feat: add Android back navigation

docs/MobileDevelopment.md

@@ -243,3 +243,33 @@ https://v2.tauri.app/develop/resources/#android
 - 仅作用于第三方浮层与运行时动态 `<style>`，不改静态主样式文件；
 - 明确排除 `body/#sheld/#chat` 等应用核心容器，避免牵连应用本体布局；
 - 不侵入第三方扩展资源加载链路（与 `third-party-runtime.js` 解耦）。
+
+---
+
+## 7. Android 返回键分层返回（Back Navigation）
+
+问题：
+
+- Android 端按系统返回键可能直接退出应用（未能按“退一层 UI”关闭弹窗/抽屉/聊天）。
+- 不要依赖覆盖 `Activity.onBackPressed()`：在较新的 Android（predictive back / `OnBackInvokedDispatcher`）路径下，Back 分发优先走 `OnBackPressedDispatcher`，`super.onBackPressed()` 也可能绕开子类 override。
+
+当前方案（Native→JS Back Bridge）：
+
+- `MainActivity` 在 `onCreate()` 里向 `onBackPressedDispatcher` 注册回调，并把 Back 交给 `AndroidBackNavigationController`：
+  - `src-tauri/gen/android/app/src/main/java/com/tauritavern/client/MainActivity.kt`
+  - `src-tauri/gen/android/app/src/main/java/com/tauritavern/client/AndroidBackNavigationController.kt`
+- controller 通过 `WebView.evaluateJavascript` 调用前端全局函数：`window.__TAURITAVERN_HANDLE_BACK__()`。
+  - JS 返回 `true`：表示已消费 Back（关闭了一层 UI），原生不退出。
+  - JS 返回 `false`：表示前端未消费，原生执行 `finish()` 退出。
+
+前端分层关闭策略：
+
+- Back 逻辑集中在 `src/tauri/main/back-navigation.js`，并在 `src/tauri/main/bootstrap.js` 启动早期安装。
+- 关闭动作必须复用现有 UI 的关闭入口（点击 close/cancel 或触发既有的“点空白收起”逻辑），避免引入新的状态机。
+- “点空白收起”要模拟 `mousedown`（SillyTavern 绑定在 `html` 的 `touchstart/mousedown` 上），仅派发 `click` 不足以关闭抽屉。
+
+维护原则：
+
+- 不修改 auto-generated 的 `src-tauri/gen/android/.../generated/*`，避免升级冲突。
+- UI 分层判断与关闭动作只写在 JS；Kotlin 不写 DOM/UI 规则，只做拦截/转发/退出决策。
+- 若未来新增/变更 UI 层级，只在 `back-navigation.js` 增加一个分支即可；更详细设计见 `docs/AndroidBackNavigation.md`。

src-tauri/gen/android/app/src/main/java/com/tauritavern/client/AndroidBackNavigationController.kt

@@ -0,0 +1,50 @@
+package com.tauritavern.client
+
+import android.webkit.WebView
+import androidx.annotation.MainThread
+import androidx.activity.OnBackPressedCallback
+import androidx.activity.OnBackPressedDispatcher
+import androidx.lifecycle.LifecycleOwner
+
+class AndroidBackNavigationController(
+  private val webViewProvider: () -> WebView?,
+  private val exitApp: () -> Unit,
+) {
+  fun register(dispatcher: OnBackPressedDispatcher, owner: LifecycleOwner) {
+    dispatcher.addCallback(
+      owner,
+      object : OnBackPressedCallback(true) {
+        override fun handleOnBackPressed() {
+          handleBackPressed()
+        }
+      },
+    )
+  }
+
+  @MainThread
+  fun handleBackPressed() {
+    val activeWebView = webViewProvider()
+    if (activeWebView == null) {
+      exitApp()
+      return
+    }
+
+    activeWebView.evaluateJavascript(HANDLE_BACK_SCRIPT) { value ->
+      if (value == "true") {
+        return@evaluateJavascript
+      }
+
+      exitApp()
+    }
+  }
+
+  companion object {
+    private val HANDLE_BACK_SCRIPT =
+      """
+      (() => {
+        const fn = window.__TAURITAVERN_HANDLE_BACK__;
+        return Boolean(typeof fn === 'function' && fn());
+      })();
+      """.trimIndent()
+  }
+}

src-tauri/gen/android/app/src/main/java/com/tauritavern/client/MainActivity.kt

@@ -23,6 +23,12 @@ class MainActivity : TauriActivity() {
       Thread(runnable, "tauritavern-main-bg").apply { priority = Thread.NORM_PRIORITY - 1 }
     }
   private var isActivityDestroyed: Boolean = false
+  private val backNavigationController: AndroidBackNavigationController by lazy {
+    AndroidBackNavigationController(
+      webViewProvider = { webView },
+      exitApp = { finish() },
+    )
+  }
   private val aiGenerationNotifier: AndroidAiGenerationNotifier by lazy {
     AndroidAiGenerationNotifier(applicationContext)
   }
@@ -81,6 +87,7 @@ class MainActivity : TauriActivity() {
     initRustlsPlatformVerifier(applicationContext)
     enableEdgeToEdge()
     super.onCreate(savedInstanceState)
+    backNavigationController.register(onBackPressedDispatcher, this)
     // Keep a foreground service for the whole app session to reduce OEM background kills.
     aiGenerationNotifier.ensureKeepAliveService()
     insetsBridge.onCreate()

src/tauri/main/back-navigation.js

@@ -0,0 +1,176 @@
+const BACK_HANDLER_KEY = '__TAURITAVERN_HANDLE_BACK__';
+
+export function installBackNavigationBridge() {
+    window[BACK_HANDLER_KEY] = handleBackNavigation;
+}
+
+function handleBackNavigation() {
+    if (closeTopmostDialogPopup()) {
+        return true;
+    }
+
+    if (closeOverlayByCloseButton()) {
+        return true;
+    }
+
+    if (closeFloatingPanel()) {
+        return true;
+    }
+
+    if (triggerBlankClickIfNeeded()) {
+        return true;
+    }
+
+    if (closeChatIfOpen()) {
+        return true;
+    }
+
+    return false;
+}
+
+function closeTopmostDialogPopup() {
+    const dialogs = Array.from(document.querySelectorAll('dialog[open]:not([closing])'));
+    if (dialogs.length === 0) {
+        return false;
+    }
+
+    const dialog = dialogs[dialogs.length - 1];
+    const closeButton = dialog.querySelector('.popup-button-close');
+    if (closeButton instanceof HTMLElement) {
+        closeButton.click();
+        return true;
+    }
+
+    if (dialog instanceof HTMLDialogElement) {
+        dialog.close();
+        return true;
+    }
+
+    return false;
+}
+
+function closeOverlayByCloseButton() {
+    const dialoguePopup = document.getElementById('dialogue_popup');
+    if (isVisible(dialoguePopup)) {
+        const cancelButton = document.getElementById('dialogue_popup_cancel');
+        if (isVisible(cancelButton)) {
+            cancelButton.click();
+            return true;
+        }
+
+        const okButton = document.getElementById('dialogue_popup_ok');
+        if (isVisible(okButton)) {
+            okButton.click();
+            return true;
+        }
+
+        return false;
+    }
+
+    const selectChatPopup = document.getElementById('select_chat_popup');
+    if (isVisible(selectChatPopup)) {
+        const closeButton = document.getElementById('select_chat_cross');
+        if (closeButton instanceof HTMLElement) {
+            closeButton.click();
+            return true;
+        }
+
+        return false;
+    }
+
+    const characterPopup = document.getElementById('character_popup');
+    if (isVisible(characterPopup)) {
+        const closeButton = document.getElementById('character_cross');
+        if (closeButton instanceof HTMLElement) {
+            closeButton.click();
+            return true;
+        }
+
+        return false;
+    }
+
+    const deleteMessageCancel = document.getElementById('dialogue_del_mes_cancel');
+    if (isVisible(deleteMessageCancel)) {
+        deleteMessageCancel.click();
+        return true;
+    }
+
+    const logprobsViewer = document.getElementById('logprobsViewer');
+    if (isVisible(logprobsViewer)) {
+        const closeButton = document.getElementById('logprobsViewerClose');
+        if (closeButton instanceof HTMLElement) {
+            closeButton.click();
+            return true;
+        }
+
+        return false;
+    }
+
+    return false;
+}
+
+function closeFloatingPanel() {
+    const closeButtons = Array.from(document.querySelectorAll('#movingDivs .floating_panel_close'));
+    for (let index = closeButtons.length - 1; index >= 0; index -= 1) {
+        const closeButton = closeButtons[index];
+        if (isVisible(closeButton)) {
+            closeButton.click();
+            return true;
+        }
+    }
+
+    return false;
+}
+
+function triggerBlankClickIfNeeded() {
+    const hasOpenDrawer = Boolean(document.querySelector('.openDrawer:not(.pinnedOpen)'));
+    const hasOptionsMenu = isVisible(document.getElementById('options'));
+    const hasExtraMessageButtons = Boolean(document.querySelector('.extraMesButtons.visible'));
+    const hasActionModal = Array.from(document.querySelectorAll('.actionButtonsModal')).some(isVisible);
+
+    if (!hasOpenDrawer && !hasOptionsMenu && !hasExtraMessageButtons && !hasActionModal) {
+        return false;
+    }
+
+    dispatchBlankClick();
+    return true;
+}
+
+function closeChatIfOpen() {
+    const welcomePanel = document.querySelector('#chat > div.welcomePanel');
+    if (isVisible(welcomePanel)) {
+        return false;
+    }
+
+    const closeChatButtons = Array.from(document.querySelectorAll('#option_close_chat'));
+    if (closeChatButtons.length === 0) {
+        return false;
+    }
+
+    const closeChatButton = closeChatButtons[closeChatButtons.length - 1];
+    if (!(closeChatButton instanceof HTMLElement)) {
+        return false;
+    }
+
+    closeChatButton.click();
+    return true;
+}
+
+function dispatchBlankClick() {
+    const root = document.documentElement;
+    root.dispatchEvent(new MouseEvent('mousedown', { bubbles: true }));
+    root.dispatchEvent(new MouseEvent('click', { bubbles: true }));
+}
+
+function isVisible(element) {
+    if (!(element instanceof HTMLElement)) {
+        return false;
+    }
+
+    if (element.getClientRects().length === 0) {
+        return false;
+    }
+
+    const style = getComputedStyle(element);
+    return style.visibility !== 'hidden';
+}

src/tauri/main/bootstrap.js

@@ -2,6 +2,7 @@ import { initializeBridge, invoke, isTauri as isTauriRuntime, convertFileSrc } f
 import { createTauriMainContext } from './context.js';
 import { createInterceptors } from './interceptors.js';
 import { createRouteRegistry } from './router.js';
+import { installBackNavigationBridge } from './back-navigation.js';
 import { installNativeShareBridge } from './share-target-bridge.js';
 import { installLanSyncPanel } from '../../scripts/tauri/sync/sync-panel.js';
 import {
@@ -183,6 +184,7 @@ export function bootstrapTauriMain() {
     }
     bootstrapped = true;
 
+    installBackNavigationBridge();
     installNativeShareBridge();
     installLanSyncPanel();