diff --git a/packages/tui/src/routes/session/index.tsx b/packages/tui/src/routes/session/index.tsx
index 6d77b0ea58fd..7789a4eb5648 100644
--- a/packages/tui/src/routes/session/index.tsx
+++ b/packages/tui/src/routes/session/index.tsx
@@ -1,5 +1,4 @@
 import {
-  batch,
   createContext,
   createEffect,
   createMemo,
@@ -247,7 +246,6 @@ export function Session() {
 
   const dimensions = useTerminalDimensions()
   const [sidebar, setSidebar] = kv.signal<"auto" | "hide">("sidebar", "auto")
-  const [sidebarOpen, setSidebarOpen] = createSignal(false)
   const [conceal, setConceal] = createSignal(true)
   const thinking = useThinkingMode()
   const thinkingMode = thinking.mode
@@ -263,7 +261,6 @@ export function Session() {
   const wide = createMemo(() => dimensions().width > 120)
   const sidebarVisible = createMemo(() => {
     if (session()?.parentID) return false
-    if (sidebarOpen()) return true
     if (sidebar() === "auto" && wide()) return true
     return false
   })
@@ -668,11 +665,7 @@ export function Session() {
       value: "session.sidebar.toggle",
       category: "Session",
       run: () => {
-        batch(() => {
-          const isVisible = sidebarVisible()
-          setSidebar(() => (isVisible ? "hide" : "auto"))
-          setSidebarOpen(!isVisible)
-        })
+        setSidebar((prev) => (prev === "auto" ? "hide" : "auto"))
         dialog.clear()
       },
     },
@@ -1322,24 +1315,7 @@ export function Session() {
             <Toast />
           </box>
           <Show when={sidebarVisible()}>
-            <Switch>
-              <Match when={wide()}>
-                <Sidebar sessionID={route.sessionID} />
-              </Match>
-              <Match when={!wide()}>
-                <box
-                  position="absolute"
-                  top={0}
-                  left={0}
-                  right={0}
-                  bottom={0}
-                  alignItems="flex-end"
-                  backgroundColor={RGBA.fromInts(0, 0, 0, 70)}
-                >
-                  <Sidebar sessionID={route.sessionID} />
-                </box>
-              </Match>
-            </Switch>
+            <Sidebar sessionID={route.sessionID} />
           </Show>
         </box>
       </context.Provider>
diff --git a/packages/tui/test/session/sidebar.test.tsx b/packages/tui/test/session/sidebar.test.tsx
new file mode 100644
index 000000000000..25d7cc716378
--- /dev/null
+++ b/packages/tui/test/session/sidebar.test.tsx
@@ -0,0 +1,146 @@
+import { createMemo, createRoot, createSignal } from "solid-js"
+import { expect, test } from "bun:test"
+
+/**
+ * The sidebar visibility logic in the session component determines
+ * whether to show the sidebar based on:
+ * 1. sidebar mode: "auto" (show when screen is wide enough) or "hide" (always hide)
+ * 2. screen width: wide() returns true when terminal width > 120
+ *
+ * Previously there was a `sidebarOpen` signal that overrode the width check,
+ * causing the sidebar to force-show when toggled on via command palette
+ * even on narrow screens (windowed mode). This was the bug.
+ *
+ * These tests validate the corrected behavior.
+ */
+
+test("sidebar hidden when mode is auto and screen is not wide", () => {
+  createRoot(() => {
+    const [sidebar] = createSignal<"auto" | "hide">("auto")
+    const [wide] = createSignal(false)
+
+    const sidebarVisible = createMemo(() => {
+      if (sidebar() === "auto" && wide()) return true
+      return false
+    })
+
+    expect(sidebarVisible()).toBe(false)
+  })
+})
+
+test("sidebar visible when mode is auto and screen is wide", () => {
+  createRoot(() => {
+    const [sidebar] = createSignal<"auto" | "hide">("auto")
+    const [wide] = createSignal(true)
+
+    const sidebarVisible = createMemo(() => {
+      if (sidebar() === "auto" && wide()) return true
+      return false
+    })
+
+    expect(sidebarVisible()).toBe(true)
+  })
+})
+
+test("sidebar hidden when mode is hide regardless of screen width", () => {
+  createRoot(() => {
+    const [sidebar] = createSignal<"auto" | "hide">("hide")
+    const [wide, setWide] = createSignal(true)
+
+    const sidebarVisible = createMemo(() => {
+      if (sidebar() === "auto" && wide()) return true
+      return false
+    })
+
+    expect(sidebarVisible()).toBe(false)
+
+    // Even when wide, sidebar is hidden because mode is "hide"
+    setWide(true)
+    expect(sidebarVisible()).toBe(false)
+  })
+})
+
+test("sidebar visibility reacts to width changes in auto mode", () => {
+  createRoot(() => {
+    const [sidebar] = createSignal<"auto" | "hide">("auto")
+    const [wide, setWide] = createSignal(false)
+
+    const sidebarVisible = createMemo(() => {
+      if (sidebar() === "auto" && wide()) return true
+      return false
+    })
+
+    expect(sidebarVisible()).toBe(false)
+
+    // Resize from narrow to wide
+    setWide(true)
+    expect(sidebarVisible()).toBe(true)
+
+    // Resize from wide back to narrow
+    setWide(false)
+    expect(sidebarVisible()).toBe(false)
+  })
+})
+
+test("toggling sidebar switches between auto and hide modes", () => {
+  createRoot(() => {
+    const [sidebar, setSidebar] = createSignal<"auto" | "hide">("auto")
+
+    // Toggle: auto -> hide
+    setSidebar("hide")
+    expect(sidebar()).toBe("hide")
+
+    // Toggle: hide -> auto
+    setSidebar("auto")
+    expect(sidebar()).toBe("auto")
+  })
+})
+
+test("toggling sidebar on with narrow window does NOT force visibility (regression test)", () => {
+  createRoot(() => {
+    const [sidebar, setSidebar] = createSignal<"auto" | "hide">("auto")
+    const [wide] = createSignal(false)
+
+    const sidebarVisible = createMemo(() => {
+      if (sidebar() === "auto" && wide()) return true
+      return false
+    })
+
+    // Initially hidden
+    expect(sidebarVisible()).toBe(false)
+
+    // Toggle: user toggles "on" (set mode to auto), but screen is still narrow
+    // The old bug: sidebarOpen would force visibility here
+    setSidebar("auto")
+
+    // The fix: sidebar should still be hidden because screen is not wide
+    expect(sidebarVisible()).toBe(false)
+  })
+})
+
+test("sidebar toggle cycle with width changes works correctly", () => {
+  createRoot(() => {
+    const [sidebar, setSidebar] = createSignal<"auto" | "hide">("hide")
+    const [wide, setWide] = createSignal(false)
+
+    const sidebarVisible = createMemo(() => {
+      if (sidebar() === "auto" && wide()) return true
+      return false
+    })
+
+    // 1. Start: hide, narrow -> not visible
+    expect(sidebarVisible()).toBe(false)
+
+    // 2. User enables sidebar, but still narrow -> should not force show
+    setSidebar("auto")
+    expect(sidebarVisible()).toBe(false)
+
+    // 3. User makes window wide -> sidebar becomes visible
+    setWide(true)
+    expect(sidebarVisible()).toBe(true)
+
+    // 4. User makes window narrow again -> sidebar hides
+    setWide(false)
+    expect(sidebarVisible()).toBe(false)
+  })
+})