diff --git a/src/components/app/AppContent.tsx b/src/components/app/AppContent.tsx
index 4dd6979a..1ba41b95 100644
--- a/src/components/app/AppContent.tsx
+++ b/src/components/app/AppContent.tsx
@@ -34,7 +34,6 @@ function AppContentInner() {
     markSessionAsInactive,
     markSessionAsProcessing,
     markSessionAsNotProcessing,
-    replaceTemporarySession,
   } = useSessionProtection();
 
   const {
@@ -191,7 +190,6 @@ function AppContentInner() {
           onSessionProcessing={markSessionAsProcessing}
           onSessionNotProcessing={markSessionAsNotProcessing}
           processingSessions={processingSessions}
-          onReplaceTemporarySession={replaceTemporarySession}
           onNavigateToSession={(targetSessionId: string, options) =>
             navigate(`/session/${targetSessionId}`, { replace: Boolean(options?.replace) })
           }
diff --git a/src/components/chat/hooks/useChatComposerState.ts b/src/components/chat/hooks/useChatComposerState.ts
index c53cd01d..bbf188b9 100644
--- a/src/components/chat/hooks/useChatComposerState.ts
+++ b/src/components/chat/hooks/useChatComposerState.ts
@@ -10,6 +10,7 @@ import type {
   TouchEvent,
 } from 'react';
 import { useDropzone } from 'react-dropzone';
+
 import { authenticatedFetch } from '../../../utils/api';
 import { thinkingModes } from '../constants/thinkingModes';
 import { grantClaudeToolPermission } from '../utils/chatPermissions';
@@ -21,6 +22,7 @@ import type {
 } from '../types/types';
 import type { Project, ProjectSession, LLMProvider } from '../../../types/app';
 import { escapeRegExp } from '../utils/chatFormatting';
+
 import { useFileMentions } from './useFileMentions';
 import { type SlashCommand, useSlashCommands } from './useSlashCommands';
 
@@ -80,9 +82,6 @@ const createFakeSubmitEvent = () => {
   return { preventDefault: () => undefined } as unknown as FormEvent<HTMLFormElement>;
 };
 
-const isTemporarySessionId = (sessionId: string | null | undefined) =>
-  Boolean(sessionId && sessionId.startsWith('new-session-'));
-
 const getNotificationSessionSummary = (
   selectedSession: ProjectSession | null,
   fallbackInput: string,
@@ -533,7 +532,12 @@ export function useChatComposerState({
 
       const effectiveSessionId =
         currentSessionId || selectedSession?.id || sessionStorage.getItem('cursorSessionId');
-      const sessionToActivate = effectiveSessionId || `new-session-${Date.now()}`;
+
+      console.log('Submitting message', {
+        content: messageContent,
+        sessionId: effectiveSessionId,
+        images: uploadedImages,
+      });
 
       const userMessage: ChatMessage = {
         type: 'user',
@@ -559,10 +563,12 @@ export function useChatComposerState({
           // Reset stale pending IDs from previous interrupted runs before creating a new one.
           sessionStorage.removeItem('pendingSessionId');
         }
+        // For new sessions we intentionally keep this as `null` until the backend
+        // emits `session_created` with the canonical provider session id.
         pendingViewSessionRef.current = { sessionId: null, startedAt: Date.now() };
       }
-      onSessionActive?.(sessionToActivate);
-      if (effectiveSessionId && !isTemporarySessionId(effectiveSessionId)) {
+      if (effectiveSessionId) {
+        onSessionActive?.(effectiveSessionId);
         onSessionProcessing?.(effectiveSessionId);
       }
 
@@ -868,7 +874,7 @@ export function useChatComposerState({
     ];
 
     const targetSessionId =
-      candidateSessionIds.find((sessionId) => Boolean(sessionId) && !isTemporarySessionId(sessionId)) || null;
+      candidateSessionIds.find((sessionId) => Boolean(sessionId)) || null;
 
     if (!targetSessionId) {
       console.warn('Abort requested but no concrete session ID is available yet.');
diff --git a/src/components/chat/hooks/useChatRealtimeHandlers.ts b/src/components/chat/hooks/useChatRealtimeHandlers.ts
index 4ae861db..86c85469 100644
--- a/src/components/chat/hooks/useChatRealtimeHandlers.ts
+++ b/src/components/chat/hooks/useChatRealtimeHandlers.ts
@@ -65,7 +65,6 @@ interface UseChatRealtimeHandlersArgs {
   onSessionInactive?: (sessionId?: string | null) => void;
   onSessionProcessing?: (sessionId?: string | null) => void;
   onSessionNotProcessing?: (sessionId?: string | null) => void;
-  onReplaceTemporarySession?: (sessionId?: string | null) => void;
   onNavigateToSession?: (sessionId: string, options?: SessionNavigationOptions) => void;
   onWebSocketReconnect?: () => void;
   sessionStore: SessionStore;
@@ -92,7 +91,6 @@ export function useChatRealtimeHandlers({
   onSessionInactive,
   onSessionProcessing,
   onSessionNotProcessing,
-  onReplaceTemporarySession,
   onNavigateToSession,
   onWebSocketReconnect,
   sessionStore,
@@ -232,7 +230,9 @@ export function useChatRealtimeHandlers({
         const newSessionId = msg.newSessionId;
         if (!newSessionId) break;
 
-        if (!currentSessionId || currentSessionId.startsWith('new-session-')) {
+        // We no longer synthesize client-side placeholder IDs. Until the provider
+        // announces `session_created`, the active id is expected to be null.
+        if (!currentSessionId) {
           console.log('Session created with ID:', newSessionId);
           console.log('Existing session ID:', currentSessionId);
           sessionStorage.setItem('pendingSessionId', newSessionId);
@@ -240,7 +240,6 @@ export function useChatRealtimeHandlers({
             pendingViewSessionRef.current.sessionId = newSessionId;
           }
           setCurrentSessionId(newSessionId);
-          onReplaceTemporarySession?.(newSessionId);
           setPendingPermissionRequests((prev) =>
             prev.map((r) => (r.sessionId ? r : { ...r, sessionId: newSessionId })),
           );
@@ -402,7 +401,6 @@ export function useChatRealtimeHandlers({
     onSessionInactive,
     onSessionProcessing,
     onSessionNotProcessing,
-    onReplaceTemporarySession,
     onNavigateToSession,
     onWebSocketReconnect,
     sessionStore,
diff --git a/src/components/chat/hooks/useChatSessionState.ts b/src/components/chat/hooks/useChatSessionState.ts
index 6bff4a88..451c3482 100644
--- a/src/components/chat/hooks/useChatSessionState.ts
+++ b/src/components/chat/hooks/useChatSessionState.ts
@@ -628,7 +628,7 @@ export function useChatSessionState({
 
   // Token usage fetch for Claude
   useEffect(() => {
-    if (!selectedProject || !selectedSession?.id || selectedSession.id.startsWith('new-session-')) {
+    if (!selectedProject || !selectedSession?.id) {
       setTokenBudget(null);
       return;
     }
diff --git a/src/components/chat/types/types.ts b/src/components/chat/types/types.ts
index 81bd5a5b..f8d492e5 100644
--- a/src/components/chat/types/types.ts
+++ b/src/components/chat/types/types.ts
@@ -108,7 +108,6 @@ export interface ChatInterfaceProps {
   onSessionProcessing?: (sessionId?: string | null) => void;
   onSessionNotProcessing?: (sessionId?: string | null) => void;
   processingSessions?: Set<string>;
-  onReplaceTemporarySession?: (sessionId?: string | null) => void;
   onNavigateToSession?: (targetSessionId: string, options?: SessionNavigationOptions) => void;
   onShowSettings?: () => void;
   autoExpandTools?: boolean;
diff --git a/src/components/chat/view/ChatInterface.tsx b/src/components/chat/view/ChatInterface.tsx
index 46e95abd..2bff948d 100644
--- a/src/components/chat/view/ChatInterface.tsx
+++ b/src/components/chat/view/ChatInterface.tsx
@@ -34,7 +34,6 @@ function ChatInterface({
   onSessionProcessing,
   onSessionNotProcessing,
   processingSessions,
-  onReplaceTemporarySession,
   onNavigateToSession,
   onShowSettings,
   autoExpandTools,
@@ -237,7 +236,6 @@ function ChatInterface({
     onSessionInactive,
     onSessionProcessing,
     onSessionNotProcessing,
-    onReplaceTemporarySession,
     onNavigateToSession,
     onWebSocketReconnect: handleWebSocketReconnect,
     sessionStore,
diff --git a/src/components/main-content/types/types.ts b/src/components/main-content/types/types.ts
index d090852d..68b03b29 100644
--- a/src/components/main-content/types/types.ts
+++ b/src/components/main-content/types/types.ts
@@ -51,7 +51,6 @@ export type MainContentProps = {
   onSessionProcessing: SessionLifecycleHandler;
   onSessionNotProcessing: SessionLifecycleHandler;
   processingSessions: Set<string>;
-  onReplaceTemporarySession: SessionLifecycleHandler;
   onNavigateToSession: (targetSessionId: string, options?: SessionNavigationOptions) => void;
   onShowSettings: () => void;
   externalMessageUpdate: number;
diff --git a/src/components/main-content/view/MainContent.tsx b/src/components/main-content/view/MainContent.tsx
index 1a9c7349..f0a29a70 100644
--- a/src/components/main-content/view/MainContent.tsx
+++ b/src/components/main-content/view/MainContent.tsx
@@ -47,7 +47,6 @@ function MainContent({
   onSessionProcessing,
   onSessionNotProcessing,
   processingSessions,
-  onReplaceTemporarySession,
   onNavigateToSession,
   onShowSettings,
   externalMessageUpdate,
@@ -137,7 +136,6 @@ function MainContent({
                 onSessionProcessing={onSessionProcessing}
                 onSessionNotProcessing={onSessionNotProcessing}
                 processingSessions={processingSessions}
-                onReplaceTemporarySession={onReplaceTemporarySession}
                 onNavigateToSession={onNavigateToSession}
                 onShowSettings={onShowSettings}
                 autoExpandTools={autoExpandTools}
diff --git a/src/hooks/useProjectsState.ts b/src/hooks/useProjectsState.ts
index d920fba2..a5397b6b 100644
--- a/src/hooks/useProjectsState.ts
+++ b/src/hooks/useProjectsState.ts
@@ -435,9 +435,7 @@ export function useProjectsState({
       }
     }
 
-    const hasActiveSession =
-      (selectedSession && activeSessions.has(selectedSession.id)) ||
-      (activeSessions.size > 0 && Array.from(activeSessions).some((id) => id.startsWith('new-session-')));
+    const hasActiveSession = Boolean(selectedSession && activeSessions.has(selectedSession.id));
 
     const updatedProjectsWithTaskMaster = mergeTaskMasterCache(projectsMessage.projects, projects);
     const updatedProjects = mergeExpandedSessionPages(projects, updatedProjectsWithTaskMaster);
diff --git a/src/hooks/useSessionProtection.ts b/src/hooks/useSessionProtection.ts
index 0c3d1bab..cbdcdda1 100644
--- a/src/hooks/useSessionProtection.ts
+++ b/src/hooks/useSessionProtection.ts
@@ -44,23 +44,6 @@ export function useSessionProtection() {
     });
   }, []);
 
-  const replaceTemporarySession = useCallback((realSessionId?: string | null) => {
-    if (!realSessionId) {
-      return;
-    }
-
-    setActiveSessions((prev) => {
-      const next = new Set<string>();
-      for (const sessionId of prev) {
-        if (!sessionId.startsWith('new-session-')) {
-          next.add(sessionId);
-        }
-      }
-      next.add(realSessionId);
-      return next;
-    });
-  }, []);
-
   return {
     activeSessions,
     processingSessions,
@@ -68,6 +51,5 @@ export function useSessionProtection() {
     markSessionAsInactive,
     markSessionAsProcessing,
     markSessionAsNotProcessing,
-    replaceTemporarySession,
   };
 }