> = new Map();
   for (const row of parentMembershipResults) {
     const userID = row.user.toString();
     if (!userIDs.includes(userID)) {
       continue;
     }
     ancestorMembershipInfo.set(userID, {
       permissionsFromParent: JSON.parse(row.permissions_from_parent),
     });
   }
   for (const row of containingMembershipResults) {
     const userID = row.user.toString();
     const ancestorMembership = ancestorMembershipInfo.get(userID);
     const memberOfContainingThread = row.containing_role > 0;
     if (ancestorMembership) {
       ancestorMembership.memberOfContainingThread = memberOfContainingThread;
     } else {
       ancestorMembershipInfo.set(userID, {
         memberOfContainingThread,
       });
     }
   }
 
   const relationshipChangeset = new RelationshipChangeset();
   const existingMemberIDs = [...existingMembershipInfo.keys()];
   if (threadID !== genesis.id) {
     relationshipChangeset.setAllRelationshipsExist(existingMemberIDs);
   }
   const parentMemberIDs = parentMembershipResults.map(row =>
     row.user.toString(),
   );
   if (parentThreadID && parentThreadID !== genesis.id) {
     relationshipChangeset.setAllRelationshipsExist(parentMemberIDs);
   }
 
   const membershipRows = [];
   const toUpdateDescendants = new Map();
   for (const userID of userIDs) {
     const existingMembership = existingMembershipInfo.get(userID);
     const oldRole = existingMembership?.oldRole ?? '-1';
     const oldPermissions = existingMembership?.oldPermissions ?? null;
     const oldPermissionsForChildren =
       existingMembership?.oldPermissionsForChildren ?? null;
 
     if (
       existingMembership &&
       oldRole === intendedRole &&
       !forcePermissionRecalculation
     ) {
       // If the old role is the same as the new one, we have nothing to update
       continue;
     } else if (Number(oldRole) > 0 && role === null) {
       // In the case where we're just trying to add somebody to a thread, if
       // they already have a role with a nonzero role then we don't need to do
       // anything
       continue;
     }
 
     let permissionsFromParent = null;
     let memberOfContainingThread = false;
     const ancestorMembership = ancestorMembershipInfo.get(userID);
     if (ancestorMembership) {
       permissionsFromParent = ancestorMembership.permissionsFromParent;
       memberOfContainingThread = ancestorMembership.memberOfContainingThread;
     }
     if (!hasContainingThreadID) {
       memberOfContainingThread = true;
     }
 
     const rolePermissions = memberOfContainingThread
       ? intendedRolePermissions
       : null;
     const targetRole = memberOfContainingThread ? intendedRole : '-1';
 
     const permissions = makePermissionsBlob(
       rolePermissions,
       permissionsFromParent,
       threadID,
       threadType,
     );
     const permissionsForChildren = makePermissionsForChildrenBlob(permissions);
     const newRole = getRoleForPermissions(targetRole, permissions);
     const userBecameMember = Number(oldRole) <= 0 && Number(newRole) > 0;
     const userLostMembership = Number(oldRole) > 0 && Number(newRole) <= 0;
 
     if (
       (intent === 'join' && Number(newRole) <= 0) ||
       (intent === 'leave' && Number(newRole) > 0)
     ) {
       throw new ServerError('invalid_parameters');
     } else if (intendedRole !== newRole) {
       console.warn(
         `changeRole called for role=${intendedRole}, but ended up setting ` +
           `role=${newRole} for userID ${userID} and threadID ${threadID}, ` +
           'probably because KNOW_OF permission was unexpectedly present or ' +
           'missing',
       );
     }
     if (
       existingMembership &&
       _isEqual(permissions)(oldPermissions) &&
       oldRole === newRole
     ) {
       // This thread and all of its descendants need no updates for this user,
       // since the corresponding memberships row is unchanged by this operation
       continue;
     }
 
     if (permissions) {
       membershipRows.push({
         operation: 'save',
         intent,
         userID,
         threadID,
         userNeedsFullThreadDetails: userBecameMember,
         permissions,
         permissionsForChildren,
         role: newRole,
         oldRole,
         unread: userBecameMember && setNewMembersToUnread,
       });
     } else {
       membershipRows.push({
         operation: 'delete',
         intent,
         userID,
         threadID,
         oldRole,
       });
     }
 
     if (permissions && !existingMembership && threadID !== genesis.id) {
       relationshipChangeset.setRelationshipsNeeded(userID, existingMemberIDs);
     }
 
     if (
       userLostMembership ||
       !_isEqual(permissionsForChildren)(oldPermissionsForChildren)
     ) {
       toUpdateDescendants.set(userID, {
         userIsMember: Number(newRole) > 0,
         permissionsForChildren,
       });
     }
   }
 
   if (toUpdateDescendants.size > 0) {
     const {
       membershipRows: descendantMembershipRows,
       relationshipChangeset: descendantRelationshipChangeset,
     } = await updateDescendantPermissions({
       threadID,
       depth,
       changesByUser: toUpdateDescendants,
     });
     pushAll(membershipRows, descendantMembershipRows);
     relationshipChangeset.addAll(descendantRelationshipChangeset);
   }
 
   return { membershipRows, relationshipChangeset };
 }
 
 type RoleThreadResult = {
   +roleColumnValue: string,
   +depth: number,
   +threadType: ThreadType,
   +parentThreadID: ?string,
   +hasContainingThreadID: boolean,
   +rolePermissions: ?ThreadRolePermissionsBlob,
 };
 async function changeRoleThreadQuery(
   threadID: string,
   role: string | -1 | 0 | null,
 ): Promise<RoleThreadResult> {
   if (role === 0 || role === -1) {
     const query = SQL`
       SELECT type, depth, parent_thread_id, containing_thread_id
       FROM threads
       WHERE id = ${threadID}
     `;
     const [result] = await dbQuery(query);
     if (result.length === 0) {
       throw new ServerError('internal_error');
     }
     const row = result[0];
     return {
       roleColumnValue: role.toString(),
       depth: row.depth,
       threadType: assertThreadType(row.type),
       parentThreadID: row.parent_thread_id
         ? row.parent_thread_id.toString()
         : null,
       hasContainingThreadID: row.containing_thread_id !== null,
       rolePermissions: null,
     };
   } else if (role !== null) {
     const query = SQL`
       SELECT t.type, t.depth, t.parent_thread_id, t.containing_thread_id,
         r.permissions
       FROM threads t
       INNER JOIN roles r ON r.thread = t.id AND r.id = ${role}
       WHERE t.id = ${threadID}
     `;
     const [result] = await dbQuery(query);
     if (result.length === 0) {
       throw new ServerError('internal_error');
     }
     const row = result[0];
     return {
       roleColumnValue: role,
       depth: row.depth,
       threadType: assertThreadType(row.type),
       parentThreadID: row.parent_thread_id
         ? row.parent_thread_id.toString()
         : null,
       hasContainingThreadID: row.containing_thread_id !== null,
       rolePermissions: JSON.parse(row.permissions),
     };
   } else {
     const query = SQL`
       SELECT t.type, t.depth, t.parent_thread_id, t.containing_thread_id,
-        t.default_role, r.permissions
+        r.permissions, r.id
       FROM threads t
-      INNER JOIN roles r ON r.thread = t.id AND r.id = t.default_role
+      INNER JOIN roles r ON r.thread = t.id 
+        AND r.special_role = ${specialRoles.DEFAULT_ROLE}
       WHERE t.id = ${threadID}
     `;
     const [result] = await dbQuery(query);
     if (result.length === 0) {
       throw new ServerError('internal_error');
     }
     const row = result[0];
     return {
-      roleColumnValue: row.default_role.toString(),
+      roleColumnValue: row.id.toString(),
       depth: row.depth,
       threadType: assertThreadType(row.type),
       parentThreadID: row.parent_thread_id
         ? row.parent_thread_id.toString()
         : null,
       hasContainingThreadID: row.containing_thread_id !== null,
       rolePermissions: JSON.parse(row.permissions),
     };
   }
 }
 
 type ChangedAncestor = {
   +threadID: string,
   +depth: number,
   +changesByUser: Map<string, AncestorChanges>,
 };
 type AncestorChanges = {
   +userIsMember: boolean,
   +permissionsForChildren: ?ThreadPermissionsBlob,
 };
 async function updateDescendantPermissions(
   initialChangedAncestor: ChangedAncestor,
 ): Promise<Changeset> {
   const membershipRows = [];
   const relationshipChangeset = new RelationshipChangeset();
 
   const initialDescendants = await fetchDescendantsForUpdate([
     initialChangedAncestor,
   ]);
 
   const depthQueue = new DepthQueue(
     getDescendantDepth,
     getDescendantKey,
     mergeDescendants,
   );
   depthQueue.addInfos(initialDescendants);
 
   let descendants;
   while ((descendants = depthQueue.getNextDepth())) {
     const descendantsAsAncestors = [];
     for (const descendant of descendants) {
       const { threadID, threadType, depth, users } = descendant;
 
       const existingMembers = [...users.entries()];
       const existingMemberIDs = existingMembers
         .filter(([, { curRole }]) => curRole)
         .map(([userID]) => userID);
       if (threadID !== genesis.id) {
         relationshipChangeset.setAllRelationshipsExist(existingMemberIDs);
       }
 
       const usersForNextLayer = new Map();
       for (const [userID, user] of users) {
         const {
           curRolePermissions,
           curPermissionsFromParent,
           curMemberOfContainingThread,
           nextMemberOfContainingThread,
           nextPermissionsFromParent,
           potentiallyNeedsUpdate,
         } = user;
         const existingMembership = !!user.curRole;
         const curRole = user.curRole ?? '-1';
         const curPermissions = user.curPermissions ?? null;
         const curPermissionsForChildren =
           user.curPermissionsForChildren ?? null;
 
         if (!potentiallyNeedsUpdate) {
           continue;
         }
 
         const permissionsFromParent =
           nextPermissionsFromParent === undefined
             ? curPermissionsFromParent
             : nextPermissionsFromParent;
         const memberOfContainingThread =
           nextMemberOfContainingThread === undefined
             ? curMemberOfContainingThread
             : nextMemberOfContainingThread;
         const targetRole = memberOfContainingThread ? curRole : '-1';
         const rolePermissions = memberOfContainingThread
           ? curRolePermissions
           : null;
 
         const permissions = makePermissionsBlob(
           rolePermissions,
           permissionsFromParent,
           threadID,
           threadType,
         );
         const permissionsForChildren =
           makePermissionsForChildrenBlob(permissions);
         const newRole = getRoleForPermissions(targetRole, permissions);
         const userLostMembership = Number(curRole) > 0 && Number(newRole) <= 0;
 
         if (_isEqual(permissions)(curPermissions) && curRole === newRole) {
           // This thread and all of its descendants need no updates for this
           // user, since the corresponding memberships row is unchanged by this
           // operation
           continue;
         }
 
         if (permissions) {
           membershipRows.push({
             operation: 'save',
             intent: 'none',
             userID,
             threadID,
             userNeedsFullThreadDetails: false,
             permissions,
             permissionsForChildren,
             role: newRole,
             oldRole: curRole,
           });
         } else {
           membershipRows.push({
             operation: 'delete',
             intent: 'none',
             userID,
             threadID,
             oldRole: curRole,
           });
         }
 
         if (permissions && !existingMembership && threadID !== genesis.id) {
           // If there was no membership row before, and we are creating one,
           // we'll need to make sure the new member has a relationship row with
           // each existing member. We expect that whoever called us already
           // generated memberships row for the new members, will will lead
           // saveMemberships to generate relationships rows between those new
           // users.
           relationshipChangeset.setRelationshipsNeeded(
             userID,
             existingMemberIDs,
           );
         }
 
         if (
           userLostMembership ||
           !_isEqual(permissionsForChildren)(curPermissionsForChildren)
         ) {
           usersForNextLayer.set(userID, {
             userIsMember: Number(newRole) > 0,
             permissionsForChildren,
           });
         }
       }
       if (usersForNextLayer.size > 0) {
         descendantsAsAncestors.push({
           threadID,
           depth,
           changesByUser: usersForNextLayer,
         });
       }
     }
 
     const nextDescendants = await fetchDescendantsForUpdate(
       descendantsAsAncestors,
     );
     depthQueue.addInfos(nextDescendants);
   }
   return { membershipRows, relationshipChangeset };
 }
 
 type DescendantUserInfo = $Shape<{
   curRole?: string,
   curRolePermissions?: ?ThreadRolePermissionsBlob,
   curPermissions?: ?ThreadPermissionsBlob,
   curPermissionsForChildren?: ?ThreadPermissionsBlob,
   curPermissionsFromParent?: ?ThreadPermissionsBlob,
   curMemberOfContainingThread?: boolean,
   nextPermissionsFromParent?: ?ThreadPermissionsBlob,
   nextMemberOfContainingThread?: boolean,
   potentiallyNeedsUpdate?: boolean,
 }>;
 type DescendantInfo = {
   +threadID: string,
   +parentThreadID: string,
   +containingThreadID: string,
   +threadType: ThreadType,
   +depth: number,
   +users: Map<string, DescendantUserInfo>,
 };
 const fetchDescendantsBatchSize = 10;
 async function fetchDescendantsForUpdate(
   ancestors: $ReadOnlyArray<ChangedAncestor>,
 ): Promise<DescendantInfo[]> {
   const threadIDs = ancestors.map(ancestor => ancestor.threadID);
 
   const rows = [];
   while (threadIDs.length > 0) {
     const batch = threadIDs.splice(0, fetchDescendantsBatchSize);
     const query = SQL`
       SELECT t.id, m.user, t.type, t.depth, t.parent_thread_id,
         t.containing_thread_id, r.permissions AS role_permissions, m.permissions,
         m.permissions_for_children, m.role,
         pm.permissions_for_children AS permissions_from_parent,
         cm.role AS containing_role
       FROM threads t
       INNER JOIN memberships m ON m.thread = t.id
       LEFT JOIN memberships pm
         ON pm.thread = t.parent_thread_id AND pm.user = m.user
       LEFT JOIN memberships cm
         ON cm.thread = t.containing_thread_id AND cm.user = m.user
       LEFT JOIN roles r ON r.id = m.role
       WHERE t.parent_thread_id IN (${batch})
         OR t.containing_thread_id IN (${batch})
     `;
     const [results] = await dbQuery(query);
     pushAll(rows, results);
   }
 
   const descendantThreadInfos: Map<string, DescendantInfo> = new Map();
   for (const row of rows) {
     const descendantThreadID = row.id.toString();
     if (!descendantThreadInfos.has(descendantThreadID)) {
       descendantThreadInfos.set(descendantThreadID, {
         threadID: descendantThreadID,
         parentThreadID: row.parent_thread_id.toString(),
         containingThreadID: row.containing_thread_id.toString(),
         threadType: assertThreadType(row.type),
         depth: row.depth,
         users: new Map(),
       });
     }
     const descendantThreadInfo = descendantThreadInfos.get(descendantThreadID);
     invariant(
       descendantThreadInfo,
       `value should exist for key ${descendantThreadID}`,
     );
     const userID = row.user.toString();
     descendantThreadInfo.users.set(userID, {
       curRole: row.role.toString(),
       curRolePermissions: JSON.parse(row.role_permissions),
       curPermissions: JSON.parse(row.permissions),
       curPermissionsForChildren: JSON.parse(row.permissions_for_children),
       curPermissionsFromParent: JSON.parse(row.permissions_from_parent),
       curMemberOfContainingThread: row.containing_role > 0,
     });
   }
 
   for (const ancestor of ancestors) {
     const { threadID, changesByUser } = ancestor;
     for (const [userID, changes] of changesByUser) {
       for (const descendantThreadInfo of descendantThreadInfos.values()) {
         const { users, parentThreadID, containingThreadID } =
           descendantThreadInfo;
         if (threadID !== parentThreadID && threadID !== containingThreadID) {
           continue;
         }
         let user = users.get(userID);
         if (!user) {
           user = {};
           users.set(userID, user);
         }
         if (threadID === parentThreadID) {
           user.nextPermissionsFromParent = changes.permissionsForChildren;
           user.potentiallyNeedsUpdate = true;
         }
         if (threadID === containingThreadID) {
           user.nextMemberOfContainingThread = changes.userIsMember;
           if (!user.nextMemberOfContainingThread) {
             user.potentiallyNeedsUpdate = true;
           }
         }
       }
     }
   }
 
   return [...descendantThreadInfos.values()];
 }
 
 function getDescendantDepth(descendant: DescendantInfo): number {
   return descendant.depth;
 }
 function getDescendantKey(descendant: DescendantInfo): string {
   return descendant.threadID;
 }
 function mergeDescendants(
   a: DescendantInfo,
   b: DescendantInfo,
 ): DescendantInfo {
   const { users: usersA, ...restA } = a;
   const { users: usersB, ...restB } = b;
   if (!_isEqual(restA)(restB)) {
     console.warn(
       `inconsistent descendantInfos ${JSON.stringify(restA)}, ` +
         JSON.stringify(restB),
     );
     throw new ServerError('internal_error');
   }
 
   const newUsers = new Map(usersA);
   for (const [userID, userFromB] of usersB) {
     const userFromA = newUsers.get(userID);
     if (!userFromA) {
       newUsers.set(userID, userFromB);
     } else {
       newUsers.set(userID, { ...userFromA, ...userFromB });
     }
   }
 
   return { ...a, users: newUsers };
 }
 
 type RecalculatePermissionsMemberInfo = {
   role?: ?string,
   permissions?: ?ThreadPermissionsBlob,
   permissionsForChildren?: ?ThreadPermissionsBlob,
   rolePermissions?: ?ThreadRolePermissionsBlob,
   memberOfContainingThread?: boolean,
   permissionsFromParent?: ?ThreadPermissionsBlob,
 };
 async function recalculateThreadPermissions(
   threadID: string,
 ): Promise<Changeset> {
   const threadQuery = SQL`
     SELECT type, depth, parent_thread_id, containing_thread_id
     FROM threads
     WHERE id = ${threadID}
   `;
   const membershipQuery = SQL`
     SELECT m.user, m.role, m.permissions, m.permissions_for_children,
       r.permissions AS role_permissions, cm.role AS containing_role
     FROM threads t
     INNER JOIN memberships m ON m.thread = t.id
     LEFT JOIN roles r ON r.id = m.role
     LEFT JOIN memberships cm
       ON cm.user = m.user AND cm.thread = t.containing_thread_id
     WHERE t.id = ${threadID}
   `;
   const parentMembershipQuery = SQL`
     SELECT pm.user, pm.permissions_for_children AS permissions_from_parent
     FROM threads t
     INNER JOIN memberships pm ON pm.thread = t.parent_thread_id
     WHERE t.id = ${threadID}
   `;
   const [[threadResults], [membershipResults], [parentMembershipResults]] =
     await Promise.all([
       dbQuery(threadQuery),
       dbQuery(membershipQuery),
       dbQuery(parentMembershipQuery),
     ]);
 
   if (threadResults.length !== 1) {
     throw new ServerError('internal_error');
   }
   const [threadResult] = threadResults;
   const threadType = assertThreadType(threadResult.type);
   const depth = threadResult.depth;
   const hasContainingThreadID = threadResult.containing_thread_id !== null;
   const parentThreadID = threadResult.parent_thread_id?.toString();
 
   const membershipInfo: Map<string, RecalculatePermissionsMemberInfo> =
     new Map();
   for (const row of membershipResults) {
     const userID = row.user.toString();
     membershipInfo.set(userID, {
       role: row.role.toString(),
       permissions: JSON.parse(row.permissions),
       permissionsForChildren: JSON.parse(row.permissions_for_children),
       rolePermissions: JSON.parse(row.role_permissions),
       memberOfContainingThread: !!(
         row.containing_role && row.containing_role > 0
       ),
     });
   }
   for (const row of parentMembershipResults) {
     const userID = row.user.toString();
     const permissionsFromParent = JSON.parse(row.permissions_from_parent);
     const membership = membershipInfo.get(userID);
     if (membership) {
       membership.permissionsFromParent = permissionsFromParent;
     } else {
       membershipInfo.set(userID, {
         permissionsFromParent: permissionsFromParent,
       });
     }
   }
 
   const relationshipChangeset = new RelationshipChangeset();
   const existingMemberIDs = membershipResults.map(row => row.user.toString());
   if (threadID !== genesis.id) {
     relationshipChangeset.setAllRelationshipsExist(existingMemberIDs);
   }
   const parentMemberIDs = parentMembershipResults.map(row =>
     row.user.toString(),
   );
   if (parentThreadID && parentThreadID !== genesis.id) {
     relationshipChangeset.setAllRelationshipsExist(parentMemberIDs);
   }
 
   const membershipRows = [];
   const toUpdateDescendants = new Map();
   for (const [userID, membership] of membershipInfo) {
     const { rolePermissions: intendedRolePermissions, permissionsFromParent } =
       membership;
     const oldPermissions = membership?.permissions ?? null;
     const oldPermissionsForChildren =
       membership?.permissionsForChildren ?? null;
 
     const existingMembership = membership.role !== undefined;
     const oldRole = membership.role ?? '-1';
     const memberOfContainingThread = hasContainingThreadID
       ? !!membership.memberOfContainingThread
       : true;
     const targetRole = memberOfContainingThread ? oldRole : '-1';
     const rolePermissions = memberOfContainingThread
       ? intendedRolePermissions
       : null;
 
     const permissions = makePermissionsBlob(
       rolePermissions,
       permissionsFromParent,
       threadID,
       threadType,
     );
     const permissionsForChildren = makePermissionsForChildrenBlob(permissions);
     const newRole = getRoleForPermissions(targetRole, permissions);
     const userLostMembership = Number(oldRole) > 0 && Number(newRole) <= 0;
 
     if (_isEqual(permissions)(oldPermissions) && oldRole === newRole) {
       // This thread and all of its descendants need no updates for this user,
       // since the corresponding memberships row is unchanged by this operation
       continue;
     }
 
     if (permissions) {
       membershipRows.push({
         operation: 'save',
         intent: 'none',
         userID,
         threadID,
         userNeedsFullThreadDetails: false,
         permissions,
         permissionsForChildren,
         role: newRole,
         oldRole,
       });
     } else {
       membershipRows.push({
         operation: 'delete',
         intent: 'none',
         userID,
         threadID,
         oldRole,
       });
     }
 
     if (permissions && !existingMembership && threadID !== genesis.id) {
       // If there was no membership row before, and we are creating one,
       // we'll need to make sure the new member has a relationship row with
       // each existing member. We handle guaranteeing that new members have
       // relationship rows with each other in saveMemberships.
       relationshipChangeset.setRelationshipsNeeded(userID, existingMemberIDs);
     }
 
     if (
       userLostMembership ||
       !_isEqual(permissionsForChildren)(oldPermissionsForChildren)
     ) {
       toUpdateDescendants.set(userID, {
         userIsMember: Number(newRole) > 0,
         permissionsForChildren,
       });
     }
   }
 
   if (toUpdateDescendants.size > 0) {
     const {
       membershipRows: descendantMembershipRows,
       relationshipChangeset: descendantRelationshipChangeset,
     } = await updateDescendantPermissions({
       threadID,
       depth,
       changesByUser: toUpdateDescendants,
     });
     pushAll(membershipRows, descendantMembershipRows);
     relationshipChangeset.addAll(descendantRelationshipChangeset);
   }
 
   return { membershipRows, relationshipChangeset };
 }
 
 const defaultSubscriptionString = JSON.stringify({
   home: false,
   pushNotifs: false,
 });
 const joinSubscriptionString = JSON.stringify({ home: true, pushNotifs: true });
 
 const membershipInsertBatchSize = 50;
 
 const visibleExtractString = `$.${threadPermissions.VISIBLE}.value`;
 
 async function saveMemberships({
   toSave,
   updateMembershipsLastMessage,
 }: {
   toSave: $ReadOnlyArray<MembershipRowToSave>,
   updateMembershipsLastMessage: boolean,
 }) {
   if (toSave.length === 0) {
     return;
   }
 
   const time = Date.now();
   const insertRows = [];
   for (const rowToSave of toSave) {
     insertRows.push([
       rowToSave.userID,
       rowToSave.threadID,
       rowToSave.role,
       time,
       rowToSave.intent === 'join'
         ? joinSubscriptionString
         : defaultSubscriptionString,
       rowToSave.permissions ? JSON.stringify(rowToSave.permissions) : null,
       rowToSave.permissionsForChildren
         ? JSON.stringify(rowToSave.permissionsForChildren)
         : null,
       rowToSave.unread ? 1 : 0,
       0,
     ]);
   }
 
   // Logic below will only update an existing membership row's `subscription`
   // column if the user is either joining or leaving the thread. That means
   // there's no way to use this function to update a user's subscription without
   // also making them join or leave the thread. The reason we do this is because
   // we need to specify a value for `subscription` here, as it's a non-null
   // column and this is an INSERT, but we don't want to require people to have
   // to know the current `subscription` when they're just using this function to
   // update the permissions of an existing membership row.
   while (insertRows.length > 0) {
     const batch = insertRows.splice(0, membershipInsertBatchSize);
     const query = SQL`
       INSERT INTO memberships (user, thread, role, creation_time, subscription,
         permissions, permissions_for_children, last_message, last_read_message)
       VALUES ${batch}
       ON DUPLICATE KEY UPDATE
         subscription = IF(
           (role <= 0 AND VALUE(role) > 0)
             OR (role > 0 AND VALUE(role) <= 0),
           VALUE(subscription),
           subscription
         ),
         role = VALUE(role),
         permissions = VALUE(permissions),
         permissions_for_children = VALUE(permissions_for_children)
     `;
     await dbQuery(query);
   }
 
   if (!updateMembershipsLastMessage) {
     return;
   }
 
   const joinRows = toSave
     .filter(row => row.intent === 'join')
     .map(row => [row.userID, row.threadID, row.unread]);
 
   if (joinRows.length === 0) {
     return;
   }
 
   const joinedUserThreadPairs = joinRows.map(([user, thread]) => [
     user,
     thread,
   ]);
 
   const unreadUserThreadPairs = joinRows
     .filter(([, , unread]) => !!unread)
     .map(([user, thread]) => [user, thread]);
 
   let lastReadMessageExpression;
   if (unreadUserThreadPairs.length === 0) {
     lastReadMessageExpression = SQL`
       GREATEST(COALESCE(all_users_query.message, 0), 
         COALESCE(last_subthread_message_for_user_query.message, 0))
     `;
   } else {
     lastReadMessageExpression = SQL`
       (CASE 
         WHEN ((mm.user, mm.thread) in (${unreadUserThreadPairs})) THEN 0
         ELSE GREATEST(COALESCE(all_users_query.message, 0), 
           COALESCE(last_subthread_message_for_user_query.message, 0))
       END)
     `;
   }
 
   // We join two subqueries with the memberships table:
   // - the first subquery calculates the oldest non-CREATE_SUB_THREAD
   //   message, which is the same for all users
   // - the second subquery calculates the oldest CREATE_SUB_THREAD messages,
   //   which can be different for each user because of visibility permissions
   // Then we set the `last_message` column to the greater value of the two.
   // For `last_read_message` we do the same but only if the user should have
   // the "unread" status set for this thread.
   const query = SQL`
     UPDATE memberships mm
     LEFT JOIN (
       SELECT thread, MAX(id) AS message
       FROM messages
       WHERE type != ${messageTypes.CREATE_SUB_THREAD}
       GROUP BY thread 
     ) all_users_query ON mm.thread = all_users_query.thread
     LEFT JOIN (
       SELECT m.thread, stm.user, MAX(m.id) AS message 
       FROM messages m
       LEFT JOIN memberships stm ON m.type = ${messageTypes.CREATE_SUB_THREAD}
         AND stm.thread = m.content
       WHERE JSON_EXTRACT(stm.permissions, ${visibleExtractString}) IS TRUE
       GROUP BY m.thread, stm.user
     ) last_subthread_message_for_user_query 
     ON mm.thread = last_subthread_message_for_user_query.thread 
       AND mm.user = last_subthread_message_for_user_query.user
     SET
       mm.last_message = GREATEST(COALESCE(all_users_query.message, 0), 
         COALESCE(last_subthread_message_for_user_query.message, 0)),
       mm.last_read_message =
   `;
   query.append(lastReadMessageExpression);
   query.append(SQL`WHERE (mm.user, mm.thread) IN (${joinedUserThreadPairs});`);
 
   await dbQuery(query);
 }
 
 async function deleteMemberships(
   toDelete: $ReadOnlyArray<MembershipRowToDelete>,
 ) {
   if (toDelete.length === 0) {
     return;
   }
 
   const time = Date.now();
   const insertRows = toDelete.map(rowToDelete => [
     rowToDelete.userID,
     rowToDelete.threadID,
     -1,
     time,
     defaultSubscriptionString,
     null,
     null,
     0,
     0,
   ]);
 
   while (insertRows.length > 0) {
     const batch = insertRows.splice(0, membershipInsertBatchSize);
     const query = SQL`
       INSERT INTO memberships (user, thread, role, creation_time, subscription,
         permissions, permissions_for_children, last_message, last_read_message)
       VALUES ${batch}
       ON DUPLICATE KEY UPDATE
         role = -1,
         permissions = NULL,
         permissions_for_children = NULL,
         subscription = ${defaultSubscriptionString},
         last_message = 0,
         last_read_message = 0
     `;
     await dbQuery(query);
   }
 }
 
 const emptyCommitMembershipChangesetConfig = Object.freeze({});
 
 // Specify non-empty changedThreadIDs to force updates to be generated for those
 // threads, presumably for reasons not covered in the changeset. calendarQuery
 // only needs to be specified if a JOIN_THREAD update will be generated for the
 // viewer, in which case it's necessary for knowing the set of entries to fetch.
 type ChangesetCommitResult = {
   ...CreateUpdatesResult,
 };
 async function commitMembershipChangeset(
   viewer: Viewer,
   changeset: Changeset,
   {
     changedThreadIDs = new Set(),
     calendarQuery,
     updatesForCurrentSession = 'return',
     updateMembershipsLastMessage = false,
   }: {
     +changedThreadIDs?: Set<string>,
     +calendarQuery?: ?CalendarQuery,
     +updatesForCurrentSession?: UpdatesForCurrentSession,
     +updateMembershipsLastMessage?: boolean,
   } = emptyCommitMembershipChangesetConfig,
 ): Promise<ChangesetCommitResult> {
   if (!viewer.loggedIn) {
     throw new ServerError('not_logged_in');
   }
   const { membershipRows, relationshipChangeset } = changeset;
 
   const membershipRowMap = new Map();
   for (const row of membershipRows) {
     const { userID, threadID } = row;
     changedThreadIDs.add(threadID);
 
     const pairString = `${userID}|${threadID}`;
     const existing = membershipRowMap.get(pairString);
     invariant(
       !existing || existing.intent === 'none' || row.intent === 'none',
       `multiple intents provided for ${pairString}`,
     );
     if (!existing || existing.intent === 'none') {
       membershipRowMap.set(pairString, row);
     }
   }
 
   const toSave = [],
     toDelete = [],
     toRescindPushNotifs = [];
   for (const row of membershipRowMap.values()) {
     if (
       row.operation === 'delete' ||
       (row.operation === 'save' && Number(row.role) <= 0)
     ) {
       const { userID, threadID } = row;
       toRescindPushNotifs.push({ userID, threadID });
     }
     if (row.operation === 'delete') {
       toDelete.push(row);
     } else {
       toSave.push(row);
     }
   }
 
   const threadsToSavedUsers = new Map();
   for (const row of membershipRowMap.values()) {
     const { userID, threadID } = row;
     let savedUsers = threadsToSavedUsers.get(threadID);
     if (!savedUsers) {
       savedUsers = [];
       threadsToSavedUsers.set(threadID, savedUsers);
     }
     savedUsers.push(userID);
   }
   for (const [threadID, savedUsers] of threadsToSavedUsers) {
     if (threadID !== genesis.id) {
       relationshipChangeset.setAllRelationshipsNeeded(savedUsers);
     }
   }
   const relationshipRows = relationshipChangeset.getRows();
 
   const [updateDatas] = await Promise.all([
     updateChangedUndirectedRelationships(relationshipRows),
     saveMemberships({ toSave, updateMembershipsLastMessage }),
     deleteMemberships(toDelete),
     rescindPushNotifsForMemberDeletion(toRescindPushNotifs),
   ]);
 
   const serverThreadInfoFetchResult = await fetchServerThreadInfos({
     threadIDs: changedThreadIDs,
   });
   const { threadInfos: serverThreadInfos } = serverThreadInfoFetchResult;
 
   const time = Date.now();
   for (const changedThreadID of changedThreadIDs) {
     const serverThreadInfo = serverThreadInfos[changedThreadID];
     for (const memberInfo of serverThreadInfo.members) {
       const pairString = `${memberInfo.id}|${serverThreadInfo.id}`;
       const membershipRow = membershipRowMap.get(pairString);
       if (membershipRow) {
         continue;
       }
       updateDatas.push({
         type: updateTypes.UPDATE_THREAD,
         userID: memberInfo.id,
         time,
         threadID: changedThreadID,
       });
     }
   }
 
   for (const row of membershipRowMap.values()) {
     const { userID, threadID } = row;
     if (row.operation === 'delete' || row.role === '-1') {
       if (row.oldRole !== '-1') {
         updateDatas.push({
           type: updateTypes.DELETE_THREAD,
           userID,
           time,
           threadID,
         });
       }
     } else if (row.userNeedsFullThreadDetails) {
       updateDatas.push({
         type: updateTypes.JOIN_THREAD,
         userID,
         time,
         threadID,
       });
     } else {
       updateDatas.push({
         type: updateTypes.UPDATE_THREAD,
         userID,
         time,
         threadID,
       });
     }
   }
 
   const threadInfoFetchResult = rawThreadInfosFromServerThreadInfos(
     viewer,
     serverThreadInfoFetchResult,
   );
   const { viewerUpdates, userInfos } = await createUpdates(updateDatas, {
     viewer,
     calendarQuery,
     ...threadInfoFetchResult,
     updatesForCurrentSession,
   });
 
   return {
     userInfos,
     viewerUpdates,
   };
 }
 
 const emptyGetChangesetCommitResultConfig = Object.freeze({});
 
 // When the user tries to create a new thread, it's possible for the client to
 // fail the creation even if a row gets added to the threads table. This may
 // occur due to a timeout (on either the client or server side), or due to some
 // error in the server code following the INSERT operation. Handling the error
 // scenario is more challenging since it would require detecting which set of
 // operations failed so we could retry them. As a result, this code is geared at
 // only handling the timeout scenario.
 async function getChangesetCommitResultForExistingThread(
   viewer: Viewer,
   threadID: string,
   otherUpdates: $ReadOnlyArray<ServerUpdateInfo>,
   {
     calendarQuery,
     updatesForCurrentSession = 'return',
   }: {
     +calendarQuery?: ?CalendarQuery,
     +updatesForCurrentSession?: UpdatesForCurrentSession,
   } = emptyGetChangesetCommitResultConfig,
 ): Promise<CreateUpdatesResult> {
   for (const update of otherUpdates) {
     if (
       update.type === updateTypes.JOIN_THREAD &&
       update.threadInfo.id === threadID
     ) {
       // If the JOIN_THREAD is already there we can expect
       // the appropriate UPDATE_USERs to be covered as well
       return { viewerUpdates: otherUpdates, userInfos: {} };
     }
   }
 
   const time = Date.now();
   const updateDatas = [
     {
       type: updateTypes.JOIN_THREAD,
       userID: viewer.userID,
       time,
       threadID,
       targetSession: viewer.session,
     },
   ];
 
   // To figure out what UserInfos might be missing, we consider the worst case:
   // the same client previously attempted to create a thread with a non-friend
   // they found via search results, but the request timed out. In this scenario
   // the viewer might never have received the UPDATE_USER that would add that
   // UserInfo to their UserStore, but the server assumed the client had gotten
   // it because createUpdates was called with UpdatesForCurrentSession=return.
   // For completeness here we query for the full list of memberships rows in the
   // thread. We can't use fetchServerThreadInfos because it skips role=-1 rows
   const membershipsQuery = SQL`
     SELECT user
     FROM memberships
     WHERE thread = ${threadID} AND user != ${viewer.userID}
   `;
   const [results] = await dbQuery(membershipsQuery);
   for (const row of results) {
     updateDatas.push({
       type: updateTypes.UPDATE_USER,
       userID: viewer.userID,
       time,
       updatedUserID: row.user.toString(),
       targetSession: viewer.session,
     });
   }
 
   const { viewerUpdates, userInfos } = await createUpdates(updateDatas, {
     viewer,
     calendarQuery,
     updatesForCurrentSession,
   });
   return { viewerUpdates: [...otherUpdates, ...viewerUpdates], userInfos };
 }
 
 const rescindPushNotifsBatchSize = 3;
 async function rescindPushNotifsForMemberDeletion(
   toRescindPushNotifs: $ReadOnlyArray<{ +userID: string, +threadID: string }>,
 ): Promise<void> {
   const queue = [...toRescindPushNotifs];
   while (queue.length > 0) {
     const batch = queue.splice(0, rescindPushNotifsBatchSize);
     await Promise.all(
       batch.map(({ userID, threadID }) =>
         rescindPushNotifs(
           SQL`n.thread = ${threadID} AND n.user = ${userID}`,
           SQL`IF(m.thread = ${threadID}, NULL, m.thread)`,
         ),
       ),
     );
   }
 }
 
 // Deprecated - use updateRolesAndPermissionsForAllThreads instead
 async function DEPRECATED_recalculateAllThreadPermissions() {
   const getAllThreads = SQL`SELECT id FROM threads`;
   const [result] = await dbQuery(getAllThreads);
 
   // We handle each thread one-by-one to avoid a situation where a permission
   // calculation for a child thread, done during a call to
   // recalculateThreadPermissions for the parent thread, can be incorrectly
   // overriden by a call to recalculateThreadPermissions for the child thread.
   // If the changeset resulting from the parent call isn't committed before the
   // calculation is done for the child, the calculation done for the child can
   // be incorrect.
   const viewer = createScriptViewer(bots.commbot.userID);
   for (const row of result) {
     const threadID = row.id.toString();
     const changeset = await recalculateThreadPermissions(threadID);
     await commitMembershipChangeset(viewer, changeset);
   }
 }
 
 async function updateRolesAndPermissionsForAllThreads() {
   const batchSize = 10;
   const fetchThreads = SQL`SELECT id, type, depth FROM threads`;
   const [result] = await dbQuery(fetchThreads);
   const allThreads = result.map(row => {
     return {
       id: row.id.toString(),
       type: assertThreadType(row.type),
       depth: row.depth,
     };
   });
 
   const viewer = createScriptViewer(bots.commbot.userID);
 
   const maxDepth = Math.max(...allThreads.map(row => row.depth));
 
   for (let depth = 0; depth <= maxDepth; depth++) {
     const threads = allThreads.filter(row => row.depth === depth);
     console.log(`recalculating permissions for threads with depth ${depth}`);
     while (threads.length > 0) {
       const batch = threads.splice(0, batchSize);
       const membershipRows = [];
       const relationshipChangeset = new RelationshipChangeset();
       await Promise.all(
         batch.map(async thread => {
           console.log(`updating roles for ${thread.id}`);
           await updateRoles(viewer, thread.id, thread.type);
           console.log(`recalculating permissions for ${thread.id}`);
           const {
             membershipRows: threadMembershipRows,
             relationshipChangeset: threadRelationshipChangeset,
           } = await recalculateThreadPermissions(thread.id);
           membershipRows.push(...threadMembershipRows);
           relationshipChangeset.addAll(threadRelationshipChangeset);
         }),
       );
       console.log(`committing batch ${JSON.stringify(batch)}`);
       await commitMembershipChangeset(viewer, {
         membershipRows,
         relationshipChangeset,
       });
     }
   }
 }
 
 export {
   changeRole,
   recalculateThreadPermissions,
   getChangesetCommitResultForExistingThread,
   saveMemberships,
   commitMembershipChangeset,
   DEPRECATED_recalculateAllThreadPermissions,
   updateRolesAndPermissionsForAllThreads,
 };