Adds KOReader Sync support (#232)

## Summary

- Adds KOReader progress sync integration, allowing CrossPoint to sync
reading positions with other
KOReader-compatible devices
- Stores credentials securely with XOR obfuscation
- Uses KOReader's partial MD5 document hashing for cross-device book
matching
  - Syncs position via percentage with estimated XPath for compatibility

# Features
- Settings: KOReader Username, Password, and Authenticate options
- Sync from chapters menu: "Sync Progress" option appears when
credentials are configured
- Bidirectional sync: Can apply remote progress or upload local progress

---------

Co-authored-by: Dave Allie <dave@daveallie.com>

lib/Epub/Epub.cpp

@@ -609,14 +609,15 @@ int Epub::getSpineIndexForTextReference() const {
   return 0;
 }
 
-// Calculate progress in book
+// Calculate progress in book (returns 0.0-1.0)
-uint8_t Epub::calculateProgress(const int currentSpineIndex, const float currentSpineRead) const {
+float Epub::calculateProgress(const int currentSpineIndex, const float currentSpineRead) const {
   const size_t bookSize = getBookSize();
   if (bookSize == 0) {
-    return 0;
+    return 0.0f;
   }
   const size_t prevChapterSize = (currentSpineIndex >= 1) ? getCumulativeSpineItemSize(currentSpineIndex - 1) : 0;
   const size_t curChapterSize = getCumulativeSpineItemSize(currentSpineIndex) - prevChapterSize;
-  const size_t sectionProgSize = currentSpineRead * curChapterSize;
+  const float sectionProgSize = currentSpineRead * static_cast<float>(curChapterSize);
-  return round(static_cast<float>(prevChapterSize + sectionProgSize) / bookSize * 100.0);
+  const float totalProgress = static_cast<float>(prevChapterSize) + sectionProgSize;
+  return totalProgress / static_cast<float>(bookSize);
 }

lib/Epub/Epub.h

@@ -62,5 +62,5 @@ class Epub {
   int getSpineIndexForTextReference() const;
 
   size_t getBookSize() const;
-  uint8_t calculateProgress(int currentSpineIndex, float currentSpineRead) const;
+  float calculateProgress(int currentSpineIndex, float currentSpineRead) const;
 };

lib/KOReaderSync/KOReaderCredentialStore.cpp

@@ -0,0 +1,168 @@
+#include "KOReaderCredentialStore.h"
+
+#include <HardwareSerial.h>
+#include <MD5Builder.h>
+#include <SDCardManager.h>
+#include <Serialization.h>
+
+// Initialize the static instance
+KOReaderCredentialStore KOReaderCredentialStore::instance;
+
+namespace {
+// File format version
+constexpr uint8_t KOREADER_FILE_VERSION = 1;
+
+// KOReader credentials file path
+constexpr char KOREADER_FILE[] = "/.crosspoint/koreader.bin";
+
+// Default sync server URL
+constexpr char DEFAULT_SERVER_URL[] = "https://sync.koreader.rocks:443";
+
+// Obfuscation key - "KOReader" in ASCII
+// This is NOT cryptographic security, just prevents casual file reading
+constexpr uint8_t OBFUSCATION_KEY[] = {0x4B, 0x4F, 0x52, 0x65, 0x61, 0x64, 0x65, 0x72};
+constexpr size_t KEY_LENGTH = sizeof(OBFUSCATION_KEY);
+}  // namespace
+
+void KOReaderCredentialStore::obfuscate(std::string& data) const {
+  for (size_t i = 0; i < data.size(); i++) {
+    data[i] ^= OBFUSCATION_KEY[i % KEY_LENGTH];
+  }
+}
+
+bool KOReaderCredentialStore::saveToFile() const {
+  // Make sure the directory exists
+  SdMan.mkdir("/.crosspoint");
+
+  FsFile file;
+  if (!SdMan.openFileForWrite("KRS", KOREADER_FILE, file)) {
+    return false;
+  }
+
+  // Write header
+  serialization::writePod(file, KOREADER_FILE_VERSION);
+
+  // Write username (plaintext - not particularly sensitive)
+  serialization::writeString(file, username);
+  Serial.printf("[%lu] [KRS] Saving username: %s\n", millis(), username.c_str());
+
+  // Write password (obfuscated)
+  std::string obfuscatedPwd = password;
+  obfuscate(obfuscatedPwd);
+  serialization::writeString(file, obfuscatedPwd);
+
+  // Write server URL
+  serialization::writeString(file, serverUrl);
+
+  // Write match method
+  serialization::writePod(file, static_cast<uint8_t>(matchMethod));
+
+  file.close();
+  Serial.printf("[%lu] [KRS] Saved KOReader credentials to file\n", millis());
+  return true;
+}
+
+bool KOReaderCredentialStore::loadFromFile() {
+  FsFile file;
+  if (!SdMan.openFileForRead("KRS", KOREADER_FILE, file)) {
+    Serial.printf("[%lu] [KRS] No credentials file found\n", millis());
+    return false;
+  }
+
+  // Read and verify version
+  uint8_t version;
+  serialization::readPod(file, version);
+  if (version != KOREADER_FILE_VERSION) {
+    Serial.printf("[%lu] [KRS] Unknown file version: %u\n", millis(), version);
+    file.close();
+    return false;
+  }
+
+  // Read username
+  if (file.available()) {
+    serialization::readString(file, username);
+  } else {
+    username.clear();
+  }
+
+  // Read and deobfuscate password
+  if (file.available()) {
+    serialization::readString(file, password);
+    obfuscate(password);  // XOR is symmetric, so same function deobfuscates
+  } else {
+    password.clear();
+  }
+
+  // Read server URL
+  if (file.available()) {
+    serialization::readString(file, serverUrl);
+  } else {
+    serverUrl.clear();
+  }
+
+  // Read match method
+  if (file.available()) {
+    uint8_t method;
+    serialization::readPod(file, method);
+    matchMethod = static_cast<DocumentMatchMethod>(method);
+  } else {
+    matchMethod = DocumentMatchMethod::FILENAME;
+  }
+
+  file.close();
+  Serial.printf("[%lu] [KRS] Loaded KOReader credentials for user: %s\n", millis(), username.c_str());
+  return true;
+}
+
+void KOReaderCredentialStore::setCredentials(const std::string& user, const std::string& pass) {
+  username = user;
+  password = pass;
+  Serial.printf("[%lu] [KRS] Set credentials for user: %s\n", millis(), user.c_str());
+}
+
+std::string KOReaderCredentialStore::getMd5Password() const {
+  if (password.empty()) {
+    return "";
+  }
+
+  // Calculate MD5 hash of password using ESP32's MD5Builder
+  MD5Builder md5;
+  md5.begin();
+  md5.add(password.c_str());
+  md5.calculate();
+
+  return md5.toString().c_str();
+}
+
+bool KOReaderCredentialStore::hasCredentials() const { return !username.empty() && !password.empty(); }
+
+void KOReaderCredentialStore::clearCredentials() {
+  username.clear();
+  password.clear();
+  saveToFile();
+  Serial.printf("[%lu] [KRS] Cleared KOReader credentials\n", millis());
+}
+
+void KOReaderCredentialStore::setServerUrl(const std::string& url) {
+  serverUrl = url;
+  Serial.printf("[%lu] [KRS] Set server URL: %s\n", millis(), url.empty() ? "(default)" : url.c_str());
+}
+
+std::string KOReaderCredentialStore::getBaseUrl() const {
+  if (serverUrl.empty()) {
+    return DEFAULT_SERVER_URL;
+  }
+
+  // Normalize URL: add http:// if no protocol specified (local servers typically don't have SSL)
+  if (serverUrl.find("://") == std::string::npos) {
+    return "http://" + serverUrl;
+  }
+
+  return serverUrl;
+}
+
+void KOReaderCredentialStore::setMatchMethod(DocumentMatchMethod method) {
+  matchMethod = method;
+  Serial.printf("[%lu] [KRS] Set match method: %s\n", millis(),
+                method == DocumentMatchMethod::FILENAME ? "Filename" : "Binary");
+}

lib/KOReaderSync/KOReaderCredentialStore.h

@@ -0,0 +1,69 @@
+#pragma once
+#include <cstdint>
+#include <string>
+
+// Document matching method for KOReader sync
+enum class DocumentMatchMethod : uint8_t {
+  FILENAME = 0,  // Match by filename (simpler, works across different file sources)
+  BINARY = 1,    // Match by partial MD5 of file content (more accurate, but files must be identical)
+};
+
+/**
+ * Singleton class for storing KOReader sync credentials on the SD card.
+ * Credentials are stored in /sd/.crosspoint/koreader.bin with basic
+ * XOR obfuscation to prevent casual reading (not cryptographically secure).
+ */
+class KOReaderCredentialStore {
+ private:
+  static KOReaderCredentialStore instance;
+  std::string username;
+  std::string password;
+  std::string serverUrl;                                            // Custom sync server URL (empty = default)
+  DocumentMatchMethod matchMethod = DocumentMatchMethod::FILENAME;  // Default to filename for compatibility
+
+  // Private constructor for singleton
+  KOReaderCredentialStore() = default;
+
+  // XOR obfuscation (symmetric - same for encode/decode)
+  void obfuscate(std::string& data) const;
+
+ public:
+  // Delete copy constructor and assignment
+  KOReaderCredentialStore(const KOReaderCredentialStore&) = delete;
+  KOReaderCredentialStore& operator=(const KOReaderCredentialStore&) = delete;
+
+  // Get singleton instance
+  static KOReaderCredentialStore& getInstance() { return instance; }
+
+  // Save/load from SD card
+  bool saveToFile() const;
+  bool loadFromFile();
+
+  // Credential management
+  void setCredentials(const std::string& user, const std::string& pass);
+  const std::string& getUsername() const { return username; }
+  const std::string& getPassword() const { return password; }
+
+  // Get MD5 hash of password for API authentication
+  std::string getMd5Password() const;
+
+  // Check if credentials are set
+  bool hasCredentials() const;
+
+  // Clear credentials
+  void clearCredentials();
+
+  // Server URL management
+  void setServerUrl(const std::string& url);
+  const std::string& getServerUrl() const { return serverUrl; }
+
+  // Get base URL for API calls (with http:// normalization if no protocol, falls back to default)
+  std::string getBaseUrl() const;
+
+  // Document matching method
+  void setMatchMethod(DocumentMatchMethod method);
+  DocumentMatchMethod getMatchMethod() const { return matchMethod; }
+};
+
+// Helper macro to access credential store
+#define KOREADER_STORE KOReaderCredentialStore::getInstance()

lib/KOReaderSync/KOReaderDocumentId.cpp

@@ -0,0 +1,96 @@
+#include "KOReaderDocumentId.h"
+
+#include <HardwareSerial.h>
+#include <MD5Builder.h>
+#include <SDCardManager.h>
+
+namespace {
+// Extract filename from path (everything after last '/')
+std::string getFilename(const std::string& path) {
+  const size_t pos = path.rfind('/');
+  if (pos == std::string::npos) {
+    return path;
+  }
+  return path.substr(pos + 1);
+}
+}  // namespace
+
+std::string KOReaderDocumentId::calculateFromFilename(const std::string& filePath) {
+  const std::string filename = getFilename(filePath);
+  if (filename.empty()) {
+    return "";
+  }
+
+  MD5Builder md5;
+  md5.begin();
+  md5.add(filename.c_str());
+  md5.calculate();
+
+  std::string result = md5.toString().c_str();
+  Serial.printf("[%lu] [KODoc] Filename hash: %s (from '%s')\n", millis(), result.c_str(), filename.c_str());
+  return result;
+}
+
+size_t KOReaderDocumentId::getOffset(int i) {
+  // Offset = 1024 << (2*i)
+  // For i = -1: 1024 >> 2 = 256
+  // For i >= 0: 1024 << (2*i)
+  if (i < 0) {
+    return CHUNK_SIZE >> (-2 * i);
+  }
+  return CHUNK_SIZE << (2 * i);
+}
+
+std::string KOReaderDocumentId::calculate(const std::string& filePath) {
+  FsFile file;
+  if (!SdMan.openFileForRead("KODoc", filePath, file)) {
+    Serial.printf("[%lu] [KODoc] Failed to open file: %s\n", millis(), filePath.c_str());
+    return "";
+  }
+
+  const size_t fileSize = file.fileSize();
+  Serial.printf("[%lu] [KODoc] Calculating hash for file: %s (size: %zu)\n", millis(), filePath.c_str(), fileSize);
+
+  // Initialize MD5 builder
+  MD5Builder md5;
+  md5.begin();
+
+  // Buffer for reading chunks
+  uint8_t buffer[CHUNK_SIZE];
+  size_t totalBytesRead = 0;
+
+  // Read from each offset (i = -1 to 10)
+  for (int i = -1; i < OFFSET_COUNT - 1; i++) {
+    const size_t offset = getOffset(i);
+
+    // Skip if offset is beyond file size
+    if (offset >= fileSize) {
+      continue;
+    }
+
+    // Seek to offset
+    if (!file.seekSet(offset)) {
+      Serial.printf("[%lu] [KODoc] Failed to seek to offset %zu\n", millis(), offset);
+      continue;
+    }
+
+    // Read up to CHUNK_SIZE bytes
+    const size_t bytesToRead = std::min(CHUNK_SIZE, fileSize - offset);
+    const size_t bytesRead = file.read(buffer, bytesToRead);
+
+    if (bytesRead > 0) {
+      md5.add(buffer, bytesRead);
+      totalBytesRead += bytesRead;
+    }
+  }
+
+  file.close();
+
+  // Calculate final hash
+  md5.calculate();
+  std::string result = md5.toString().c_str();
+
+  Serial.printf("[%lu] [KODoc] Hash calculated: %s (from %zu bytes)\n", millis(), result.c_str(), totalBytesRead);
+
+  return result;
+}

lib/KOReaderSync/KOReaderDocumentId.h

@@ -0,0 +1,45 @@
+#pragma once
+#include <string>
+
+/**
+ * Calculate KOReader document ID (partial MD5 hash).
+ *
+ * KOReader identifies documents using a partial MD5 hash of the file content.
+ * The algorithm reads 1024 bytes at specific offsets and computes the MD5 hash
+ * of the concatenated data.
+ *
+ * Offsets are calculated as: 1024 << (2*i) for i = -1 to 10
+ * Producing: 256, 1024, 4096, 16384, 65536, 262144, 1048576, 4194304,
+ *            16777216, 67108864, 268435456, 1073741824 bytes
+ *
+ * If an offset is beyond the file size, it is skipped.
+ */
+class KOReaderDocumentId {
+ public:
+  /**
+   * Calculate the KOReader document hash for a file (binary/content-based).
+   *
+   * @param filePath Path to the file (typically an EPUB)
+   * @return 32-character lowercase hex string, or empty string on failure
+   */
+  static std::string calculate(const std::string& filePath);
+
+  /**
+   * Calculate document hash from filename only (filename-based sync mode).
+   * This is simpler and works when files have the same name across devices.
+   *
+   * @param filePath Path to the file (only the filename portion is used)
+   * @return 32-character lowercase hex MD5 of the filename
+   */
+  static std::string calculateFromFilename(const std::string& filePath);
+
+ private:
+  // Size of each chunk to read at each offset
+  static constexpr size_t CHUNK_SIZE = 1024;
+
+  // Number of offsets to try (i = -1 to 10, so 12 offsets)
+  static constexpr int OFFSET_COUNT = 12;
+
+  // Calculate offset for index i: 1024 << (2*i)
+  static size_t getOffset(int i);
+};

lib/KOReaderSync/KOReaderSyncClient.cpp

@@ -0,0 +1,198 @@
+#include "KOReaderSyncClient.h"
+
+#include <ArduinoJson.h>
+#include <HTTPClient.h>
+#include <HardwareSerial.h>
+#include <WiFi.h>
+#include <WiFiClientSecure.h>
+
+#include <ctime>
+
+#include "KOReaderCredentialStore.h"
+
+namespace {
+// Device identifier for CrossPoint reader
+constexpr char DEVICE_NAME[] = "CrossPoint";
+constexpr char DEVICE_ID[] = "crosspoint-reader";
+
+void addAuthHeaders(HTTPClient& http) {
+  http.addHeader("Accept", "application/vnd.koreader.v1+json");
+  http.addHeader("x-auth-user", KOREADER_STORE.getUsername().c_str());
+  http.addHeader("x-auth-key", KOREADER_STORE.getMd5Password().c_str());
+}
+
+bool isHttpsUrl(const std::string& url) { return url.rfind("https://", 0) == 0; }
+}  // namespace
+
+KOReaderSyncClient::Error KOReaderSyncClient::authenticate() {
+  if (!KOREADER_STORE.hasCredentials()) {
+    Serial.printf("[%lu] [KOSync] No credentials configured\n", millis());
+    return NO_CREDENTIALS;
+  }
+
+  std::string url = KOREADER_STORE.getBaseUrl() + "/users/auth";
+  Serial.printf("[%lu] [KOSync] Authenticating: %s\n", millis(), url.c_str());
+
+  HTTPClient http;
+  std::unique_ptr<WiFiClientSecure> secureClient;
+  WiFiClient plainClient;
+
+  if (isHttpsUrl(url)) {
+    secureClient.reset(new WiFiClientSecure);
+    secureClient->setInsecure();
+    http.begin(*secureClient, url.c_str());
+  } else {
+    http.begin(plainClient, url.c_str());
+  }
+  addAuthHeaders(http);
+
+  const int httpCode = http.GET();
+  http.end();
+
+  Serial.printf("[%lu] [KOSync] Auth response: %d\n", millis(), httpCode);
+
+  if (httpCode == 200) {
+    return OK;
+  } else if (httpCode == 401) {
+    return AUTH_FAILED;
+  } else if (httpCode < 0) {
+    return NETWORK_ERROR;
+  }
+  return SERVER_ERROR;
+}
+
+KOReaderSyncClient::Error KOReaderSyncClient::getProgress(const std::string& documentHash,
+                                                          KOReaderProgress& outProgress) {
+  if (!KOREADER_STORE.hasCredentials()) {
+    Serial.printf("[%lu] [KOSync] No credentials configured\n", millis());
+    return NO_CREDENTIALS;
+  }
+
+  std::string url = KOREADER_STORE.getBaseUrl() + "/syncs/progress/" + documentHash;
+  Serial.printf("[%lu] [KOSync] Getting progress: %s\n", millis(), url.c_str());
+
+  HTTPClient http;
+  std::unique_ptr<WiFiClientSecure> secureClient;
+  WiFiClient plainClient;
+
+  if (isHttpsUrl(url)) {
+    secureClient.reset(new WiFiClientSecure);
+    secureClient->setInsecure();
+    http.begin(*secureClient, url.c_str());
+  } else {
+    http.begin(plainClient, url.c_str());
+  }
+  addAuthHeaders(http);
+
+  const int httpCode = http.GET();
+
+  if (httpCode == 200) {
+    // Parse JSON response from response string
+    String responseBody = http.getString();
+    http.end();
+
+    JsonDocument doc;
+    const DeserializationError error = deserializeJson(doc, responseBody);
+
+    if (error) {
+      Serial.printf("[%lu] [KOSync] JSON parse failed: %s\n", millis(), error.c_str());
+      return JSON_ERROR;
+    }
+
+    outProgress.document = documentHash;
+    outProgress.progress = doc["progress"].as<std::string>();
+    outProgress.percentage = doc["percentage"].as<float>();
+    outProgress.device = doc["device"].as<std::string>();
+    outProgress.deviceId = doc["device_id"].as<std::string>();
+    outProgress.timestamp = doc["timestamp"].as<int64_t>();
+
+    Serial.printf("[%lu] [KOSync] Got progress: %.2f%% at %s\n", millis(), outProgress.percentage * 100,
+                  outProgress.progress.c_str());
+    return OK;
+  }
+
+  http.end();
+
+  Serial.printf("[%lu] [KOSync] Get progress response: %d\n", millis(), httpCode);
+
+  if (httpCode == 401) {
+    return AUTH_FAILED;
+  } else if (httpCode == 404) {
+    return NOT_FOUND;
+  } else if (httpCode < 0) {
+    return NETWORK_ERROR;
+  }
+  return SERVER_ERROR;
+}
+
+KOReaderSyncClient::Error KOReaderSyncClient::updateProgress(const KOReaderProgress& progress) {
+  if (!KOREADER_STORE.hasCredentials()) {
+    Serial.printf("[%lu] [KOSync] No credentials configured\n", millis());
+    return NO_CREDENTIALS;
+  }
+
+  std::string url = KOREADER_STORE.getBaseUrl() + "/syncs/progress";
+  Serial.printf("[%lu] [KOSync] Updating progress: %s\n", millis(), url.c_str());
+
+  HTTPClient http;
+  std::unique_ptr<WiFiClientSecure> secureClient;
+  WiFiClient plainClient;
+
+  if (isHttpsUrl(url)) {
+    secureClient.reset(new WiFiClientSecure);
+    secureClient->setInsecure();
+    http.begin(*secureClient, url.c_str());
+  } else {
+    http.begin(plainClient, url.c_str());
+  }
+  addAuthHeaders(http);
+  http.addHeader("Content-Type", "application/json");
+
+  // Build JSON body (timestamp not required per API spec)
+  JsonDocument doc;
+  doc["document"] = progress.document;
+  doc["progress"] = progress.progress;
+  doc["percentage"] = progress.percentage;
+  doc["device"] = DEVICE_NAME;
+  doc["device_id"] = DEVICE_ID;
+
+  std::string body;
+  serializeJson(doc, body);
+
+  Serial.printf("[%lu] [KOSync] Request body: %s\n", millis(), body.c_str());
+
+  const int httpCode = http.PUT(body.c_str());
+  http.end();
+
+  Serial.printf("[%lu] [KOSync] Update progress response: %d\n", millis(), httpCode);
+
+  if (httpCode == 200 || httpCode == 202) {
+    return OK;
+  } else if (httpCode == 401) {
+    return AUTH_FAILED;
+  } else if (httpCode < 0) {
+    return NETWORK_ERROR;
+  }
+  return SERVER_ERROR;
+}
+
+const char* KOReaderSyncClient::errorString(Error error) {
+  switch (error) {
+    case OK:
+      return "Success";
+    case NO_CREDENTIALS:
+      return "No credentials configured";
+    case NETWORK_ERROR:
+      return "Network error";
+    case AUTH_FAILED:
+      return "Authentication failed";
+    case SERVER_ERROR:
+      return "Server error (try again later)";
+    case JSON_ERROR:
+      return "JSON parse error";
+    case NOT_FOUND:
+      return "No progress found";
+    default:
+      return "Unknown error";
+  }
+}

lib/KOReaderSync/KOReaderSyncClient.h

@@ -0,0 +1,59 @@
+#pragma once
+#include <string>
+
+/**
+ * Progress data from KOReader sync server.
+ */
+struct KOReaderProgress {
+  std::string document;  // Document hash
+  std::string progress;  // XPath-like progress string
+  float percentage;      // Progress percentage (0.0 to 1.0)
+  std::string device;    // Device name
+  std::string deviceId;  // Device ID
+  int64_t timestamp;     // Unix timestamp of last update
+};
+
+/**
+ * HTTP client for KOReader sync API.
+ *
+ * Base URL: https://sync.koreader.rocks:443/
+ *
+ * API Endpoints:
+ *   GET /users/auth - Authenticate (validate credentials)
+ *   GET /syncs/progress/:document - Get progress for a document
+ *   PUT /syncs/progress - Update progress for a document
+ *
+ * Authentication:
+ *   x-auth-user: username
+ *   x-auth-key: MD5 hash of password
+ */
+class KOReaderSyncClient {
+ public:
+  enum Error { OK = 0, NO_CREDENTIALS, NETWORK_ERROR, AUTH_FAILED, SERVER_ERROR, JSON_ERROR, NOT_FOUND };
+
+  /**
+   * Authenticate with the sync server (validate credentials).
+   * @return OK on success, error code on failure
+   */
+  static Error authenticate();
+
+  /**
+   * Get reading progress for a document.
+   * @param documentHash The document hash (from KOReaderDocumentId)
+   * @param outProgress Output: the progress data
+   * @return OK on success, NOT_FOUND if no progress exists, error code on failure
+   */
+  static Error getProgress(const std::string& documentHash, KOReaderProgress& outProgress);
+
+  /**
+   * Update reading progress for a document.
+   * @param progress The progress data to upload
+   * @return OK on success, error code on failure
+   */
+  static Error updateProgress(const KOReaderProgress& progress);
+
+  /**
+   * Get human-readable error message.
+   */
+  static const char* errorString(Error error);
+};

lib/KOReaderSync/ProgressMapper.cpp

@@ -0,0 +1,112 @@
+#include "ProgressMapper.h"
+
+#include <HardwareSerial.h>
+
+#include <cmath>
+
+KOReaderPosition ProgressMapper::toKOReader(const std::shared_ptr<Epub>& epub, const CrossPointPosition& pos) {
+  KOReaderPosition result;
+
+  // Calculate page progress within current spine item
+  float intraSpineProgress = 0.0f;
+  if (pos.totalPages > 0) {
+    intraSpineProgress = static_cast<float>(pos.pageNumber) / static_cast<float>(pos.totalPages);
+  }
+
+  // Calculate overall book progress (0.0-1.0)
+  result.percentage = epub->calculateProgress(pos.spineIndex, intraSpineProgress);
+
+  // Generate XPath with estimated paragraph position based on page
+  result.xpath = generateXPath(pos.spineIndex, pos.pageNumber, pos.totalPages);
+
+  // Get chapter info for logging
+  const int tocIndex = epub->getTocIndexForSpineIndex(pos.spineIndex);
+  const std::string chapterName = (tocIndex >= 0) ? epub->getTocItem(tocIndex).title : "unknown";
+
+  Serial.printf("[%lu] [ProgressMapper] CrossPoint -> KOReader: chapter='%s', page=%d/%d -> %.2f%% at %s\n", millis(),
+                chapterName.c_str(), pos.pageNumber, pos.totalPages, result.percentage * 100, result.xpath.c_str());
+
+  return result;
+}
+
+CrossPointPosition ProgressMapper::toCrossPoint(const std::shared_ptr<Epub>& epub, const KOReaderPosition& koPos,
+                                                int totalPagesInSpine) {
+  CrossPointPosition result;
+  result.spineIndex = 0;
+  result.pageNumber = 0;
+  result.totalPages = totalPagesInSpine;
+
+  const size_t bookSize = epub->getBookSize();
+  if (bookSize == 0) {
+    return result;
+  }
+
+  // First, try to get spine index from XPath (DocFragment)
+  int xpathSpineIndex = parseDocFragmentIndex(koPos.xpath);
+  if (xpathSpineIndex >= 0 && xpathSpineIndex < epub->getSpineItemsCount()) {
+    result.spineIndex = xpathSpineIndex;
+    // When we have XPath, go to page 0 of the spine - byte-based page calculation is unreliable
+    result.pageNumber = 0;
+  } else {
+    // Fall back to percentage-based lookup for both spine and page
+    const size_t targetBytes = static_cast<size_t>(bookSize * koPos.percentage);
+
+    // Find the spine item that contains this byte position
+    for (int i = 0; i < epub->getSpineItemsCount(); i++) {
+      const size_t cumulativeSize = epub->getCumulativeSpineItemSize(i);
+      if (cumulativeSize >= targetBytes) {
+        result.spineIndex = i;
+        break;
+      }
+    }
+
+    // Estimate page number within the spine item using percentage (only when no XPath)
+    if (totalPagesInSpine > 0 && result.spineIndex < epub->getSpineItemsCount()) {
+      const size_t prevCumSize = (result.spineIndex > 0) ? epub->getCumulativeSpineItemSize(result.spineIndex - 1) : 0;
+      const size_t currentCumSize = epub->getCumulativeSpineItemSize(result.spineIndex);
+      const size_t spineSize = currentCumSize - prevCumSize;
+
+      if (spineSize > 0) {
+        const size_t bytesIntoSpine = (targetBytes > prevCumSize) ? (targetBytes - prevCumSize) : 0;
+        const float intraSpineProgress = static_cast<float>(bytesIntoSpine) / static_cast<float>(spineSize);
+        const float clampedProgress = std::max(0.0f, std::min(1.0f, intraSpineProgress));
+        result.pageNumber = static_cast<int>(clampedProgress * totalPagesInSpine);
+        result.pageNumber = std::max(0, std::min(result.pageNumber, totalPagesInSpine - 1));
+      }
+    }
+  }
+
+  Serial.printf("[%lu] [ProgressMapper] KOReader -> CrossPoint: %.2f%% at %s -> spine=%d, page=%d\n", millis(),
+                koPos.percentage * 100, koPos.xpath.c_str(), result.spineIndex, result.pageNumber);
+
+  return result;
+}
+
+std::string ProgressMapper::generateXPath(int spineIndex, int pageNumber, int totalPages) {
+  // KOReader uses 1-based DocFragment indices
+  // Use a simple xpath pointing to the DocFragment - KOReader will use the percentage for fine positioning
+  // Avoid specifying paragraph numbers as they may not exist in the target document
+  return "/body/DocFragment[" + std::to_string(spineIndex + 1) + "]/body";
+}
+
+int ProgressMapper::parseDocFragmentIndex(const std::string& xpath) {
+  // Look for DocFragment[N] pattern
+  const size_t start = xpath.find("DocFragment[");
+  if (start == std::string::npos) {
+    return -1;
+  }
+
+  const size_t numStart = start + 12;  // Length of "DocFragment["
+  const size_t numEnd = xpath.find(']', numStart);
+  if (numEnd == std::string::npos) {
+    return -1;
+  }
+
+  try {
+    const int docFragmentIndex = std::stoi(xpath.substr(numStart, numEnd - numStart));
+    // KOReader uses 1-based indices, we use 0-based
+    return docFragmentIndex - 1;
+  } catch (...) {
+    return -1;
+  }
+}

lib/KOReaderSync/ProgressMapper.h

@@ -0,0 +1,72 @@
+#pragma once
+#include <Epub.h>
+
+#include <memory>
+#include <string>
+
+/**
+ * CrossPoint position representation.
+ */
+struct CrossPointPosition {
+  int spineIndex;  // Current spine item (chapter) index
+  int pageNumber;  // Current page within the spine item
+  int totalPages;  // Total pages in the current spine item
+};
+
+/**
+ * KOReader position representation.
+ */
+struct KOReaderPosition {
+  std::string xpath;  // XPath-like progress string
+  float percentage;   // Progress percentage (0.0 to 1.0)
+};
+
+/**
+ * Maps between CrossPoint and KOReader position formats.
+ *
+ * CrossPoint tracks position as (spineIndex, pageNumber).
+ * KOReader uses XPath-like strings + percentage.
+ *
+ * Since CrossPoint discards HTML structure during parsing, we generate
+ * synthetic XPath strings based on spine index, using percentage as the
+ * primary sync mechanism.
+ */
+class ProgressMapper {
+ public:
+  /**
+   * Convert CrossPoint position to KOReader format.
+   *
+   * @param epub The EPUB book
+   * @param pos CrossPoint position
+   * @return KOReader position
+   */
+  static KOReaderPosition toKOReader(const std::shared_ptr<Epub>& epub, const CrossPointPosition& pos);
+
+  /**
+   * Convert KOReader position to CrossPoint format.
+   *
+   * Note: The returned pageNumber may be approximate since different
+   * rendering settings produce different page counts.
+   *
+   * @param epub The EPUB book
+   * @param koPos KOReader position
+   * @param totalPagesInSpine Total pages in the target spine item (for page estimation)
+   * @return CrossPoint position
+   */
+  static CrossPointPosition toCrossPoint(const std::shared_ptr<Epub>& epub, const KOReaderPosition& koPos,
+                                         int totalPagesInSpine = 0);
+
+ private:
+  /**
+   * Generate XPath for KOReader compatibility.
+   * Format: /body/DocFragment[spineIndex+1]/body/p[estimatedParagraph]
+   * Paragraph is estimated based on page position within the chapter.
+   */
+  static std::string generateXPath(int spineIndex, int pageNumber, int totalPages);
+
+  /**
+   * Parse DocFragment index from XPath string.
+   * Returns -1 if not found.
+   */
+  static int parseDocFragmentIndex(const std::string& xpath);
+};

src/activities/reader/EpubReaderActivity.cpp

@@ -118,9 +118,11 @@ void EpubReaderActivity::loop() {
   if (mappedInput.wasReleased(MappedInputManager::Button::Confirm)) {
     // Don't start activity transition while rendering
     xSemaphoreTake(renderingMutex, portMAX_DELAY);
+    const int currentPage = section ? section->currentPage : 0;
+    const int totalPages = section ? section->pageCount : 0;
     exitActivity();
     enterNewActivity(new EpubReaderChapterSelectionActivity(
-        this->renderer, this->mappedInput, epub, currentSpineIndex,
+        this->renderer, this->mappedInput, epub, epub->getPath(), currentSpineIndex, currentPage, totalPages,
         [this] {
           exitActivity();
           updateRequired = true;
@@ -133,6 +135,16 @@ void EpubReaderActivity::loop() {
           }
           exitActivity();
           updateRequired = true;
+        },
+        [this](const int newSpineIndex, const int newPage) {
+          // Handle sync position
+          if (currentSpineIndex != newSpineIndex || (section && section->currentPage != newPage)) {
+            currentSpineIndex = newSpineIndex;
+            nextPageNumber = newPage;
+            section.reset();
+          }
+          exitActivity();
+          updateRequired = true;
         }));
     xSemaphoreGive(renderingMutex);
   }
@@ -430,11 +442,13 @@ void EpubReaderActivity::renderStatusBar(const int orientedMarginRight, const in
   if (showProgress) {
     // Calculate progress in book
     const float sectionChapterProg = static_cast<float>(section->currentPage) / section->pageCount;
-    const uint8_t bookProgress = epub->calculateProgress(currentSpineIndex, sectionChapterProg);
+    const float bookProgress = epub->calculateProgress(currentSpineIndex, sectionChapterProg) * 100;
 
     // Right aligned text for progress counter
-    const std::string progress = std::to_string(section->currentPage + 1) + "/" + std::to_string(section->pageCount) +
+    char progressStr[32];
-                                 "  " + std::to_string(bookProgress) + "%";
+    snprintf(progressStr, sizeof(progressStr), "%d/%d  %.1f%%", section->currentPage + 1, section->pageCount,
+             bookProgress);
+    const std::string progress = progressStr;
     progressTextWidth = renderer.getTextWidth(SMALL_FONT_ID, progress.c_str());
     renderer.drawText(SMALL_FONT_ID, renderer.getScreenWidth() - orientedMarginRight - progressTextWidth, textY,
                       progress.c_str());

src/activities/reader/EpubReaderChapterSelectionActivity.cpp

@@ -2,6 +2,8 @@
 
 #include <GfxRenderer.h>
 
+#include "KOReaderCredentialStore.h"
+#include "KOReaderSyncActivity.h"
 #include "MappedInputManager.h"
 #include "fontIds.h"
 
@@ -10,6 +12,26 @@ namespace {
 constexpr int SKIP_PAGE_MS = 700;
 }  // namespace
 
+bool EpubReaderChapterSelectionActivity::hasSyncOption() const { return KOREADER_STORE.hasCredentials(); }
+
+int EpubReaderChapterSelectionActivity::getTotalItems() const {
+  // Add 2 for sync options (top and bottom) if credentials are configured
+  const int syncCount = hasSyncOption() ? 2 : 0;
+  return epub->getTocItemsCount() + syncCount;
+}
+
+bool EpubReaderChapterSelectionActivity::isSyncItem(int index) const {
+  if (!hasSyncOption()) return false;
+  // First item and last item are sync options
+  return index == 0 || index == getTotalItems() - 1;
+}
+
+int EpubReaderChapterSelectionActivity::tocIndexFromItemIndex(int itemIndex) const {
+  // Account for the sync option at the top
+  const int offset = hasSyncOption() ? 1 : 0;
+  return itemIndex - offset;
+}
+
 int EpubReaderChapterSelectionActivity::getPageItems() const {
   // Layout constants used in renderScreen
   constexpr int startY = 60;
@@ -34,17 +56,21 @@ void EpubReaderChapterSelectionActivity::taskTrampoline(void* param) {
 }
 
 void EpubReaderChapterSelectionActivity::onEnter() {
-  Activity::onEnter();
+  ActivityWithSubactivity::onEnter();
 
   if (!epub) {
     return;
   }
 
   renderingMutex = xSemaphoreCreateMutex();
+
+  // Account for sync option offset when finding current TOC index
+  const int syncOffset = hasSyncOption() ? 1 : 0;
   selectorIndex = epub->getTocIndexForSpineIndex(currentSpineIndex);
   if (selectorIndex == -1) {
     selectorIndex = 0;
   }
+  selectorIndex += syncOffset;  // Offset for top sync option
 
   // Trigger first update
   updateRequired = true;
@@ -57,7 +83,7 @@ void EpubReaderChapterSelectionActivity::onEnter() {
 }
 
 void EpubReaderChapterSelectionActivity::onExit() {
-  Activity::onExit();
+  ActivityWithSubactivity::onExit();
 
   // Wait until not rendering to delete task to avoid killing mid-instruction to EPD
   xSemaphoreTake(renderingMutex, portMAX_DELAY);
@@ -69,7 +95,30 @@ void EpubReaderChapterSelectionActivity::onExit() {
   renderingMutex = nullptr;
 }
 
+void EpubReaderChapterSelectionActivity::launchSyncActivity() {
+  xSemaphoreTake(renderingMutex, portMAX_DELAY);
+  exitActivity();
+  enterNewActivity(new KOReaderSyncActivity(
+      renderer, mappedInput, epub, epubPath, currentSpineIndex, currentPage, totalPagesInSpine,
+      [this]() {
+        // On cancel
+        exitActivity();
+        updateRequired = true;
+      },
+      [this](int newSpineIndex, int newPage) {
+        // On sync complete
+        exitActivity();
+        onSyncPosition(newSpineIndex, newPage);
+      }));
+  xSemaphoreGive(renderingMutex);
+}
+
 void EpubReaderChapterSelectionActivity::loop() {
+  if (subActivity) {
+    subActivity->loop();
+    return;
+  }
+
   const bool prevReleased = mappedInput.wasReleased(MappedInputManager::Button::Up) ||
                             mappedInput.wasReleased(MappedInputManager::Button::Left);
   const bool nextReleased = mappedInput.wasReleased(MappedInputManager::Button::Down) ||
@@ -77,9 +126,18 @@ void EpubReaderChapterSelectionActivity::loop() {
 
   const bool skipPage = mappedInput.getHeldTime() > SKIP_PAGE_MS;
   const int pageItems = getPageItems();
+  const int totalItems = getTotalItems();
 
   if (mappedInput.wasReleased(MappedInputManager::Button::Confirm)) {
-    const auto newSpineIndex = epub->getSpineIndexForTocIndex(selectorIndex);
+    // Check if sync option is selected (first or last item)
+    if (isSyncItem(selectorIndex)) {
+      launchSyncActivity();
+      return;
+    }
+
+    // Get TOC index (account for top sync offset)
+    const int tocIndex = tocIndexFromItemIndex(selectorIndex);
+    const auto newSpineIndex = epub->getSpineIndexForTocIndex(tocIndex);
     if (newSpineIndex == -1) {
       onGoBack();
     } else {
@@ -89,17 +147,16 @@ void EpubReaderChapterSelectionActivity::loop() {
     onGoBack();
   } else if (prevReleased) {
     if (skipPage) {
-      selectorIndex =
+      selectorIndex = ((selectorIndex / pageItems - 1) * pageItems + totalItems) % totalItems;
-          ((selectorIndex / pageItems - 1) * pageItems + epub->getTocItemsCount()) % epub->getTocItemsCount();
     } else {
-      selectorIndex = (selectorIndex + epub->getTocItemsCount() - 1) % epub->getTocItemsCount();
+      selectorIndex = (selectorIndex + totalItems - 1) % totalItems;
     }
     updateRequired = true;
   } else if (nextReleased) {
     if (skipPage) {
-      selectorIndex = ((selectorIndex / pageItems + 1) * pageItems) % epub->getTocItemsCount();
+      selectorIndex = ((selectorIndex / pageItems + 1) * pageItems) % totalItems;
     } else {
-      selectorIndex = (selectorIndex + 1) % epub->getTocItemsCount();
+      selectorIndex = (selectorIndex + 1) % totalItems;
     }
     updateRequired = true;
   }
@@ -107,7 +164,7 @@ void EpubReaderChapterSelectionActivity::loop() {
 
 void EpubReaderChapterSelectionActivity::displayTaskLoop() {
   while (true) {
-    if (updateRequired) {
+    if (updateRequired && !subActivity) {
       updateRequired = false;
       xSemaphoreTake(renderingMutex, portMAX_DELAY);
       renderScreen();
@@ -122,6 +179,7 @@ void EpubReaderChapterSelectionActivity::renderScreen() {
 
   const auto pageWidth = renderer.getScreenWidth();
   const int pageItems = getPageItems();
+  const int totalItems = getTotalItems();
 
   const std::string title =
       renderer.truncatedText(UI_12_FONT_ID, epub->getTitle().c_str(), pageWidth - 40, EpdFontFamily::BOLD);
@@ -129,11 +187,20 @@ void EpubReaderChapterSelectionActivity::renderScreen() {
 
   const auto pageStartIndex = selectorIndex / pageItems * pageItems;
   renderer.fillRect(0, 60 + (selectorIndex % pageItems) * 30 - 2, pageWidth - 1, 30);
-  for (int tocIndex = pageStartIndex; tocIndex < epub->getTocItemsCount() && tocIndex < pageStartIndex + pageItems;
+
-       tocIndex++) {
+  for (int itemIndex = pageStartIndex; itemIndex < totalItems && itemIndex < pageStartIndex + pageItems; itemIndex++) {
-    auto item = epub->getTocItem(tocIndex);
+    const int displayY = 60 + (itemIndex % pageItems) * 30;
-    renderer.drawText(UI_10_FONT_ID, 20 + (item.level - 1) * 15, 60 + (tocIndex % pageItems) * 30, item.title.c_str(),
+    const bool isSelected = (itemIndex == selectorIndex);
-                      tocIndex != selectorIndex);
+
+    if (isSyncItem(itemIndex)) {
+      // Draw sync option (at top or bottom)
+      renderer.drawText(UI_10_FONT_ID, 20, displayY, ">> Sync Progress", !isSelected);
+    } else {
+      // Draw TOC item (account for top sync offset)
+      const int tocIndex = tocIndexFromItemIndex(itemIndex);
+      auto item = epub->getTocItem(tocIndex);
+      renderer.drawText(UI_10_FONT_ID, 20 + (item.level - 1) * 15, displayY, item.title.c_str(), !isSelected);
+    }
   }
 
   const auto labels = mappedInput.mapLabels("« Back", "Select", "Up", "Down");

src/activities/reader/EpubReaderChapterSelectionActivity.h

@@ -6,36 +6,59 @@
 
 #include <memory>
 
-#include "../Activity.h"
+#include "../ActivityWithSubactivity.h"
 
-class EpubReaderChapterSelectionActivity final : public Activity {
+class EpubReaderChapterSelectionActivity final : public ActivityWithSubactivity {
   std::shared_ptr<Epub> epub;
+  std::string epubPath;
   TaskHandle_t displayTaskHandle = nullptr;
   SemaphoreHandle_t renderingMutex = nullptr;
   int currentSpineIndex = 0;
+  int currentPage = 0;
+  int totalPagesInSpine = 0;
   int selectorIndex = 0;
   bool updateRequired = false;
   const std::function<void()> onGoBack;
   const std::function<void(int newSpineIndex)> onSelectSpineIndex;
+  const std::function<void(int newSpineIndex, int newPage)> onSyncPosition;
 
   // Number of items that fit on a page, derived from logical screen height.
   // This adapts automatically when switching between portrait and landscape.
   int getPageItems() const;
 
+  // Total items including sync options (top and bottom)
+  int getTotalItems() const;
+
+  // Check if sync option is available (credentials configured)
+  bool hasSyncOption() const;
+
+  // Check if given item index is a sync option (first or last)
+  bool isSyncItem(int index) const;
+
+  // Convert item index to TOC index (accounting for top sync option offset)
+  int tocIndexFromItemIndex(int itemIndex) const;
+
   static void taskTrampoline(void* param);
   [[noreturn]] void displayTaskLoop();
   void renderScreen();
+  void launchSyncActivity();
 
  public:
   explicit EpubReaderChapterSelectionActivity(GfxRenderer& renderer, MappedInputManager& mappedInput,
-                                              const std::shared_ptr<Epub>& epub, const int currentSpineIndex,
+                                              const std::shared_ptr<Epub>& epub, const std::string& epubPath,
-                                              const std::function<void()>& onGoBack,
+                                              const int currentSpineIndex, const int currentPage,
-                                              const std::function<void(int newSpineIndex)>& onSelectSpineIndex)
+                                              const int totalPagesInSpine, const std::function<void()>& onGoBack,
-      : Activity("EpubReaderChapterSelection", renderer, mappedInput),
+                                              const std::function<void(int newSpineIndex)>& onSelectSpineIndex,
+                                              const std::function<void(int newSpineIndex, int newPage)>& onSyncPosition)
+      : ActivityWithSubactivity("EpubReaderChapterSelection", renderer, mappedInput),
         epub(epub),
+        epubPath(epubPath),
         currentSpineIndex(currentSpineIndex),
+        currentPage(currentPage),
+        totalPagesInSpine(totalPagesInSpine),
         onGoBack(onGoBack),
-        onSelectSpineIndex(onSelectSpineIndex) {}
+        onSelectSpineIndex(onSelectSpineIndex),
+        onSyncPosition(onSyncPosition) {}
   void onEnter() override;
   void onExit() override;
   void loop() override;

src/activities/reader/KOReaderSyncActivity.cpp

@@ -0,0 +1,439 @@
+#include "KOReaderSyncActivity.h"
+
+#include <GfxRenderer.h>
+#include <WiFi.h>
+#include <esp_sntp.h>
+
+#include "KOReaderCredentialStore.h"
+#include "KOReaderDocumentId.h"
+#include "MappedInputManager.h"
+#include "activities/network/WifiSelectionActivity.h"
+#include "fontIds.h"
+
+namespace {
+void syncTimeWithNTP() {
+  // Stop SNTP if already running (can't reconfigure while running)
+  if (esp_sntp_enabled()) {
+    esp_sntp_stop();
+  }
+
+  // Configure SNTP
+  esp_sntp_setoperatingmode(ESP_SNTP_OPMODE_POLL);
+  esp_sntp_setservername(0, "pool.ntp.org");
+  esp_sntp_init();
+
+  // Wait for time to sync (with timeout)
+  int retry = 0;
+  const int maxRetries = 50;  // 5 seconds max
+  while (sntp_get_sync_status() != SNTP_SYNC_STATUS_COMPLETED && retry < maxRetries) {
+    vTaskDelay(100 / portTICK_PERIOD_MS);
+    retry++;
+  }
+
+  if (retry < maxRetries) {
+    Serial.printf("[%lu] [KOSync] NTP time synced\n", millis());
+  } else {
+    Serial.printf("[%lu] [KOSync] NTP sync timeout, using fallback\n", millis());
+  }
+}
+}  // namespace
+
+void KOReaderSyncActivity::taskTrampoline(void* param) {
+  auto* self = static_cast<KOReaderSyncActivity*>(param);
+  self->displayTaskLoop();
+}
+
+void KOReaderSyncActivity::onWifiSelectionComplete(const bool success) {
+  exitActivity();
+
+  if (!success) {
+    Serial.printf("[%lu] [KOSync] WiFi connection failed, exiting\n", millis());
+    onCancel();
+    return;
+  }
+
+  Serial.printf("[%lu] [KOSync] WiFi connected, starting sync\n", millis());
+
+  xSemaphoreTake(renderingMutex, portMAX_DELAY);
+  state = SYNCING;
+  statusMessage = "Syncing time...";
+  xSemaphoreGive(renderingMutex);
+  updateRequired = true;
+
+  // Sync time with NTP before making API requests
+  syncTimeWithNTP();
+
+  xSemaphoreTake(renderingMutex, portMAX_DELAY);
+  statusMessage = "Calculating document hash...";
+  xSemaphoreGive(renderingMutex);
+  updateRequired = true;
+
+  performSync();
+}
+
+void KOReaderSyncActivity::performSync() {
+  // Calculate document hash based on user's preferred method
+  if (KOREADER_STORE.getMatchMethod() == DocumentMatchMethod::FILENAME) {
+    documentHash = KOReaderDocumentId::calculateFromFilename(epubPath);
+  } else {
+    documentHash = KOReaderDocumentId::calculate(epubPath);
+  }
+  if (documentHash.empty()) {
+    xSemaphoreTake(renderingMutex, portMAX_DELAY);
+    state = SYNC_FAILED;
+    statusMessage = "Failed to calculate document hash";
+    xSemaphoreGive(renderingMutex);
+    updateRequired = true;
+    return;
+  }
+
+  Serial.printf("[%lu] [KOSync] Document hash: %s\n", millis(), documentHash.c_str());
+
+  xSemaphoreTake(renderingMutex, portMAX_DELAY);
+  statusMessage = "Fetching remote progress...";
+  xSemaphoreGive(renderingMutex);
+  updateRequired = true;
+  vTaskDelay(10 / portTICK_PERIOD_MS);
+
+  // Fetch remote progress
+  const auto result = KOReaderSyncClient::getProgress(documentHash, remoteProgress);
+
+  if (result == KOReaderSyncClient::NOT_FOUND) {
+    // No remote progress - offer to upload
+    xSemaphoreTake(renderingMutex, portMAX_DELAY);
+    state = NO_REMOTE_PROGRESS;
+    hasRemoteProgress = false;
+    xSemaphoreGive(renderingMutex);
+    updateRequired = true;
+    return;
+  }
+
+  if (result != KOReaderSyncClient::OK) {
+    xSemaphoreTake(renderingMutex, portMAX_DELAY);
+    state = SYNC_FAILED;
+    statusMessage = KOReaderSyncClient::errorString(result);
+    xSemaphoreGive(renderingMutex);
+    updateRequired = true;
+    return;
+  }
+
+  // Convert remote progress to CrossPoint position
+  hasRemoteProgress = true;
+  KOReaderPosition koPos = {remoteProgress.progress, remoteProgress.percentage};
+  remotePosition = ProgressMapper::toCrossPoint(epub, koPos, totalPagesInSpine);
+
+  // Calculate local progress in KOReader format (for display)
+  CrossPointPosition localPos = {currentSpineIndex, currentPage, totalPagesInSpine};
+  localProgress = ProgressMapper::toKOReader(epub, localPos);
+
+  xSemaphoreTake(renderingMutex, portMAX_DELAY);
+  state = SHOWING_RESULT;
+  selectedOption = 0;  // Default to "Apply"
+  xSemaphoreGive(renderingMutex);
+  updateRequired = true;
+}
+
+void KOReaderSyncActivity::performUpload() {
+  xSemaphoreTake(renderingMutex, portMAX_DELAY);
+  state = UPLOADING;
+  statusMessage = "Uploading progress...";
+  xSemaphoreGive(renderingMutex);
+  updateRequired = true;
+  vTaskDelay(10 / portTICK_PERIOD_MS);
+
+  // Convert current position to KOReader format
+  CrossPointPosition localPos = {currentSpineIndex, currentPage, totalPagesInSpine};
+  KOReaderPosition koPos = ProgressMapper::toKOReader(epub, localPos);
+
+  KOReaderProgress progress;
+  progress.document = documentHash;
+  progress.progress = koPos.xpath;
+  progress.percentage = koPos.percentage;
+
+  const auto result = KOReaderSyncClient::updateProgress(progress);
+
+  if (result != KOReaderSyncClient::OK) {
+    xSemaphoreTake(renderingMutex, portMAX_DELAY);
+    state = SYNC_FAILED;
+    statusMessage = KOReaderSyncClient::errorString(result);
+    xSemaphoreGive(renderingMutex);
+    updateRequired = true;
+    return;
+  }
+
+  xSemaphoreTake(renderingMutex, portMAX_DELAY);
+  state = UPLOAD_COMPLETE;
+  xSemaphoreGive(renderingMutex);
+  updateRequired = true;
+}
+
+void KOReaderSyncActivity::onEnter() {
+  ActivityWithSubactivity::onEnter();
+
+  renderingMutex = xSemaphoreCreateMutex();
+
+  xTaskCreate(&KOReaderSyncActivity::taskTrampoline, "KOSyncTask",
+              4096,               // Stack size (larger for network operations)
+              this,               // Parameters
+              1,                  // Priority
+              &displayTaskHandle  // Task handle
+  );
+
+  // Check for credentials first
+  if (!KOREADER_STORE.hasCredentials()) {
+    state = NO_CREDENTIALS;
+    updateRequired = true;
+    return;
+  }
+
+  // Turn on WiFi
+  Serial.printf("[%lu] [KOSync] Turning on WiFi...\n", millis());
+  WiFi.mode(WIFI_STA);
+
+  // Check if already connected
+  if (WiFi.status() == WL_CONNECTED) {
+    Serial.printf("[%lu] [KOSync] Already connected to WiFi\n", millis());
+    state = SYNCING;
+    statusMessage = "Syncing time...";
+    updateRequired = true;
+
+    // Perform sync directly (will be handled in loop)
+    xTaskCreate(
+        [](void* param) {
+          auto* self = static_cast<KOReaderSyncActivity*>(param);
+          // Sync time first
+          syncTimeWithNTP();
+          xSemaphoreTake(self->renderingMutex, portMAX_DELAY);
+          self->statusMessage = "Calculating document hash...";
+          xSemaphoreGive(self->renderingMutex);
+          self->updateRequired = true;
+          self->performSync();
+          vTaskDelete(nullptr);
+        },
+        "SyncTask", 4096, this, 1, nullptr);
+    return;
+  }
+
+  // Launch WiFi selection subactivity
+  Serial.printf("[%lu] [KOSync] Launching WifiSelectionActivity...\n", millis());
+  enterNewActivity(new WifiSelectionActivity(renderer, mappedInput,
+                                             [this](const bool connected) { onWifiSelectionComplete(connected); }));
+}
+
+void KOReaderSyncActivity::onExit() {
+  ActivityWithSubactivity::onExit();
+
+  // Turn off wifi
+  WiFi.disconnect(false);
+  delay(100);
+  WiFi.mode(WIFI_OFF);
+  delay(100);
+
+  // Wait until not rendering to delete task
+  xSemaphoreTake(renderingMutex, portMAX_DELAY);
+  if (displayTaskHandle) {
+    vTaskDelete(displayTaskHandle);
+    displayTaskHandle = nullptr;
+  }
+  vSemaphoreDelete(renderingMutex);
+  renderingMutex = nullptr;
+}
+
+void KOReaderSyncActivity::displayTaskLoop() {
+  while (true) {
+    if (updateRequired) {
+      updateRequired = false;
+      xSemaphoreTake(renderingMutex, portMAX_DELAY);
+      render();
+      xSemaphoreGive(renderingMutex);
+    }
+    vTaskDelay(10 / portTICK_PERIOD_MS);
+  }
+}
+
+void KOReaderSyncActivity::render() {
+  if (subActivity) {
+    return;
+  }
+
+  const auto pageWidth = renderer.getScreenWidth();
+
+  renderer.clearScreen();
+  renderer.drawCenteredText(UI_12_FONT_ID, 15, "KOReader Sync", true, EpdFontFamily::BOLD);
+
+  if (state == NO_CREDENTIALS) {
+    renderer.drawCenteredText(UI_10_FONT_ID, 280, "No credentials configured", true, EpdFontFamily::BOLD);
+    renderer.drawCenteredText(UI_10_FONT_ID, 320, "Set up KOReader account in Settings");
+
+    const auto labels = mappedInput.mapLabels("Back", "", "", "");
+    renderer.drawButtonHints(UI_10_FONT_ID, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
+    renderer.displayBuffer();
+    return;
+  }
+
+  if (state == SYNCING || state == UPLOADING) {
+    renderer.drawCenteredText(UI_10_FONT_ID, 300, statusMessage.c_str(), true, EpdFontFamily::BOLD);
+    renderer.displayBuffer();
+    return;
+  }
+
+  if (state == SHOWING_RESULT) {
+    // Show comparison
+    renderer.drawCenteredText(UI_10_FONT_ID, 120, "Progress found!", true, EpdFontFamily::BOLD);
+
+    // Get chapter names from TOC
+    const int remoteTocIndex = epub->getTocIndexForSpineIndex(remotePosition.spineIndex);
+    const int localTocIndex = epub->getTocIndexForSpineIndex(currentSpineIndex);
+    const std::string remoteChapter = (remoteTocIndex >= 0)
+                                          ? epub->getTocItem(remoteTocIndex).title
+                                          : ("Section " + std::to_string(remotePosition.spineIndex + 1));
+    const std::string localChapter = (localTocIndex >= 0) ? epub->getTocItem(localTocIndex).title
+                                                          : ("Section " + std::to_string(currentSpineIndex + 1));
+
+    // Remote progress - chapter and page
+    renderer.drawText(UI_10_FONT_ID, 20, 160, "Remote:", true);
+    char remoteChapterStr[128];
+    snprintf(remoteChapterStr, sizeof(remoteChapterStr), "  %s", remoteChapter.c_str());
+    renderer.drawText(UI_10_FONT_ID, 20, 185, remoteChapterStr);
+    char remotePageStr[64];
+    snprintf(remotePageStr, sizeof(remotePageStr), "  Page %d, %.2f%% overall", remotePosition.pageNumber + 1,
+             remoteProgress.percentage * 100);
+    renderer.drawText(UI_10_FONT_ID, 20, 210, remotePageStr);
+
+    if (!remoteProgress.device.empty()) {
+      char deviceStr[64];
+      snprintf(deviceStr, sizeof(deviceStr), "  From: %s", remoteProgress.device.c_str());
+      renderer.drawText(UI_10_FONT_ID, 20, 235, deviceStr);
+    }
+
+    // Local progress - chapter and page
+    renderer.drawText(UI_10_FONT_ID, 20, 270, "Local:", true);
+    char localChapterStr[128];
+    snprintf(localChapterStr, sizeof(localChapterStr), "  %s", localChapter.c_str());
+    renderer.drawText(UI_10_FONT_ID, 20, 295, localChapterStr);
+    char localPageStr[64];
+    snprintf(localPageStr, sizeof(localPageStr), "  Page %d/%d, %.2f%% overall", currentPage + 1, totalPagesInSpine,
+             localProgress.percentage * 100);
+    renderer.drawText(UI_10_FONT_ID, 20, 320, localPageStr);
+
+    // Options
+    const int optionY = 350;
+    const int optionHeight = 30;
+
+    // Apply option
+    if (selectedOption == 0) {
+      renderer.fillRect(0, optionY - 2, pageWidth - 1, optionHeight);
+    }
+    renderer.drawText(UI_10_FONT_ID, 20, optionY, "Apply remote progress", selectedOption != 0);
+
+    // Upload option
+    if (selectedOption == 1) {
+      renderer.fillRect(0, optionY + optionHeight - 2, pageWidth - 1, optionHeight);
+    }
+    renderer.drawText(UI_10_FONT_ID, 20, optionY + optionHeight, "Upload local progress", selectedOption != 1);
+
+    // Cancel option
+    if (selectedOption == 2) {
+      renderer.fillRect(0, optionY + optionHeight * 2 - 2, pageWidth - 1, optionHeight);
+    }
+    renderer.drawText(UI_10_FONT_ID, 20, optionY + optionHeight * 2, "Cancel", selectedOption != 2);
+
+    const auto labels = mappedInput.mapLabels("", "Select", "", "");
+    renderer.drawButtonHints(UI_10_FONT_ID, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
+    renderer.displayBuffer();
+    return;
+  }
+
+  if (state == NO_REMOTE_PROGRESS) {
+    renderer.drawCenteredText(UI_10_FONT_ID, 280, "No remote progress found", true, EpdFontFamily::BOLD);
+    renderer.drawCenteredText(UI_10_FONT_ID, 320, "Upload current position?");
+
+    const auto labels = mappedInput.mapLabels("Cancel", "Upload", "", "");
+    renderer.drawButtonHints(UI_10_FONT_ID, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
+    renderer.displayBuffer();
+    return;
+  }
+
+  if (state == UPLOAD_COMPLETE) {
+    renderer.drawCenteredText(UI_10_FONT_ID, 300, "Progress uploaded!", true, EpdFontFamily::BOLD);
+
+    const auto labels = mappedInput.mapLabels("Back", "", "", "");
+    renderer.drawButtonHints(UI_10_FONT_ID, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
+    renderer.displayBuffer();
+    return;
+  }
+
+  if (state == SYNC_FAILED) {
+    renderer.drawCenteredText(UI_10_FONT_ID, 280, "Sync failed", true, EpdFontFamily::BOLD);
+    renderer.drawCenteredText(UI_10_FONT_ID, 320, statusMessage.c_str());
+
+    const auto labels = mappedInput.mapLabels("Back", "", "", "");
+    renderer.drawButtonHints(UI_10_FONT_ID, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
+    renderer.displayBuffer();
+    return;
+  }
+}
+
+void KOReaderSyncActivity::loop() {
+  if (subActivity) {
+    subActivity->loop();
+    return;
+  }
+
+  if (state == NO_CREDENTIALS || state == SYNC_FAILED || state == UPLOAD_COMPLETE) {
+    if (mappedInput.wasPressed(MappedInputManager::Button::Back)) {
+      onCancel();
+    }
+    return;
+  }
+
+  if (state == SHOWING_RESULT) {
+    // Navigate options
+    if (mappedInput.wasPressed(MappedInputManager::Button::Up) ||
+        mappedInput.wasPressed(MappedInputManager::Button::Left)) {
+      selectedOption = (selectedOption + 2) % 3;  // Wrap around
+      updateRequired = true;
+    } else if (mappedInput.wasPressed(MappedInputManager::Button::Down) ||
+               mappedInput.wasPressed(MappedInputManager::Button::Right)) {
+      selectedOption = (selectedOption + 1) % 3;
+      updateRequired = true;
+    }
+
+    if (mappedInput.wasPressed(MappedInputManager::Button::Confirm)) {
+      if (selectedOption == 0) {
+        // Apply remote progress
+        onSyncComplete(remotePosition.spineIndex, remotePosition.pageNumber);
+      } else if (selectedOption == 1) {
+        // Upload local progress
+        performUpload();
+      } else {
+        // Cancel
+        onCancel();
+      }
+    }
+
+    if (mappedInput.wasPressed(MappedInputManager::Button::Back)) {
+      onCancel();
+    }
+    return;
+  }
+
+  if (state == NO_REMOTE_PROGRESS) {
+    if (mappedInput.wasPressed(MappedInputManager::Button::Confirm)) {
+      // Calculate hash if not done yet
+      if (documentHash.empty()) {
+        if (KOREADER_STORE.getMatchMethod() == DocumentMatchMethod::FILENAME) {
+          documentHash = KOReaderDocumentId::calculateFromFilename(epubPath);
+        } else {
+          documentHash = KOReaderDocumentId::calculate(epubPath);
+        }
+      }
+      performUpload();
+    }
+
+    if (mappedInput.wasPressed(MappedInputManager::Button::Back)) {
+      onCancel();
+    }
+    return;
+  }
+}

src/activities/reader/KOReaderSyncActivity.h

@@ -0,0 +1,98 @@
+#pragma once
+#include <Epub.h>
+#include <freertos/FreeRTOS.h>
+#include <freertos/semphr.h>
+#include <freertos/task.h>
+
+#include <functional>
+#include <memory>
+
+#include "KOReaderSyncClient.h"
+#include "ProgressMapper.h"
+#include "activities/ActivityWithSubactivity.h"
+
+/**
+ * Activity for syncing reading progress with KOReader sync server.
+ *
+ * Flow:
+ * 1. Connect to WiFi (if not connected)
+ * 2. Calculate document hash
+ * 3. Fetch remote progress
+ * 4. Show comparison and options (Apply/Upload/Cancel)
+ * 5. Apply or upload progress
+ */
+class KOReaderSyncActivity final : public ActivityWithSubactivity {
+ public:
+  using OnCancelCallback = std::function<void()>;
+  using OnSyncCompleteCallback = std::function<void(int newSpineIndex, int newPageNumber)>;
+
+  explicit KOReaderSyncActivity(GfxRenderer& renderer, MappedInputManager& mappedInput,
+                                const std::shared_ptr<Epub>& epub, const std::string& epubPath, int currentSpineIndex,
+                                int currentPage, int totalPagesInSpine, OnCancelCallback onCancel,
+                                OnSyncCompleteCallback onSyncComplete)
+      : ActivityWithSubactivity("KOReaderSync", renderer, mappedInput),
+        epub(epub),
+        epubPath(epubPath),
+        currentSpineIndex(currentSpineIndex),
+        currentPage(currentPage),
+        totalPagesInSpine(totalPagesInSpine),
+        remoteProgress{},
+        remotePosition{},
+        localProgress{},
+        onCancel(std::move(onCancel)),
+        onSyncComplete(std::move(onSyncComplete)) {}
+
+  void onEnter() override;
+  void onExit() override;
+  void loop() override;
+  bool preventAutoSleep() override { return state == CONNECTING || state == SYNCING; }
+
+ private:
+  enum State {
+    WIFI_SELECTION,
+    CONNECTING,
+    SYNCING,
+    SHOWING_RESULT,
+    UPLOADING,
+    UPLOAD_COMPLETE,
+    NO_REMOTE_PROGRESS,
+    SYNC_FAILED,
+    NO_CREDENTIALS
+  };
+
+  std::shared_ptr<Epub> epub;
+  std::string epubPath;
+  int currentSpineIndex;
+  int currentPage;
+  int totalPagesInSpine;
+
+  TaskHandle_t displayTaskHandle = nullptr;
+  SemaphoreHandle_t renderingMutex = nullptr;
+  bool updateRequired = false;
+
+  State state = WIFI_SELECTION;
+  std::string statusMessage;
+  std::string documentHash;
+
+  // Remote progress data
+  bool hasRemoteProgress = false;
+  KOReaderProgress remoteProgress;
+  CrossPointPosition remotePosition;
+
+  // Local progress as KOReader format (for display)
+  KOReaderPosition localProgress;
+
+  // Selection in result screen (0=Apply, 1=Upload, 2=Cancel)
+  int selectedOption = 0;
+
+  OnCancelCallback onCancel;
+  OnSyncCompleteCallback onSyncComplete;
+
+  void onWifiSelectionComplete(bool success);
+  void performSync();
+  void performUpload();
+
+  static void taskTrampoline(void* param);
+  [[noreturn]] void displayTaskLoop();
+  void render();
+};

src/activities/settings/KOReaderAuthActivity.cpp

@@ -0,0 +1,167 @@
+#include "KOReaderAuthActivity.h"
+
+#include <GfxRenderer.h>
+#include <WiFi.h>
+
+#include "KOReaderCredentialStore.h"
+#include "KOReaderSyncClient.h"
+#include "MappedInputManager.h"
+#include "activities/network/WifiSelectionActivity.h"
+#include "fontIds.h"
+
+void KOReaderAuthActivity::taskTrampoline(void* param) {
+  auto* self = static_cast<KOReaderAuthActivity*>(param);
+  self->displayTaskLoop();
+}
+
+void KOReaderAuthActivity::onWifiSelectionComplete(const bool success) {
+  exitActivity();
+
+  if (!success) {
+    xSemaphoreTake(renderingMutex, portMAX_DELAY);
+    state = FAILED;
+    errorMessage = "WiFi connection failed";
+    xSemaphoreGive(renderingMutex);
+    updateRequired = true;
+    return;
+  }
+
+  xSemaphoreTake(renderingMutex, portMAX_DELAY);
+  state = AUTHENTICATING;
+  statusMessage = "Authenticating...";
+  xSemaphoreGive(renderingMutex);
+  updateRequired = true;
+
+  performAuthentication();
+}
+
+void KOReaderAuthActivity::performAuthentication() {
+  const auto result = KOReaderSyncClient::authenticate();
+
+  xSemaphoreTake(renderingMutex, portMAX_DELAY);
+  if (result == KOReaderSyncClient::OK) {
+    state = SUCCESS;
+    statusMessage = "Successfully authenticated!";
+  } else {
+    state = FAILED;
+    errorMessage = KOReaderSyncClient::errorString(result);
+  }
+  xSemaphoreGive(renderingMutex);
+  updateRequired = true;
+}
+
+void KOReaderAuthActivity::onEnter() {
+  ActivityWithSubactivity::onEnter();
+
+  renderingMutex = xSemaphoreCreateMutex();
+
+  xTaskCreate(&KOReaderAuthActivity::taskTrampoline, "KOAuthTask",
+              4096,               // Stack size
+              this,               // Parameters
+              1,                  // Priority
+              &displayTaskHandle  // Task handle
+  );
+
+  // Turn on WiFi
+  WiFi.mode(WIFI_STA);
+
+  // Check if already connected
+  if (WiFi.status() == WL_CONNECTED) {
+    state = AUTHENTICATING;
+    statusMessage = "Authenticating...";
+    updateRequired = true;
+
+    // Perform authentication in a separate task
+    xTaskCreate(
+        [](void* param) {
+          auto* self = static_cast<KOReaderAuthActivity*>(param);
+          self->performAuthentication();
+          vTaskDelete(nullptr);
+        },
+        "AuthTask", 4096, this, 1, nullptr);
+    return;
+  }
+
+  // Launch WiFi selection
+  enterNewActivity(new WifiSelectionActivity(renderer, mappedInput,
+                                             [this](const bool connected) { onWifiSelectionComplete(connected); }));
+}
+
+void KOReaderAuthActivity::onExit() {
+  ActivityWithSubactivity::onExit();
+
+  // Turn off wifi
+  WiFi.disconnect(false);
+  delay(100);
+  WiFi.mode(WIFI_OFF);
+  delay(100);
+
+  xSemaphoreTake(renderingMutex, portMAX_DELAY);
+  if (displayTaskHandle) {
+    vTaskDelete(displayTaskHandle);
+    displayTaskHandle = nullptr;
+  }
+  vSemaphoreDelete(renderingMutex);
+  renderingMutex = nullptr;
+}
+
+void KOReaderAuthActivity::displayTaskLoop() {
+  while (true) {
+    if (updateRequired && !subActivity) {
+      updateRequired = false;
+      xSemaphoreTake(renderingMutex, portMAX_DELAY);
+      render();
+      xSemaphoreGive(renderingMutex);
+    }
+    vTaskDelay(10 / portTICK_PERIOD_MS);
+  }
+}
+
+void KOReaderAuthActivity::render() {
+  if (subActivity) {
+    return;
+  }
+
+  renderer.clearScreen();
+  renderer.drawCenteredText(UI_12_FONT_ID, 15, "KOReader Auth", true, EpdFontFamily::BOLD);
+
+  if (state == AUTHENTICATING) {
+    renderer.drawCenteredText(UI_10_FONT_ID, 300, statusMessage.c_str(), true, EpdFontFamily::BOLD);
+    renderer.displayBuffer();
+    return;
+  }
+
+  if (state == SUCCESS) {
+    renderer.drawCenteredText(UI_10_FONT_ID, 280, "Success!", true, EpdFontFamily::BOLD);
+    renderer.drawCenteredText(UI_10_FONT_ID, 320, "KOReader sync is ready to use");
+
+    const auto labels = mappedInput.mapLabels("Done", "", "", "");
+    renderer.drawButtonHints(UI_10_FONT_ID, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
+    renderer.displayBuffer();
+    return;
+  }
+
+  if (state == FAILED) {
+    renderer.drawCenteredText(UI_10_FONT_ID, 280, "Authentication Failed", true, EpdFontFamily::BOLD);
+    renderer.drawCenteredText(UI_10_FONT_ID, 320, errorMessage.c_str());
+
+    const auto labels = mappedInput.mapLabels("Back", "", "", "");
+    renderer.drawButtonHints(UI_10_FONT_ID, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
+    renderer.displayBuffer();
+    return;
+  }
+}
+
+void KOReaderAuthActivity::loop() {
+  if (subActivity) {
+    subActivity->loop();
+    return;
+  }
+
+  if (state == SUCCESS || state == FAILED) {
+    if (mappedInput.wasPressed(MappedInputManager::Button::Back) ||
+        mappedInput.wasPressed(MappedInputManager::Button::Confirm)) {
+      onComplete();
+    }
+  }
+}

src/activities/settings/KOReaderAuthActivity.h

@@ -0,0 +1,44 @@
+#pragma once
+#include <freertos/FreeRTOS.h>
+#include <freertos/semphr.h>
+#include <freertos/task.h>
+
+#include <functional>
+
+#include "activities/ActivityWithSubactivity.h"
+
+/**
+ * Activity for testing KOReader credentials.
+ * Connects to WiFi and authenticates with the KOReader sync server.
+ */
+class KOReaderAuthActivity final : public ActivityWithSubactivity {
+ public:
+  explicit KOReaderAuthActivity(GfxRenderer& renderer, MappedInputManager& mappedInput,
+                                const std::function<void()>& onComplete)
+      : ActivityWithSubactivity("KOReaderAuth", renderer, mappedInput), onComplete(onComplete) {}
+
+  void onEnter() override;
+  void onExit() override;
+  void loop() override;
+  bool preventAutoSleep() override { return state == CONNECTING || state == AUTHENTICATING; }
+
+ private:
+  enum State { WIFI_SELECTION, CONNECTING, AUTHENTICATING, SUCCESS, FAILED };
+
+  TaskHandle_t displayTaskHandle = nullptr;
+  SemaphoreHandle_t renderingMutex = nullptr;
+  bool updateRequired = false;
+
+  State state = WIFI_SELECTION;
+  std::string statusMessage;
+  std::string errorMessage;
+
+  const std::function<void()> onComplete;
+
+  void onWifiSelectionComplete(bool success);
+  void performAuthentication();
+
+  static void taskTrampoline(void* param);
+  [[noreturn]] void displayTaskLoop();
+  void render();
+};

src/activities/settings/KOReaderSettingsActivity.cpp

@@ -0,0 +1,213 @@
+#include "KOReaderSettingsActivity.h"
+
+#include <GfxRenderer.h>
+
+#include <cstring>
+
+#include "KOReaderAuthActivity.h"
+#include "KOReaderCredentialStore.h"
+#include "MappedInputManager.h"
+#include "activities/util/KeyboardEntryActivity.h"
+#include "fontIds.h"
+
+namespace {
+constexpr int MENU_ITEMS = 5;
+const char* menuNames[MENU_ITEMS] = {"Username", "Password", "Sync Server URL", "Document Matching", "Authenticate"};
+}  // namespace
+
+void KOReaderSettingsActivity::taskTrampoline(void* param) {
+  auto* self = static_cast<KOReaderSettingsActivity*>(param);
+  self->displayTaskLoop();
+}
+
+void KOReaderSettingsActivity::onEnter() {
+  ActivityWithSubactivity::onEnter();
+
+  renderingMutex = xSemaphoreCreateMutex();
+  selectedIndex = 0;
+  updateRequired = true;
+
+  xTaskCreate(&KOReaderSettingsActivity::taskTrampoline, "KOReaderSettingsTask",
+              4096,               // Stack size
+              this,               // Parameters
+              1,                  // Priority
+              &displayTaskHandle  // Task handle
+  );
+}
+
+void KOReaderSettingsActivity::onExit() {
+  ActivityWithSubactivity::onExit();
+
+  xSemaphoreTake(renderingMutex, portMAX_DELAY);
+  if (displayTaskHandle) {
+    vTaskDelete(displayTaskHandle);
+    displayTaskHandle = nullptr;
+  }
+  vSemaphoreDelete(renderingMutex);
+  renderingMutex = nullptr;
+}
+
+void KOReaderSettingsActivity::loop() {
+  if (subActivity) {
+    subActivity->loop();
+    return;
+  }
+
+  if (mappedInput.wasPressed(MappedInputManager::Button::Back)) {
+    onBack();
+    return;
+  }
+
+  if (mappedInput.wasPressed(MappedInputManager::Button::Confirm)) {
+    handleSelection();
+    return;
+  }
+
+  if (mappedInput.wasPressed(MappedInputManager::Button::Up) ||
+      mappedInput.wasPressed(MappedInputManager::Button::Left)) {
+    selectedIndex = (selectedIndex + MENU_ITEMS - 1) % MENU_ITEMS;
+    updateRequired = true;
+  } else if (mappedInput.wasPressed(MappedInputManager::Button::Down) ||
+             mappedInput.wasPressed(MappedInputManager::Button::Right)) {
+    selectedIndex = (selectedIndex + 1) % MENU_ITEMS;
+    updateRequired = true;
+  }
+}
+
+void KOReaderSettingsActivity::handleSelection() {
+  xSemaphoreTake(renderingMutex, portMAX_DELAY);
+
+  if (selectedIndex == 0) {
+    // Username
+    exitActivity();
+    enterNewActivity(new KeyboardEntryActivity(
+        renderer, mappedInput, "KOReader Username", KOREADER_STORE.getUsername(), 10,
+        64,     // maxLength
+        false,  // not password
+        [this](const std::string& username) {
+          KOREADER_STORE.setCredentials(username, KOREADER_STORE.getPassword());
+          KOREADER_STORE.saveToFile();
+          exitActivity();
+          updateRequired = true;
+        },
+        [this]() {
+          exitActivity();
+          updateRequired = true;
+        }));
+  } else if (selectedIndex == 1) {
+    // Password
+    exitActivity();
+    enterNewActivity(new KeyboardEntryActivity(
+        renderer, mappedInput, "KOReader Password", KOREADER_STORE.getPassword(), 10,
+        64,     // maxLength
+        false,  // show characters
+        [this](const std::string& password) {
+          KOREADER_STORE.setCredentials(KOREADER_STORE.getUsername(), password);
+          KOREADER_STORE.saveToFile();
+          exitActivity();
+          updateRequired = true;
+        },
+        [this]() {
+          exitActivity();
+          updateRequired = true;
+        }));
+  } else if (selectedIndex == 2) {
+    // Sync Server URL - prefill with https:// if empty to save typing
+    const std::string currentUrl = KOREADER_STORE.getServerUrl();
+    const std::string prefillUrl = currentUrl.empty() ? "https://" : currentUrl;
+    exitActivity();
+    enterNewActivity(new KeyboardEntryActivity(
+        renderer, mappedInput, "Sync Server URL", prefillUrl, 10,
+        128,    // maxLength - URLs can be long
+        false,  // not password
+        [this](const std::string& url) {
+          // Clear if user just left the prefilled https://
+          const std::string urlToSave = (url == "https://" || url == "http://") ? "" : url;
+          KOREADER_STORE.setServerUrl(urlToSave);
+          KOREADER_STORE.saveToFile();
+          exitActivity();
+          updateRequired = true;
+        },
+        [this]() {
+          exitActivity();
+          updateRequired = true;
+        }));
+  } else if (selectedIndex == 3) {
+    // Document Matching - toggle between Filename and Binary
+    const auto current = KOREADER_STORE.getMatchMethod();
+    const auto newMethod =
+        (current == DocumentMatchMethod::FILENAME) ? DocumentMatchMethod::BINARY : DocumentMatchMethod::FILENAME;
+    KOREADER_STORE.setMatchMethod(newMethod);
+    KOREADER_STORE.saveToFile();
+    updateRequired = true;
+  } else if (selectedIndex == 4) {
+    // Authenticate
+    if (!KOREADER_STORE.hasCredentials()) {
+      // Can't authenticate without credentials - just show message briefly
+      xSemaphoreGive(renderingMutex);
+      return;
+    }
+    exitActivity();
+    enterNewActivity(new KOReaderAuthActivity(renderer, mappedInput, [this] {
+      exitActivity();
+      updateRequired = true;
+    }));
+  }
+
+  xSemaphoreGive(renderingMutex);
+}
+
+void KOReaderSettingsActivity::displayTaskLoop() {
+  while (true) {
+    if (updateRequired && !subActivity) {
+      updateRequired = false;
+      xSemaphoreTake(renderingMutex, portMAX_DELAY);
+      render();
+      xSemaphoreGive(renderingMutex);
+    }
+    vTaskDelay(10 / portTICK_PERIOD_MS);
+  }
+}
+
+void KOReaderSettingsActivity::render() {
+  renderer.clearScreen();
+
+  const auto pageWidth = renderer.getScreenWidth();
+
+  // Draw header
+  renderer.drawCenteredText(UI_12_FONT_ID, 15, "KOReader Sync", true, EpdFontFamily::BOLD);
+
+  // Draw selection highlight
+  renderer.fillRect(0, 60 + selectedIndex * 30 - 2, pageWidth - 1, 30);
+
+  // Draw menu items
+  for (int i = 0; i < MENU_ITEMS; i++) {
+    const int settingY = 60 + i * 30;
+    const bool isSelected = (i == selectedIndex);
+
+    renderer.drawText(UI_10_FONT_ID, 20, settingY, menuNames[i], !isSelected);
+
+    // Draw status for each item
+    const char* status = "";
+    if (i == 0) {
+      status = KOREADER_STORE.getUsername().empty() ? "[Not Set]" : "[Set]";
+    } else if (i == 1) {
+      status = KOREADER_STORE.getPassword().empty() ? "[Not Set]" : "[Set]";
+    } else if (i == 2) {
+      status = KOREADER_STORE.getServerUrl().empty() ? "[Not Set]" : "[Set]";
+    } else if (i == 3) {
+      status = KOREADER_STORE.getMatchMethod() == DocumentMatchMethod::FILENAME ? "[Filename]" : "[Binary]";
+    } else if (i == 4) {
+      status = KOREADER_STORE.hasCredentials() ? "" : "[Set credentials first]";
+    }
+
+    const auto width = renderer.getTextWidth(UI_10_FONT_ID, status);
+    renderer.drawText(UI_10_FONT_ID, pageWidth - 20 - width, settingY, status, !isSelected);
+  }
+
+  // Draw button hints
+  const auto labels = mappedInput.mapLabels("« Back", "Select", "", "");
+  renderer.drawButtonHints(UI_10_FONT_ID, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
+
+  renderer.displayBuffer();
+}

src/activities/settings/KOReaderSettingsActivity.h

@@ -0,0 +1,36 @@
+#pragma once
+#include <freertos/FreeRTOS.h>
+#include <freertos/semphr.h>
+#include <freertos/task.h>
+
+#include <functional>
+
+#include "activities/ActivityWithSubactivity.h"
+
+/**
+ * Submenu for KOReader Sync settings.
+ * Shows username, password, and authenticate options.
+ */
+class KOReaderSettingsActivity final : public ActivityWithSubactivity {
+ public:
+  explicit KOReaderSettingsActivity(GfxRenderer& renderer, MappedInputManager& mappedInput,
+                                    const std::function<void()>& onBack)
+      : ActivityWithSubactivity("KOReaderSettings", renderer, mappedInput), onBack(onBack) {}
+
+  void onEnter() override;
+  void onExit() override;
+  void loop() override;
+
+ private:
+  TaskHandle_t displayTaskHandle = nullptr;
+  SemaphoreHandle_t renderingMutex = nullptr;
+  bool updateRequired = false;
+
+  int selectedIndex = 0;
+  const std::function<void()> onBack;
+
+  static void taskTrampoline(void* param);
+  [[noreturn]] void displayTaskLoop();
+  void render();
+  void handleSelection();
+};

src/activities/settings/SettingsActivity.cpp

@@ -7,6 +7,7 @@
 
 #include "CalibreSettingsActivity.h"
 #include "CrossPointSettings.h"
+#include "KOReaderSettingsActivity.h"
 #include "MappedInputManager.h"
 #include "OtaUpdateActivity.h"
 #include "fontIds.h"
@@ -42,6 +43,7 @@ const SettingInfo settingsList[settingsCount] = {
                       {"1 min", "5 min", "10 min", "15 min", "30 min"}),
     SettingInfo::Enum("Refresh Frequency", &CrossPointSettings::refreshFrequency,
                       {"1 page", "5 pages", "10 pages", "15 pages", "30 pages"}),
+    SettingInfo::Action("KOReader Sync"),
     SettingInfo::Action("Calibre Settings"),
     SettingInfo::Action("Check for updates")};
 }  // namespace
@@ -116,7 +118,6 @@ void SettingsActivity::loop() {
 }
 
 void SettingsActivity::toggleCurrentSetting() {
-  // Validate index
   if (selectedSettingIndex < 0 || selectedSettingIndex >= settingsCount) {
     return;
   }
@@ -140,7 +141,15 @@ void SettingsActivity::toggleCurrentSetting() {
       SETTINGS.*(setting.valuePtr) = currentValue + setting.valueRange.step;
     }
   } else if (setting.type == SettingType::ACTION) {
-    if (strcmp(setting.name, "Calibre Settings") == 0) {
+    if (strcmp(setting.name, "KOReader Sync") == 0) {
+      xSemaphoreTake(renderingMutex, portMAX_DELAY);
+      exitActivity();
+      enterNewActivity(new KOReaderSettingsActivity(renderer, mappedInput, [this] {
+        exitActivity();
+        updateRequired = true;
+      }));
+      xSemaphoreGive(renderingMutex);
+    } else if (strcmp(setting.name, "Calibre Settings") == 0) {
       xSemaphoreTake(renderingMutex, portMAX_DELAY);
       exitActivity();
       enterNewActivity(new CalibreSettingsActivity(renderer, mappedInput, [this] {
@@ -187,18 +196,19 @@ void SettingsActivity::render() const {
   // Draw header
   renderer.drawCenteredText(UI_12_FONT_ID, 15, "Settings", true, EpdFontFamily::BOLD);
 
-  // Draw selection
+  // Draw selection highlight
   renderer.fillRect(0, 60 + selectedSettingIndex * 30 - 2, pageWidth - 1, 30);
 
   // Draw all settings
   for (int i = 0; i < settingsCount; i++) {
     const int settingY = 60 + i * 30;  // 30 pixels between settings
+    const bool isSelected = (i == selectedSettingIndex);
 
     // Draw setting name
-    renderer.drawText(UI_10_FONT_ID, 20, settingY, settingsList[i].name, i != selectedSettingIndex);
+    renderer.drawText(UI_10_FONT_ID, 20, settingY, settingsList[i].name, !isSelected);
 
     // Draw value based on setting type
-    std::string valueText = "";
+    std::string valueText;
     if (settingsList[i].type == SettingType::TOGGLE && settingsList[i].valuePtr != nullptr) {
       const bool value = SETTINGS.*(settingsList[i].valuePtr);
       valueText = value ? "ON" : "OFF";
@@ -208,8 +218,10 @@ void SettingsActivity::render() const {
     } else if (settingsList[i].type == SettingType::VALUE && settingsList[i].valuePtr != nullptr) {
       valueText = std::to_string(SETTINGS.*(settingsList[i].valuePtr));
     }
-    const auto width = renderer.getTextWidth(UI_10_FONT_ID, valueText.c_str());
+    if (!valueText.empty()) {
-    renderer.drawText(UI_10_FONT_ID, pageWidth - 20 - width, settingY, valueText.c_str(), i != selectedSettingIndex);
+      const auto width = renderer.getTextWidth(UI_10_FONT_ID, valueText.c_str());
+      renderer.drawText(UI_10_FONT_ID, pageWidth - 20 - width, settingY, valueText.c_str(), !isSelected);
+    }
   }
 
   // Draw version text above button hints

src/main.cpp

@@ -12,6 +12,7 @@
 #include "Battery.h"
 #include "CrossPointSettings.h"
 #include "CrossPointState.h"
+#include "KOReaderCredentialStore.h"
 #include "MappedInputManager.h"
 #include "activities/boot_sleep/BootActivity.h"
 #include "activities/boot_sleep/SleepActivity.h"
@@ -289,6 +290,7 @@ void setup() {
   }
 
   SETTINGS.loadFromFile();
+  KOREADER_STORE.loadFromFile();
 
   // verify power button press duration after we've read settings.
   verifyWakeupLongPress();