diff --git a/ui/src/ui/app-render.ts b/ui/src/ui/app-render.ts
index e950e93be..d444cfd21 100644
--- a/ui/src/ui/app-render.ts
+++ b/ui/src/ui/app-render.ts
@@ -497,13 +497,12 @@ export function renderApp(state: AppViewState) {
               onSplitRatioChange: (ratio: number) => state.handleSplitRatioChange(ratio),
               assistantName: state.assistantName,
               assistantAvatar: state.assistantAvatar,
-              // Delete session (hidden for main session)
+              // Delete session (disabled for main session)
               showDeleteConfirm: state.chatDeleteConfirm,
-              onDeleteClick:
+              isMainSession:
                 state.sessionKey === "main" ||
-                parseAgentSessionKey(state.sessionKey)?.rest === "main"
-                  ? undefined
-                  : () => (state.chatDeleteConfirm = true),
+                parseAgentSessionKey(state.sessionKey)?.rest === "main",
+              onDeleteClick: () => (state.chatDeleteConfirm = true),
               onDeleteConfirm: async () => {
                 state.chatDeleteConfirm = false;
                 const { deleteSession } = await import("./controllers/sessions");
diff --git a/ui/src/ui/views/chat.ts b/ui/src/ui/views/chat.ts
index 31beb8541..c7c8b38aa 100644
--- a/ui/src/ui/views/chat.ts
+++ b/ui/src/ui/views/chat.ts
@@ -70,6 +70,7 @@ export type ChatProps = {
   onChatScroll?: (event: Event) => void;
   // Delete session
   showDeleteConfirm?: boolean;
+  isMainSession?: boolean;
   onDeleteClick?: () => void;
   onDeleteConfirm?: () => void;
   onDeleteCancel?: () => void;
@@ -407,9 +408,9 @@ export function renderChat(props: ChatProps) {
               ? html`
                   <button
                     class="btn danger"
-                    ?disabled=${!props.connected || isBusy}
+                    ?disabled=${!props.connected || isBusy || props.isMainSession}
                     @click=${props.onDeleteClick}
-                    title="Delete this session"
+                    title=${props.isMainSession ? "Cannot delete main session" : "Delete this session"}
                   >
                     Delete
                   </button>