diff --git a/lib/I18n/translations/english.yaml b/lib/I18n/translations/english.yaml
index a23195ad..8c5f0d88 100644
--- a/lib/I18n/translations/english.yaml
+++ b/lib/I18n/translations/english.yaml
@@ -248,6 +248,7 @@ STR_NO_UPDATE: "No update available"
 STR_UPDATE_FAILED: "Update failed"
 STR_UPDATE_COMPLETE: "Update complete"
 STR_POWER_ON_HINT: "Press and hold power button to turn back on"
+STR_RESTARTING_HINT: "Restarting... If device does not restart, hold the power button for a few seconds."
 STR_NO_ENTRIES: "No entries found"
 STR_DOWNLOADING: "Downloading..."
 STR_DOWNLOAD_FAILED: "Download failed"
@@ -625,4 +626,17 @@ STR_BIONIC_READING: "Bionic Reading"
 STR_BTN_ACT_TOGGLE_BIONIC_READING: "Toggle Bionic Reading"
 STR_BTN_ACT_CYCLE_FONT_SIZE: "Change Font Size"
 STR_BTN_ACT_CYCLE_ORIENTATION: "Change Orientation"
-STR_RESTART_DEVICE: "Restart Device"
\ No newline at end of file
+STR_RESTART_DEVICE: "Restart Device"
+STR_SD_FIRMWARE_UPDATE: "SD Card Firmware Update"
+STR_SELECT_FIRMWARE_FILE: "Select firmware file (.bin)"
+STR_NO_BIN_FILES: "No .bin files found"
+STR_VALIDATING_FIRMWARE: "Validating firmware..."
+STR_INVALID_FIRMWARE: "Invalid firmware file"
+STR_FIRMWARE_TOO_LARGE: "Firmware too large for partition"
+STR_FIRMWARE_TOO_SMALL: "Firmware file is too small"
+STR_FIRMWARE_UPDATE_PROMPT: "Update firmware?"
+STR_FIRMWARE_FILE_OPEN_FAILED: "Cannot open file"
+STR_FIRMWARE_WRITE_FAILED: "Firmware write failed"
+STR_FIRMWARE_UPDATE_DO_NOT_POWER_OFF: "Do not power off!"
+STR_RECOVERY_MODE: "Recovery Mode"
+STR_RECOVERY_MODE_HINT: "Place firmware.bin on SD card root and select it"
\ No newline at end of file
diff --git a/src/activities/ActivityResult.h b/src/activities/ActivityResult.h
index dfb3d769..df00c7eb 100644
--- a/src/activities/ActivityResult.h
+++ b/src/activities/ActivityResult.h
@@ -62,13 +62,18 @@ struct FootnoteResult {
   std::string href;
 };
 
+struct FilePathResult {
+  std::string path;
+};
+
 struct StarredPageResult {
   int spineIndex = 0;
   int pageNumber = 0;
 };
 
-using ResultVariant = std::variant<std::monostate, WifiResult, KeyboardResult, MenuResult, ChapterResult, PercentResult,
-                                   PageResult, SyncResult, NetworkModeResult, FootnoteResult, StarredPageResult>;
+using ResultVariant =
+    std::variant<std::monostate, WifiResult, KeyboardResult, MenuResult, ChapterResult, PercentResult, PageResult,
+                 SyncResult, NetworkModeResult, FootnoteResult, FilePathResult, StarredPageResult>;
 
 struct ActivityResult {
   bool isCancelled = false;
diff --git a/src/activities/home/FileBrowserActivity.cpp b/src/activities/home/FileBrowserActivity.cpp
index 8532d76c..0cb28fd2 100644
--- a/src/activities/home/FileBrowserActivity.cpp
+++ b/src/activities/home/FileBrowserActivity.cpp
@@ -93,10 +93,14 @@ void FileBrowserActivity::loadFiles() {
       files.emplace_back(std::string(name) + "/");
     } else {
       std::string_view filename{name};
-      if (FsHelpers::hasEpubExtension(filename) || FsHelpers::hasXtcExtension(filename) ||
-          FsHelpers::hasTxtExtension(filename) || FsHelpers::hasMarkdownExtension(filename) ||
-          FsHelpers::hasBmpExtension(filename) || FsHelpers::hasJpgExtension(filename) ||
-          FsHelpers::hasPngExtension(filename)) {
+      if (mode == Mode::PickFirmware) {
+        if (FsHelpers::checkFileExtension(filename, ".bin")) {
+          files.emplace_back(filename);
+        }
+      } else if (FsHelpers::hasEpubExtension(filename) || FsHelpers::hasXtcExtension(filename) ||
+                 FsHelpers::hasTxtExtension(filename) || FsHelpers::hasMarkdownExtension(filename) ||
+                 FsHelpers::hasBmpExtension(filename) || FsHelpers::hasJpgExtension(filename) ||
+                 FsHelpers::hasPngExtension(filename)) {
         files.emplace_back(filename);
       }
     }
@@ -143,10 +147,13 @@ void FileBrowserActivity::loop() {
   while (buttonEvents.consumeEvent(ev)) {
     if (ev.button == MappedInputManager::Button::Back) {
       if (ev.type == ButtonEventManager::PressType::Long) {
-        onGoHome();
-        return;
+        if (mode == Mode::Books) {
+          onGoHome();
+          return;
+        }
+        // PickFirmware: long Back = same as short Back (cancel / up dir)
       }
-      if (ev.type == ButtonEventManager::PressType::Short) {
+      if (ev.type == ButtonEventManager::PressType::Short || ev.type == ButtonEventManager::PressType::Long) {
         if (basepath != "/") {
           const std::string oldPath = basepath;
           basepath.replace(basepath.find_last_of('/'), std::string::npos, "");
@@ -157,6 +164,12 @@ void FileBrowserActivity::loop() {
           const size_t idx = findEntry(dirName);
           selectorIndex = (idx < files.size()) ? idx : 0;
           requestUpdate();
+        } else if (mode == Mode::PickFirmware) {
+          // At root in PickFirmware: cancel back to caller.
+          ActivityResult res;
+          res.isCancelled = true;
+          setResult(std::move(res));
+          finish();
         } else {
           onGoHome();
         }
@@ -180,6 +193,15 @@ void FileBrowserActivity::loop() {
         loadFiles();
         selectorIndex = 0;
         requestUpdate();
+      } else if (mode == Mode::PickFirmware) {
+        // Firmware picker: return the selected path to the caller.
+        std::string cleanBasePath = basepath;
+        if (cleanBasePath.back() != '/') cleanBasePath += "/";
+        ActivityResult res{FilePathResult{cleanBasePath + entry}};
+        res.isCancelled = false;
+        setResult(std::move(res));
+        finish();
+        return;
       } else {
         std::string fullPath = basepath;
         if (fullPath.back() != '/') fullPath += "/";
@@ -300,15 +322,18 @@ void FileBrowserActivity::render(RenderLock&&) {
   const auto& metrics = UITheme::getInstance().getMetrics();
   const Rect contentRect = UITheme::getContentRect(renderer, true, true);
 
-  std::string folderName = (basepath == "/") ? tr(STR_SD_CARD) : basepath.substr(basepath.rfind('/') + 1);
+  std::string folderName =
+      (mode == Mode::PickFirmware)
+          ? std::string(tr(STR_SELECT_FIRMWARE_FILE))
+          : ((basepath == "/") ? std::string(tr(STR_SD_CARD)) : basepath.substr(basepath.rfind('/') + 1));
   GUI.drawHeader(renderer, Rect{contentRect.x, metrics.topPadding, contentRect.width, metrics.headerHeight},
                  folderName.c_str());
 
   const int contentTop = metrics.topPadding + metrics.headerHeight + metrics.verticalSpacing;
   const int contentHeight = contentRect.height - contentTop - metrics.verticalSpacing;
   if (files.empty()) {
-    renderer.drawText(UI_10_FONT_ID, contentRect.x + metrics.contentSidePadding, contentTop + 20,
-                      tr(STR_NO_FILES_FOUND));
+    const char* emptyMsg = (mode == Mode::PickFirmware) ? tr(STR_NO_BIN_FILES) : tr(STR_NO_FILES_FOUND);
+    renderer.drawText(UI_10_FONT_ID, contentRect.x + metrics.contentSidePadding, contentTop + 20, emptyMsg);
   } else {
     GUI.drawList(
         renderer, Rect{contentRect.x, contentTop, contentRect.width, contentHeight}, files.size(), selectorIndex,
@@ -319,12 +344,14 @@ void FileBrowserActivity::render(RenderLock&&) {
   // Side buttons (Up/Down) navigate; show their hints on the side
   GUI.drawSideButtonHints(renderer, tr(STR_DIR_UP), tr(STR_DIR_DOWN));
 
-  // Front buttons: Back=Back(subdir)/Home(root), Confirm=Open, Left=hidden long-press delete, Right=Info
+  // Front buttons
+  const char* backLabel = (basepath == "/") ? (mode == Mode::PickFirmware ? tr(STR_BACK) : tr(STR_HOME)) : tr(STR_BACK);
+  const bool selectingFirmwareFile = mode == Mode::PickFirmware && !files.empty() && files[selectorIndex].back() != '/';
+  const char* confirmLabel = files.empty() ? "" : (selectingFirmwareFile ? tr(STR_SELECT) : tr(STR_OPEN));
   const bool hasInfo =
-      !files.empty() && files[selectorIndex].back() != '/' &&
+      mode == Mode::Books && !files.empty() && files[selectorIndex].back() != '/' &&
       (FsHelpers::hasEpubExtension(files[selectorIndex]) || FsHelpers::hasXtcExtension(files[selectorIndex]));
-  const auto labels = mappedInput.mapLabels(basepath == "/" ? tr(STR_HOME) : tr(STR_BACK),
-                                            files.empty() ? "" : tr(STR_OPEN), "", hasInfo ? tr(STR_INFO) : "");
+  const auto labels = mappedInput.mapLabels(backLabel, confirmLabel, "", hasInfo ? tr(STR_INFO) : "");
   GUI.drawButtonHints(renderer, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
 
   renderer.displayBuffer();
diff --git a/src/activities/home/FileBrowserActivity.h b/src/activities/home/FileBrowserActivity.h
index 991e1c55..53b04599 100644
--- a/src/activities/home/FileBrowserActivity.h
+++ b/src/activities/home/FileBrowserActivity.h
@@ -9,6 +9,10 @@
 #include "util/ButtonNavigator.h"
 
 class FileBrowserActivity final : public Activity {
+ public:
+  // Books = standard reader browser; PickFirmware = filter to .bin only and return path via ActivityResult.
+  enum class Mode { Books, PickFirmware };
+
  private:
   // Deletion
   void clearFileMetadata(const std::string& fullPath);
@@ -17,6 +21,8 @@ class FileBrowserActivity final : public Activity {
 
   size_t selectorIndex = 0;
 
+  Mode mode = Mode::Books;
+
   // Files state
   std::string basepath = "/";
   std::string focusName;  // entry to select on first load (e.g. the file just returned from)
@@ -28,8 +34,9 @@ class FileBrowserActivity final : public Activity {
 
  public:
   explicit FileBrowserActivity(GfxRenderer& renderer, MappedInputManager& mappedInput, std::string initialPath = "/",
-                               std::string focusName = {})
+                               std::string focusName = {}, Mode mode = Mode::Books)
       : Activity("FileBrowser", renderer, mappedInput),
+        mode(mode),
         basepath(initialPath.empty() ? "/" : std::move(initialPath)),
         focusName(std::move(focusName)) {}
   void onEnter() override;
diff --git a/src/activities/network/WifiSelectionActivity.cpp b/src/activities/network/WifiSelectionActivity.cpp
index 0046b862..d373506b 100644
--- a/src/activities/network/WifiSelectionActivity.cpp
+++ b/src/activities/network/WifiSelectionActivity.cpp
@@ -862,7 +862,14 @@ void WifiSelectionActivity::renderForgetPrompt() const {
   }
   renderer.drawCenteredText(UI_10_FONT_ID, top, ssidInfo.c_str());
 
-  renderer.drawCenteredText(UI_10_FONT_ID, top + 40, tr(STR_FORGET_AND_REMOVE));
+  const auto& metrics = UITheme::getInstance().getMetrics();
+  const int hintWidth = pageWidth - 2 * metrics.contentSidePadding;
+  const auto forgetLines = renderer.wrappedText(UI_10_FONT_ID, tr(STR_FORGET_AND_REMOVE), hintWidth, 3);
+  int forgetY = top + 40;
+  for (const auto& line : forgetLines) {
+    renderer.drawCenteredText(UI_10_FONT_ID, forgetY, line.c_str());
+    forgetY += height;
+  }
 
   // Draw Cancel/Forget network buttons
   const int buttonY = top + 80;
@@ -904,34 +911,15 @@ void WifiSelectionActivity::renderCaptivePortal() const {
   const int sp = metrics.verticalSpacing;
   constexpr int QR_SIZE = 320;
 
-  // Pre-compute URL line count so we can vertically centre everything
-  const char* url = captivePortalUrl.c_str();
-  int urlLineCount = 0;
-  {
-    int rem = static_cast<int>(captivePortalUrl.size());
-    int off = 0;
-    while (rem > 0) {
-      int lo = 1, hi = rem;
-      while (lo < hi) {
-        const int mid = (lo + hi + 1) / 2;
-        char tmp[512];
-        snprintf(tmp, sizeof(tmp), "%.*s", mid, url + off);
-        if (renderer.getTextWidth(SMALL_FONT_ID, tmp) <= maxWidth)
-          lo = mid;
-        else
-          hi = mid - 1;
-      }
-      urlLineCount++;
-      off += lo;
-      rem -= lo;
-    }
-  }
+  // Pre-compute wrapped hint and URL lines so we can vertically centre everything
+  const std::string hintText = std::string(tr(STR_CAPTIVE_PORTAL_HINT_1)) + " " + tr(STR_CAPTIVE_PORTAL_HINT_2);
+  const auto hintLines = renderer.wrappedText(UI_10_FONT_ID, hintText.c_str(), maxWidth, 4);
+  const auto urlLines = renderer.wrappedText(SMALL_FONT_ID, captivePortalUrl.c_str(), maxWidth, 10);
 
-  const int totalHeight = lh12 + sp       // title
-                          + lh10          // hint line 1
-                          + lh10 + sp     // hint line 2
-                          + QR_SIZE + sp  // QR code
-                          + urlLineCount * lhSmall;
+  const int totalHeight = lh12 + sp                                         // title
+                          + static_cast<int>(hintLines.size()) * lh10 + sp  // hint
+                          + QR_SIZE + sp                                    // QR code
+                          + static_cast<int>(urlLines.size()) * lhSmall;
 
   // contentRect covers the full screen minus button hints; subtract the header
   // and sub-header that render() always draws above us.
@@ -941,35 +929,19 @@ void WifiSelectionActivity::renderCaptivePortal() const {
 
   renderer.drawCenteredText(UI_12_FONT_ID, y, tr(STR_CAPTIVE_PORTAL_DETECTED), true, EpdFontFamily::BOLD);
   y += lh12 + sp;
-  renderer.drawCenteredText(UI_10_FONT_ID, y, tr(STR_CAPTIVE_PORTAL_HINT_1));
-  y += lh10;
-  renderer.drawCenteredText(UI_10_FONT_ID, y, tr(STR_CAPTIVE_PORTAL_HINT_2));
-  y += lh10 + sp;
+  for (const auto& line : hintLines) {
+    renderer.drawCenteredText(UI_10_FONT_ID, y, line.c_str());
+    y += lh10;
+  }
+  y += sp;
 
   const int qrX = contentRect.x + (contentRect.width - QR_SIZE) / 2;
   QrUtils::drawQrCode(renderer, Rect{qrX, y, QR_SIZE, QR_SIZE}, captivePortalUrl);
   y += QR_SIZE + sp;
 
-  // Split URL into as many lines as needed
-  int remaining = static_cast<int>(captivePortalUrl.size());
-  int offset = 0;
-  while (remaining > 0) {
-    int lo = 1, hi = remaining;
-    while (lo < hi) {
-      const int mid = (lo + hi + 1) / 2;
-      char tmp[512];
-      snprintf(tmp, sizeof(tmp), "%.*s", mid, url + offset);
-      if (renderer.getTextWidth(SMALL_FONT_ID, tmp) <= maxWidth)
-        lo = mid;
-      else
-        hi = mid - 1;
-    }
-    char line[512];
-    snprintf(line, sizeof(line), "%.*s", lo, url + offset);
-    renderer.drawCenteredText(SMALL_FONT_ID, y, line);
+  for (const auto& line : urlLines) {
+    renderer.drawCenteredText(SMALL_FONT_ID, y, line.c_str());
     y += lhSmall;
-    offset += lo;
-    remaining -= lo;
   }
 
   const auto labels = mappedInput.mapLabels(tr(STR_BACK), tr(STR_CAPTIVE_PORTAL_DONE), "", "");
diff --git a/src/activities/settings/ClearCacheActivity.cpp b/src/activities/settings/ClearCacheActivity.cpp
index 34216aba..698e0a46 100644
--- a/src/activities/settings/ClearCacheActivity.cpp
+++ b/src/activities/settings/ClearCacheActivity.cpp
@@ -28,11 +28,23 @@ void ClearCacheActivity::render(RenderLock&&) {
                  tr(STR_CLEAR_READING_CACHE));
 
   const int midY = contentRect.y + contentRect.height / 2;
+  const int lineHeight = renderer.getLineHeight(UI_10_FONT_ID);
+  const int warnWidth = contentRect.width - 2 * metrics.contentSidePadding;
   if (state == WARNING) {
-    renderer.drawCenteredText(UI_10_FONT_ID, midY - 60, tr(STR_CLEAR_CACHE_WARNING_1), true);
+    const auto warn1Lines = renderer.wrappedText(UI_10_FONT_ID, tr(STR_CLEAR_CACHE_WARNING_1), warnWidth, 3);
+    int y = midY - 60;
+    for (const auto& line : warn1Lines) {
+      renderer.drawCenteredText(UI_10_FONT_ID, y, line.c_str());
+      y += lineHeight;
+    }
     renderer.drawCenteredText(UI_10_FONT_ID, midY - 30, tr(STR_CLEAR_CACHE_WARNING_2), true, EpdFontFamily::BOLD);
-    renderer.drawCenteredText(UI_10_FONT_ID, midY + 10, tr(STR_CLEAR_CACHE_WARNING_3), true);
-    renderer.drawCenteredText(UI_10_FONT_ID, midY + 30, tr(STR_CLEAR_CACHE_WARNING_4), true);
+    const std::string warn34 = std::string(tr(STR_CLEAR_CACHE_WARNING_3)) + " " + tr(STR_CLEAR_CACHE_WARNING_4);
+    const auto warn34Lines = renderer.wrappedText(UI_10_FONT_ID, warn34.c_str(), warnWidth, 3);
+    y = midY + 10;
+    for (const auto& line : warn34Lines) {
+      renderer.drawCenteredText(UI_10_FONT_ID, y, line.c_str());
+      y += lineHeight;
+    }
 
     const auto labels = mappedInput.mapLabels(tr(STR_CANCEL), tr(STR_CLEAR_BUTTON), "", "");
     GUI.drawButtonHints(renderer, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
diff --git a/src/activities/settings/OtaUpdateActivity.cpp b/src/activities/settings/OtaUpdateActivity.cpp
index 4a8ff8db..d2943679 100644
--- a/src/activities/settings/OtaUpdateActivity.cpp
+++ b/src/activities/settings/OtaUpdateActivity.cpp
@@ -160,7 +160,13 @@ void OtaUpdateActivity::render(RenderLock&&) {
     GUI.drawButtonHints(renderer, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
   } else if (state == FINISHED) {
     renderer.drawCenteredText(UI_10_FONT_ID, top, tr(STR_UPDATE_COMPLETE), true, EpdFontFamily::BOLD);
-    renderer.drawCenteredText(UI_10_FONT_ID, top + height + metrics.verticalSpacing, tr(STR_POWER_ON_HINT));
+    const int hintWidth = contentRect.width - 2 * metrics.contentSidePadding;
+    const auto hintLines = renderer.wrappedText(UI_10_FONT_ID, tr(STR_POWER_ON_HINT), hintWidth, 4);
+    int hintY = top + height + metrics.verticalSpacing;
+    for (const auto& line : hintLines) {
+      renderer.drawCenteredText(UI_10_FONT_ID, hintY, line.c_str());
+      hintY += height;
+    }
   }
 
   renderer.displayBuffer();
diff --git a/src/activities/settings/SdFirmwareUpdateActivity.cpp b/src/activities/settings/SdFirmwareUpdateActivity.cpp
new file mode 100644
index 00000000..1ffb72af
--- /dev/null
+++ b/src/activities/settings/SdFirmwareUpdateActivity.cpp
@@ -0,0 +1,244 @@
+#include "SdFirmwareUpdateActivity.h"
+
+#include <Arduino.h>
+#include <GfxRenderer.h>
+#include <HalStorage.h>
+#include <I18n.h>
+#include <Logging.h>
+#include <esp_ota_ops.h>
+
+#include "MappedInputManager.h"
+#include "activities/home/FileBrowserActivity.h"
+#include "activities/util/ConfirmationActivity.h"
+#include "components/UITheme.h"
+#include "fontIds.h"
+#include "network/FirmwareFlasher.h"
+
+void SdFirmwareUpdateActivity::onEnter() {
+  Activity::onEnter();
+  LOG_INF("FW", "SdFirmwareUpdateActivity build=%s %s recovery=%d", __DATE__, __TIME__, recoveryMode ? 1 : 0);
+  state = State::PICKING;
+  launchPicker();
+}
+
+void SdFirmwareUpdateActivity::launchPicker() {
+  startActivityForResult(std::make_unique<FileBrowserActivity>(renderer, mappedInput, "/", std::string{},
+                                                               FileBrowserActivity::Mode::PickFirmware),
+                         [this](const ActivityResult& result) { onPickerResult(result); });
+}
+
+void SdFirmwareUpdateActivity::onPickerResult(const ActivityResult& result) {
+  if (result.isCancelled) {
+    if (recoveryMode) {
+      launchPicker();
+      return;
+    }
+    finish();
+    return;
+  }
+
+  const auto* path = std::get_if<FilePathResult>(&result.data);
+  if (!path) {
+    LOG_ERR("FW", "Picker returned no path");
+    finish();
+    return;
+  }
+  firmwarePath = path->path;
+  LOG_DBG("FW", "Selected: %s", firmwarePath.c_str());
+
+  {
+    RenderLock lock(*this);
+    state = State::VALIDATING;
+  }
+  requestUpdateAndWait();
+
+  if (!validateFirmware()) {
+    RenderLock lock(*this);
+    state = State::FAILED;
+    requestUpdate();
+    return;
+  }
+
+  promptConfirmation();
+}
+
+bool SdFirmwareUpdateActivity::validateFirmware() {
+  HalFile file;
+  if (!Storage.openFileForRead("FW", firmwarePath.c_str(), file) || !file) {
+    errorMessage = tr(STR_FIRMWARE_FILE_OPEN_FAILED);
+    return false;
+  }
+  firmwareSize = file.fileSize();
+  file.close();
+
+  const esp_partition_t* dest = esp_ota_get_next_update_partition(nullptr);
+  if (!dest) {
+    LOG_ERR("FW", "no next-update partition available");
+    errorMessage = tr(STR_INVALID_FIRMWARE);
+    return false;
+  }
+  const size_t partitionLimit = dest->size;
+  if (firmwareSize > partitionLimit) {
+    LOG_ERR("FW", "firmware (%u bytes) exceeds partition (%u bytes)", static_cast<unsigned>(firmwareSize),
+            static_cast<unsigned>(partitionLimit));
+    errorMessage = tr(STR_FIRMWARE_TOO_LARGE);
+    return false;
+  }
+
+  const auto vr = firmware_flash::validateImageFile(firmwarePath.c_str(), partitionLimit);
+  if (vr != firmware_flash::Result::OK) {
+    LOG_ERR("FW", "image validation failed: %s", firmware_flash::resultName(vr));
+    if (vr == firmware_flash::Result::TOO_LARGE) {
+      errorMessage = tr(STR_FIRMWARE_TOO_LARGE);
+    } else if (vr == firmware_flash::Result::TOO_SMALL) {
+      errorMessage = tr(STR_FIRMWARE_TOO_SMALL);
+    } else {
+      errorMessage = tr(STR_INVALID_FIRMWARE);
+    }
+    return false;
+  }
+  return true;
+}
+
+void SdFirmwareUpdateActivity::promptConfirmation() {
+  {
+    RenderLock lock(*this);
+    state = State::CONFIRMING;
+  }
+  std::string heading = tr(STR_FIRMWARE_UPDATE_PROMPT);
+  std::string body = firmwarePath;
+  const auto pos = body.find_last_of('/');
+  if (pos != std::string::npos) body = body.substr(pos + 1);
+
+  startActivityForResult(std::make_unique<ConfirmationActivity>(renderer, mappedInput, heading, body),
+                         [this](const ActivityResult& result) { onConfirmationResult(result); });
+}
+
+void SdFirmwareUpdateActivity::onConfirmationResult(const ActivityResult& result) {
+  if (result.isCancelled) {
+    if (recoveryMode) {
+      launchPicker();
+      return;
+    }
+    finish();
+    return;
+  }
+
+  {
+    RenderLock lock(*this);
+    state = State::UPDATING;
+    writtenBytes = 0;
+    lastRenderedPercent = 101;
+  }
+  requestUpdateAndWait();
+  performUpdate();
+}
+
+void SdFirmwareUpdateActivity::performUpdate() {
+  LOG_INF("FW", "SD update: %s (%u bytes)", firmwarePath.c_str(), static_cast<unsigned>(firmwareSize));
+
+  auto progressCb = +[](size_t written, size_t total, void* ctx) {
+    auto* self = static_cast<SdFirmwareUpdateActivity*>(ctx);
+    self->writtenBytes = written;
+    self->firmwareSize = total;
+    self->requestUpdate(true);
+  };
+
+  const auto result = firmware_flash::flashFromSdPath(firmwarePath.c_str(), progressCb, this);
+  if (result != firmware_flash::Result::OK) {
+    LOG_ERR("FW", "flash failed: %s", firmware_flash::resultName(result));
+    errorMessage = tr(STR_FIRMWARE_WRITE_FAILED);
+    RenderLock lock(*this);
+    state = State::FAILED;
+    requestUpdate();
+    return;
+  }
+
+  LOG_INF("FW", "SD firmware update complete, restarting");
+  {
+    RenderLock lock(*this);
+    state = State::SUCCESS;
+  }
+  requestUpdateAndWait();
+  delay(1500);
+  ESP.restart();
+}
+
+void SdFirmwareUpdateActivity::loop() {
+  if (state == State::FAILED) {
+    if (mappedInput.wasPressed(MappedInputManager::Button::Back) ||
+        mappedInput.wasPressed(MappedInputManager::Button::Confirm)) {
+      if (recoveryMode) {
+        state = State::PICKING;
+        launchPicker();
+        return;
+      }
+      finish();
+    }
+  }
+}
+
+void SdFirmwareUpdateActivity::render(RenderLock&&) {
+  const auto& metrics = UITheme::getInstance().getMetrics();
+  const auto pageWidth = renderer.getScreenWidth();
+  const auto pageHeight = renderer.getScreenHeight();
+
+  renderer.clearScreen();
+
+  const char* headerText = recoveryMode ? tr(STR_RECOVERY_MODE) : tr(STR_SD_FIRMWARE_UPDATE);
+  GUI.drawHeader(renderer, Rect{0, metrics.topPadding, pageWidth, metrics.headerHeight}, headerText);
+
+  const auto lineHeight = renderer.getLineHeight(UI_10_FONT_ID);
+  const auto top = (pageHeight - lineHeight) / 2;
+
+  if (state == State::VALIDATING) {
+    renderer.drawCenteredText(UI_10_FONT_ID, top, tr(STR_VALIDATING_FIRMWARE));
+  } else if (state == State::UPDATING) {
+    const unsigned int pct = firmwareSize > 0 ? static_cast<unsigned int>((writtenBytes * 100) / firmwareSize) : 0;
+    if (pct == lastRenderedPercent) {
+      return;
+    }
+    lastRenderedPercent = pct;
+
+    renderer.drawCenteredText(UI_10_FONT_ID, top, tr(STR_UPDATING), true, EpdFontFamily::BOLD);
+
+    int y = top + lineHeight + metrics.verticalSpacing;
+    GUI.drawProgressBar(
+        renderer,
+        Rect{metrics.contentSidePadding, y, pageWidth - metrics.contentSidePadding * 2, metrics.progressBarHeight},
+        static_cast<int>(pct), 100);
+    y += metrics.progressBarHeight + metrics.verticalSpacing;
+    renderer.drawCenteredText(UI_10_FONT_ID, y, (std::to_string(pct) + "%").c_str());
+    y += lineHeight + metrics.verticalSpacing;
+    renderer.drawCenteredText(UI_10_FONT_ID, y, tr(STR_FIRMWARE_UPDATE_DO_NOT_POWER_OFF));
+  } else if (state == State::SUCCESS) {
+    renderer.drawCenteredText(UI_10_FONT_ID, top, tr(STR_UPDATE_COMPLETE), true, EpdFontFamily::BOLD);
+    const int hintWidth = pageWidth - 2 * metrics.contentSidePadding;
+    const auto hintLines = renderer.wrappedText(UI_10_FONT_ID, tr(STR_RESTARTING_HINT), hintWidth, 4);
+    int hintY = top + lineHeight + metrics.verticalSpacing;
+    for (const auto& line : hintLines) {
+      renderer.drawCenteredText(UI_10_FONT_ID, hintY, line.c_str());
+      hintY += lineHeight;
+    }
+  } else if (state == State::FAILED) {
+    renderer.drawCenteredText(UI_10_FONT_ID, top, tr(STR_UPDATE_FAILED), true, EpdFontFamily::BOLD);
+    if (!errorMessage.empty()) {
+      renderer.drawCenteredText(UI_10_FONT_ID, top + lineHeight + metrics.verticalSpacing, errorMessage.c_str());
+    }
+    const auto labels = mappedInput.mapLabels(tr(STR_BACK), "", "", "");
+    GUI.drawButtonHints(renderer, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
+  } else {
+    // PICKING / CONFIRMING: a sub-activity is on top, nothing to draw.
+    if (recoveryMode) {
+      const int hintWidth = pageWidth - 2 * metrics.contentSidePadding;
+      const auto hintLines = renderer.wrappedText(UI_10_FONT_ID, tr(STR_RECOVERY_MODE_HINT), hintWidth, 4);
+      int hintY = top;
+      for (const auto& line : hintLines) {
+        renderer.drawCenteredText(UI_10_FONT_ID, hintY, line.c_str());
+        hintY += lineHeight;
+      }
+    }
+  }
+
+  renderer.displayBuffer();
+}
diff --git a/src/activities/settings/SdFirmwareUpdateActivity.h b/src/activities/settings/SdFirmwareUpdateActivity.h
new file mode 100644
index 00000000..4de520b5
--- /dev/null
+++ b/src/activities/settings/SdFirmwareUpdateActivity.h
@@ -0,0 +1,56 @@
+#pragma once
+
+#include <string>
+
+#include "activities/Activity.h"
+
+/**
+ * SD-card based firmware update activity.
+ *
+ * Flow:
+ *  1) onEnter -> push FileBrowserActivity in PickFirmware mode (only .bin files visible).
+ *  2) On result: validate the .bin (header magic, size fits OTA partition).
+ *  3) Push ConfirmationActivity ("Update firmware?").
+ *  4) On confirm: stream the file into the OTA partition via raw esp_partition APIs,
+ *     drawing a progress bar; on success ESP.restart().
+ *
+ * Used both from Settings -> System -> "SD Card Firmware Update", and as the only
+ * activity launched in boot recovery mode (left side button + power on X3).
+ */
+class SdFirmwareUpdateActivity : public Activity {
+ public:
+  enum class State {
+    PICKING,
+    VALIDATING,
+    CONFIRMING,
+    UPDATING,
+    SUCCESS,
+    FAILED,
+  };
+
+  explicit SdFirmwareUpdateActivity(GfxRenderer& renderer, MappedInputManager& mappedInput, bool recoveryMode = false)
+      : Activity("SdFirmwareUpdate", renderer, mappedInput), recoveryMode(recoveryMode) {}
+
+  void onEnter() override;
+  void loop() override;
+  void render(RenderLock&&) override;
+  bool preventAutoSleep() override { return state == State::UPDATING || state == State::VALIDATING; }
+  bool skipLoopDelay() override { return state == State::UPDATING; }
+
+ private:
+  State state = State::PICKING;
+  bool recoveryMode = false;
+
+  std::string firmwarePath;
+  size_t firmwareSize = 0;
+  size_t writtenBytes = 0;
+  unsigned int lastRenderedPercent = 101;
+  std::string errorMessage;
+
+  void launchPicker();
+  void onPickerResult(const ActivityResult& result);
+  bool validateFirmware();
+  void promptConfirmation();
+  void onConfirmationResult(const ActivityResult& result);
+  void performUpdate();
+};
diff --git a/src/activities/settings/SettingActionDispatch.cpp b/src/activities/settings/SettingActionDispatch.cpp
index ba48c3ba..9c7c2d2d 100644
--- a/src/activities/settings/SettingActionDispatch.cpp
+++ b/src/activities/settings/SettingActionDispatch.cpp
@@ -10,6 +10,7 @@
 #include "LanguageSelectActivity.h"
 #include "OpdsServerListActivity.h"
 #include "OtaUpdateActivity.h"
+#include "SdFirmwareUpdateActivity.h"
 #include "StatusBarSettingsActivity.h"
 #include "SyncTimeActivity.h"
 #include "SystemInformationActivity.h"
@@ -39,6 +40,8 @@ std::unique_ptr<Activity> createActivityForAction(SettingAction action, GfxRende
       return std::make_unique<ClearCacheActivity>(renderer, mappedInput);
     case SettingAction::CheckForUpdates:
       return std::make_unique<OtaUpdateActivity>(renderer, mappedInput);
+    case SettingAction::SdFirmwareUpdate:
+      return std::make_unique<SdFirmwareUpdateActivity>(renderer, mappedInput);
     case SettingAction::Language:
       return std::make_unique<LanguageSelectActivity>(renderer, mappedInput);
     case SettingAction::Weather:
diff --git a/src/activities/settings/SettingInfo.h b/src/activities/settings/SettingInfo.h
index 745e48d8..bc7a4f70 100644
--- a/src/activities/settings/SettingInfo.h
+++ b/src/activities/settings/SettingInfo.h
@@ -23,6 +23,7 @@ enum class SettingAction {
   Network,
   ClearCache,
   CheckForUpdates,
+  SdFirmwareUpdate,
   Language,
   SystemInfo,
   DetectTimezone,
diff --git a/src/activities/settings/SettingsActivity.cpp b/src/activities/settings/SettingsActivity.cpp
index e6f362a2..d21274a0 100644
--- a/src/activities/settings/SettingsActivity.cpp
+++ b/src/activities/settings/SettingsActivity.cpp
@@ -150,6 +150,9 @@ void SettingsActivity::onEnter() {
   addToMoved(systemSettings, lastSystemSub,
              std::move(SettingInfo::Action(StrId::STR_CHECK_UPDATES, SettingAction::CheckForUpdates)
                            .withSubcategory(StrId::STR_MENU_SYS_SYSTEM)));
+  addToMoved(systemSettings, lastSystemSub,
+             std::move(SettingInfo::Action(StrId::STR_SD_FIRMWARE_UPDATE, SettingAction::SdFirmwareUpdate)
+                           .withSubcategory(StrId::STR_MENU_SYS_SYSTEM)));
   addToMoved(systemSettings, lastSystemSub,
              std::move(SettingInfo::Action(StrId::STR_SYSTEM_INFO, SettingAction::SystemInfo)
                            .withSubcategory(StrId::STR_MENU_SYS_SYSTEM)));
diff --git a/src/main.cpp b/src/main.cpp
index a80fd3dc..f8751668 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -30,6 +30,7 @@
 #include "WeatherSettingsStore.h"
 #include "activities/Activity.h"
 #include "activities/ActivityManager.h"
+#include "activities/settings/SdFirmwareUpdateActivity.h"
 #include "components/UITheme.h"
 #include "fontIds.h"
 #include "util/ButtonNavigator.h"
@@ -235,6 +236,25 @@ void setup() {
     LOG_DBG("MAIN", "Power button verification passed, millis=%lu", millis());
   }
 
+  // Recovery firmware mode: hold left side button (BTN_UP) together with the power button at
+  // boot to skip directly to the SD-card firmware update screen. Useful on devices where USB
+  // flashing has been locked down (e.g. recent X3 firmware).
+  bool recoveryFirmwareMode = false;
+  if (wakeupReason == HalGPIO::WakeupReason::PowerButton) {
+    // Refresh the cached button state a few times — isPressed() needs ~half a second to settle
+    // after boot per the HalGPIO contract. Use a millis-based deadline so we always wait the full
+    // settle window even if the loop body takes longer than expected on slow boots.
+    const unsigned long settleStart = millis();
+    while (millis() - settleStart < 500) {
+      gpio.update();
+      delay(10);
+    }
+    if (gpio.isPressed(HalGPIO::BTN_UP)) {
+      recoveryFirmwareMode = true;
+      LOG_INF("MAIN", "Recovery firmware mode (UP + POWER held at boot)");
+    }
+  }
+
   // SD Card Initialization
   // We need 6 open files concurrently when parsing a new chapter
   if (!Storage.begin()) {
@@ -268,10 +288,12 @@ void setup() {
   RECENT_BOOKS.loadFromFile();
   GLOBAL_BOOKMARKS.load();
 
-  // Boot to home screen if no book is open, last sleep was not from reader, back button is held, or reader activity
-  // crashed (indicated by readerActivityLoadCount > 0)
-  if (APP_STATE.openEpubPath.empty() || !APP_STATE.lastSleepFromReader ||
-      mappedInputManager.isPressed(MappedInputManager::Button::Back) || APP_STATE.readerActivityLoadCount > 0) {
+  if (recoveryFirmwareMode) {
+    // Skip normal home/reader routing: jump straight into the SD firmware picker.
+    activityManager.replaceActivity(
+        std::make_unique<SdFirmwareUpdateActivity>(renderer, mappedInputManager, /*recoveryMode=*/true));
+  } else if (APP_STATE.openEpubPath.empty() || !APP_STATE.lastSleepFromReader ||
+             mappedInputManager.isPressed(MappedInputManager::Button::Back) || APP_STATE.readerActivityLoadCount > 0) {
     activityManager.goHome();
   } else {
     // Clear app state to avoid getting into a boot loop if the epub doesn't load
diff --git a/src/network/FirmwareFlasher.cpp b/src/network/FirmwareFlasher.cpp
new file mode 100644
index 00000000..316b03f8
--- /dev/null
+++ b/src/network/FirmwareFlasher.cpp
@@ -0,0 +1,300 @@
+#include "FirmwareFlasher.h"
+
+#include <Arduino.h>
+#include <HalStorage.h>
+#include <Logging.h>
+#include <esp_ota_ops.h>
+#include <esp_partition.h>
+#include <mbedtls/sha256.h>
+#include <spi_flash_mmap.h>
+
+#include <algorithm>
+#include <cstring>
+#include <memory>
+
+#include "OtaBootSwitch.h"
+
+namespace firmware_flash {
+
+namespace {
+constexpr uint8_t ESP_IMAGE_MAGIC = 0xE9;
+constexpr size_t MIN_FIRMWARE_SIZE = 64 * 1024;
+constexpr size_t SEC = SPI_FLASH_SEC_SIZE;  // 4 KiB
+constexpr size_t BLK = 64 * 1024;           // 64 KiB block-erase granularity
+constexpr size_t CHUNK = 4096;
+constexpr size_t SHA_TRAILER = 32;
+constexpr uint8_t CHECKSUM_SEED = 0xEF;
+constexpr size_t HEADER_SIZE = 24;
+constexpr size_t SEG_HEADER_SIZE = 8;
+}  // namespace
+
+const char* resultName(Result r) {
+  switch (r) {
+    case Result::OK:
+      return "OK";
+    case Result::OPEN_FAIL:
+      return "OPEN_FAIL";
+    case Result::TOO_SMALL:
+      return "TOO_SMALL";
+    case Result::TOO_LARGE:
+      return "TOO_LARGE";
+    case Result::BAD_MAGIC:
+      return "BAD_MAGIC";
+    case Result::BAD_SEGMENTS:
+      return "BAD_SEGMENTS";
+    case Result::BAD_CHECKSUM:
+      return "BAD_CHECKSUM";
+    case Result::BAD_SHA:
+      return "BAD_SHA";
+    case Result::BAD_SIZE:
+      return "BAD_SIZE";
+    case Result::NO_PARTITION:
+      return "NO_PARTITION";
+    case Result::OOM:
+      return "OOM";
+    case Result::READ_FAIL:
+      return "READ_FAIL";
+    case Result::ERASE_FAIL:
+      return "ERASE_FAIL";
+    case Result::WRITE_FAIL:
+      return "WRITE_FAIL";
+    case Result::OTADATA_FAIL:
+      return "OTADATA_FAIL";
+  }
+  return "?";
+}
+
+namespace {
+// Stream `length` bytes from `file`, feeding them through XOR-checksum and SHA256 accumulators.
+Result feedHashAndChecksum(HalFile& file, size_t length, uint8_t* xorAccum, mbedtls_sha256_context* sha, uint8_t* buf) {
+  size_t remaining = length;
+  while (remaining > 0) {
+    const size_t want = std::min<size_t>(CHUNK, remaining);
+    const int got = file.read(buf, want);
+    if (got <= 0 || static_cast<size_t>(got) != want) return Result::READ_FAIL;
+    if (sha) mbedtls_sha256_update(sha, buf, want);
+    if (xorAccum) {
+      uint8_t acc = *xorAccum;
+      for (size_t i = 0; i < want; i++) acc ^= buf[i];
+      *xorAccum = acc;
+    }
+    remaining -= want;
+  }
+  return Result::OK;
+}
+}  // namespace
+
+Result validateImageFile(const char* sdPath, size_t partitionSize) {
+  HalFile file;
+  if (!Storage.openFileForRead("FLASH", sdPath, file) || !file) {
+    LOG_ERR("FLASH", "validate: open failed: %s", sdPath);
+    return Result::OPEN_FAIL;
+  }
+
+  const size_t fileSize = file.fileSize();
+  if (fileSize < MIN_FIRMWARE_SIZE) {
+    LOG_ERR("FLASH", "validate: too small: %u", static_cast<unsigned>(fileSize));
+    file.close();
+    return Result::TOO_SMALL;
+  }
+  if (partitionSize > 0 && fileSize > partitionSize) {
+    LOG_ERR("FLASH", "validate: too large: %u > %u", static_cast<unsigned>(fileSize),
+            static_cast<unsigned>(partitionSize));
+    file.close();
+    return Result::TOO_LARGE;
+  }
+
+  uint8_t header[HEADER_SIZE];
+  if (file.read(header, HEADER_SIZE) != static_cast<int>(HEADER_SIZE)) {
+    LOG_ERR("FLASH", "validate: header read failed");
+    file.close();
+    return Result::READ_FAIL;
+  }
+  if (header[0] != ESP_IMAGE_MAGIC) {
+    LOG_ERR("FLASH", "validate: bad magic 0x%02X", header[0]);
+    file.close();
+    return Result::BAD_MAGIC;
+  }
+  const uint8_t segCount = header[1];
+  const bool hashAppended = header[23] != 0;
+
+  auto buf = std::unique_ptr<uint8_t[]>(new (std::nothrow) uint8_t[CHUNK]);
+  if (!buf) {
+    file.close();
+    return Result::OOM;
+  }
+
+  mbedtls_sha256_context shaCtx;
+  mbedtls_sha256_init(&shaCtx);
+  mbedtls_sha256_starts(&shaCtx, /*is224=*/0);
+  mbedtls_sha256_update(&shaCtx, header, HEADER_SIZE);
+
+  uint8_t xorAccum = CHECKSUM_SEED;
+  size_t pos = HEADER_SIZE;
+
+  for (uint8_t i = 0; i < segCount; i++) {
+    if (pos + SEG_HEADER_SIZE > fileSize) {
+      LOG_ERR("FLASH", "validate: seg %u header overruns EOF at %u", i, static_cast<unsigned>(pos));
+      mbedtls_sha256_free(&shaCtx);
+      file.close();
+      return Result::BAD_SEGMENTS;
+    }
+    uint8_t segHdr[SEG_HEADER_SIZE];
+    if (file.read(segHdr, SEG_HEADER_SIZE) != static_cast<int>(SEG_HEADER_SIZE)) {
+      mbedtls_sha256_free(&shaCtx);
+      file.close();
+      return Result::READ_FAIL;
+    }
+    mbedtls_sha256_update(&shaCtx, segHdr, SEG_HEADER_SIZE);
+    pos += SEG_HEADER_SIZE;
+
+    uint32_t dataLen;
+    std::memcpy(&dataLen, segHdr + 4, sizeof(dataLen));
+    if (pos + dataLen > fileSize) {
+      LOG_ERR("FLASH", "validate: seg %u data overruns EOF (%u + %u > %u)", i, static_cast<unsigned>(pos),
+              static_cast<unsigned>(dataLen), static_cast<unsigned>(fileSize));
+      mbedtls_sha256_free(&shaCtx);
+      file.close();
+      return Result::BAD_SEGMENTS;
+    }
+
+    const Result feedRes = feedHashAndChecksum(file, dataLen, &xorAccum, &shaCtx, buf.get());
+    if (feedRes != Result::OK) {
+      mbedtls_sha256_free(&shaCtx);
+      file.close();
+      return feedRes;
+    }
+    pos += dataLen;
+  }
+
+  // pad_end is the 16-byte aligned offset at which the checksum byte sits at pad_end - 1.
+  const size_t padEnd = (pos + 16) & ~static_cast<size_t>(15);
+  const size_t expectedTotal = padEnd + (hashAppended ? SHA_TRAILER : 0);
+  if (expectedTotal != fileSize) {
+    LOG_ERR("FLASH", "validate: size mismatch body+pad=%u sha=%u expected=%u actual=%u", static_cast<unsigned>(padEnd),
+            static_cast<unsigned>(hashAppended ? SHA_TRAILER : 0), static_cast<unsigned>(expectedTotal),
+            static_cast<unsigned>(fileSize));
+    mbedtls_sha256_free(&shaCtx);
+    file.close();
+    return Result::BAD_SIZE;
+  }
+
+  const size_t padLen = padEnd - pos;
+  uint8_t padBuf[16];
+  if (padLen > sizeof(padBuf)) {
+    mbedtls_sha256_free(&shaCtx);
+    file.close();
+    return Result::BAD_SIZE;
+  }
+  if (padLen > 0 && file.read(padBuf, padLen) != static_cast<int>(padLen)) {
+    mbedtls_sha256_free(&shaCtx);
+    file.close();
+    return Result::READ_FAIL;
+  }
+  mbedtls_sha256_update(&shaCtx, padBuf, padLen);
+
+  const uint8_t storedChecksum = padBuf[padLen - 1];
+  if ((xorAccum & 0xFF) != storedChecksum) {
+    LOG_ERR("FLASH", "validate: checksum mismatch computed=0x%02X stored=0x%02X", xorAccum, storedChecksum);
+    mbedtls_sha256_free(&shaCtx);
+    file.close();
+    return Result::BAD_CHECKSUM;
+  }
+
+  if (hashAppended) {
+    uint8_t computed[SHA_TRAILER];
+    mbedtls_sha256_finish(&shaCtx, computed);
+    uint8_t stored[SHA_TRAILER];
+    if (file.read(stored, SHA_TRAILER) != static_cast<int>(SHA_TRAILER)) {
+      mbedtls_sha256_free(&shaCtx);
+      file.close();
+      return Result::READ_FAIL;
+    }
+    if (std::memcmp(computed, stored, SHA_TRAILER) != 0) {
+      LOG_ERR("FLASH", "validate: SHA256 mismatch");
+      mbedtls_sha256_free(&shaCtx);
+      file.close();
+      return Result::BAD_SHA;
+    }
+  }
+
+  mbedtls_sha256_free(&shaCtx);
+  file.close();
+  return Result::OK;
+}
+
+Result flashFromSdPath(const char* sdPath, ProgressCb onProgress, void* ctx, bool alreadyValidated) {
+  const esp_partition_t* dest = esp_ota_get_next_update_partition(nullptr);
+  if (!dest) {
+    LOG_ERR("FLASH", "no next-update partition");
+    return Result::NO_PARTITION;
+  }
+
+  if (!alreadyValidated) {
+    const Result validateRes = validateImageFile(sdPath, dest->size);
+    if (validateRes != Result::OK) {
+      LOG_ERR("FLASH", "image validation failed: %s", resultName(validateRes));
+      return validateRes;
+    }
+  }
+
+  HalFile file;
+  if (!Storage.openFileForRead("FLASH", sdPath, file) || !file) {
+    LOG_ERR("FLASH", "open failed: %s", sdPath);
+    return Result::OPEN_FAIL;
+  }
+
+  const size_t firmwareSize = file.fileSize();
+  LOG_INF("FLASH", "src=%s size=%u dest=%s @0x%x partsize=%u", sdPath, static_cast<unsigned>(firmwareSize), dest->label,
+          static_cast<unsigned>(dest->address), static_cast<unsigned>(dest->size));
+
+  auto buffer = std::unique_ptr<uint8_t[]>(new (std::nothrow) uint8_t[CHUNK]);
+  if (!buffer) {
+    LOG_ERR("FLASH", "OOM");
+    file.close();
+    return Result::OOM;
+  }
+
+  // Interleave erase + write so the progress bar advances 0→100% smoothly.
+  size_t streamPos = 0;
+  size_t erasedUpto = 0;
+  while (streamPos < firmwareSize) {
+    if (streamPos >= erasedUpto) {
+      size_t eraseLen = std::min<size_t>(BLK, dest->size - streamPos);
+      eraseLen = (eraseLen + SEC - 1) & ~(SEC - 1);
+      eraseLen = std::min<size_t>(eraseLen, dest->size - streamPos);
+      if (esp_partition_erase_range(dest, streamPos, eraseLen) != ESP_OK) {
+        LOG_ERR("FLASH", "erase @%u (len=%u) failed", static_cast<unsigned>(streamPos),
+                static_cast<unsigned>(eraseLen));
+        file.close();
+        return Result::ERASE_FAIL;
+      }
+      erasedUpto = streamPos + eraseLen;
+    }
+
+    const size_t want = std::min<size_t>(CHUNK, firmwareSize - streamPos);
+    const int read = file.read(buffer.get(), want);
+    if (read <= 0 || static_cast<size_t>(read) != want) {
+      LOG_ERR("FLASH", "read @%u: got=%d want=%u", static_cast<unsigned>(streamPos), read, static_cast<unsigned>(want));
+      file.close();
+      return Result::READ_FAIL;
+    }
+    if (esp_partition_write(dest, streamPos, buffer.get(), want) != ESP_OK) {
+      LOG_ERR("FLASH", "write @%u failed", static_cast<unsigned>(streamPos));
+      file.close();
+      return Result::WRITE_FAIL;
+    }
+    streamPos += want;
+    if (onProgress) onProgress(streamPos, firmwareSize, ctx);
+    delay(1);
+  }
+  file.close();
+
+  if (!ota_boot::switchTo(dest)) {
+    LOG_ERR("FLASH", "otadata switch failed");
+    return Result::OTADATA_FAIL;
+  }
+  return Result::OK;
+}
+
+}  // namespace firmware_flash
diff --git a/src/network/FirmwareFlasher.h b/src/network/FirmwareFlasher.h
new file mode 100644
index 00000000..fd247498
--- /dev/null
+++ b/src/network/FirmwareFlasher.h
@@ -0,0 +1,60 @@
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+
+// Flash a firmware image from an SD-card path into the next OTA app
+// partition, then switch otadata so the X3/X4 stock bootloader picks it up
+// on next boot. Mirrors the web flasher: raw esp_partition_erase_range +
+// esp_partition_write + ota_boot::switchTo (no Arduino Update class, no
+// esp_image_verify — those reject our patched image on X4 silicon).
+//
+// Both the SD update activity and the OTA path land here. OTA first
+// downloads the firmware to an SD-card cache file, then calls this.
+
+namespace firmware_flash {
+
+enum class Result {
+  OK,
+  OPEN_FAIL,
+  TOO_SMALL,
+  TOO_LARGE,
+  BAD_MAGIC,
+  BAD_SEGMENTS,  // segment table malformed or runs past EOF
+  BAD_CHECKSUM,  // ESP image XOR checksum mismatch
+  BAD_SHA,       // SHA256 trailer mismatch (hash_appended images)
+  BAD_SIZE,      // body+pad+sha length doesn't match file size
+  NO_PARTITION,
+  OOM,
+  READ_FAIL,
+  ERASE_FAIL,
+  WRITE_FAIL,
+  OTADATA_FAIL,
+};
+
+// Progress callback: called after every chunk write. `written`/`total` are bytes.
+using ProgressCb = void (*)(size_t written, size_t total, void* ctx);
+
+// Open `sdPath`, validate it looks like an ESP32 image, then stream it into the
+// next OTA app partition with interleaved 64 KiB erase + sector writes. On
+// success switches otadata via ota_boot::switchTo. Caller is responsible for
+// ESP.restart() afterwards.
+//
+// `alreadyValidated` lets callers that have just run `validateImageFile()`
+// themselves (e.g. SdFirmwareUpdateActivity, which validates before showing
+// the user the confirmation prompt) skip the redundant second pass. Defaults
+// to false so callers without prior validation keep the defense-in-depth check.
+Result flashFromSdPath(const char* sdPath, ProgressCb onProgress, void* ctx, bool alreadyValidated = false);
+
+// Full-image integrity check that mirrors the bootloader's verification:
+// header magic, segment table walk, XOR checksum, and SHA256 trailer (when
+// hash_appended == 1). Run this before flashing a candidate firmware so a
+// truncated/corrupted .bin never reaches otadata.
+//
+// `partitionSize` is the size of the destination OTA partition; pass 0 to
+// skip the size-fits-partition check. Streams the file in CHUNK-sized reads.
+Result validateImageFile(const char* sdPath, size_t partitionSize);
+
+const char* resultName(Result r);
+
+}  // namespace firmware_flash
diff --git a/src/network/OtaBootSwitch.cpp b/src/network/OtaBootSwitch.cpp
new file mode 100644
index 00000000..7c3ca762
--- /dev/null
+++ b/src/network/OtaBootSwitch.cpp
@@ -0,0 +1,86 @@
+#include "OtaBootSwitch.h"
+
+#include <Logging.h>
+#include <esp_rom_crc.h>
+#include <spi_flash_mmap.h>
+#include <string.h>
+
+namespace ota_boot {
+
+uint32_t computeSeqCrc(uint32_t seq) {
+  return esp_rom_crc32_le(UINT32_MAX, reinterpret_cast<const uint8_t*>(&seq), kOtaSeqCrcLen);
+}
+
+bool switchTo(const esp_partition_t* dest) {
+  if (!dest) return false;
+
+  const esp_partition_t* otadata =
+      esp_partition_find_first(ESP_PARTITION_TYPE_DATA, ESP_PARTITION_SUBTYPE_DATA_OTA, nullptr);
+  if (!otadata) {
+    LOG_ERR("BOOT", "otadata partition not found");
+    return false;
+  }
+  if (otadata->size < 2 * SPI_FLASH_SEC_SIZE) {
+    LOG_ERR("BOOT", "otadata too small: %u", static_cast<unsigned>(otadata->size));
+    return false;
+  }
+
+  SelectEntry slots[2] = {};
+  if (esp_partition_read(otadata, 0, &slots[0], sizeof(SelectEntry)) != ESP_OK ||
+      esp_partition_read(otadata, SPI_FLASH_SEC_SIZE, &slots[1], sizeof(SelectEntry)) != ESP_OK) {
+    LOG_ERR("BOOT", "otadata read failed");
+    return false;
+  }
+
+  // Pick the slot with valid CRC and highest seq, ignoring INVALID/ABORTED.
+  int activeIdx = -1;
+  uint32_t activeSeq = 0;
+  for (int i = 0; i < 2; ++i) {
+    if (slots[i].ota_seq == 0xFFFFFFFFu) continue;
+    if (slots[i].crc != computeSeqCrc(slots[i].ota_seq)) continue;
+    if (slots[i].ota_state == kOtaImgInvalid || slots[i].ota_state == kOtaImgAborted) continue;
+    if (activeIdx < 0 || slots[i].ota_seq > activeSeq) {
+      activeIdx = i;
+      activeSeq = slots[i].ota_seq;
+    }
+  }
+  LOG_INF("BOOT", "otadata: active slot=%d seq=%u", activeIdx, static_cast<unsigned>(activeSeq));
+
+  // ota_seq encoding: (seq - 1) % NUM_OTA_PARTITIONS picks the partition.
+  const uint32_t destOtaIdx =
+      static_cast<uint32_t>(dest->subtype) - static_cast<uint32_t>(ESP_PARTITION_SUBTYPE_APP_OTA_0);
+  if (destOtaIdx > 15) {
+    LOG_ERR("BOOT", "dest is not an OTA app partition (subtype=0x%02X)", dest->subtype);
+    return false;
+  }
+
+  // Find smallest seq > activeSeq such that (seq-1) % 2 == destOtaIdx,
+  // assuming 2 OTA partitions (matches our partitions.csv with ota_0 + ota_1).
+  uint32_t newSeq = activeSeq + 1;
+  while (((newSeq - 1u) % 2u) != (destOtaIdx % 2u)) ++newSeq;
+
+  SelectEntry next = {};
+  next.ota_seq = newSeq;
+  memset(next.seq_label, 0xFF, sizeof(next.seq_label));
+  next.ota_state = kOtaImgNew;
+  next.crc = computeSeqCrc(next.ota_seq);
+
+  // Write to the OTHER slot (so the bootloader sees a higher seq there).
+  const int targetSlot = (activeIdx == 0) ? 1 : 0;
+  const size_t targetOff = static_cast<size_t>(targetSlot) * SPI_FLASH_SEC_SIZE;
+
+  if (esp_partition_erase_range(otadata, targetOff, SPI_FLASH_SEC_SIZE) != ESP_OK) {
+    LOG_ERR("BOOT", "otadata erase failed (slot=%d)", targetSlot);
+    return false;
+  }
+  if (esp_partition_write(otadata, targetOff, &next, sizeof(next)) != ESP_OK) {
+    LOG_ERR("BOOT", "otadata write failed (slot=%d)", targetSlot);
+    return false;
+  }
+
+  LOG_INF("BOOT", "otadata: wrote slot=%d seq=%u crc=0x%08x -> %s", targetSlot, static_cast<unsigned>(newSeq),
+          static_cast<unsigned>(next.crc), dest->label);
+  return true;
+}
+
+}  // namespace ota_boot
diff --git a/src/network/OtaBootSwitch.h b/src/network/OtaBootSwitch.h
new file mode 100644
index 00000000..3c52f7be
--- /dev/null
+++ b/src/network/OtaBootSwitch.h
@@ -0,0 +1,43 @@
+#pragma once
+
+#include <esp_partition.h>
+
+#include <cstddef>
+#include <cstdint>
+
+// X4 (and X3) factory bootloaders accept our patch_firmware_image.py-patched
+// firmware.bin (web flasher proves this), but the running ESP-IDF's
+// esp_image_verify rejects with bogus efuse-blk-rev errors. Both SD-card and
+// OTA update paths bypass that runtime check by writing the OTA app partition
+// raw and updating otadata directly — same scheme as the web flasher
+// (crosspoint-reader-docs/src/lib/flasher/OtaPartition.ts).
+//
+// Layout reference: esp_flash_partitions.h. CRC covers ota_seq (4 bytes) only.
+
+namespace ota_boot {
+
+struct __attribute__((packed)) SelectEntry {
+  uint32_t ota_seq;
+  uint8_t seq_label[20];
+  uint32_t ota_state;
+  uint32_t crc;
+};
+static_assert(sizeof(SelectEntry) == 32, "SelectEntry must be 32 bytes");
+
+constexpr uint32_t kOtaImgNew = 0;      // ESP_OTA_IMG_NEW
+constexpr uint32_t kOtaImgInvalid = 3;  // ESP_OTA_IMG_INVALID
+constexpr uint32_t kOtaImgAborted = 4;  // ESP_OTA_IMG_ABORTED
+constexpr size_t kOtaSeqCrcLen = 4;
+
+// CRC32-LE over the 4-byte ota_seq, init UINT32_MAX. Matches IDF and web flasher.
+uint32_t computeSeqCrc(uint32_t seq);
+
+// Switch the bootloader's selected app partition to `dest` by writing a fresh
+// otadata entry into the inactive otadata slot. Bypasses esp_ota_set_boot_partition's
+// esp_image_verify call. The bytes in `dest` must already be a valid app image
+// (e.g. patch_firmware_image.py output) — caller is responsible for that.
+//
+// Returns true on success.
+bool switchTo(const esp_partition_t* dest);
+
+}  // namespace ota_boot