diff --git a/android/app/src/main/java/com/hyzq/boss/MainActivity.java b/android/app/src/main/java/com/hyzq/boss/MainActivity.java
index bc683ad..a0ecd4e 100644
--- a/android/app/src/main/java/com/hyzq/boss/MainActivity.java
+++ b/android/app/src/main/java/com/hyzq/boss/MainActivity.java
@@ -22,6 +22,9 @@ import java.util.concurrent.Executors;
 
 public class MainActivity extends AppCompatActivity {
     public static final String EXTRA_INITIAL_TAB = "initial_tab";
+    private static final String UI_PREFS = "boss_native_client";
+    private static final String KEY_LAST_ROOT_TAB = "last_root_tab";
+    private static final long ROOT_BACK_EXIT_WINDOW_MS = 1_500L;
 
     private final ExecutorService executor = Executors.newSingleThreadExecutor();
 
@@ -45,8 +48,9 @@ public class MainActivity extends AppCompatActivity {
 
     private String activeTab = "conversations";
     private String preferredEntryTab = "conversations";
-    private boolean explicitTabRequest = false;
+    private @Nullable String requestedInitialTab;
     private boolean userSelectedTab = false;
+    private long lastRootBackPressedAt = 0L;
     private @Nullable JSONObject sessionData;
     private @Nullable JSONObject otaData;
     private @Nullable JSONArray conversationsData;
@@ -78,10 +82,17 @@ public class MainActivity extends AppCompatActivity {
     public void onBackPressed() {
         if (contentPanel.getVisibility() == View.VISIBLE && !"conversations".equals(activeTab)) {
             setActiveTab("conversations", false);
+            persistLastRootTab("conversations");
             return;
         }
         if (contentPanel.getVisibility() == View.VISIBLE) {
-            moveTaskToBack(true);
+            long now = System.currentTimeMillis();
+            if (now - lastRootBackPressedAt < ROOT_BACK_EXIT_WINDOW_MS) {
+                moveTaskToBack(true);
+                return;
+            }
+            lastRootBackPressedAt = now;
+            showMessage("再按一次返回，应用进入后台");
             return;
         }
         super.onBackPressed();
@@ -126,12 +137,12 @@ public class MainActivity extends AppCompatActivity {
     }
 
     private void applyInitialTab(@Nullable Intent intent) {
-        explicitTabRequest = false;
+        requestedInitialTab = null;
         String requested = intent == null ? null : intent.getStringExtra(EXTRA_INITIAL_TAB);
         if ("devices".equals(requested) || "me".equals(requested) || "conversations".equals(requested)) {
-            activeTab = requested;
-            explicitTabRequest = true;
+            requestedInitialTab = requested;
         }
+        activeTab = RootTabMemory.resolveInitialTab(requestedInitialTab, readLastRootTab(), preferredEntryTab);
     }
 
     private void bootstrapSession() {
@@ -261,18 +272,18 @@ public class MainActivity extends AppCompatActivity {
         activeTab = tab;
         if (fromUser) {
             userSelectedTab = true;
+            persistLastRootTab(tab);
         }
+        lastRootBackPressedAt = 0L;
         updateTabStyles();
         renderCurrentTab();
     }
 
     private void maybeApplyPreferredEntry() {
-        if (explicitTabRequest || userSelectedTab) {
+        if (userSelectedTab) {
             return;
         }
-        if ("devices".equals(preferredEntryTab) || "me".equals(preferredEntryTab) || "conversations".equals(preferredEntryTab)) {
-            activeTab = preferredEntryTab;
-        }
+        activeTab = RootTabMemory.resolveInitialTab(requestedInitialTab, readLastRootTab(), preferredEntryTab);
     }
 
     private void renderCurrentTab() {
@@ -495,4 +506,16 @@ public class MainActivity extends AppCompatActivity {
         }
         return null;
     }
+
+    private void persistLastRootTab(String tab) {
+        getSharedPreferences(UI_PREFS, MODE_PRIVATE)
+                .edit()
+                .putString(KEY_LAST_ROOT_TAB, tab)
+                .apply();
+    }
+
+    private @Nullable String readLastRootTab() {
+        return getSharedPreferences(UI_PREFS, MODE_PRIVATE)
+                .getString(KEY_LAST_ROOT_TAB, null);
+    }
 }
diff --git a/android/app/src/main/java/com/hyzq/boss/RootTabMemory.java b/android/app/src/main/java/com/hyzq/boss/RootTabMemory.java
new file mode 100644
index 0000000..bb400c1
--- /dev/null
+++ b/android/app/src/main/java/com/hyzq/boss/RootTabMemory.java
@@ -0,0 +1,28 @@
+package com.hyzq.boss;
+
+public final class RootTabMemory {
+    private RootTabMemory() {}
+
+    public static String resolveInitialTab(String explicitTab, String storedTab, String preferredTab) {
+        String explicit = normalize(explicitTab);
+        if (explicit != null) {
+            return explicit;
+        }
+        String stored = normalize(storedTab);
+        if (stored != null) {
+            return stored;
+        }
+        String preferred = normalize(preferredTab);
+        if (preferred != null) {
+            return preferred;
+        }
+        return "conversations";
+    }
+
+    private static String normalize(String tab) {
+        if ("conversations".equals(tab) || "devices".equals(tab) || "me".equals(tab)) {
+            return tab;
+        }
+        return null;
+    }
+}
diff --git a/android/app/src/test/java/com/hyzq/boss/RootTabMemoryTest.java b/android/app/src/test/java/com/hyzq/boss/RootTabMemoryTest.java
new file mode 100644
index 0000000..8eb42de
--- /dev/null
+++ b/android/app/src/test/java/com/hyzq/boss/RootTabMemoryTest.java
@@ -0,0 +1,27 @@
+package com.hyzq.boss;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+public class RootTabMemoryTest {
+    @Test
+    public void resolveInitialTab_prefersExplicitTab() {
+        assertEquals("devices", RootTabMemory.resolveInitialTab("devices", "me", "conversations"));
+    }
+
+    @Test
+    public void resolveInitialTab_fallsBackToStoredTab() {
+        assertEquals("me", RootTabMemory.resolveInitialTab(null, "me", "devices"));
+    }
+
+    @Test
+    public void resolveInitialTab_usesPreferredEntryBeforeDefault() {
+        assertEquals("devices", RootTabMemory.resolveInitialTab(null, null, "devices"));
+    }
+
+    @Test
+    public void resolveInitialTab_defaultsToConversations() {
+        assertEquals("conversations", RootTabMemory.resolveInitialTab(null, null, null));
+    }
+}