diff --git a/src/servers/api/saved-sessions/saved-sessions.ts b/src/servers/api/saved-sessions/saved-sessions.ts
index e5c20048..78d0a339 100644
--- a/src/servers/api/saved-sessions/saved-sessions.ts
+++ b/src/servers/api/saved-sessions/saved-sessions.ts
@@ -81,7 +81,7 @@ savedSessionsRouter.get('/:id', async (ctx) => {
 savedSessionsRouter.put('/:id', async (ctx) => {
   const user = ctx.get('user');
   const id = Number(ctx.req.param('id'));
-  const { sessionId } = ctx.get('body') as { sessionId: string };
+  const { sessionId, resumedMessageCount } = ctx.get('body') as { sessionId: string; resumedMessageCount?: number };
 
   if (Number.isNaN(id)) {
     return ctx.json({ error: 'Invalid id' }, 400);
@@ -93,12 +93,6 @@ savedSessionsRouter.put('/:id', async (ctx) => {
 
   const homeDir = getHomeDirForRole(user.email, user.role);
 
-  // Load existing saved session to get previous messages
-  const existing = await getSavedSession(id, user.id);
-  if (!existing) {
-    return ctx.json({ error: 'Not found' }, 404);
-  }
-
   let meta;
   let newMessages: Message[];
   try {
@@ -109,14 +103,21 @@ savedSessionsRouter.put('/:id', async (ctx) => {
     return ctx.json({ error: 'Session not found on disk' }, 404);
   }
 
-  // Merge: old DB messages (from before resume) + new disk messages (from this session)
-  const oldMessages = (existing.rawMessages ?? []) as Message[];
-  const mergedMessages = [...oldMessages, ...newMessages];
+  // If resuming, merge original pre-resume messages with new disk messages
+  let finalMessages = newMessages;
+  if (resumedMessageCount && resumedMessageCount > 0) {
+    const existing = await getSavedSession(id, user.id);
+    if (!existing) {
+      return ctx.json({ error: 'Not found' }, 404);
+    }
+    const oldMessages = ((existing.rawMessages ?? []) as Message[]).slice(0, resumedMessageCount);
+    finalMessages = [...oldMessages, ...newMessages];
+  }
 
   const updated = await updateSavedSessionMessages(
     id,
     user.id,
-    mergedMessages,
+    finalMessages,
     meta.cost as unknown as Record<string, unknown>,
   );
 
diff --git a/src/workspaces/officerdev/src/apps/Chat/ChatPanelWrapper.tsx b/src/workspaces/officerdev/src/apps/Chat/ChatPanelWrapper.tsx
index 229f023f..742c5013 100644
--- a/src/workspaces/officerdev/src/apps/Chat/ChatPanelWrapper.tsx
+++ b/src/workspaces/officerdev/src/apps/Chat/ChatPanelWrapper.tsx
@@ -41,6 +41,7 @@ const ChatPanelInner = ({
   const savedIdRef = useRef(savedId);
   savedIdRef.current = savedId;
   const chatSessionRef = useRef<string | null>(null);
+  const resumedMessageCountRef = useRef(initialMessages?.length ?? 0);
 
   const handleTurnComplete = useCallback(
     (hadToolCalls: boolean) => {
@@ -48,7 +49,8 @@ const ChatPanelInner = ({
       const id = savedIdRef.current;
       const sid = chatSessionRef.current;
       if (id != null && sid) {
-        updateSessionMessages(id, sid).catch(() => {});
+        const count = resumedMessageCountRef.current;
+        updateSessionMessages(id, sid, count > 0 ? count : undefined).catch(() => {});
       }
     },
     [onTurnComplete, updateSessionMessages],
diff --git a/src/workspaces/officerdev/src/apps/ChatHistory/ChatDetailPanel.tsx b/src/workspaces/officerdev/src/apps/ChatHistory/ChatDetailPanel.tsx
index f1eb742f..3a2103d7 100644
--- a/src/workspaces/officerdev/src/apps/ChatHistory/ChatDetailPanel.tsx
+++ b/src/workspaces/officerdev/src/apps/ChatHistory/ChatDetailPanel.tsx
@@ -95,12 +95,14 @@ function NewChat({ resumeSummary, initialMessages, savedId: initialSavedId }: Ne
   const savedIdRef = useRef(savedId);
   savedIdRef.current = savedId;
   const chatSessionRef = useRef<string | null>(null);
+  const resumedMessageCountRef = useRef(initialMessages?.length ?? 0);
 
   const onTurnComplete = useCallback(() => {
     const id = savedIdRef.current;
     const sid = chatSessionRef.current;
     if (id != null && sid) {
-      updateSessionMessages(id, sid).catch(() => {});
+      const count = resumedMessageCountRef.current;
+      updateSessionMessages(id, sid, count > 0 ? count : undefined).catch(() => {});
     }
   }, [updateSessionMessages]);
 
diff --git a/src/workspaces/state/src/useSavedSessions.ts b/src/workspaces/state/src/useSavedSessions.ts
index 6ab1ad01..e8c11286 100644
--- a/src/workspaces/state/src/useSavedSessions.ts
+++ b/src/workspaces/state/src/useSavedSessions.ts
@@ -88,8 +88,8 @@ export function useSavedSessions() {
     return client.post<ResumeResult>(`/saved-sessions/${id}/resume`);
   }
 
-  async function updateSessionMessages(savedId: number, sessionId: string) {
-    await client.put(`/saved-sessions/${savedId}`, { sessionId });
+  async function updateSessionMessages(savedId: number, sessionId: string, resumedMessageCount?: number) {
+    await client.put(`/saved-sessions/${savedId}`, { sessionId, resumedMessageCount });
   }
 
   return {