Fix some issues with the splash screen

- fix a use-after-free involving the alerts container that was
   happening when showing the first screen
 - fix some issues where the splash screen wouldn't come up as early as
   it needs to when another bootup task was making heavy use of the spi
   bus

src/drivers/display.cpp

@@ -213,6 +213,12 @@ auto Display::SetDutyCycle(uint_fast8_t new_duty, bool fade) -> void {
 }
 
 void Display::SendInitialisationSequence(const uint8_t* data) {
+  // Hold the SPI bus for the entire init sequence, as otherwise SD init may
+  // grab it and delay showing the boot splash. The total time until boot is
+  // finished may be increased by doing this, but a short boot with no feedback
+  // feels worse than a longer boot that doesn't tell you anything.
+  spi_device_acquire_bus(handle_, portMAX_DELAY);
+
   // First byte of the data is the number of commands.
   for (int i = *(data++); i > 0; i--) {
     uint8_t command = *(data++);
@@ -232,6 +238,8 @@ void Display::SendInitialisationSequence(const uint8_t* data) {
       vTaskDelay(pdMS_TO_TICKS(sleep_duration_ms));
     }
   }
+
+  spi_device_release_bus(handle_);
 }
 
 void Display::SendCommandWithData(uint8_t command,

src/tangara/system_fsm/running.cpp

@@ -75,7 +75,6 @@ void Running::react(const SdDetectChanged& ev) {
   }
 
   if (ev.has_sd_card && !sStorage) {
-    vTaskDelay(pdMS_TO_TICKS(500));
     mountStorage();
   }
 

src/tangara/ui/lvgl_task.cpp

@@ -43,8 +43,8 @@ auto UiTask::Main() -> void {
   lv_group_t* current_group = nullptr;
   auto* events = events::queues::Ui();
   while (true) {
-    while (events->Service(0)) {
-    }
+    while (events->Service(0))
+      ;
 
     std::shared_ptr<Screen> screen = UiState::current_screen();
     if (screen != current_screen_ && screen != nullptr) {

src/tangara/ui/screen_splash.hpp

@@ -20,7 +20,7 @@ class Splash : public Screen {
   Splash();
   ~Splash();
 
-  auto canPop() -> bool override { return false; }
+  auto canPop() -> bool override { return true; }
 
  private:
   lv_obj_t* container_;

src/tangara/ui/ui_fsm.cpp

@@ -294,7 +294,7 @@ void UiState::react(const internal::InitDisplay& ev) {
   drivers::displays::InitialisationData init_data = drivers::displays::kST7735R;
 
   // HACK: correct the display size for our prototypes.
-  // nvs.DisplaySize({161, 130});
+  // ev.nvs.DisplaySize({161, 130});
 
   auto actual_size = ev.nvs.DisplaySize();
   init_data.width = actual_size.first.value_or(init_data.width);
@@ -307,12 +307,14 @@ void UiState::react(const internal::InitDisplay& ev) {
   sDisplay->SetDisplayOn(!ev.gpios.IsLocked());
 }
 
-void UiState::PushScreen(std::shared_ptr<Screen> screen) {
+void UiState::PushScreen(std::shared_ptr<Screen> screen, bool replace) {
   lv_obj_set_parent(sAlertContainer, screen->alert());
 
   if (sCurrentScreen) {
     sCurrentScreen->onHidden();
-    sScreens.push(sCurrentScreen);
+    if (!replace) {
+      sScreens.push(sCurrentScreen);
+    }
   }
   sCurrentScreen = screen;
   sCurrentScreen->onShown();
@@ -568,7 +570,7 @@ void Lua::entry() {
     registry.AddPropertyModule(
         "backstack",
         {
-            {"push", [&](lua_State* s) { return PushLuaScreen(s); }},
+            {"push", [&](lua_State* s) { return PushLuaScreen(s, false); }},
             {"pop", [&](lua_State* s) { return PopLuaScreen(s); }},
             {"reset", [&](lua_State* s) { return ResetLuaScreen(s); }},
         });
@@ -603,7 +605,6 @@ void Lua::entry() {
     sBluetoothConnected.setDirect(bt.IsConnected());
     sBluetoothDevices.setDirect(bt.KnownDevices());
 
-    sCurrentScreen.reset();
     if (sServices->sd() == drivers::SdState::kMounted) {
       sLua->RunScript("/sdcard/config.lua");
     }
@@ -611,7 +612,7 @@ void Lua::entry() {
   }
 }
 
-auto Lua::PushLuaScreen(lua_State* s) -> int {
+auto Lua::PushLuaScreen(lua_State* s, bool replace) -> int {
   // Ensure the arg looks right before continuing.
   luaL_checktype(s, 1, LUA_TTABLE);
 
@@ -641,7 +642,7 @@ auto Lua::PushLuaScreen(lua_State* s) -> int {
 
   // Finally, push the now-initialised screen as if it were a regular C++
   // screen.
-  PushScreen(new_screen);
+  PushScreen(new_screen, replace);
 
   return 0;
 }
@@ -662,12 +663,11 @@ auto Lua::ResetLuaScreen(lua_State* s) -> int {
       ESP_LOGW(kTag, "ignoring reset as popping is blocked");
       return 0;
     }
-    sCurrentScreen->onHidden();
   }
   while (!sScreens.empty()) {
     sScreens.pop();
   }
-  return PushLuaScreen(s);
+  return PushLuaScreen(s, true);
 }
 
 auto Lua::QueueNext(lua_State*) -> int {

src/tangara/ui/ui_fsm.hpp

@@ -83,7 +83,7 @@ class UiState : public tinyfsm::Fsm<UiState> {
   void react(const internal::ReindexDatabase&){};
 
  protected:
-  void PushScreen(std::shared_ptr<Screen>);
+  void PushScreen(std::shared_ptr<Screen>, bool);
   int PopScreen();
 
   static std::unique_ptr<UiTask> sTask;
@@ -159,7 +159,7 @@ class Lua : public UiState {
   using UiState::react;
 
  private:
-  auto PushLuaScreen(lua_State*) -> int;
+  auto PushLuaScreen(lua_State*, bool) -> int;
   auto PopLuaScreen(lua_State*) -> int;
   auto ResetLuaScreen(lua_State*) -> int;