diff --git a/apps/web/src/components/ChatView.tsx b/apps/web/src/components/ChatView.tsx
index eaead424fb..d06ba60b71 100644
--- a/apps/web/src/components/ChatView.tsx
+++ b/apps/web/src/components/ChatView.tsx
@@ -34,7 +34,15 @@ import {
   resolveModelSlugForProvider,
   supportsClaudeUltrathinkKeyword,
 } from "@t3tools/shared/model";
-import { useCallback, useEffect, useLayoutEffect, useMemo, useRef, useState } from "react";
+import {
+  useCallback,
+  useEffect,
+  useLayoutEffect,
+  useMemo,
+  useRef,
+  useState,
+  type ReactNode,
+} from "react";
 import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
 import { useDebouncedValue } from "@tanstack/react-pacer";
 import { useNavigate, useSearch } from "@tanstack/react-router";
@@ -93,6 +101,11 @@ import {
 import { basenameOfPath } from "../vscode-icons";
 import { useTheme } from "../hooks/useTheme";
 import { useTurnDiffSummaries } from "../hooks/useTurnDiffSummaries";
+import { useMediaQuery } from "../hooks/useMediaQuery";
+import {
+  RIGHT_PANEL_INLINE_LAYOUT_MEDIA_QUERY,
+  RIGHT_PANEL_SHEET_CLASS_NAME,
+} from "../rightPanelLayout";
 import BranchToolbar from "./BranchToolbar";
 import { resolveShortcutCommand, shortcutLabelForCommand } from "../keybindings";
 import PlanSidebar from "./PlanSidebar";
@@ -178,6 +191,7 @@ import {
   SendPhase,
 } from "./ChatView.logic";
 import { useLocalStorage } from "~/hooks/useLocalStorage";
+import { Sheet, SheetPopup } from "./ui/sheet";
 
 const ATTACHMENT_PREVIEW_HANDOFF_TTL_MS = 5000;
 const IMAGE_SIZE_LIMIT_LABEL = `${Math.round(PROVIDER_SEND_TURN_MAX_IMAGE_BYTES / (1024 * 1024))}MB`;
@@ -236,6 +250,28 @@ interface ChatViewProps {
   threadId: ThreadId;
 }
 
+function PlanSidebarSheet(props: { children: ReactNode; open: boolean; onClose: () => void }) {
+  return (
+    <Sheet
+      open={props.open}
+      onOpenChange={(open) => {
+        if (!open) {
+          props.onClose();
+        }
+      }}
+    >
+      <SheetPopup
+        side="right"
+        showCloseButton={false}
+        keepMounted
+        className={RIGHT_PANEL_SHEET_CLASS_NAME}
+      >
+        {props.children}
+      </SheetPopup>
+    </Sheet>
+  );
+}
+
 export default function ChatView({ threadId }: ChatViewProps) {
   const threads = useStore((store) => store.threads);
   const projects = useStore((store) => store.projects);
@@ -334,6 +370,7 @@ export default function ChatView({ threadId }: ChatViewProps) {
     useState<Record<string, number>>({});
   const [expandedWorkGroups, setExpandedWorkGroups] = useState<Record<string, boolean>>({});
   const [planSidebarOpen, setPlanSidebarOpen] = useState(false);
+  const shouldUsePlanSidebarSheet = useMediaQuery(RIGHT_PANEL_INLINE_LAYOUT_MEDIA_QUERY);
   const [isComposerFooterCompact, setIsComposerFooterCompact] = useState(false);
   // Tracks whether the user explicitly dismissed the sidebar for the active turn.
   const planSidebarDismissedForTurnRef = useRef<string | null>(null);
@@ -1630,6 +1667,13 @@ export default function ChatView({ threadId }: ChatViewProps) {
       return !open;
     });
   }, [activePlan?.turnId, sidebarProposedPlan?.turnId]);
+  const closePlanSidebar = useCallback(() => {
+    setPlanSidebarOpen(false);
+    const turnKey = activePlan?.turnId ?? sidebarProposedPlan?.turnId ?? null;
+    if (turnKey) {
+      planSidebarDismissedForTurnRef.current = turnKey;
+    }
+  }, [activePlan?.turnId, sidebarProposedPlan?.turnId]);
 
   const persistThreadSettingsForNextTurn = useCallback(
     async (input: {
@@ -4136,26 +4180,34 @@ export default function ChatView({ threadId }: ChatViewProps) {
         {/* end chat column */}
 
         {/* Plan sidebar */}
-        {planSidebarOpen ? (
+        {planSidebarOpen && !shouldUsePlanSidebarSheet ? (
           <PlanSidebar
             activePlan={activePlan}
             activeProposedPlan={sidebarProposedPlan}
             markdownCwd={gitCwd ?? undefined}
             workspaceRoot={activeProject?.cwd ?? undefined}
             timestampFormat={timestampFormat}
-            onClose={() => {
-              setPlanSidebarOpen(false);
-              // Track that the user explicitly dismissed for this turn so auto-open won't fight them.
-              const turnKey = activePlan?.turnId ?? sidebarProposedPlan?.turnId ?? null;
-              if (turnKey) {
-                planSidebarDismissedForTurnRef.current = turnKey;
-              }
-            }}
+            mode="sidebar"
+            onClose={closePlanSidebar}
           />
         ) : null}
       </div>
       {/* end horizontal flex container */}
 
+      {shouldUsePlanSidebarSheet && planSidebarOpen ? (
+        <PlanSidebarSheet open onClose={closePlanSidebar}>
+          <PlanSidebar
+            activePlan={activePlan}
+            activeProposedPlan={activeProposedPlan}
+            markdownCwd={gitCwd ?? undefined}
+            workspaceRoot={activeProject?.cwd ?? undefined}
+            timestampFormat={timestampFormat}
+            mode="sheet"
+            onClose={closePlanSidebar}
+          />
+        </PlanSidebarSheet>
+      ) : null}
+
       {(() => {
         if (!terminalState.terminalOpen || !activeProject) {
           return null;
diff --git a/apps/web/src/components/PlanSidebar.tsx b/apps/web/src/components/PlanSidebar.tsx
index 47bee930cc..4c3fa67704 100644
--- a/apps/web/src/components/PlanSidebar.tsx
+++ b/apps/web/src/components/PlanSidebar.tsx
@@ -56,6 +56,7 @@ interface PlanSidebarProps {
   markdownCwd: string | undefined;
   workspaceRoot: string | undefined;
   timestampFormat: TimestampFormat;
+  mode?: "sheet" | "sidebar";
   onClose: () => void;
 }
 
@@ -65,6 +66,7 @@ const PlanSidebar = memo(function PlanSidebar({
   markdownCwd,
   workspaceRoot,
   timestampFormat,
+  mode = "sidebar",
   onClose,
 }: PlanSidebarProps) {
   const [proposedPlanExpanded, setProposedPlanExpanded] = useState(false);
@@ -118,7 +120,14 @@ const PlanSidebar = memo(function PlanSidebar({
   }, [planMarkdown, workspaceRoot]);
 
   return (
-    <div className="flex h-full w-[340px] shrink-0 flex-col border-l border-border/70 bg-card/50">
+    <div
+      className={cn(
+        "flex min-h-0 flex-col bg-card/50",
+        mode === "sidebar"
+          ? "h-full w-[340px] shrink-0 border-l border-border/70"
+          : "h-full w-full",
+      )}
+    >
       {/* Header */}
       <div className="flex h-12 shrink-0 items-center justify-between border-b border-border/60 px-3">
         <div className="flex items-center gap-2">
diff --git a/apps/web/src/rightPanelLayout.ts b/apps/web/src/rightPanelLayout.ts
new file mode 100644
index 0000000000..c94f52a9cb
--- /dev/null
+++ b/apps/web/src/rightPanelLayout.ts
@@ -0,0 +1,2 @@
+export const RIGHT_PANEL_INLINE_LAYOUT_MEDIA_QUERY = "(max-width: 1180px)";
+export const RIGHT_PANEL_SHEET_CLASS_NAME = "w-[min(88vw,820px)] max-w-[820px] p-0";
diff --git a/apps/web/src/routes/_chat.$threadId.tsx b/apps/web/src/routes/_chat.$threadId.tsx
index 8e7a5d3ba8..741c74f397 100644
--- a/apps/web/src/routes/_chat.$threadId.tsx
+++ b/apps/web/src/routes/_chat.$threadId.tsx
@@ -17,12 +17,15 @@ import {
   stripDiffSearchParams,
 } from "../diffRouteSearch";
 import { useMediaQuery } from "../hooks/useMediaQuery";
+import {
+  RIGHT_PANEL_INLINE_LAYOUT_MEDIA_QUERY,
+  RIGHT_PANEL_SHEET_CLASS_NAME,
+} from "../rightPanelLayout";
 import { useStore } from "../store";
 import { Sheet, SheetPopup } from "../components/ui/sheet";
 import { Sidebar, SidebarInset, SidebarProvider, SidebarRail } from "~/components/ui/sidebar";
 
 const DiffPanel = lazy(() => import("../components/DiffPanel"));
-const DIFF_INLINE_LAYOUT_MEDIA_QUERY = "(max-width: 1180px)";
 const DIFF_INLINE_SIDEBAR_WIDTH_STORAGE_KEY = "chat_diff_sidebar_width";
 const DIFF_INLINE_DEFAULT_WIDTH = "clamp(28rem,48vw,44rem)";
 const DIFF_INLINE_SIDEBAR_MIN_WIDTH = 26 * 16;
@@ -46,7 +49,7 @@ const DiffPanelSheet = (props: {
         side="right"
         showCloseButton={false}
         keepMounted
-        className="w-[min(88vw,820px)] max-w-[820px] p-0"
+        className={RIGHT_PANEL_SHEET_CLASS_NAME}
       >
         {props.children}
       </SheetPopup>
@@ -173,7 +176,7 @@ function ChatThreadRouteView() {
   );
   const routeThreadExists = threadExists || draftThreadExists;
   const diffOpen = search.diff === "1";
-  const shouldUseDiffSheet = useMediaQuery(DIFF_INLINE_LAYOUT_MEDIA_QUERY);
+  const shouldUseDiffSheet = useMediaQuery(RIGHT_PANEL_INLINE_LAYOUT_MEDIA_QUERY);
   // TanStack Router keeps active route components mounted across param-only navigations
   // unless remountDeps are configured, so this stays warm across thread switches.
   const [hasOpenedDiff, setHasOpenedDiff] = useState(diffOpen);