refactor(sync): replace the session-status setState monkeypatch with an owned API

The global session-status store patched its own setState to derive
active membership for callers replacing statusById — a boundary that
silently trusted any caller passing both fields to keep them consistent.
replaceGlobalSessionStatusById is now the one sanctioned way to swap the
map from outside the event reducers; the runtime-switch reset and the
tests that replaced the map directly go through it, and the patch is
gone. Follow-up to #3126 review.

packages/ui/src/apps/runtimeEndpointReset.ts

@@ -15,7 +15,7 @@ import { useFilesViewTabsStore } from '@/stores/useFilesViewTabsStore';
 import { useTerminalStore } from '@/stores/useTerminalStore';
 import { useSessionUIStore } from '@/sync/session-ui-store';
 import { resetStreamingState } from '@/sync/streaming';
-import { useGlobalSessionStatusStore } from '@/sync/global-session-status';
+import { useGlobalSessionStatusStore, replaceGlobalSessionStatusById } from '@/sync/global-session-status';
 import { resetSessionOrdering } from '@/sync/session-ordering';
 import { resetSessionActivityTiming } from '@/sync/session-activity-timing';
 import { syncDesktopSettings } from '@/lib/persistence';
@@ -57,7 +57,7 @@ export const resetAppForRuntimeEndpointChange = (detail: RuntimeEndpointChangedD
   // Cross-project session list (mobile sessions sheet & co) belongs to the
   // previous instance — drop it so stale sessions can't linger after a switch.
   useGlobalSessionsStore.getState().resetForRuntimeSwitch();
-  useGlobalSessionStatusStore.setState({ statusById: new Map() });
+  replaceGlobalSessionStatusById(new Map());
   resetSessionOrdering();
   // Turn timings belong to the previous instance's sessions, and the reset also
   // restarts the resume window so the switch is treated as a fresh load.

packages/ui/src/components/session/sidebar/list/sessionCollection.test.ts

@@ -4,7 +4,7 @@ import type { Event } from '@opencode-ai/sdk/v2/client';
 import React, { act } from 'react';
 import { createRoot, type Root } from 'react-dom/client';
 import { deriveRecentSessions } from '../recent/activitySections';
-import { applyGlobalSessionStatusEvent, useGlobalSessionStatusStore } from '@/sync/global-session-status';
+import { applyGlobalSessionStatusEvent, useGlobalSessionStatusStore , replaceGlobalSessionStatusById} from '@/sync/global-session-status';
 import {
   buildSidebarSessionProjection,
   getDescendantIds,
@@ -270,7 +270,7 @@ describe('useRecentSessionCollection', () => {
     };
 
     try {
-      useGlobalSessionStatusStore.setState({ statusById: new Map() });
+      replaceGlobalSessionStatusById(new Map());
       await act(async () => root.render(React.createElement(Harness)));
       expect(renderedIds).toEqual([]);
 
@@ -296,7 +296,7 @@ describe('useRecentSessionCollection', () => {
       expect(timeReadCount).toBe(activeDeriveOperationCount);
     } finally {
       await act(async () => root.unmount());
-      useGlobalSessionStatusStore.setState({ statusById: new Map() });
+      replaceGlobalSessionStatusById(new Map());
       dom.restore();
     }
   });

packages/ui/src/components/session/sidebar/sessions/collapsedActivityIndicator.behavior.test.tsx

@@ -2,7 +2,7 @@ import { describe, expect, test } from 'bun:test';
 import React, { act } from 'react';
 import { createRoot } from 'react-dom/client';
 import type { Session } from '@opencode-ai/sdk/v2';
-import { useGlobalSessionStatusStore } from '@/sync/global-session-status';
+import { useGlobalSessionStatusStore , replaceGlobalSessionStatusById} from '@/sync/global-session-status';
 import { useNotificationStore } from '@/sync/notification-store';
 import { useCollapsedSessionActivityState } from './collapsedActivityState';
 import type { SessionNode } from '../types';
@@ -15,7 +15,7 @@ describe('collapsed activity scalar selector', () => {
   test('does not rerender for unrelated updates and rerenders for relevant scalar changes', async () => {
     const dom = installHookTestDom();
     const root = createRoot(dom.container);
-    useGlobalSessionStatusStore.setState({ statusById: new Map() });
+    replaceGlobalSessionStatusById(new Map());
     useNotificationStore.setState({
       list: [],
       index: { session: { unseenCount: {}, unseenHasError: {} }, project: { unseenCount: {}, unseenHasError: {} } },
@@ -30,9 +30,7 @@ describe('collapsed activity scalar selector', () => {
     try {
       await act(async () => root.render(React.createElement(Harness)));
       const initialRenders = capture.renders;
-      await act(async () => useGlobalSessionStatusStore.setState({
-        statusById: new Map([['unrelated', { status: { type: 'busy' }, directory: '/other' }]]),
-      }));
+      await act(async () => replaceGlobalSessionStatusById(new Map([['unrelated', { status: { type: 'busy' }, directory: '/other' }]])));
       await act(async () => useNotificationStore.getState().append({
         type: 'turn-complete', session: 'unrelated', time: Date.now(), viewed: false,
       }));
@@ -43,14 +41,12 @@ describe('collapsed activity scalar selector', () => {
       }));
       expect(capture.state).toBe('unread');
       const unreadRenders = capture.renders;
-      await act(async () => useGlobalSessionStatusStore.setState({
-        statusById: new Map([['relevant', { status: { type: 'busy' }, directory: '/workspace' }]]),
-      }));
+      await act(async () => replaceGlobalSessionStatusById(new Map([['relevant', { status: { type: 'busy' }, directory: '/workspace' }]])));
       expect(capture.state).toBe('active');
       expect(capture.renders).toBe(unreadRenders + 1);
     } finally {
       await act(async () => root.unmount());
-      useGlobalSessionStatusStore.setState({ statusById: new Map() });
+      replaceGlobalSessionStatusById(new Map());
       useNotificationStore.setState({
         list: [],
         index: { session: { unseenCount: {}, unseenHasError: {} }, project: { unseenCount: {}, unseenHasError: {} } },

packages/ui/src/sync/global-session-status.test.ts

@@ -5,12 +5,13 @@ import {
   applyGlobalSessionStatusEvents,
   applyGlobalSessionStatusSnapshot,
   useGlobalSessionStatusStore,
+  replaceGlobalSessionStatusById,
 } from "./global-session-status"
 import { resetSessionOrdering, useSessionOrderingStore } from "./session-ordering"
 import { resetSessionActivityTiming, useSessionActivityTimingStore } from "./session-activity-timing"
 
 beforeEach(() => {
-  useGlobalSessionStatusStore.setState({ statusById: new Map() })
+  replaceGlobalSessionStatusById(new Map())
   resetSessionOrdering()
   resetSessionActivityTiming()
 })
@@ -162,7 +163,7 @@ describe("global session status index", () => {
       properties: { sessionID: "session-a", status: { type: "busy" } },
     } as Event)
 
-    useGlobalSessionStatusStore.setState({ statusById: new Map() })
+    replaceGlobalSessionStatusById(new Map())
 
     expect(activeSessionIds()?.size).toBe(0)
   })

packages/ui/src/sync/global-session-status.ts

@@ -40,61 +40,28 @@ const initialState: GlobalSessionStatusState = {
 export const useGlobalSessionStatusStore = create<GlobalSessionStatusState>(() => initialState);
 useGlobalSessionStatusStore.subscribe(() => countSyncPerformance('globalStatusPublications'));
 
-// Runtime switching currently replaces statusById directly. Keep that boundary
-// synchronized without making normal status mutations derive membership again.
-const storeSetState = useGlobalSessionStatusStore.setState;
-type GlobalSessionStatusStateUpdate = GlobalSessionStatusState
-  | Partial<GlobalSessionStatusState>
-  | ((state: GlobalSessionStatusState) => GlobalSessionStatusState | Partial<GlobalSessionStatusState>);
-
-function setSynchronizedState(
-  partial: GlobalSessionStatusStateUpdate,
-  replace?: false,
-): void;
-function setSynchronizedState(
-  partial: GlobalSessionStatusState | ((state: GlobalSessionStatusState) => GlobalSessionStatusState),
-  replace: true,
-): void;
-function setSynchronizedState(partial: GlobalSessionStatusStateUpdate, replace?: boolean): void {
-  if (partial instanceof Function) {
-    if (replace === true) {
-      // SAFETY: Zustand's `replace: true` overload only accepts a complete state or a complete-state updater.
-      storeSetState(partial as GlobalSessionStatusState | ((state: GlobalSessionStatusState) => GlobalSessionStatusState), true);
-    } else {
-      storeSetState(partial, replace);
-    }
-    return;
-  }
-  if (partial.statusById === undefined || partial.activeSessionIds) {
-    if (replace === true) {
-      // SAFETY: Zustand's `replace: true` overload only accepts a complete state or a complete-state updater.
-      storeSetState(partial as GlobalSessionStatusState, true);
-    } else {
-      storeSetState(partial, replace);
-    }
-    return;
-  }
-
-  const nextStatusById = partial.statusById;
+/**
+ * Replaces the status map wholesale and derives active membership from it.
+ * This is the ONE sanctioned way to swap statusById from outside the event
+ * reducers (runtime switch, tests) — previously a setState monkeypatch
+ * derived membership for arbitrary callers, which silently trusted any
+ * caller passing both fields to keep them consistent.
+ */
+export const replaceGlobalSessionStatusById = (statusById: Map<string, GlobalSessionStatusEntry>): void => {
   const current = useGlobalSessionStatusStore.getState();
   const nextActiveSessionIds = new Set<string>();
-  for (const [sessionId, entry] of nextStatusById) {
+  for (const [sessionId, entry] of statusById) {
     if (entry.status.type === 'busy' || entry.status.type === 'retry') {
       nextActiveSessionIds.add(sessionId);
     }
   }
   const sameMembership = nextActiveSessionIds.size === current.activeSessionIds.size
     && [...nextActiveSessionIds].every((sessionId) => current.activeSessionIds.has(sessionId));
-  const nextState = {
-    ...current,
-    ...partial,
+  useGlobalSessionStatusStore.setState({
+    statusById,
     activeSessionIds: sameMembership ? current.activeSessionIds : nextActiveSessionIds,
-  };
-  if (replace === true) storeSetState(nextState, true);
-  else storeSetState(nextState, replace);
-}
-
-useGlobalSessionStatusStore.setState = setSynchronizedState;
+  });
+};
 
 const normalizeStatusType = (type: string | undefined): ActiveStatusType | 'idle' => {
   if (type === 'busy') return 'busy';