diff --git a/src/__tests__/lib/exampleData.js b/src/__tests__/lib/exampleData.js
index c6d4af8c6a0..fba60defcce 100644
--- a/src/__tests__/lib/exampleData.js
+++ b/src/__tests__/lib/exampleData.js
@@ -24,6 +24,7 @@ import type {
   MessageFetchStartAction,
   MessageFetchCompleteAction,
   Action,
+  PerAccountAction,
   PerAccountState,
   GlobalState,
   CaughtUpState,
@@ -765,7 +766,7 @@ export const action = Object.freeze({
 export const mkActionEventNewMessage = (
   message: Message,
   args?: {| caughtUp?: CaughtUpState, local_message_id?: number, ownUserId?: UserId |},
-): Action =>
+): PerAccountAction =>
   deepFreeze({
     type: EVENT_NEW_MESSAGE,
     id: 1001,
diff --git a/src/account/accountActions.js b/src/account/accountActions.js
index 42439a648be..8d67c1615d4 100644
--- a/src/account/accountActions.js
+++ b/src/account/accountActions.js
@@ -1,10 +1,10 @@
 /* @flow strict-local */
 import * as NavigationService from '../nav/NavigationService';
-import type { Action, ThunkAction, GlobalThunkAction } from '../types';
+import type { AllAccountsAction, ThunkAction, GlobalThunkAction } from '../types';
 import { ACCOUNT_SWITCH, ACCOUNT_REMOVE, LOGIN_SUCCESS, LOGOUT } from '../actionConstants';
 import { resetToAccountPicker, resetToMainTabs } from '../nav/navActions';
 
-const accountSwitchPlain = (index: number): Action => ({
+const accountSwitchPlain = (index: number): AllAccountsAction => ({
   type: ACCOUNT_SWITCH,
   index,
 });
@@ -14,12 +14,12 @@ export const accountSwitch = (index: number): GlobalThunkAction<void> => (dispat
   dispatch(accountSwitchPlain(index));
 };
 
-export const removeAccount = (index: number): Action => ({
+export const removeAccount = (index: number): AllAccountsAction => ({
   type: ACCOUNT_REMOVE,
   index,
 });
 
-const loginSuccessPlain = (realm: URL, email: string, apiKey: string): Action => ({
+const loginSuccessPlain = (realm: URL, email: string, apiKey: string): AllAccountsAction => ({
   type: LOGIN_SUCCESS,
   realm,
   email,
@@ -34,7 +34,7 @@ export const loginSuccess = (realm: URL, email: string, apiKey: string): ThunkAc
   dispatch(loginSuccessPlain(realm, email, apiKey));
 };
 
-const logoutPlain = (): Action => ({
+const logoutPlain = (): AllAccountsAction => ({
   type: LOGOUT,
 });
 
diff --git a/src/actionConstants.js b/src/actionConstants.js
index 1c7bb14e285..c246460b01e 100644
--- a/src/actionConstants.js
+++ b/src/actionConstants.js
@@ -50,7 +50,7 @@ export const MESSAGE_FETCH_ERROR: 'MESSAGE_FETCH_ERROR' = 'MESSAGE_FETCH_ERROR';
 export const MESSAGE_FETCH_COMPLETE: 'MESSAGE_FETCH_COMPLETE' = 'MESSAGE_FETCH_COMPLETE';
 
 export const PRESENCE_RESPONSE: 'PRESENCE_RESPONSE' = 'PRESENCE_RESPONSE';
-export const SETTINGS_CHANGE: 'SETTINGS_CHANGE' = 'SETTINGS_CHANGE';
+export const SET_GLOBAL_SETTINGS: 'SET_GLOBAL_SETTINGS' = 'SET_GLOBAL_SETTINGS';
 export const DEBUG_FLAG_TOGGLE: 'DEBUG_FLAG_TOGGLE' = 'DEBUG_FLAG_TOGGLE';
 export const DISMISS_SERVER_COMPAT_NOTICE: 'DISMISS_SERVER_COMPAT_NOTICE' =
   'DISMISS_SERVER_COMPAT_NOTICE';
diff --git a/src/actionTypes.js b/src/actionTypes.js
index d8aa59e9fd0..0b4f025dedf 100644
--- a/src/actionTypes.js
+++ b/src/actionTypes.js
@@ -1,4 +1,5 @@
 /* @flow strict-local */
+import { ensureUnreachable } from './generics';
 import {
   REHYDRATE,
   APP_ONLINE,
@@ -18,7 +19,7 @@ import {
   REGISTER_START,
   REGISTER_ABORT,
   REGISTER_COMPLETE,
-  SETTINGS_CHANGE,
+  SET_GLOBAL_SETTINGS,
   DRAFT_UPDATE,
   PRESENCE_RESPONSE,
   MESSAGE_SEND_START,
@@ -84,7 +85,7 @@ import type {
   Topic,
   PresenceState,
   RealmEmojiById,
-  SettingsState,
+  GlobalSettingsState,
   CaughtUpState,
   MuteState,
   AlertWordsState,
@@ -559,9 +560,9 @@ export type EventAction =
   | EventUserGroupAction
   | EventUserStatusUpdateAction;
 
-type SettingsChangeAction = {|
-  type: typeof SETTINGS_CHANGE,
-  update: $Shape<SettingsState>,
+type SetGlobalSettingsAction = {|
+  type: typeof SET_GLOBAL_SETTINGS,
+  update: $Shape<$Exact<GlobalSettingsState>>,
 |};
 
 type DraftUpdateAction = {|
@@ -607,9 +608,17 @@ type InitTopicsAction = {|
   streamId: number,
 |};
 
+/* eslint-disable spaced-comment */
+
+////
+//
+// The `Action` union type, and some subtypes.
 //
-// The `Action` union type.
+////
+
 //
+// First, some convenience unions without much meaning.
+// (We should perhaps just inline these below.)
 
 type AccountAction = AccountSwitchAction | AccountRemoveAction | LoginSuccessAction | LogoutAction;
 
@@ -623,29 +632,183 @@ type MessageAction = MessageFetchStartAction | MessageFetchErrorAction | Message
 
 type OutboxAction = MessageSendStartAction | MessageSendCompleteAction | DeleteOutboxMessageAction;
 
-type RealmAction = RegisterCompleteAction | UnackPushTokenAction | AckPushTokenAction;
+//
+// Then, the primary subtypes of `Action`.  Each of these should have some
+// coherent meaning in terms of what kind of state it applies to; and they
+// should have no overlap.  (Subtypes that might overlap are formed below
+// as unions of these primary subtypes.)
 
-type SessionAction =
-  | RehydrateAction
-  | AppOnlineAction
-  | AppOrientationAction
-  | GotPushTokenAction
-  | DebugFlagToggleAction
-  | DismissServerCompatNoticeAction
-  | ToggleOutboxSendingAction;
+/* eslint-disable semi-style */
 
-/** Covers all actions we ever `dispatch`. */
-// The grouping here is completely arbitrary; don't worry about it.
-export type Action =
+/**
+ * Plain actions applying to this account's state.
+ *
+ * That is, these should only be dispatched from a per-account context, and
+ * they apply to the account the caller is acting on.  In a pre-#5006 world,
+ * that means the active account.
+ */
+// prettier-ignore
+export type PerAccountAction =
+  // The grouping here is completely arbitrary; don't worry about it.
   | EventAction
-  | AccountAction
   | LoadingAction
   | MessageAction
   | OutboxAction
-  | RealmAction
-  | SessionAction
+  | RegisterCompleteAction
   | DraftUpdateAction
   | PresenceResponseAction
-  | SettingsChangeAction
   | InitTopicsAction
-  | ClearTypingAction;
+  | ClearTypingAction
+  // state.session
+  | DismissServerCompatNoticeAction
+  | ToggleOutboxSendingAction
+  ;
+
+/** Plain actions applying to other accounts' per-account state. */
+// prettier-ignore
+export type AllAccountsAction =
+  // This affects all the per-account states as well as everything else.
+  | RehydrateAction
+  // These can rearrange the `state.accounts` list itself.
+  | AccountAction
+  // These two are about a specific account… but not just the active one,
+  // and they encode which one they mean.
+  | AckPushTokenAction | UnackPushTokenAction
+  ;
+
+/** Plain actions not affecting any per-account state. */
+// prettier-ignore
+export type AccountIndependentAction =
+  | SetGlobalSettingsAction
+  // state.session
+  | AppOnlineAction
+  | AppOrientationAction
+  | GotPushTokenAction
+  | DebugFlagToggleAction
+  ;
+
+//
+// `Action` itself.
+
+/**
+ * Covers all plain actions we ever `dispatch`.
+ *
+ * For *all* actions we ever dispatch, see also the thunk action types in
+ * `reduxTypes.js`.
+ */
+// prettier-ignore
+export type Action =
+  // This should consist of the primary subtypes defined just above.
+  | PerAccountAction
+  | AllAccountsAction
+  | AccountIndependentAction
+  ;
+
+//
+// Other subtypes of `Action`.
+//
+// These should be unions of the primary subtypes, to express different
+// meanings about what contexts the actions can be used in.
+
+/** Plain actions that per-account reducers may respond to. */
+// prettier-ignore
+export type PerAccountApplicableAction =
+  | PerAccountAction
+  | AllAccountsAction
+  ;
+
+// Plain actions that global reducers may respond to are... well, at the
+// moment we have no reducers that act only on global state.  Our state
+// subtrees `session` and `settings` mix global with per-account state,
+// while `accounts` contains per-account state for all accounts, and its
+// reducer does respond to some of PerAccountAction as well as
+// AllAccountsAction.
+// TODO(#5006): Make a GlobalApplicableAction for global session and
+//   settings state, once those are separate from per-account.
+
+// TODO(#5006): would be nice to assert these types have empty intersection
+// (a: PerAccountApplicableAction & AccountIndependentAction): empty => a; // eslint-disable-line
+// (a: GlobalApplicableAction & PerAccountAction): empty => a; // eslint-disable-line
+
+/** Actions that can be dispatched without reference to a specific account. */
+// prettier-ignore
+export type DispatchableWithoutAccountAction =
+  | AllAccountsAction
+  | AccountIndependentAction
+  ;
+
+/** True just if the action is a PerAccountApplicableAction. */
+export function isPerAccountApplicableAction(action: Action): boolean {
+  switch (action.type) {
+    case EVENT:
+    case EVENT_ALERT_WORDS:
+    case EVENT_MESSAGE_DELETE:
+    case EVENT_MUTED_TOPICS:
+    case EVENT_MUTED_USERS:
+    case EVENT_NEW_MESSAGE:
+    case EVENT_PRESENCE:
+    case EVENT_REACTION_ADD:
+    case EVENT_REACTION_REMOVE:
+    case EVENT_REALM_EMOJI_UPDATE:
+    case EVENT_REALM_FILTERS:
+    case EVENT_SUBMESSAGE:
+    case EVENT_SUBSCRIPTION:
+    case EVENT_TYPING_START:
+    case EVENT_TYPING_STOP:
+    case EVENT_UPDATE_DISPLAY_SETTINGS:
+    case EVENT_UPDATE_GLOBAL_NOTIFICATIONS_SETTINGS:
+    case EVENT_UPDATE_MESSAGE:
+    case EVENT_UPDATE_MESSAGE_FLAGS:
+    case EVENT_USER_ADD:
+    case EVENT_USER_GROUP_ADD:
+    case EVENT_USER_GROUP_ADD_MEMBERS:
+    case EVENT_USER_GROUP_REMOVE:
+    case EVENT_USER_GROUP_REMOVE_MEMBERS:
+    case EVENT_USER_GROUP_UPDATE:
+    case EVENT_USER_REMOVE:
+    case EVENT_USER_STATUS_UPDATE:
+    case EVENT_USER_UPDATE:
+    case DEAD_QUEUE:
+    case REGISTER_START:
+    case REGISTER_ABORT:
+    case REGISTER_COMPLETE:
+    case MESSAGE_FETCH_COMPLETE:
+    case MESSAGE_FETCH_ERROR:
+    case MESSAGE_FETCH_START:
+    case MESSAGE_SEND_COMPLETE:
+    case MESSAGE_SEND_START:
+    case DELETE_OUTBOX_MESSAGE:
+    case DRAFT_UPDATE:
+    case PRESENCE_RESPONSE:
+    case INIT_TOPICS:
+    case CLEAR_TYPING:
+    case DISMISS_SERVER_COMPAT_NOTICE:
+    case TOGGLE_OUTBOX_SENDING:
+      (action: PerAccountAction);
+      (action: PerAccountApplicableAction);
+      return true;
+
+    case REHYDRATE:
+    case ACCOUNT_SWITCH:
+    case ACCOUNT_REMOVE:
+    case LOGIN_SUCCESS:
+    case LOGOUT:
+    case ACK_PUSH_TOKEN:
+    case UNACK_PUSH_TOKEN:
+      (action: AllAccountsAction);
+      (action: PerAccountApplicableAction);
+      return true;
+
+    case SET_GLOBAL_SETTINGS:
+    case APP_ONLINE:
+    case APP_ORIENTATION:
+    case GOT_PUSH_TOKEN:
+    case DEBUG_FLAG_TOGGLE:
+      (action: AccountIndependentAction);
+      return false;
+
+    default:
+      ensureUnreachable(action);
+      return false;
+  }
+}
diff --git a/src/alertWords/alertWordsReducer.js b/src/alertWords/alertWordsReducer.js
index 44724d439d1..5efd814821c 100644
--- a/src/alertWords/alertWordsReducer.js
+++ b/src/alertWords/alertWordsReducer.js
@@ -1,11 +1,14 @@
 /* @flow strict-local */
-import type { AlertWordsState, Action } from '../types';
+import type { AlertWordsState, PerAccountApplicableAction } from '../types';
 import { REGISTER_COMPLETE, EVENT_ALERT_WORDS, ACCOUNT_SWITCH, LOGOUT } from '../actionConstants';
 import { NULL_ARRAY } from '../nullObjects';
 
 const initialState = NULL_ARRAY;
 
-export default (state: AlertWordsState = initialState, action: Action): AlertWordsState => {
+export default (
+  state: AlertWordsState = initialState,
+  action: PerAccountApplicableAction,
+): AlertWordsState => {
   switch (action.type) {
     case LOGOUT:
     case ACCOUNT_SWITCH:
diff --git a/src/boot/reducers.js b/src/boot/reducers.js
index 7d475c90932..aaff0400d30 100644
--- a/src/boot/reducers.js
+++ b/src/boot/reducers.js
@@ -1,6 +1,14 @@
 /* @flow strict-local */
 import config from '../config';
-import type { Action, GlobalState, MigrationsState } from '../types';
+import type {
+  Action,
+  PerAccountState,
+  PerAccountApplicableAction,
+  GlobalState,
+  MigrationsState,
+} from '../types';
+import { dubPerAccountState } from '../reduxTypes';
+import { isPerAccountApplicableAction } from '../actionTypes';
 
 import accounts from '../account/accountsReducer';
 import alertWords from '../alertWords/alertWordsReducer';
@@ -40,12 +48,19 @@ function maybeLogSlowReducer(action, key: $Keys<GlobalState>, startMs, endMs) {
   }
 }
 
-function applyReducer<Key: $Keys<GlobalState>, State>(
+/**
+ * Apply a sub-reducer, with perf logging if enabled.
+ *
+ * The `globalState` argument is the "global" state relative to this
+ * sub-reducer: so type GS is `GlobalState` for a global reducer, and
+ * `PerAccountState` for a per-account reducer.
+ */
+function applyReducer<GS, A: Action, Key: $Keys<GS> & $Keys<GlobalState>, State>(
   key: Key,
-  reducer: (void | State, Action, GlobalState) => State,
+  reducer: (void | State, A, GS) => State,
   state: void | State,
-  action: Action,
-  globalState: void | GlobalState,
+  action: A,
+  globalState: void | GS,
 ): State {
   let startMs = undefined;
   if (enableReduxSlowReducerWarnings) {
@@ -62,51 +77,74 @@ function applyReducer<Key: $Keys<GlobalState>, State>(
      Then on the other hand it's helpful because we want each reducer that
      ever does use the globalState parameter to require it -- so that Flow
      can help us be sure to pass it at the reducer's many other call sites,
-     in tests.  That means it has to be `globalState: GlobalState`, not
-     `globalState : void | GlobalState`.
+     in tests.  That means it has to be `globalState: GS`, not
+     `globalState : void | GS`.
    */
-  const castGlobalState: GlobalState = globalState;
+  const castGlobalState: GS = globalState;
 
   const nextState = reducer(state, action, castGlobalState);
 
   if (startMs !== undefined) {
     const endMs = Date.now();
-    maybeLogSlowReducer(action, key, startMs, endMs);
+    maybeLogSlowReducer((action: Action), key, startMs, endMs);
   }
 
   return nextState;
 }
 
 // Based on Redux upstream's combineReducers.
-export default (state: void | GlobalState, action: Action): GlobalState => {
+export default (globalState: void | GlobalState, origAction: Action): GlobalState => {
+  let nextPerAccountState = globalState;
+  if (!nextPerAccountState || isPerAccountApplicableAction(origAction)) {
+    // Update the per-account state.  We do this when the action is a
+    // PerAccountApplicableAction... and also when it's the store
+    // initialization action, signalled by the previous state being void.
+
+    /* $FlowFixMe[incompatible-type]: TODO teach Flow that
+           isPerAccountApplicableAction checks this */
+    const action: PerAccountApplicableAction = origAction;
+    const state: void | PerAccountState = globalState ? dubPerAccountState(globalState) : undefined;
+
+    // prettier-ignore
+    nextPerAccountState = {
+      alertWords: applyReducer('alertWords', alertWords, state?.alertWords, action, state),
+      caughtUp: applyReducer('caughtUp', caughtUp, state?.caughtUp, action, state),
+      drafts: applyReducer('drafts', drafts, state?.drafts, action, state),
+      fetching: applyReducer('fetching', fetching, state?.fetching, action, state),
+      flags: applyReducer('flags', flags, state?.flags, action, state),
+      messages: applyReducer('messages', messages, state?.messages, action, state),
+      narrows: applyReducer('narrows', narrows, state?.narrows, action, state),
+      mute: applyReducer('mute', mute, state?.mute, action, state),
+      mutedUsers: applyReducer('mutedUsers', mutedUsers, state?.mutedUsers, action, state),
+      outbox: applyReducer('outbox', outbox, state?.outbox, action, state),
+      pmConversations: applyReducer('pmConversations', pmConversations, state?.pmConversations, action, state),
+      presence: applyReducer('presence', presence, state?.presence, action, state),
+      realm: applyReducer('realm', realm, state?.realm, action, state),
+      streams: applyReducer('streams', streams, state?.streams, action, state),
+      subscriptions: applyReducer('subscriptions', subscriptions, state?.subscriptions, action, state),
+      topics: applyReducer('topics', topics, state?.topics, action, state),
+      typing: applyReducer('typing', typing, state?.typing, action, state),
+      unread: applyReducer('unread', unread, state?.unread, action, state),
+      userGroups: applyReducer('userGroups', userGroups, state?.userGroups, action, state),
+      userStatus: applyReducer('userStatus', userStatus, state?.userStatus, action, state),
+      users: applyReducer('users', users, state?.users, action, state),
+    };
+  }
+
+  const state = globalState;
+  const action = origAction;
+
   // prettier-ignore
   const nextState = {
-    migrations: applyReducer('migrations', migrations, state?.migrations, action, state),
-    accounts: applyReducer('accounts', accounts, state?.accounts, action, state),
-    alertWords: applyReducer('alertWords', alertWords, state?.alertWords, action, state),
-    caughtUp: applyReducer('caughtUp', caughtUp, state?.caughtUp, action, state),
-    drafts: applyReducer('drafts', drafts, state?.drafts, action, state),
-    fetching: applyReducer('fetching', fetching, state?.fetching, action, state),
-    flags: applyReducer('flags', flags, state?.flags, action, state),
-    messages: applyReducer('messages', messages, state?.messages, action, state),
-    narrows: applyReducer('narrows', narrows, state?.narrows, action, state),
-    mute: applyReducer('mute', mute, state?.mute, action, state),
-    mutedUsers: applyReducer('mutedUsers', mutedUsers, state?.mutedUsers, action, state),
-    outbox: applyReducer('outbox', outbox, state?.outbox, action, state),
-    pmConversations: applyReducer('pmConversations', pmConversations, state?.pmConversations, action, state),
-    presence: applyReducer('presence', presence, state?.presence, action, state),
-    realm: applyReducer('realm', realm, state?.realm, action, state),
+    ...nextPerAccountState,
+
+    // TODO(#5006): These mix together per-account and global state.
     session: applyReducer('session', session, state?.session, action, state),
     settings: applyReducer('settings', settings, state?.settings, action, state),
-    streams: applyReducer('streams', streams, state?.streams, action, state),
-    subscriptions: applyReducer('subscriptions', subscriptions, state?.subscriptions, action, state),
-    topics: applyReducer('topics', topics, state?.topics, action, state),
-    typing: applyReducer('typing', typing, state?.typing, action, state),
-    // $FlowFixMe[incompatible-call] TODO(#5006)
-    unread: applyReducer('unread', unread, state?.unread, action, state),
-    userGroups: applyReducer('userGroups', userGroups, state?.userGroups, action, state),
-    userStatus: applyReducer('userStatus', userStatus, state?.userStatus, action, state),
-    users: applyReducer('users', users, state?.users, action, state),
+
+    // All other state.
+    migrations: applyReducer('migrations', migrations, state?.migrations, action, state),
+    accounts: applyReducer('accounts', accounts, state?.accounts, action, state),
   };
 
   if (state && Object.keys(nextState).every(key => nextState[key] === state[key])) {
diff --git a/src/caughtup/caughtUpReducer.js b/src/caughtup/caughtUpReducer.js
index 07b6a107bc8..83f2f96546d 100644
--- a/src/caughtup/caughtUpReducer.js
+++ b/src/caughtup/caughtUpReducer.js
@@ -1,5 +1,5 @@
 /* @flow strict-local */
-import type { CaughtUpState, Action } from '../types';
+import type { CaughtUpState, PerAccountApplicableAction } from '../types';
 import {
   REGISTER_COMPLETE,
   LOGOUT,
@@ -15,7 +15,10 @@ import { isSearchNarrow, keyFromNarrow } from '../utils/narrow';
 
 const initialState: CaughtUpState = NULL_OBJECT;
 
-export default (state: CaughtUpState = initialState, action: Action): CaughtUpState => {
+export default (
+  state: CaughtUpState = initialState,
+  action: PerAccountApplicableAction,
+): CaughtUpState => {
   switch (action.type) {
     case REGISTER_COMPLETE:
     case LOGOUT:
diff --git a/src/chat/fetchingReducer.js b/src/chat/fetchingReducer.js
index 76fdcb4fe38..248cd872e69 100644
--- a/src/chat/fetchingReducer.js
+++ b/src/chat/fetchingReducer.js
@@ -1,5 +1,5 @@
 /* @flow strict-local */
-import type { FetchingState, Action } from '../types';
+import type { FetchingState, PerAccountApplicableAction } from '../types';
 import {
   LOGOUT,
   LOGIN_SUCCESS,
@@ -63,7 +63,10 @@ const messageFetchComplete = (state, action) => {
   };
 };
 
-export default (state: FetchingState = initialState, action: Action): FetchingState => {
+export default (
+  state: FetchingState = initialState,
+  action: PerAccountApplicableAction,
+): FetchingState => {
   switch (action.type) {
     case LOGOUT:
     case LOGIN_SUCCESS:
diff --git a/src/chat/flagsReducer.js b/src/chat/flagsReducer.js
index f016ae16d28..67416a26f9f 100644
--- a/src/chat/flagsReducer.js
+++ b/src/chat/flagsReducer.js
@@ -1,7 +1,7 @@
 /* @flow strict-local */
 import invariant from 'invariant';
 
-import type { Action, FlagsState, Message } from '../types';
+import type { PerAccountApplicableAction, FlagsState, Message } from '../types';
 import {
   REGISTER_COMPLETE,
   MESSAGE_FETCH_COMPLETE,
@@ -110,7 +110,10 @@ const eventUpdateMessageFlags = (state, action) => {
   return state;
 };
 
-export default (state: FlagsState = initialState, action: Action): FlagsState => {
+export default (
+  state: FlagsState = initialState,
+  action: PerAccountApplicableAction,
+): FlagsState => {
   switch (action.type) {
     case REGISTER_COMPLETE:
     case LOGOUT:
diff --git a/src/chat/narrowsReducer.js b/src/chat/narrowsReducer.js
index dc8a3557499..0ee59dde570 100644
--- a/src/chat/narrowsReducer.js
+++ b/src/chat/narrowsReducer.js
@@ -3,7 +3,7 @@
 import union from 'lodash.union';
 import Immutable from 'immutable';
 
-import type { NarrowsState, Action } from '../types';
+import type { NarrowsState, PerAccountApplicableAction } from '../types';
 import { ensureUnreachable } from '../types';
 import {
   REGISTER_COMPLETE,
@@ -150,7 +150,10 @@ const eventUpdateMessageFlags = (state, action) => {
   return state;
 };
 
-export default (state: NarrowsState = initialState, action: Action): NarrowsState => {
+export default (
+  state: NarrowsState = initialState,
+  action: PerAccountApplicableAction,
+): NarrowsState => {
   switch (action.type) {
     case REGISTER_COMPLETE:
     case LOGOUT:
diff --git a/src/drafts/draftsActions.js b/src/drafts/draftsActions.js
index 27e41a55e93..9b2a094b8e9 100644
--- a/src/drafts/draftsActions.js
+++ b/src/drafts/draftsActions.js
@@ -1,8 +1,8 @@
 /* @flow strict-local */
-import type { Narrow, Action } from '../types';
+import type { Narrow, PerAccountAction } from '../types';
 import { DRAFT_UPDATE } from '../actionConstants';
 
-export const draftUpdate = (narrow: Narrow, content: string): Action => ({
+export const draftUpdate = (narrow: Narrow, content: string): PerAccountAction => ({
   type: DRAFT_UPDATE,
   narrow,
   content,
diff --git a/src/drafts/draftsReducer.js b/src/drafts/draftsReducer.js
index cb6675b3fc3..9f3110ee872 100644
--- a/src/drafts/draftsReducer.js
+++ b/src/drafts/draftsReducer.js
@@ -1,5 +1,5 @@
 /* @flow strict-local */
-import type { DraftsState, Action } from '../types';
+import type { DraftsState, PerAccountApplicableAction } from '../types';
 import { DRAFT_UPDATE, LOGOUT, ACCOUNT_SWITCH } from '../actionConstants';
 import { NULL_OBJECT } from '../nullObjects';
 import { keyFromNarrow } from '../utils/narrow';
@@ -22,7 +22,10 @@ const draftUpdate = (state, action) => {
   return state[narrowStr] === action.content ? state : { ...state, [narrowStr]: action.content };
 };
 
-export default (state: DraftsState = initialState, action: Action): DraftsState => {
+export default (
+  state: DraftsState = initialState,
+  action: PerAccountApplicableAction,
+): DraftsState => {
   switch (action.type) {
     case LOGOUT:
     case ACCOUNT_SWITCH:
diff --git a/src/message/fetchActions.js b/src/message/fetchActions.js
index f56d77d3de9..a5226de8509 100644
--- a/src/message/fetchActions.js
+++ b/src/message/fetchActions.js
@@ -1,7 +1,14 @@
 /* @flow strict-local */
 import * as logging from '../utils/logging';
 import * as NavigationService from '../nav/NavigationService';
-import type { Narrow, PerAccountState, Message, Action, ThunkAction, UserId } from '../types';
+import type {
+  Narrow,
+  PerAccountState,
+  Message,
+  PerAccountAction,
+  ThunkAction,
+  UserId,
+} from '../types';
 import { ensureUnreachable } from '../types';
 import type { RegisterAbortReason } from '../actionTypes';
 import type { InitialData } from '../api/initialDataTypes';
@@ -39,14 +46,18 @@ import { ZulipVersion } from '../utils/zulipVersion';
 import { getAllUsersById, getHaveServerData, getOwnUserId } from '../users/userSelectors';
 import { MIN_RECENTPMS_SERVER_VERSION } from '../pm-conversations/pmConversationsModel';
 
-const messageFetchStart = (narrow: Narrow, numBefore: number, numAfter: number): Action => ({
+const messageFetchStart = (
+  narrow: Narrow,
+  numBefore: number,
+  numAfter: number,
+): PerAccountAction => ({
   type: MESSAGE_FETCH_START,
   narrow,
   numBefore,
   numAfter,
 });
 
-const messageFetchError = (args: {| narrow: Narrow, error: Error |}): Action => {
+const messageFetchError = (args: {| narrow: Narrow, error: Error |}): PerAccountAction => {
   const { narrow, error } = args;
   return {
     type: MESSAGE_FETCH_ERROR,
@@ -64,7 +75,7 @@ const messageFetchComplete = (args: {|
   foundNewest: boolean,
   foundOldest: boolean,
   ownUserId: UserId,
-|}): Action => {
+|}): PerAccountAction => {
   const {
     messages,
     narrow,
@@ -192,11 +203,11 @@ export const fetchNewer = (narrow: Narrow): ThunkAction<void> => (dispatch, getS
   }
 };
 
-const registerStart = (): Action => ({
+const registerStart = (): PerAccountAction => ({
   type: REGISTER_START,
 });
 
-const registerAbortPlain = (reason: RegisterAbortReason): Action => ({
+const registerAbortPlain = (reason: RegisterAbortReason): PerAccountAction => ({
   type: REGISTER_ABORT,
   reason,
 });
@@ -256,7 +267,7 @@ export const registerAbort = (reason: RegisterAbortReason): ThunkAction<Promise<
   }
 };
 
-const registerComplete = (data: InitialData): Action => ({
+const registerComplete = (data: InitialData): PerAccountAction => ({
   type: REGISTER_COMPLETE,
   data,
 });
diff --git a/src/message/messagesReducer.js b/src/message/messagesReducer.js
index 2b480e272a0..5877a0520a9 100644
--- a/src/message/messagesReducer.js
+++ b/src/message/messagesReducer.js
@@ -3,7 +3,7 @@
 import omit from 'lodash.omit';
 import Immutable from 'immutable';
 
-import type { MessagesState, Message, Action } from '../types';
+import type { MessagesState, Message, PerAccountApplicableAction } from '../types';
 import {
   REGISTER_COMPLETE,
   LOGOUT,
@@ -63,7 +63,10 @@ const eventNewMessage = (state, action) => {
   return state.set(action.message.id, omit(action.message, 'flags'));
 };
 
-export default (state: MessagesState = initialState, action: Action): MessagesState => {
+export default (
+  state: MessagesState = initialState,
+  action: PerAccountApplicableAction,
+): MessagesState => {
   switch (action.type) {
     case REGISTER_COMPLETE:
     case LOGOUT:
diff --git a/src/mute/muteReducer.js b/src/mute/muteReducer.js
index 79d5e15e68f..0e2ecab87ad 100644
--- a/src/mute/muteReducer.js
+++ b/src/mute/muteReducer.js
@@ -1,11 +1,11 @@
 /* @flow strict-local */
-import type { MuteState, Action } from '../types';
+import type { MuteState, PerAccountApplicableAction } from '../types';
 import { REGISTER_COMPLETE, LOGOUT, ACCOUNT_SWITCH, EVENT_MUTED_TOPICS } from '../actionConstants';
 import { NULL_ARRAY } from '../nullObjects';
 
 const initialState: MuteState = NULL_ARRAY;
 
-export default (state: MuteState = initialState, action: Action): MuteState => {
+export default (state: MuteState = initialState, action: PerAccountApplicableAction): MuteState => {
   switch (action.type) {
     case LOGOUT:
     case ACCOUNT_SWITCH:
diff --git a/src/mute/mutedUsersReducer.js b/src/mute/mutedUsersReducer.js
index 0b8a645edfa..d84ef4cf61b 100644
--- a/src/mute/mutedUsersReducer.js
+++ b/src/mute/mutedUsersReducer.js
@@ -1,7 +1,7 @@
 /* @flow strict-local */
 import Immutable from 'immutable';
 
-import type { MutedUsersState, Action, UserId } from '../types';
+import type { MutedUsersState, PerAccountApplicableAction, UserId } from '../types';
 import {
   REGISTER_COMPLETE,
   LOGIN_SUCCESS,
@@ -17,7 +17,10 @@ function mutedUsersToMap(muted_users: $ReadOnlyArray<MutedUser>): Immutable.Map<
   return Immutable.Map(muted_users.map(muted_user => [muted_user.id, muted_user.timestamp]));
 }
 
-export default (state: MutedUsersState = initialState, action: Action): MutedUsersState => {
+export default (
+  state: MutedUsersState = initialState,
+  action: PerAccountApplicableAction,
+): MutedUsersState => {
   switch (action.type) {
     case LOGOUT:
     case ACCOUNT_SWITCH:
diff --git a/src/notification/notificationActions.js b/src/notification/notificationActions.js
index 8d7559ad659..e1428d72f0e 100644
--- a/src/notification/notificationActions.js
+++ b/src/notification/notificationActions.js
@@ -6,7 +6,8 @@ import type {
   Dispatch,
   GlobalDispatch,
   Identity,
-  Action,
+  AccountIndependentAction,
+  AllAccountsAction,
   ThunkAction,
   GlobalThunkAction,
 } from '../types';
@@ -27,17 +28,17 @@ import { doNarrow } from '../message/messagesActions';
 import { accountSwitch } from '../account/accountActions';
 import { getIdentities, getAccount, tryGetActiveAccountState } from '../account/accountsSelectors';
 
-export const gotPushToken = (pushToken: string | null): Action => ({
+export const gotPushToken = (pushToken: string | null): AccountIndependentAction => ({
   type: GOT_PUSH_TOKEN,
   pushToken,
 });
 
-export const unackPushToken = (identity: Identity): Action => ({
+export const unackPushToken = (identity: Identity): AllAccountsAction => ({
   type: UNACK_PUSH_TOKEN,
   identity,
 });
 
-const ackPushToken = (pushToken: string, identity: Identity): Action => ({
+const ackPushToken = (pushToken: string, identity: Identity): AllAccountsAction => ({
   type: ACK_PUSH_TOKEN,
   identity,
   pushToken,
diff --git a/src/outbox/outboxActions.js b/src/outbox/outboxActions.js
index 9f2db4795ab..818f0ccce79 100644
--- a/src/outbox/outboxActions.js
+++ b/src/outbox/outboxActions.js
@@ -13,7 +13,7 @@ import type {
   Stream,
   UserOrBot,
   UserId,
-  Action,
+  PerAccountAction,
   ThunkAction,
 } from '../types';
 import type { SubsetProperties } from '../generics';
@@ -31,22 +31,22 @@ import { caseNarrowPartial, isConversationNarrow } from '../utils/narrow';
 import { BackoffMachine } from '../utils/async';
 import { recipientsOfPrivateMessage, streamNameOfStreamMessage } from '../utils/recipient';
 
-export const messageSendStart = (outbox: Outbox): Action => ({
+export const messageSendStart = (outbox: Outbox): PerAccountAction => ({
   type: MESSAGE_SEND_START,
   outbox,
 });
 
-export const toggleOutboxSending = (sending: boolean): Action => ({
+export const toggleOutboxSending = (sending: boolean): PerAccountAction => ({
   type: TOGGLE_OUTBOX_SENDING,
   sending,
 });
 
-export const deleteOutboxMessage = (localMessageId: number): Action => ({
+export const deleteOutboxMessage = (localMessageId: number): PerAccountAction => ({
   type: DELETE_OUTBOX_MESSAGE,
   local_message_id: localMessageId,
 });
 
-export const messageSendComplete = (localMessageId: number): Action => ({
+export const messageSendComplete = (localMessageId: number): PerAccountAction => ({
   type: MESSAGE_SEND_COMPLETE,
   local_message_id: localMessageId,
 });
diff --git a/src/outbox/outboxReducer.js b/src/outbox/outboxReducer.js
index a9b9f3802de..b5c0a0f31ce 100644
--- a/src/outbox/outboxReducer.js
+++ b/src/outbox/outboxReducer.js
@@ -1,5 +1,5 @@
 /* @flow strict-local */
-import type { OutboxState, Action, Outbox } from '../types';
+import type { OutboxState, PerAccountApplicableAction, Outbox } from '../types';
 import {
   REGISTER_COMPLETE,
   MESSAGE_SEND_START,
@@ -22,7 +22,10 @@ const messageSendStart = (state, action) => {
   return [...state, { ...action.outbox }];
 };
 
-export default (state: OutboxState = initialState, action: Action): OutboxState => {
+export default (
+  state: OutboxState = initialState,
+  action: PerAccountApplicableAction,
+): OutboxState => {
   switch (action.type) {
     case REGISTER_COMPLETE:
       return filterArray(state, (outbox: Outbox) => !outbox.isSent);
diff --git a/src/pm-conversations/pmConversationsModel.js b/src/pm-conversations/pmConversationsModel.js
index 08cfebae8e3..ceeb4acc77a 100644
--- a/src/pm-conversations/pmConversationsModel.js
+++ b/src/pm-conversations/pmConversationsModel.js
@@ -11,7 +11,7 @@ import {
 } from '../actionConstants';
 import { makeUserId } from '../api/idTypes';
 
-import type { Action, PmMessage, PmOutbox, UserId } from '../types';
+import type { PerAccountApplicableAction, PmMessage, PmOutbox, UserId } from '../types';
 import { recipientsOfPrivateMessage } from '../utils/recipient';
 import { ZulipVersion } from '../utils/zulipVersion';
 
@@ -181,7 +181,7 @@ function insertMessage(state, message, ownUserId) {
 
 export function reducer(
   state: PmConversationsState = initialState,
-  action: Action,
+  action: PerAccountApplicableAction,
 ): PmConversationsState {
   switch (action.type) {
     case LOGOUT:
diff --git a/src/presence/presenceReducer.js b/src/presence/presenceReducer.js
index 87ad19b2520..4f203e6def1 100644
--- a/src/presence/presenceReducer.js
+++ b/src/presence/presenceReducer.js
@@ -1,5 +1,5 @@
 /* @flow strict-local */
-import type { PresenceState, Action } from '../types';
+import type { PresenceState, PerAccountApplicableAction } from '../types';
 import {
   LOGOUT,
   LOGIN_SUCCESS,
@@ -14,7 +14,10 @@ import objectEntries from '../utils/objectEntries';
 
 const initialState: PresenceState = NULL_OBJECT;
 
-export default (state: PresenceState = initialState, action: Action): PresenceState => {
+export default (
+  state: PresenceState = initialState,
+  action: PerAccountApplicableAction,
+): PresenceState => {
   switch (action.type) {
     case LOGOUT:
     case LOGIN_SUCCESS:
diff --git a/src/realm/realmReducer.js b/src/realm/realmReducer.js
index 639bd32b914..a2159d24dcb 100644
--- a/src/realm/realmReducer.js
+++ b/src/realm/realmReducer.js
@@ -1,5 +1,10 @@
 /* @flow strict-local */
-import type { RealmState, Action, RealmEmojiById, VideoChatProvider } from '../types';
+import type {
+  RealmState,
+  PerAccountApplicableAction,
+  RealmEmojiById,
+  VideoChatProvider,
+} from '../types';
 import {
   REGISTER_COMPLETE,
   EVENT_REALM_EMOJI_UPDATE,
@@ -50,7 +55,10 @@ function getVideoChatProvider({
   }
 }
 
-export default (state: RealmState = initialState, action: Action): RealmState => {
+export default (
+  state: RealmState = initialState,
+  action: PerAccountApplicableAction,
+): RealmState => {
   switch (action.type) {
     case LOGOUT:
     case LOGIN_SUCCESS:
diff --git a/src/reduxTypes.js b/src/reduxTypes.js
index 7edf0a2cc1b..cb771dc0d25 100644
--- a/src/reduxTypes.js
+++ b/src/reduxTypes.js
@@ -11,7 +11,7 @@ import type Immutable from 'immutable';
 import type { InputSelector } from 'reselect';
 
 import type { Account, Outbox } from './types';
-import type { Action } from './actionTypes';
+import type { Action, DispatchableWithoutAccountAction } from './actionTypes';
 import type {
   Topic,
   Message,
@@ -556,7 +556,7 @@ export type ThunkAction<T> = (Dispatch, () => PerAccountState, ThunkExtras) => T
 
 /** The Redux `dispatch` for a global context. */
 export interface GlobalDispatch {
-  <A: Action>(action: A): A;
+  <A: DispatchableWithoutAccountAction>(action: A): A;
   <T>(GlobalThunkAction<T>): T;
 }
 
@@ -576,4 +576,5 @@ export type GlobalThunkAction<T> = (GlobalDispatch, () => GlobalState) => T;
 (d: Dispatch): GlobalDispatch => d;
 //   $FlowExpectedError[incompatible-exact]
 //   $FlowExpectedError[prop-missing]
+//   $FlowExpectedError[incompatible-return]
 <T>(a: GlobalThunkAction<T>): ThunkAction<T> => a;
diff --git a/src/session/sessionActions.js b/src/session/sessionActions.js
index 93986f7308c..4b2b7c150d6 100644
--- a/src/session/sessionActions.js
+++ b/src/session/sessionActions.js
@@ -1,5 +1,5 @@
 /* @flow strict-local */
-import type { Action, Orientation } from '../types';
+import type { PerAccountAction, AccountIndependentAction, Orientation } from '../types';
 import {
   APP_ONLINE,
   APP_ORIENTATION,
@@ -8,26 +8,26 @@ import {
   DISMISS_SERVER_COMPAT_NOTICE,
 } from '../actionConstants';
 
-export const appOnline = (isOnline: boolean | null): Action => ({
+export const appOnline = (isOnline: boolean | null): AccountIndependentAction => ({
   type: APP_ONLINE,
   isOnline,
 });
 
-export const deadQueue = (): Action => ({
+export const deadQueue = (): PerAccountAction => ({
   type: DEAD_QUEUE,
 });
 
-export const appOrientation = (orientation: Orientation): Action => ({
+export const appOrientation = (orientation: Orientation): AccountIndependentAction => ({
   type: APP_ORIENTATION,
   orientation,
 });
 
-export const debugFlagToggle = (key: string, value: boolean): Action => ({
+export const debugFlagToggle = (key: string, value: boolean): AccountIndependentAction => ({
   type: DEBUG_FLAG_TOGGLE,
   key,
   value,
 });
 
-export const dismissCompatNotice = (): Action => ({
+export const dismissCompatNotice = (): PerAccountAction => ({
   type: DISMISS_SERVER_COMPAT_NOTICE,
 });
diff --git a/src/settings/LanguageScreen.js b/src/settings/LanguageScreen.js
index 79196162459..d7b4d6aca47 100644
--- a/src/settings/LanguageScreen.js
+++ b/src/settings/LanguageScreen.js
@@ -9,7 +9,7 @@ import { useGlobalSelector, useDispatch } from '../react-redux';
 import { Screen } from '../common';
 import LanguagePicker from './LanguagePicker';
 import { getGlobalSettings } from '../selectors';
-import { settingsChange } from '../actions';
+import { setGlobalSettings } from '../actions';
 
 type Props = $ReadOnly<{|
   navigation: AppNavigationProp<'language'>,
@@ -24,7 +24,7 @@ export default function LanguageScreen(props: Props): Node {
 
   const handleLocaleChange = useCallback(
     (value: string) => {
-      dispatch(settingsChange({ language: value }));
+      dispatch(setGlobalSettings({ language: value }));
     },
     [dispatch],
   );
diff --git a/src/settings/NotificationsScreen.js b/src/settings/NotificationsScreen.js
index 15aa9705b14..e77cd2f800a 100644
--- a/src/settings/NotificationsScreen.js
+++ b/src/settings/NotificationsScreen.js
@@ -5,11 +5,10 @@ import type { Node } from 'react';
 
 import type { RouteProp } from '../react-navigation';
 import type { AppNavigationProp } from '../nav/AppNavigator';
-import { useSelector, useDispatch } from '../react-redux';
+import { useSelector } from '../react-redux';
 import { getAuth, getSettings } from '../selectors';
 import { SwitchRow, Screen } from '../common';
 import * as api from '../api';
-import { settingsChange } from '../actions';
 
 type Props = $ReadOnly<{|
   navigation: AppNavigationProp<'notifications'>,
@@ -22,7 +21,9 @@ export default function NotificationsScreen(props: Props): Node {
   const offlineNotification = useSelector(state => getSettings(state).offlineNotification);
   const onlineNotification = useSelector(state => getSettings(state).onlineNotification);
   const streamNotification = useSelector(state => getSettings(state).streamNotification);
-  const dispatch = useDispatch();
+
+  // TODO(#3999): It'd be good to show "working on it" UI feedback while a
+  //   request is pending, after the user touches a switch.
 
   const handleOfflineNotificationChange = useCallback(() => {
     api.toggleMobilePushSettings({
@@ -30,8 +31,7 @@ export default function NotificationsScreen(props: Props): Node {
       opp: 'offline_notification_change',
       value: !offlineNotification,
     });
-    dispatch(settingsChange({ offlineNotification: !offlineNotification }));
-  }, [offlineNotification, auth, dispatch]);
+  }, [offlineNotification, auth]);
 
   const handleOnlineNotificationChange = useCallback(() => {
     api.toggleMobilePushSettings({
@@ -39,8 +39,7 @@ export default function NotificationsScreen(props: Props): Node {
       opp: 'online_notification_change',
       value: !onlineNotification,
     });
-    dispatch(settingsChange({ onlineNotification: !onlineNotification }));
-  }, [onlineNotification, auth, dispatch]);
+  }, [onlineNotification, auth]);
 
   const handleStreamNotificationChange = useCallback(() => {
     api.toggleMobilePushSettings({
@@ -48,8 +47,7 @@ export default function NotificationsScreen(props: Props): Node {
       opp: 'stream_notification_change',
       value: !streamNotification,
     });
-    dispatch(settingsChange({ streamNotification: !streamNotification }));
-  }, [streamNotification, auth, dispatch]);
+  }, [streamNotification, auth]);
 
   return (
     <Screen title="Notifications">
diff --git a/src/settings/SettingsScreen.js b/src/settings/SettingsScreen.js
index 266efff4550..472d3b106f4 100644
--- a/src/settings/SettingsScreen.js
+++ b/src/settings/SettingsScreen.js
@@ -16,7 +16,7 @@ import {
   IconMoreHorizontal,
 } from '../common/Icons';
 import {
-  settingsChange,
+  setGlobalSettings,
   navigateToNotifications,
   navigateToLanguage,
   navigateToDiagnostics,
@@ -38,7 +38,7 @@ export default function SettingsScreen(props: Props): Node {
   const dispatch = useDispatch();
 
   const handleThemeChange = useCallback(() => {
-    dispatch(settingsChange({ theme: theme === 'default' ? 'night' : 'default' }));
+    dispatch(setGlobalSettings({ theme: theme === 'default' ? 'night' : 'default' }));
   }, [theme, dispatch]);
 
   return (
@@ -48,14 +48,14 @@ export default function SettingsScreen(props: Props): Node {
         label="Open links with in-app browser"
         value={shouldUseInAppBrowser(browser)}
         onValueChange={value => {
-          dispatch(settingsChange({ browser: value ? 'embedded' : 'external' }));
+          dispatch(setGlobalSettings({ browser: value ? 'embedded' : 'external' }));
         }}
       />
       <SwitchRow
         label="Do not mark messages read on scroll"
         value={doNotMarkMessagesAsRead}
         onValueChange={value => {
-          dispatch(settingsChange({ doNotMarkMessagesAsRead: value }));
+          dispatch(setGlobalSettings({ doNotMarkMessagesAsRead: value }));
         }}
       />
       <NestedNavRow
diff --git a/src/settings/__tests__/settingsReducer-test.js b/src/settings/__tests__/settingsReducer-test.js
index ebaaa57a8bd..573c481360e 100644
--- a/src/settings/__tests__/settingsReducer-test.js
+++ b/src/settings/__tests__/settingsReducer-test.js
@@ -1,7 +1,10 @@
 /* @flow strict-local */
 import deepFreeze from 'deep-freeze';
 
-import { SETTINGS_CHANGE, EVENT_UPDATE_GLOBAL_NOTIFICATIONS_SETTINGS } from '../../actionConstants';
+import {
+  SET_GLOBAL_SETTINGS,
+  EVENT_UPDATE_GLOBAL_NOTIFICATIONS_SETTINGS,
+} from '../../actionConstants';
 import settingsReducer from '../settingsReducer';
 import * as eg from '../../__tests__/lib/exampleData';
 
@@ -37,10 +40,10 @@ describe('settingsReducer', () => {
     });
   });
 
-  describe('SETTINGS_CHANGE', () => {
+  describe('SET_GLOBAL_SETTINGS', () => {
     test('changes value of a key', () => {
       const action = deepFreeze({
-        type: SETTINGS_CHANGE,
+        type: SET_GLOBAL_SETTINGS,
         update: { theme: 'night' },
       });
 
diff --git a/src/settings/settingsActions.js b/src/settings/settingsActions.js
index 731e58a1e71..94de7553180 100644
--- a/src/settings/settingsActions.js
+++ b/src/settings/settingsActions.js
@@ -1,8 +1,10 @@
 /* @flow strict-local */
-import type { Action, SettingsState } from '../types';
-import { SETTINGS_CHANGE } from '../actionConstants';
+import type { AccountIndependentAction, GlobalSettingsState } from '../types';
+import { SET_GLOBAL_SETTINGS } from '../actionConstants';
 
-export const settingsChange = (update: $Shape<SettingsState>): Action => ({
-  type: SETTINGS_CHANGE,
+export const setGlobalSettings = (
+  update: $Shape<$Exact<GlobalSettingsState>>,
+): AccountIndependentAction => ({
+  type: SET_GLOBAL_SETTINGS,
   update,
 });
diff --git a/src/settings/settingsReducer.js b/src/settings/settingsReducer.js
index e1aada75c52..0cb43a1d48b 100644
--- a/src/settings/settingsReducer.js
+++ b/src/settings/settingsReducer.js
@@ -1,7 +1,7 @@
 /* @flow strict-local */
 import type { SettingsState, Action } from '../types';
 import {
-  SETTINGS_CHANGE,
+  SET_GLOBAL_SETTINGS,
   REGISTER_COMPLETE,
   EVENT_UPDATE_GLOBAL_NOTIFICATIONS_SETTINGS,
 } from '../actionConstants';
@@ -28,7 +28,7 @@ export default (state: SettingsState = initialState, action: Action): SettingsSt
         streamNotification: action.data.enable_stream_push_notifications,
       };
 
-    case SETTINGS_CHANGE:
+    case SET_GLOBAL_SETTINGS:
       return {
         ...state,
         ...action.update,
diff --git a/src/streams/streamsReducer.js b/src/streams/streamsReducer.js
index fd73adc2cb4..3473809b83a 100644
--- a/src/streams/streamsReducer.js
+++ b/src/streams/streamsReducer.js
@@ -1,6 +1,6 @@
 /* @flow strict-local */
 import { EventTypes } from '../api/eventTypes';
-import type { Action, StreamsState } from '../types';
+import type { PerAccountApplicableAction, StreamsState } from '../types';
 import { ensureUnreachable } from '../types';
 import { LOGOUT, ACCOUNT_SWITCH, EVENT, REGISTER_COMPLETE } from '../actionConstants';
 import { NULL_ARRAY } from '../nullObjects';
@@ -8,7 +8,10 @@ import { filterArray } from '../utils/immutability';
 
 const initialState: StreamsState = NULL_ARRAY;
 
-export default (state: StreamsState = initialState, action: Action): StreamsState => {
+export default (
+  state: StreamsState = initialState,
+  action: PerAccountApplicableAction,
+): StreamsState => {
   switch (action.type) {
     case REGISTER_COMPLETE:
       return action.data.streams || initialState;
diff --git a/src/subscriptions/subscriptionsReducer.js b/src/subscriptions/subscriptionsReducer.js
index c61ca6883a2..3b28221f08d 100644
--- a/src/subscriptions/subscriptionsReducer.js
+++ b/src/subscriptions/subscriptionsReducer.js
@@ -1,6 +1,6 @@
 /* @flow strict-local */
 import { EventTypes } from '../api/eventTypes';
-import type { SubscriptionsState, Action } from '../types';
+import type { SubscriptionsState, PerAccountApplicableAction } from '../types';
 import { ensureUnreachable } from '../types';
 import {
   LOGOUT,
@@ -20,7 +20,10 @@ const updateSubscription = (state, event) =>
     sub.stream_id === event.stream_id ? { ...sub, [event.property]: event.value } : sub,
   );
 
-export default (state: SubscriptionsState = initialState, action: Action): SubscriptionsState => {
+export default (
+  state: SubscriptionsState = initialState,
+  action: PerAccountApplicableAction,
+): SubscriptionsState => {
   switch (action.type) {
     case LOGOUT:
     case LOGIN_SUCCESS:
diff --git a/src/topics/topicActions.js b/src/topics/topicActions.js
index e45c04771c0..6e653368e94 100644
--- a/src/topics/topicActions.js
+++ b/src/topics/topicActions.js
@@ -1,5 +1,5 @@
 /* @flow strict-local */
-import type { Narrow, Topic, Action, ThunkAction, Outbox } from '../types';
+import type { Narrow, Topic, PerAccountAction, ThunkAction, Outbox } from '../types';
 import * as api from '../api';
 import { INIT_TOPICS } from '../actionConstants';
 import { isStreamNarrow, streamNameOfNarrow } from '../utils/narrow';
@@ -7,7 +7,7 @@ import { getAuth, getStreams } from '../selectors';
 import { deleteOutboxMessage } from '../actions';
 import { getOutbox } from '../directSelectors';
 
-export const initTopics = (topics: Topic[], streamId: number): Action => ({
+export const initTopics = (topics: Topic[], streamId: number): PerAccountAction => ({
   type: INIT_TOPICS,
   topics,
   streamId,
diff --git a/src/topics/topicsReducer.js b/src/topics/topicsReducer.js
index 8695a2065b5..6a264215614 100644
--- a/src/topics/topicsReducer.js
+++ b/src/topics/topicsReducer.js
@@ -1,5 +1,5 @@
 /* @flow strict-local */
-import type { TopicsState, Action } from '../types';
+import type { TopicsState, PerAccountApplicableAction } from '../types';
 import { LOGOUT, ACCOUNT_SWITCH, INIT_TOPICS, EVENT_NEW_MESSAGE } from '../actionConstants';
 import { NULL_OBJECT } from '../nullObjects';
 import { replaceItemInArray } from '../utils/immutability';
@@ -36,7 +36,10 @@ const eventNewMessage = (state, action) => {
   };
 };
 
-export default (state: TopicsState = initialState, action: Action): TopicsState => {
+export default (
+  state: TopicsState = initialState,
+  action: PerAccountApplicableAction,
+): TopicsState => {
   switch (action.type) {
     case LOGOUT:
     case ACCOUNT_SWITCH:
diff --git a/src/typing/__tests__/typingReducer-test.js b/src/typing/__tests__/typingReducer-test.js
index 53ee68b6b30..ff07e217309 100644
--- a/src/typing/__tests__/typingReducer-test.js
+++ b/src/typing/__tests__/typingReducer-test.js
@@ -2,7 +2,7 @@
 
 import deepFreeze from 'deep-freeze';
 
-import type { Action, User } from '../../types';
+import type { PerAccountAction, User } from '../../types';
 import { EVENT_TYPING_START, EVENT_TYPING_STOP } from '../../actionConstants';
 import typingReducer from '../typingReducer';
 import { NULL_OBJECT } from '../../nullObjects';
@@ -18,7 +18,7 @@ describe('typingReducer', () => {
     sender: User,
     recipients: $ReadOnlyArray<User>,
     time: number,
-  |}): Action => {
+  |}): PerAccountAction => {
     const { op, sender, recipients, time } = args;
     const base = {
       id: 123,
diff --git a/src/typing/typingActions.js b/src/typing/typingActions.js
index ebb5f725865..d5676b31220 100644
--- a/src/typing/typingActions.js
+++ b/src/typing/typingActions.js
@@ -1,10 +1,10 @@
 /* @flow strict-local */
-import type { Action, ThunkAction } from '../types';
+import type { PerAccountAction, ThunkAction } from '../types';
 
 import { sleep } from '../utils/async';
 import { getTyping } from '../directSelectors';
 
-export const clearTyping = (outdatedNotifications: string[]): Action => ({
+export const clearTyping = (outdatedNotifications: string[]): PerAccountAction => ({
   type: 'CLEAR_TYPING',
   outdatedNotifications,
 });
diff --git a/src/typing/typingReducer.js b/src/typing/typingReducer.js
index f85d3af58da..196dfb96b85 100644
--- a/src/typing/typingReducer.js
+++ b/src/typing/typingReducer.js
@@ -1,5 +1,5 @@
 /* @flow strict-local */
-import type { Action, TypingState } from '../types';
+import type { PerAccountApplicableAction, TypingState } from '../types';
 import {
   EVENT_TYPING_START,
   EVENT_TYPING_STOP,
@@ -83,7 +83,10 @@ const clearTyping = (state, action) => {
   return newState;
 };
 
-export default (state: TypingState = initialState, action: Action): TypingState => {
+export default (
+  state: TypingState = initialState,
+  action: PerAccountApplicableAction,
+): TypingState => {
   switch (action.type) {
     case EVENT_TYPING_START:
       return eventTypingStart(state, action);
diff --git a/src/unread/unreadHuddlesReducer.js b/src/unread/unreadHuddlesReducer.js
index 0fd4c357a48..c24b40cfda3 100644
--- a/src/unread/unreadHuddlesReducer.js
+++ b/src/unread/unreadHuddlesReducer.js
@@ -1,7 +1,7 @@
 /* @flow strict-local */
 import invariant from 'invariant';
 
-import type { Action } from '../types';
+import type { PerAccountApplicableAction } from '../types';
 import type { UnreadHuddlesState } from './unreadModelTypes';
 import {
   REGISTER_COMPLETE,
@@ -54,7 +54,10 @@ const eventUpdateMessageFlags = (state, action) => {
   return state;
 };
 
-export default (state: UnreadHuddlesState = initialState, action: Action): UnreadHuddlesState => {
+export default (
+  state: UnreadHuddlesState = initialState,
+  action: PerAccountApplicableAction,
+): UnreadHuddlesState => {
   switch (action.type) {
     case LOGOUT:
     case ACCOUNT_SWITCH:
diff --git a/src/unread/unreadMentionsReducer.js b/src/unread/unreadMentionsReducer.js
index 30b69f4e2db..cca0fd1cd68 100644
--- a/src/unread/unreadMentionsReducer.js
+++ b/src/unread/unreadMentionsReducer.js
@@ -1,7 +1,7 @@
 /* @flow strict-local */
 import invariant from 'invariant';
 
-import type { Action } from '../types';
+import type { PerAccountApplicableAction } from '../types';
 import type { UnreadMentionsState } from './unreadModelTypes';
 import {
   REGISTER_COMPLETE,
@@ -34,7 +34,10 @@ const eventUpdateMessageFlags = (state, action) => {
   return state;
 };
 
-export default (state: UnreadMentionsState = initialState, action: Action): UnreadMentionsState => {
+export default (
+  state: UnreadMentionsState = initialState,
+  action: PerAccountApplicableAction,
+): UnreadMentionsState => {
   switch (action.type) {
     case LOGOUT:
     case ACCOUNT_SWITCH:
diff --git a/src/unread/unreadModel.js b/src/unread/unreadModel.js
index 1a3e6e83e6f..1218b5da2c3 100644
--- a/src/unread/unreadModel.js
+++ b/src/unread/unreadModel.js
@@ -2,7 +2,7 @@
 import Immutable from 'immutable';
 import invariant from 'invariant';
 
-import type { Action } from '../actionTypes';
+import type { PerAccountApplicableAction } from '../actionTypes';
 import type {
   UnreadState,
   UnreadStreamsState,
@@ -118,7 +118,7 @@ function deleteMessages(
 
 function streamsReducer(
   state: UnreadStreamsState = initialStreamsState,
-  action: Action,
+  action: PerAccountApplicableAction,
   globalState: PerAccountState,
 ): UnreadStreamsState {
   switch (action.type) {
@@ -210,7 +210,7 @@ function streamsReducer(
 
 export const reducer = (
   state: void | UnreadState,
-  action: Action,
+  action: PerAccountApplicableAction,
   globalState: PerAccountState,
 ): UnreadState => {
   const nextState = {
diff --git a/src/unread/unreadPmsReducer.js b/src/unread/unreadPmsReducer.js
index 232c9edeb09..0724ce1987b 100644
--- a/src/unread/unreadPmsReducer.js
+++ b/src/unread/unreadPmsReducer.js
@@ -1,7 +1,7 @@
 /* @flow strict-local */
 import invariant from 'invariant';
 
-import type { Action } from '../types';
+import type { PerAccountApplicableAction } from '../types';
 import type { UnreadPmsState } from './unreadModelTypes';
 import {
   REGISTER_COMPLETE,
@@ -52,7 +52,10 @@ const eventUpdateMessageFlags = (state, action) => {
   return state;
 };
 
-export default (state: UnreadPmsState = initialState, action: Action): UnreadPmsState => {
+export default (
+  state: UnreadPmsState = initialState,
+  action: PerAccountApplicableAction,
+): UnreadPmsState => {
   switch (action.type) {
     case LOGOUT:
     case ACCOUNT_SWITCH:
diff --git a/src/user-groups/userGroupsReducer.js b/src/user-groups/userGroupsReducer.js
index 07c97a5b6bb..c13741dffb5 100644
--- a/src/user-groups/userGroupsReducer.js
+++ b/src/user-groups/userGroupsReducer.js
@@ -1,5 +1,5 @@
 /* @flow strict-local */
-import type { UserGroupsState, Action } from '../types';
+import type { UserGroupsState, PerAccountApplicableAction } from '../types';
 import {
   LOGOUT,
   LOGIN_SUCCESS,
@@ -45,7 +45,10 @@ const eventUserGroupRemoveMembers = (state, action) =>
         },
   );
 
-export default (state: UserGroupsState = initialState, action: Action): UserGroupsState => {
+export default (
+  state: UserGroupsState = initialState,
+  action: PerAccountApplicableAction,
+): UserGroupsState => {
   switch (action.type) {
     case LOGOUT:
     case LOGIN_SUCCESS:
diff --git a/src/user-status/userStatusReducer.js b/src/user-status/userStatusReducer.js
index 93da107a890..f72041c1b45 100644
--- a/src/user-status/userStatusReducer.js
+++ b/src/user-status/userStatusReducer.js
@@ -1,5 +1,5 @@
 /* @flow strict-local */
-import type { UserStatusState, Action } from '../types';
+import type { UserStatusState, PerAccountApplicableAction } from '../types';
 import {
   LOGOUT,
   LOGIN_SUCCESS,
@@ -11,7 +11,10 @@ import { NULL_OBJECT } from '../nullObjects';
 
 const initialState: UserStatusState = NULL_OBJECT;
 
-export default (state: UserStatusState = initialState, action: Action): UserStatusState => {
+export default (
+  state: UserStatusState = initialState,
+  action: PerAccountApplicableAction,
+): UserStatusState => {
   switch (action.type) {
     case LOGOUT:
     case LOGIN_SUCCESS:
diff --git a/src/users/usersReducer.js b/src/users/usersReducer.js
index b79332d692d..5343a293c8a 100644
--- a/src/users/usersReducer.js
+++ b/src/users/usersReducer.js
@@ -1,5 +1,5 @@
 /* @flow strict-local */
-import type { UsersState, Action } from '../types';
+import type { UsersState, PerAccountApplicableAction } from '../types';
 import {
   LOGOUT,
   LOGIN_SUCCESS,
@@ -13,7 +13,10 @@ import { NULL_ARRAY } from '../nullObjects';
 
 const initialState: UsersState = NULL_ARRAY;
 
-export default (state: UsersState = initialState, action: Action): UsersState => {
+export default (
+  state: UsersState = initialState,
+  action: PerAccountApplicableAction,
+): UsersState => {
   switch (action.type) {
     case LOGOUT:
     case LOGIN_SUCCESS: