diff --git a/docs/modernization/build-inventory.md b/docs/modernization/build-inventory.md
index f708f00..47493f9 100644
--- a/docs/modernization/build-inventory.md
+++ b/docs/modernization/build-inventory.md
@@ -446,8 +446,9 @@ Known local toolchain state:
   platform clipboard bridges.
 - `pp_platform_api` exposes the SDK-free `PlatformServices` interface for
   clipboard text, cursor visibility, virtual-keyboard visibility, external
-  file display, file sharing, native app/window close, per-frame platform
-  hooks, picker callbacks, and prepared-file save/download handoff; Windows
+  file display, file sharing, native app/window close, UI-thread lifecycle
+  hooks, per-frame platform hooks, picker callbacks, and prepared-file
+  save/download handoff; Windows
   live app execution now uses injected
   `WindowsPlatformServices` from
   `src/platform_windows/windows_platform_services.*` in `pp_platform_windows`,
diff --git a/docs/modernization/debt.md b/docs/modernization/debt.md
index 140d2d3..ee5e906 100644
--- a/docs/modernization/debt.md
+++ b/docs/modernization/debt.md
@@ -35,7 +35,7 @@ agent or engineer to remove them without reconstructing context from chat.
 | DEBT-0014 | Open | Modernization | `windows-clangcl-asan` now configures as a headless Ninja/clang-cl preset and uses the release MSVC runtime required by ASan, but local builds still fail because installed clang-cl 18.1.8 is paired with VS 2026-preview STL headers that require Clang 20 or newer | Sanitizer validation should be local and repeatable, but this machine's compiler/header pairing is incompatible | `cmake --fresh --preset windows-clangcl-asan`; `cmake --build --preset windows-clangcl-asan --target pp_foundation` | Install/use Clang 20+ with the VS 2026 STL, or point the preset at a compatible VS 2022 toolchain, then make `platform-build.ps1 -Presets windows-clangcl-asan` pass for the headless matrix |
 | DEBT-0015 | Open | Modernization | Cursor visibility requests now consume pure `pp_app_core` planning through `pano_cli plan-cursor-visibility`, `App::show_cursor`/`App::hide_cursor` dispatch through `PlatformServices` without platform guards, and Windows live execution uses injected `WindowsPlatformServices`, but macOS cursor execution still reaches the retained fallback adapter | Keep canvas cursor behavior stable while platform shells are extracted incrementally | `pp_app_core_document_platform_io_tests`; `pano_cli plan-cursor-visibility --visible`; `ctest --preset desktop-fast --build-config Debug` | Cursor visibility execution is owned by injected `pp_platform_*` services for every supported platform |
 | DEBT-0016 | Open | Modernization | Clipboard get/set requests now consume pure `pp_app_core` planning through `pano_cli plan-clipboard-read` and `pano_cli plan-clipboard-write`, and Windows live execution uses injected `WindowsPlatformServices`, but Apple/Android clipboard execution still reaches retained fallback adapter branches from `App::clipboard_get_text` and `App::clipboard_set_text` | Keep picker/color text clipboard behavior stable while platform shells are extracted incrementally | `pp_app_core_document_platform_io_tests`; `pano_cli plan-clipboard-write --text #ff00aa`; `ctest --preset desktop-fast --build-config Debug` | Clipboard execution is owned by injected `pp_platform_*` services for every supported platform |
-| DEBT-0017 | Open | Modernization | `App::clipboard_get_text`, `App::clipboard_set_text`, `App::show_cursor`, `App::hide_cursor`, `App::showKeyboard`, `App::hideKeyboard`, `App::display_file`, `App::share_file`, native app/window close, per-frame platform hooks, `App::pick_image`, `App::pick_file`, the non-writer `App::pick_file_save`, `App::pick_dir`, and prepared-file save/download handoff now call the SDK-free `pp::platform::PlatformServices` interface, and Windows injects `WindowsPlatformServices` from `src/platform_windows/windows_platform_services.*`; non-Windows live implementations still use `src/platform_legacy/legacy_platform_services.*`, a named fallback adapter that forwards to retained Apple/Android/Linux/Web bridge functions and retained no-op branches | Preserve behavior while moving platform execution behind a testable service boundary before platform shell implementations are injected | `pp_platform_api_tests`; `pp_app_core_document_platform_io_tests`; `ctest --preset desktop-fast --build-config Debug`; `powershell -ExecutionPolicy Bypass -File scripts\automation\package-smoke.ps1 -Preset windows-msvc-default -Configuration Debug` | Replace `src/platform_legacy/legacy_platform_services.*` with injected `pp_platform_*` service implementations owned by each non-Windows platform shell |
+| DEBT-0017 | Open | Modernization | `App::clipboard_get_text`, `App::clipboard_set_text`, `App::show_cursor`, `App::hide_cursor`, `App::showKeyboard`, `App::hideKeyboard`, `App::display_file`, `App::share_file`, native app/window close, UI-thread lifecycle hooks, per-frame platform hooks, `App::pick_image`, `App::pick_file`, the non-writer `App::pick_file_save`, `App::pick_dir`, and prepared-file save/download handoff now call the SDK-free `pp::platform::PlatformServices` interface, and Windows injects `WindowsPlatformServices` from `src/platform_windows/windows_platform_services.*`; non-Windows live implementations still use `src/platform_legacy/legacy_platform_services.*`, a named fallback adapter that forwards to retained Apple/Android/Linux/Web bridge functions and retained no-op branches | Preserve behavior while moving platform execution behind a testable service boundary before platform shell implementations are injected | `pp_platform_api_tests`; `pp_app_core_document_platform_io_tests`; `ctest --preset desktop-fast --build-config Debug`; `powershell -ExecutionPolicy Bypass -File scripts\automation\package-smoke.ps1 -Preset windows-msvc-default -Configuration Debug` | Replace `src/platform_legacy/legacy_platform_services.*` with injected `pp_platform_*` service implementations owned by each non-Windows platform shell |
 
 ## Closed Debt
 
diff --git a/docs/modernization/roadmap.md b/docs/modernization/roadmap.md
index 30aa918..92581b0 100644
--- a/docs/modernization/roadmap.md
+++ b/docs/modernization/roadmap.md
@@ -469,8 +469,9 @@ cursor bridges continue.
 app-core clipboard text decisions used by live clipboard get/set requests
 before retained platform clipboard bridges continue.
 `pp_platform_api` now owns a headless `PlatformServices` interface for
-clipboard text, cursor visibility, virtual-keyboard visibility, external file
-display, file sharing, image/file/save-file pickers, and directory pickers.
+clipboard text, cursor visibility, virtual-keyboard visibility, UI-thread
+lifecycle hooks, external file display, file sharing, image/file/save-file
+pickers, and directory pickers.
 Windows installs an injected `WindowsPlatformServices` implementation from
 `src/platform_windows/windows_platform_services.*` in `pp_platform_windows`;
 other platforms still route through the debt-tracked legacy fallback adapter
@@ -490,6 +491,10 @@ The UI loop's per-frame platform hooks now dispatch through
 `PlatformServices`: Windows stylus timeout polling and FPS-title updates live
 in `WindowsPlatformServices`, while Linux FPS-title updates remain in the
 legacy adapter pending Phase 6 platform shell extraction.
+The UI thread's platform attach/detach hooks now also dispatch through
+`PlatformServices`, preserving Android JNI attach/detach behavior in the
+legacy adapter while removing direct Android lifecycle calls from the main app
+loop.
 `pano_cli plan-cloud-upload` exposes the app-core cloud upload decision used by
 the live cloud upload command for missing-canvas, new-document warning, publish
 prompt, and dirty-document save-before-upload states before legacy UI, canvas,
@@ -1004,8 +1009,9 @@ Results:
   interface for clipboard read/write, empty clipboard writes, cursor
   visibility dispatch, virtual-keyboard visibility dispatch, external file
   display dispatch, file sharing dispatch, native app/window close dispatch,
-  per-frame platform hook dispatch, picker callback dispatch, and
-  prepared-file save/download callback dispatch. The live Windows app now
+  UI-thread lifecycle dispatch, per-frame platform hook dispatch, picker
+  callback dispatch, and prepared-file save/download callback dispatch. The
+  live Windows app now
   consumes this interface through an injected
   `WindowsPlatformServices` instance isolated in
   `src/platform_windows/windows_platform_services.*`; other platforms still
diff --git a/src/app.cpp b/src/app.cpp
index 855179f..bdf9149 100644
--- a/src/app.cpp
+++ b/src/app.cpp
@@ -20,8 +20,6 @@
 void android_async_lock();
 void android_async_swap();
 void android_async_unlock();
-void android_attach_jni();
-void android_detach_jni();
 #elif _WIN32
 bool async_lock_try();
 void async_lock();
@@ -1083,9 +1081,7 @@ void App::ui_thread_main()
     ui_thread_id = std::this_thread::get_id();
     ui_running = true;
 
-#if __ANDROID__
-    android_attach_jni();
-#endif
+    attach_ui_thread();
 
     LOG("ui thread init()");
     init();
@@ -1169,9 +1165,7 @@ void App::ui_thread_main()
             rendered_frames++;
         }
     }
-#if __ANDROID__
-    android_detach_jni();
-#endif
+    detach_ui_thread();
 }
 
 void App::render_thread_start()
diff --git a/src/app.h b/src/app.h
index baf4ad1..f367ad9 100644
--- a/src/app.h
+++ b/src/app.h
@@ -190,6 +190,8 @@ public:
     void display_file(std::string path);
     void share_file(std::string path);
     void request_app_close();
+    void attach_ui_thread();
+    void detach_ui_thread();
     void update_platform_frame(float delta_time_seconds);
     void report_rendered_frames(int frames);
     void save_prepared_file(
diff --git a/src/app_events.cpp b/src/app_events.cpp
index 8eb6015..0d179ae 100644
--- a/src/app_events.cpp
+++ b/src/app_events.cpp
@@ -219,6 +219,16 @@ void App::request_app_close()
     active_platform_services().request_app_close();
 }
 
+void App::attach_ui_thread()
+{
+    active_platform_services().attach_ui_thread();
+}
+
+void App::detach_ui_thread()
+{
+    active_platform_services().detach_ui_thread();
+}
+
 void App::update_platform_frame(float delta_time_seconds)
 {
     active_platform_services().update_platform_frame(delta_time_seconds);
diff --git a/src/platform_api/platform_services.h b/src/platform_api/platform_services.h
index d04c582..2f41e32 100644
--- a/src/platform_api/platform_services.h
+++ b/src/platform_api/platform_services.h
@@ -18,6 +18,8 @@ public:
     [[nodiscard]] virtual bool set_clipboard_text(std::string_view text) = 0;
     virtual void set_cursor_visible(bool visible) = 0;
     virtual void set_virtual_keyboard_visible(bool visible) = 0;
+    virtual void attach_ui_thread() = 0;
+    virtual void detach_ui_thread() = 0;
     virtual void update_platform_frame(float delta_time_seconds) = 0;
     virtual void report_rendered_frames(int frames) = 0;
     virtual void display_file(std::string_view path) = 0;
diff --git a/src/platform_legacy/legacy_platform_services.cpp b/src/platform_legacy/legacy_platform_services.cpp
index 310fdae..9deb503 100644
--- a/src/platform_legacy/legacy_platform_services.cpp
+++ b/src/platform_legacy/legacy_platform_services.cpp
@@ -6,6 +6,8 @@
 
 #ifdef __ANDROID__
 void displayKeyboard(bool pShow);
+void android_attach_jni();
+void android_detach_jni();
 void android_pick_file(std::function<void(std::string)> callback);
 void android_pick_file_save(std::function<void(std::string)> callback);
 std::string android_get_clipboard();
@@ -88,6 +90,20 @@ public:
 #endif
     }
 
+    void attach_ui_thread() override
+    {
+#ifdef __ANDROID__
+        android_attach_jni();
+#endif
+    }
+
+    void detach_ui_thread() override
+    {
+#ifdef __ANDROID__
+        android_detach_jni();
+#endif
+    }
+
     void update_platform_frame(float delta_time_seconds) override
     {
         (void)delta_time_seconds;
diff --git a/src/platform_windows/windows_platform_services.cpp b/src/platform_windows/windows_platform_services.cpp
index 9771148..4005e30 100644
--- a/src/platform_windows/windows_platform_services.cpp
+++ b/src/platform_windows/windows_platform_services.cpp
@@ -170,6 +170,14 @@ public:
         (void)visible;
     }
 
+    void attach_ui_thread() override
+    {
+    }
+
+    void detach_ui_thread() override
+    {
+    }
+
     void update_platform_frame(float delta_time_seconds) override
     {
         win32_update_stylus(delta_time_seconds);
diff --git a/tests/platform_api/platform_services_tests.cpp b/tests/platform_api/platform_services_tests.cpp
index ad21ce7..30a9477 100644
--- a/tests/platform_api/platform_services_tests.cpp
+++ b/tests/platform_api/platform_services_tests.cpp
@@ -40,6 +40,16 @@ public:
         keyboard_visible = visible;
     }
 
+    void attach_ui_thread() override
+    {
+        ++ui_thread_attaches;
+    }
+
+    void detach_ui_thread() override
+    {
+        ++ui_thread_detaches;
+    }
+
     void update_platform_frame(float delta_time_seconds) override
     {
         ++platform_frame_updates;
@@ -110,6 +120,8 @@ public:
     int clipboard_writes = 0;
     int cursor_updates = 0;
     int keyboard_updates = 0;
+    int ui_thread_attaches = 0;
+    int ui_thread_detaches = 0;
     int platform_frame_updates = 0;
     int frame_reports = 0;
     int display_file_requests = 0;
@@ -177,6 +189,18 @@ void platform_services_dispatch_visibility_updates(pp::tests::Harness& harness)
     PP_EXPECT(harness, !fake.keyboard_visible);
 }
 
+void platform_services_dispatch_ui_thread_lifecycle(pp::tests::Harness& harness)
+{
+    FakePlatformServices fake("unused");
+    pp::platform::PlatformServices& services = fake;
+
+    services.attach_ui_thread();
+    services.detach_ui_thread();
+
+    PP_EXPECT(harness, fake.ui_thread_attaches == 1);
+    PP_EXPECT(harness, fake.ui_thread_detaches == 1);
+}
+
 void platform_services_dispatch_frame_hooks(pp::tests::Harness& harness)
 {
     FakePlatformServices fake("unused");
@@ -263,6 +287,7 @@ int main()
     harness.run("platform services dispatch clipboard reads and writes", platform_services_dispatch_clipboard_reads_and_writes);
     harness.run("platform services preserve empty clipboard writes", platform_services_preserve_empty_clipboard_writes);
     harness.run("platform services dispatch visibility updates", platform_services_dispatch_visibility_updates);
+    harness.run("platform services dispatch UI thread lifecycle", platform_services_dispatch_ui_thread_lifecycle);
     harness.run("platform services dispatch frame hooks", platform_services_dispatch_frame_hooks);
     harness.run("platform services dispatch file actions", platform_services_dispatch_file_actions);
     harness.run("platform services dispatch picker callbacks", platform_services_dispatch_picker_callbacks);