fix: eliminate e-ink ghosting on menu navigation

Problem: E-ink display showed significant ghosting when navigating between
menu screens. The HALF_REFRESH LUT was not applied consistently when
entering or re-entering menu activities.

Root Cause:
1. HALF_REFRESH only triggered on initial activity creation, not re-entry
2. Race conditions between main loop and display task
3. Empty directory early return bypassed HALF_REFRESH logic

Solution:
- FileSelectionActivity: Track lastRenderedPath to detect directory changes
  Use HALF_REFRESH when path differs. Mutex-protect updateRequired writes.
- Other menus: Reset isFirstRender in onEnter() for HALF_REFRESH on entry

UI improvements:
- FileSelectionActivity: Header shows Browse/path, improved empty state
- XtcReaderChapterSelectionActivity: Layout consistency, text truncation
- EpubReaderChapterSelectionActivity: Text truncation and button hints

src/activities/home/HomeActivity.cpp

@@ -18,6 +18,7 @@ int HomeActivity::getMenuItemCount() const { return hasContinueReading ? 4 : 3;
 
 void HomeActivity::onEnter() {
   Activity::onEnter();
+  isFirstRender = true;
 
   renderingMutex = xSemaphoreCreateMutex();
 
@@ -318,5 +319,10 @@ void HomeActivity::render() const {
 
   ScreenComponents::drawBattery(renderer, margin, pageHeight - 68);
 
-  renderer.displayBuffer();
+  if (isFirstRender) {
+    renderer.displayBuffer(EInkDisplay::HALF_REFRESH);
+    isFirstRender = false;
+  } else {
+    renderer.displayBuffer();
+  }
 }

src/activities/home/HomeActivity.h

@@ -12,6 +12,7 @@ class HomeActivity final : public Activity {
   SemaphoreHandle_t renderingMutex = nullptr;
   int selectorIndex = 0;
   bool updateRequired = false;
+  mutable bool isFirstRender = true;
   bool hasContinueReading = false;
   std::string lastBookTitle;
   std::string lastBookAuthor;

src/activities/reader/EpubReaderChapterSelectionActivity.cpp

@@ -34,6 +34,7 @@ void EpubReaderChapterSelectionActivity::taskTrampoline(void* param) {
 
 void EpubReaderChapterSelectionActivity::onEnter() {
   Activity::onEnter();
+  isFirstRender = true;
 
   if (!epub) {
     return;
@@ -139,9 +140,20 @@ void EpubReaderChapterSelectionActivity::renderScreen() {
        tocIndex++) {
     auto item = epub->getTocItem(tocIndex);
     const int indentPx = (item.level - 1) * 12;
+    const auto truncatedTitle = renderer.truncatedText(UI_10_FONT_ID, item.title.c_str(),
+                                                        pageWidth - horizontalMargin * 2 - 8 - indentPx);
     renderer.drawText(UI_10_FONT_ID, horizontalMargin + 4 + indentPx, listStartY + (tocIndex % pageItems) * rowHeight,
-                      item.title.c_str(), tocIndex != selectorIndex);
+                      truncatedTitle.c_str(), tocIndex != selectorIndex);
   }
 
-  renderer.displayBuffer();
+  // Draw button hints
+  const auto labels = mappedInput.mapLabels("« Back", "Go", "", "");
+  renderer.drawButtonHints(UI_10_FONT_ID, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
+
+  if (isFirstRender) {
+    renderer.displayBuffer(EInkDisplay::HALF_REFRESH);
+    isFirstRender = false;
+  } else {
+    renderer.displayBuffer();
+  }
 }

src/activities/reader/EpubReaderChapterSelectionActivity.h

@@ -15,6 +15,7 @@ class EpubReaderChapterSelectionActivity final : public Activity {
   int currentSpineIndex = 0;
   int selectorIndex = 0;
   bool updateRequired = false;
+  mutable bool isFirstRender = true;
   const std::function<void()> onGoBack;
   const std::function<void(int newSpineIndex)> onSelectSpineIndex;
 

src/activities/reader/FileSelectionActivity.cpp

@@ -11,8 +11,8 @@ constexpr int PAGE_ITEMS = 20;
 constexpr int SKIP_PAGE_MS = 700;
 constexpr unsigned long GO_HOME_MS = 1000;
 constexpr int headerY = 16;
-constexpr int separatorY = 42;
-constexpr int listStartY = 54;
+constexpr int separatorY = 48;
+constexpr int listStartY = 60;
 constexpr int rowHeight = 28;
 constexpr int horizontalMargin = 16;
 }  // namespace
@@ -70,6 +70,7 @@ void FileSelectionActivity::loadFiles() {
 
 void FileSelectionActivity::onEnter() {
   Activity::onEnter();
+  lastRenderedPath.clear();  // Force HALF_REFRESH on first render
 
   renderingMutex = xSemaphoreCreateMutex();
 
@@ -107,8 +108,10 @@ void FileSelectionActivity::loop() {
   if (mappedInput.isPressed(MappedInputManager::Button::Back) && mappedInput.getHeldTime() >= GO_HOME_MS) {
     if (basepath != "/") {
       basepath = "/";
+      xSemaphoreTake(renderingMutex, portMAX_DELAY);
       loadFiles();
       updateRequired = true;
+      xSemaphoreGive(renderingMutex);
     }
     return;
   }
@@ -128,8 +131,10 @@ void FileSelectionActivity::loop() {
     if (basepath.back() != '/') basepath += "/";
     if (files[selectorIndex].back() == '/') {
       basepath += files[selectorIndex].substr(0, files[selectorIndex].length() - 1);
+      xSemaphoreTake(renderingMutex, portMAX_DELAY);
       loadFiles();
       updateRequired = true;
+      xSemaphoreGive(renderingMutex);
     } else {
       onSelect(basepath + files[selectorIndex]);
     }
@@ -139,8 +144,10 @@ void FileSelectionActivity::loop() {
       if (basepath != "/") {
         basepath.replace(basepath.find_last_of('/'), std::string::npos, "");
         if (basepath.empty()) basepath = "/";
+        xSemaphoreTake(renderingMutex, portMAX_DELAY);
         loadFiles();
         updateRequired = true;
+        xSemaphoreGive(renderingMutex);
       } else {
         onGoHome();
       }
@@ -151,25 +158,29 @@ void FileSelectionActivity::loop() {
     } else {
       selectorIndex = (selectorIndex + files.size() - 1) % files.size();
     }
+    xSemaphoreTake(renderingMutex, portMAX_DELAY);
     updateRequired = true;
+    xSemaphoreGive(renderingMutex);
   } else if (nextReleased) {
     if (skipPage) {
       selectorIndex = ((selectorIndex / PAGE_ITEMS + 1) * PAGE_ITEMS) % files.size();
     } else {
       selectorIndex = (selectorIndex + 1) % files.size();
     }
+    xSemaphoreTake(renderingMutex, portMAX_DELAY);
     updateRequired = true;
+    xSemaphoreGive(renderingMutex);
   }
 }
 
 void FileSelectionActivity::displayTaskLoop() {
   while (true) {
+    xSemaphoreTake(renderingMutex, portMAX_DELAY);
     if (updateRequired) {
       updateRequired = false;
-      xSemaphoreTake(renderingMutex, portMAX_DELAY);
       render();
-      xSemaphoreGive(renderingMutex);
     }
+    xSemaphoreGive(renderingMutex);
     vTaskDelay(10 / portTICK_PERIOD_MS);
   }
 }
@@ -179,8 +190,11 @@ void FileSelectionActivity::render() const {
 
   const auto pageWidth = renderer.getScreenWidth();
 
-  // Draw header
-  renderer.drawCenteredText(UI_12_FONT_ID, headerY, "Books", true, EpdFontFamily::BOLD);
+  // Draw header with path
+  const std::string pathDisplay = basepath == "/" ? "Browse" : basepath;
+  const auto truncatedPath = renderer.truncatedText(UI_12_FONT_ID, pathDisplay.c_str(),
+                                                     pageWidth - horizontalMargin * 2, EpdFontFamily::BOLD);
+  renderer.drawCenteredText(UI_12_FONT_ID, headerY, truncatedPath.c_str(), true, EpdFontFamily::BOLD);
 
   // Subtle separator line under header
   renderer.drawLine(horizontalMargin, separatorY, pageWidth - horizontalMargin, separatorY);
@@ -190,8 +204,16 @@ void FileSelectionActivity::render() const {
   renderer.drawButtonHints(UI_10_FONT_ID, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
 
   if (files.empty()) {
-    renderer.drawText(UI_10_FONT_ID, horizontalMargin + 4, listStartY, "No books found");
-    renderer.displayBuffer();
+    const int emptyY = listStartY + 40;
+    renderer.drawCenteredText(UI_10_FONT_ID, emptyY, "No files found");
+    renderer.drawCenteredText(SMALL_FONT_ID, emptyY + 24, "Supported: .epub, .xtc, .xtch");
+    // Use HALF_REFRESH when directory changed
+    if (basepath != lastRenderedPath) {
+      lastRenderedPath = basepath;
+      renderer.displayBuffer(EInkDisplay::HALF_REFRESH);
+    } else {
+      renderer.displayBuffer();
+    }
     return;
   }
 
@@ -203,5 +225,11 @@ void FileSelectionActivity::render() const {
                       i != selectorIndex);
   }
 
-  renderer.displayBuffer();
+  // Use HALF_REFRESH when directory changed (basepath differs from last render)
+  if (basepath != lastRenderedPath) {
+    lastRenderedPath = basepath;
+    renderer.displayBuffer(EInkDisplay::HALF_REFRESH);
+  } else {
+    renderer.displayBuffer();
+  }
 }

src/activities/reader/FileSelectionActivity.h

@@ -16,6 +16,7 @@ class FileSelectionActivity final : public Activity {
   std::vector<std::string> files;
   int selectorIndex = 0;
   bool updateRequired = false;
+  mutable std::string lastRenderedPath;
   const std::function<void(const std::string&)> onSelect;
   const std::function<void()> onGoHome;
 

src/activities/reader/XtcReaderChapterSelectionActivity.cpp

@@ -43,6 +43,7 @@ void XtcReaderChapterSelectionActivity::taskTrampoline(void* param) {
 
 void XtcReaderChapterSelectionActivity::onEnter() {
   Activity::onEnter();
+  isFirstRender = true;
 
   if (!xtc) {
     return;
@@ -130,22 +131,49 @@ void XtcReaderChapterSelectionActivity::renderScreen() {
 
   const auto pageWidth = renderer.getScreenWidth();
   const int pageItems = getPageItems();
-  renderer.drawCenteredText(UI_12_FONT_ID, 15, "Select Chapter", true, EpdFontFamily::BOLD);
+
+  // Layout constants matching other screens
+  constexpr int headerY = 16;
+  constexpr int separatorY = 42;
+  constexpr int listStartY = 54;
+  constexpr int rowHeight = 28;
+  constexpr int horizontalMargin = 16;
+
+  // Draw header
+  renderer.drawCenteredText(UI_12_FONT_ID, headerY, "Chapters", true, EpdFontFamily::BOLD);
+
+  // Subtle separator line under header
+  renderer.drawLine(horizontalMargin, separatorY, pageWidth - horizontalMargin, separatorY);
 
   const auto& chapters = xtc->getChapters();
   if (chapters.empty()) {
-    renderer.drawCenteredText(UI_10_FONT_ID, 120, "No chapters");
+    const int emptyY = listStartY + 40;
+    renderer.drawCenteredText(UI_10_FONT_ID, emptyY, "No chapters found");
     renderer.displayBuffer();
     return;
   }
 
+  // Draw selection highlight
   const auto pageStartIndex = selectorIndex / pageItems * pageItems;
-  renderer.fillRect(0, 60 + (selectorIndex % pageItems) * 30 - 2, pageWidth - 1, 30);
+  renderer.fillRect(0, listStartY + (selectorIndex % pageItems) * rowHeight - 2, pageWidth - 1, rowHeight);
+
+  // Draw chapter list
   for (int i = pageStartIndex; i < static_cast<int>(chapters.size()) && i < pageStartIndex + pageItems; i++) {
     const auto& chapter = chapters[i];
     const char* title = chapter.name.empty() ? "Unnamed" : chapter.name.c_str();
-    renderer.drawText(UI_10_FONT_ID, 20, 60 + (i % pageItems) * 30, title, i != selectorIndex);
+    const auto truncatedTitle = renderer.truncatedText(UI_10_FONT_ID, title, pageWidth - horizontalMargin * 2 - 8);
+    renderer.drawText(UI_10_FONT_ID, horizontalMargin + 4, listStartY + (i % pageItems) * rowHeight,
+                      truncatedTitle.c_str(), i != selectorIndex);
   }
 
-  renderer.displayBuffer();
+  // Draw button hints
+  const auto labels = mappedInput.mapLabels("« Back", "Go", "", "");
+  renderer.drawButtonHints(UI_10_FONT_ID, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
+
+  if (isFirstRender) {
+    renderer.displayBuffer(EInkDisplay::HALF_REFRESH);
+    isFirstRender = false;
+  } else {
+    renderer.displayBuffer();
+  }
 }

src/activities/reader/XtcReaderChapterSelectionActivity.h

@@ -15,6 +15,7 @@ class XtcReaderChapterSelectionActivity final : public Activity {
   uint32_t currentPage = 0;
   int selectorIndex = 0;
   bool updateRequired = false;
+  mutable bool isFirstRender = true;
   const std::function<void()> onGoBack;
   const std::function<void(uint32_t newPage)> onSelectPage;
 

src/activities/settings/SettingsActivity.cpp

@@ -53,6 +53,7 @@ void SettingsActivity::taskTrampoline(void* param) {
 
 void SettingsActivity::onEnter() {
   Activity::onEnter();
+  isFirstRender = true;
 
   renderingMutex = xSemaphoreCreateMutex();
 
@@ -215,6 +216,11 @@ void SettingsActivity::render() const {
   const auto labels = mappedInput.mapLabels("« Save", "Toggle", "", "");
   renderer.drawButtonHints(UI_10_FONT_ID, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
 
-  // Always use standard refresh for settings screen
-  renderer.displayBuffer();
+  // Use HALF_REFRESH on first render to clear ghosting, then FAST_REFRESH
+  if (isFirstRender) {
+    renderer.displayBuffer(EInkDisplay::HALF_REFRESH);
+    isFirstRender = false;
+  } else {
+    renderer.displayBuffer();
+  }
 }

src/activities/settings/SettingsActivity.h

@@ -25,6 +25,7 @@ class SettingsActivity final : public ActivityWithSubactivity {
   TaskHandle_t displayTaskHandle = nullptr;
   SemaphoreHandle_t renderingMutex = nullptr;
   bool updateRequired = false;
+  mutable bool isFirstRender = true;
   int selectedSettingIndex = 0;  // Currently selected setting
   const std::function<void()> onGoHome;