diff --git a/apps/web/src/components/ChatView.tsx b/apps/web/src/components/ChatView.tsx
index 99e0421b403..9621f5f1674 100644
--- a/apps/web/src/components/ChatView.tsx
+++ b/apps/web/src/components/ChatView.tsx
@@ -117,6 +117,11 @@ import { useTurnDiffSummaries } from "../hooks/useTurnDiffSummaries";
 import { isCommandPaletteOpen } from "../commandPaletteBus";
 import { buildTemporaryWorktreeBranchName } from "@t3tools/shared/git";
 import { useMediaQuery } from "../hooks/useMediaQuery";
+import {
+  clearPlanSidebarDismissal,
+  dismissPlanSidebarForTurn,
+  isPlanSidebarDismissedForTurn,
+} from "../planSidebarDismissal";
 import { RIGHT_PANEL_INLINE_LAYOUT_MEDIA_QUERY } from "../rightPanelLayout";
 import {
   selectActiveRightPanel,
@@ -1310,8 +1315,6 @@ function ChatViewContent(props: ChatViewProps) {
   const [pendingUserInputQuestionIndexByRequestId, setPendingUserInputQuestionIndexByRequestId] =
     useState<Record<string, number>>({});
   const shouldUsePlanSidebarSheet = useMediaQuery(RIGHT_PANEL_INLINE_LAYOUT_MEDIA_QUERY);
-  // Tracks whether the user explicitly dismissed the sidebar for the active turn.
-  const planSidebarDismissedForTurnRef = useRef<string | null>(null);
   // When set, the thread-change reset effect will open the sidebar instead of closing it.
   // Used by "Implement in a new thread" to carry the sidebar-open intent across navigation.
   const planSidebarOpenOnNextThreadRef = useRef(false);
@@ -3110,18 +3113,21 @@ function ChatViewContent(props: ChatViewProps) {
     handleInteractionModeChange(interactionMode === "plan" ? "default" : "plan");
   }, [handleInteractionModeChange, interactionMode]);
   const dismissPlanSidebarForCurrentTurn = useCallback(() => {
-    planSidebarDismissedForTurnRef.current =
-      activePlan?.turnId ?? sidebarProposedPlan?.turnId ?? "__dismissed__";
-  }, [activePlan?.turnId, sidebarProposedPlan?.turnId]);
+    if (!activeThreadKey) return;
+    dismissPlanSidebarForTurn(
+      activeThreadKey,
+      activePlan?.turnId ?? sidebarProposedPlan?.turnId ?? "__dismissed__",
+    );
+  }, [activeThreadKey, activePlan?.turnId, sidebarProposedPlan?.turnId]);
   const togglePlanSidebar = useCallback(() => {
     if (!activeThreadRef) return;
     if (planSidebarOpen) {
       dismissPlanSidebarForCurrentTurn();
-    } else {
-      planSidebarDismissedForTurnRef.current = null;
+    } else if (activeThreadKey) {
+      clearPlanSidebarDismissal(activeThreadKey);
     }
     useRightPanelStore.getState().toggle(activeThreadRef, "plan");
-  }, [activeThreadRef, dismissPlanSidebarForCurrentTurn, planSidebarOpen]);
+  }, [activeThreadKey, activeThreadRef, dismissPlanSidebarForCurrentTurn, planSidebarOpen]);
   const closePlanSidebar = useCallback(() => {
     if (!activeThreadRef) return;
     setMaximizedRightPanelThreadKey(null);
@@ -3283,7 +3289,7 @@ function ChatViewContent(props: ChatViewProps) {
     (surface: RightPanelSurface) => {
       if (!activeThreadRef) return;
       if (surface.kind === "plan") {
-        planSidebarDismissedForTurnRef.current = null;
+        clearPlanSidebarDismissal(scopedThreadKey(activeThreadRef));
       } else if (planSidebarOpen) {
         dismissPlanSidebarForCurrentTurn();
       }
@@ -3852,10 +3858,10 @@ function ChatViewContent(props: ChatViewProps) {
     if (planSidebarOpenOnNextThreadRef.current) {
       planSidebarOpenOnNextThreadRef.current = false;
       if (activeThreadRef) {
+        clearPlanSidebarDismissal(scopedThreadKey(activeThreadRef));
         useRightPanelStore.getState().open(activeThreadRef, "plan");
       }
     }
-    planSidebarDismissedForTurnRef.current = null;
     // activeThreadRef resets transitively with the active thread.
   }, [activeThread?.id]);
 
@@ -3868,10 +3874,9 @@ function ChatViewContent(props: ChatViewProps) {
     const latestTurnId = activeLatestTurn?.turnId ?? null;
     if (latestTurnId && activePlan.turnId !== latestTurnId) return;
     const turnKey = activePlan.turnId ?? sidebarProposedPlan?.turnId ?? "__dismissed__";
-    if (planSidebarDismissedForTurnRef.current === turnKey) return;
-    if (activeThreadRef) {
-      useRightPanelStore.getState().open(activeThreadRef, "plan");
-    }
+    if (!activeThreadRef) return;
+    if (isPlanSidebarDismissedForTurn(scopedThreadKey(activeThreadRef), turnKey)) return;
+    useRightPanelStore.getState().open(activeThreadRef, "plan");
   }, [
     activePlan,
     activeLatestTurn?.turnId,
@@ -5412,8 +5417,8 @@ function ChatViewContent(props: ChatViewProps) {
         // "default" mode here means the agent is executing the plan, which produces
         // step-tracking activities that the sidebar will display.
         if (nextInteractionMode === "default" && autoOpenPlanSidebar) {
-          planSidebarDismissedForTurnRef.current = null;
           if (activeThreadRef) {
+            clearPlanSidebarDismissal(scopedThreadKey(activeThreadRef));
             useRightPanelStore.getState().open(activeThreadRef, "plan");
           }
         }
diff --git a/apps/web/src/planSidebarDismissal.ts b/apps/web/src/planSidebarDismissal.ts
new file mode 100644
index 00000000000..b92cfaf899e
--- /dev/null
+++ b/apps/web/src/planSidebarDismissal.ts
@@ -0,0 +1,21 @@
+/**
+ * Tracks which turn's plan sidebar the user explicitly dismissed, per thread.
+ *
+ * Kept outside React state so a dismissal survives leaving and re-entering a
+ * thread (ChatView resets its per-thread refs on navigation). Dismissals are
+ * keyed by turn, so when a new turn produces fresh plan steps the sidebar
+ * still auto-opens.
+ */
+const dismissedTurnByThreadKey = new Map<string, string>();
+
+export function dismissPlanSidebarForTurn(threadKey: string, turnKey: string): void {
+  dismissedTurnByThreadKey.set(threadKey, turnKey);
+}
+
+export function clearPlanSidebarDismissal(threadKey: string): void {
+  dismissedTurnByThreadKey.delete(threadKey);
+}
+
+export function isPlanSidebarDismissedForTurn(threadKey: string, turnKey: string): boolean {
+  return dismissedTurnByThreadKey.get(threadKey) === turnKey;
+}