redux types: Distinguish PerAccountState from GlobalState

Now the fact that Flow still passes means that we don't have any
place where we have a PerAccountState, and try to pass it off
(without an explicit assumeSecretlyGlobalState, that is) as a
GlobalState.

src/reduxTypes.js

@@ -27,7 +27,7 @@ import type {
   UserPresence,
   UserStatusMapObject,
 } from './api/apiTypes';
-import type { SessionState } from './session/sessionReducer';
+import type { PerAccountSessionState, SessionState } from './session/sessionReducer';
 import type { PmConversationsState } from './pm-conversations/pmConversationsModel';
 import type { UnreadState } from './unread/unreadModelTypes';
 
@@ -376,42 +376,29 @@ export type UsersState = $ReadOnlyArray<User>;
  * parts of our code will in that future operate on a particular account and
  * which parts will operate on all accounts' data or none.
  */
-// And *initially* initially, the type literally just is GlobalState.
-// That'll change in just a few commits, though.
-export type PerAccountState = GlobalState;
+export type PerAccountState = $ReadOnly<{
+  // TODO accounts
 
-/**
- * Our complete Redux state tree.
- *
- * Each property is a subtree maintained by its own reducer function.  These
- * are named in a regular pattern; see also `src/boot/reducers.js`.
- *
- * We use `redux-persist` to write parts of this state tree to persistent
- * device storage that survives when the app is closed, and to read it back
- * ("rehydrate" it) from that storage at launch time.  See `src/boot/store.js`.
- * Other parts of the state tree are not persisted.
- *
- * See in particular `discardKeys`, `storeKeys`, and `cacheKeys`, which
- * identify which subtrees are persisted and which are not.
- */
-export type GlobalState = $ReadOnly<{|
-  accounts: AccountsState,
+  // Jumbles of per-account state and client state.
+  session: PerAccountSessionState,
+  settings: PerAccountSettingsState,
+
+  // Per-account state that's *not* from the server.
+  drafts: DraftsState,
+  outbox: OutboxState,
+
+  // Per-account state: server data for the active account.
   alertWords: AlertWordsState,
   caughtUp: CaughtUpState,
-  drafts: DraftsState,
   fetching: FetchingState,
   flags: FlagsState,
   messages: MessagesState,
-  migrations: MigrationsState,
   mute: MuteState,
   mutedUsers: MutedUsersState,
   narrows: NarrowsState,
-  outbox: OutboxState,
   pmConversations: PmConversationsState,
   presence: PresenceState,
   realm: RealmState,
-  session: SessionState,
-  settings: SettingsState,
   streams: StreamsState,
   subscriptions: SubscriptionsState,
   topics: TopicsState,
@@ -420,6 +407,37 @@ export type GlobalState = $ReadOnly<{|
   userGroups: UserGroupsState,
   userStatus: UserStatusState,
   users: UsersState,
+
+  ...
+}>;
+
+/**
+ * Our complete Redux state tree.
+ *
+ * Each property is a subtree maintained by its own reducer function.  These
+ * are named in a regular pattern; see also `src/boot/reducers.js`.
+ *
+ * We use `redux-persist` to write parts of this state tree to persistent
+ * device storage that survives when the app is closed, and to read it back
+ * ("rehydrate" it) from that storage at launch time.  See `src/boot/store.js`.
+ * Other parts of the state tree are not persisted.
+ *
+ * See in particular `discardKeys`, `storeKeys`, and `cacheKeys`, which
+ * identify which subtrees are persisted and which are not.
+ */
+export type GlobalState = $ReadOnly<{|
+  ...$Exact<PerAccountState>,
+
+  // Metadata for the global state, as persisted on disk.
+  migrations: MigrationsState,
+
+  // Jumbles of per-account state and client state.
+  session: SessionState,
+  settings: SettingsState,
+
+  // Per-account state but for all accounts together.
+  // Mix of server data and otherwise.
+  accounts: AccountsState,
 |}>;
 
 // For now, under our single-active-account model, we want a GlobalState
@@ -436,7 +454,8 @@ export type GlobalState = $ReadOnly<{|
  * TODO(#5006): We'll have to fix and eliminate each call to this.
  */
 export function assumeSecretlyGlobalState(state: PerAccountState): GlobalState {
-  // For *right* now, this doesn't even have a fixme, because the types alias.
+  // $FlowFixMe[incompatible-exact]
+  // $FlowFixMe[prop-missing]
   return state;
 }