Merge branch 'develop' of https://github.com/crosspoint-reader/crosspoint-reader into feat-bluetooth

lib/EpdFont/FontDecompressor.cpp

@@ -33,12 +33,24 @@ void FontDecompressor::freePageBuffer() {
 }
 
 void FontDecompressor::freeHotGroup() {
-  hotGroup.clear();
-  hotGroup.shrink_to_fit();
+  free(hotGroup);
+  hotGroup = nullptr;
+  hotGroupCapacity = 0;
   hotGroupFont = nullptr;
   hotGroupIndex = UINT16_MAX;
-  hotGlyphBuf.clear();
-  hotGlyphBuf.shrink_to_fit();
+  free(hotGlyphBuf);
+  hotGlyphBuf = nullptr;
+  hotGlyphBufCapacity = 0;
+}
+
+bool FontDecompressor::ensureCapacity(uint8_t*& buf, uint32_t& capacity, uint32_t needed) {
+  if (capacity >= needed) return true;
+  // Grow-only, free-then-malloc: every caller fully rewrites the buffer after a grow, so the
+  // old contents are dead -- freeing first gives the allocator its best shot on a tight heap.
+  free(buf);
+  buf = static_cast<uint8_t*>(malloc(needed));  // owned by FontDecompressor, freed in freeHotGroup()
+  capacity = buf ? needed : 0;
+  return buf != nullptr;
 }
 
 uint16_t FontDecompressor::getGroupIndex(const EpdFontData* fontData, uint32_t glyphIndex) {
@@ -170,24 +182,20 @@ const uint8_t* FontDecompressor::getBitmap(const EpdFontData* fontData, const Ep
   }
 
   // Check if hot group already has this group decompressed — if not, decompress it
-  if (!(!hotGroup.empty() && hotGroupFont == fontData && hotGroupIndex == groupIndex)) {
+  if (!(hotGroup != nullptr && hotGroupFont == fontData && hotGroupIndex == groupIndex)) {
     stats.cacheMisses++;
     const EpdFontGroup& group = fontData->groups[groupIndex];
 
-    hotGroup.resize(group.uncompressedSize);
-    if (hotGroup.empty()) {
+    // ensureCapacity may free the buffer, so the cached-group identity dies with it either way.
+    hotGroupFont = nullptr;
+    hotGroupIndex = UINT16_MAX;
+    if (!ensureCapacity(hotGroup, hotGroupCapacity, group.uncompressedSize)) {
       LOG_ERR("FDC", "Failed to allocate %u bytes for hot group %u", group.uncompressedSize, groupIndex);
-      hotGroupFont = nullptr;
-      hotGroupIndex = UINT16_MAX;
       stats.getBitmapTimeUs += micros() - tStart;
       return nullptr;
     }
 
-    if (!decompressGroup(fontData, groupIndex, hotGroup.data(), group.uncompressedSize)) {
-      hotGroup.clear();
-      hotGroup.shrink_to_fit();
-      hotGroupFont = nullptr;
-      hotGroupIndex = UINT16_MAX;
+    if (!decompressGroup(fontData, groupIndex, hotGroup, group.uncompressedSize)) {
       stats.getBitmapTimeUs += micros() - tStart;
       return nullptr;
     }
@@ -200,18 +208,16 @@ const uint8_t* FontDecompressor::getBitmap(const EpdFontData* fontData, const Ep
   }
 
   // Compact just the requested glyph from byte-aligned data into scratch buffer
-  if (glyph->dataLength > hotGlyphBuf.size()) {
-    hotGlyphBuf.resize(glyph->dataLength);
-  }
-  if (hotGlyphBuf.empty()) {
+  if (!ensureCapacity(hotGlyphBuf, hotGlyphBufCapacity, glyph->dataLength)) {
+    LOG_ERR("FDC", "Failed to allocate %u bytes for glyph scratch", (unsigned)glyph->dataLength);
     stats.getBitmapTimeUs += micros() - tStart;
     return nullptr;
   }
 
   uint32_t alignedOff = getAlignedOffset(fontData, groupIndex, glyphIndex);
-  compactSingleGlyph(&hotGroup[alignedOff], hotGlyphBuf.data(), glyph->width, glyph->height);
+  compactSingleGlyph(&hotGroup[alignedOff], hotGlyphBuf, glyph->width, glyph->height);
   stats.getBitmapTimeUs += micros() - tStart;
-  return hotGlyphBuf.data();
+  return hotGlyphBuf;
 }
 
 // --- Prewarm: pre-decompress glyph bitmaps for a page of text ---

lib/EpdFont/FontDecompressor.h

@@ -2,8 +2,6 @@
 
 #include <InflateReader.h>
 
-#include <vector>
-
 #include "EpdFontData.h"
 
 class FontDecompressor {
@@ -67,13 +65,22 @@ class FontDecompressor {
 
   // Hot group: last decompressed group (byte-aligned) for non-prewarmed fallback path.
   // Kept in byte-aligned format; individual glyphs are compacted on demand into hotGlyphBuf.
+  // Nothrow high-water malloc buffers, NOT std::vector: getBitmap() runs on the render path,
+  // and under -fno-exceptions a vector resize that hits OOM abort()s the firmware instead of
+  // failing (field crash: hotGroup.resize() -> std::bad_alloc -> abort with ~11 KB free).
+  // ensureCapacity() returns false on OOM so the caller can skip the glyph gracefully.
   const EpdFontData* hotGroupFont = nullptr;
   uint16_t hotGroupIndex = UINT16_MAX;
-  std::vector<uint8_t> hotGroup;
+  uint8_t* hotGroup = nullptr;  // owned; freed in freeHotGroup()/dtor
+  uint32_t hotGroupCapacity = 0;
 
   // Scratch buffer for compacting a single glyph from the hot group.
-  // Valid until the next getBitmap() call.
-  std::vector<uint8_t> hotGlyphBuf;
+  // Valid until the next getBitmap() call. Same ownership/OOM contract as hotGroup.
+  uint8_t* hotGlyphBuf = nullptr;
+  uint32_t hotGlyphBufCapacity = 0;
+
+  // Grow (never shrink) an owned buffer to at least `needed` bytes; false on OOM, buffer freed.
+  static bool ensureCapacity(uint8_t*& buf, uint32_t& capacity, uint32_t needed);
 
   void freePageBuffer();
   void freeHotGroup();

lib/Epub/Epub/Page.cpp

@@ -39,7 +39,17 @@ std::unique_ptr<PageLine> PageLine::deserialize(HalFile& file) {
   serialization::readPod(file, yPos);
 
   auto tb = TextBlock::deserialize(file);
-  return std::unique_ptr<PageLine>(new PageLine(std::move(tb), xPos, yPos));
+  if (!tb) {
+    LOG_ERR("PGE", "Deserialization failed: null TextBlock");
+    return nullptr;
+  }
+
+  auto* line = new (std::nothrow) PageLine(std::move(tb), xPos, yPos);
+  if (!line) {
+    LOG_ERR("PGE", "Deserialization failed: could not allocate PageLine");
+    return nullptr;
+  }
+  return std::unique_ptr<PageLine>(line);
 }
 
 void PageImage::render(GfxRenderer& renderer, const int fontId, const int xOffset, const int yOffset) {
@@ -159,9 +169,15 @@ std::unique_ptr<Page> Page::deserialize(HalFile& file) {
 
     if (tag == TAG_PageLine) {
       auto pl = PageLine::deserialize(file);
+      if (!pl) {
+        return nullptr;
+      }
       page->elements.push_back(std::move(pl));
     } else if (tag == TAG_PageImage) {
       auto pi = PageImage::deserialize(file);
+      if (!pi) {
+        return nullptr;
+      }
       page->elements.push_back(std::move(pi));
     } else if (tag == TAG_PageHorizontalRule) {
       auto rule = PageHorizontalRule::deserialize(file);

lib/Epub/Epub/ParsedText.cpp

@@ -2,6 +2,7 @@
 
 #include <BidiUtils.h>
 #include <GfxRenderer.h>
+#include <Logging.h>
 #include <Utf8.h>
 
 #include <algorithm>
@@ -1133,8 +1134,14 @@ void ParsedText::extractLine(const size_t breakIndex, const int pageWidth, const
   }
 
   if (!lineHasFocusSplit) {
-    processLine(std::make_shared<TextBlock>(std::move(lineWords), std::move(lineXPos), std::move(lineWordStyles),
-                                            std::vector<uint8_t>{}, std::vector<uint16_t>{}, blockStyle));
+    // TextBlock flattens the vectors into its arena; they stay owned here and die at return.
+    auto block = std::make_shared<TextBlock>(lineWords, lineXPos, lineWordStyles, std::vector<uint8_t>{},
+                                             std::vector<uint16_t>{}, blockStyle);
+    if (!block->valid()) {
+      LOG_ERR("PTX", "Dropping line: TextBlock arena allocation failed");
+      return;
+    }
+    processLine(std::move(block));
     return;
   }
 
@@ -1179,6 +1186,10 @@ void ParsedText::extractLine(const size_t breakIndex, const int pageWidth, const
     }
   }
 
-  processLine(std::make_shared<TextBlock>(std::move(outWords), std::move(outXPos), std::move(outStyles),
-                                          std::move(outBoundaries), std::move(outSuffixX), blockStyle));
+  auto block = std::make_shared<TextBlock>(outWords, outXPos, outStyles, outBoundaries, outSuffixX, blockStyle);
+  if (!block->valid()) {
+    LOG_ERR("PTX", "Dropping line: TextBlock arena allocation failed");
+    return;
+  }
+  processLine(std::move(block));
 }

lib/Epub/Epub/Section.cpp

@@ -11,8 +11,9 @@
 #include "parsers/ChapterHtmlSlimParser.h"
 
 namespace {
-// v28: text decoration bits now include line-through in serialized wordStyles.
-constexpr uint8_t SECTION_FILE_VERSION = 28;
+// v29: TextBlock word data stored as one flat arena (offset table + NUL-terminated
+// text blob) instead of length-prefixed strings and per-field arrays.
+constexpr uint8_t SECTION_FILE_VERSION = 29;
 // Written into the version field while a build is in progress; patched to
 // SECTION_FILE_VERSION only when the build is finalized. An abandoned /
 // crash-interrupted .bin therefore carries version 0, which loadSectionFile rejects
@@ -25,7 +26,11 @@ constexpr uint8_t SECTION_FILE_INCOMPLETE_VERSION = 0;
 // rebuilding in the background. Uses the same header layout as SECTION_FILE_VERSION,
 // so finalized files are untouched by this feature; older firmware treats the sentinel
 // as an unknown version and rebuilds, which is a safe downgrade.
-constexpr uint8_t SECTION_FILE_PARTIAL_VERSION = 0xFE;
+// MUST change in lockstep with SECTION_FILE_VERSION: the sentinel IS the partial's
+// format version, so a stale-format partial otherwise passes the header check and
+// only fails (noisily, via the block-decode error path) when a page is loaded.
+// Derived so the pairing can't be forgotten: 0xFE for v28, 0xFD for v29, ...
+constexpr uint8_t SECTION_FILE_PARTIAL_VERSION = 0xFE - (SECTION_FILE_VERSION - 28);
 constexpr uint32_t HEADER_SIZE = sizeof(uint8_t) + sizeof(int) + sizeof(float) + sizeof(bool) + sizeof(uint8_t) +
                                  sizeof(uint16_t) + sizeof(uint16_t) + sizeof(uint16_t) + sizeof(bool) + sizeof(bool) +
                                  sizeof(uint8_t) + sizeof(bool) + sizeof(uint32_t) + sizeof(uint32_t) +
@@ -733,10 +738,10 @@ std::string Section::getTextFromSectionFile() {
       if (el->getTag() == TAG_PageLine) {
         const auto& line = static_cast<const PageLine&>(*el);
         if (line.getBlock()) {
-          const auto& words = line.getBlock()->getWords();
-          for (const auto& w : words) {
+          const auto& block = *line.getBlock();
+          for (uint16_t i = 0; i < block.wordCount(); i++) {
             if (!fullText.empty()) fullText += " ";
-            fullText += w;
+            fullText += block.wordText(i);
           }
         }
       }

lib/Epub/Epub/blocks/BlockStyle.h

@@ -32,6 +32,11 @@ struct BlockStyle {
   bool isRtl = false;              // true if resolved direction is RTL
   bool directionDefined = false;   // true if direction was explicitly set in CSS/HTML
 
+  // Set when this block was created by a <br> element. Used by startNewTextBlock to inject
+  // a full line-height gap when the <br> block stays empty (section-break use case).
+  // NOT propagated through getCombinedBlockStyle so it can't leak into sibling blocks.
+  bool fromBrElement = false;
+
   // Combined insets (margin + padding)
   [[nodiscard]] int16_t leftInset() const { return marginLeft + paddingLeft; }
   [[nodiscard]] int16_t rightInset() const { return marginRight + paddingRight; }
@@ -92,6 +97,9 @@ struct BlockStyle {
       result.directionDefined = true;
     }
 
+    // fromBrElement is consumed by startNewTextBlock when an empty <br> block
+    // is merged with the following paragraph; never propagate it further.
+    result.fromBrElement = false;
     return result;
   }
 

lib/Epub/Epub/blocks/TextBlock.cpp

@@ -3,19 +3,114 @@
 #include <BidiUtils.h>
 #include <GfxRenderer.h>
 #include <Logging.h>
+#include <Memory.h>
 #include <Serialization.h>
 
 #include <cstring>
 
-void TextBlock::render(const GfxRenderer& renderer, const int fontId, const int x, const int y) const {
+size_t TextBlock::arenaSize(const uint16_t wordCount, const bool hasFocus, const uint16_t textBytes) {
+  // Layout documented in TextBlock.h: 16-bit arrays first, then 8-bit arrays, then text.
+  size_t size = static_cast<size_t>(wordCount) * (sizeof(uint16_t) + sizeof(int16_t) + sizeof(uint8_t));
+  if (hasFocus) {
+    size += static_cast<size_t>(wordCount) * (sizeof(uint16_t) + sizeof(uint8_t));
+  }
+  return size + textBytes;
+}
+
+void TextBlock::bindArenaPointers() {
+  uint8_t* base = arena.get();
+  const size_t wc = numWords;
+  textOffArr = reinterpret_cast<const uint16_t*>(base);
+  xposArr = reinterpret_cast<const int16_t*>(base + wc * 2);
+  size_t off = wc * 4;
+  if (focusPresent) {
+    focusSuffixXArr = reinterpret_cast<const uint16_t*>(base + off);
+    off += wc * 2;
+  }
+  stylesArr = base + off;
+  off += wc;
+  if (focusPresent) {
+    focusBoundaryArr = base + off;
+    off += wc;
+  }
+  textArr = reinterpret_cast<const char*>(base + off);
+}
+
+TextBlock::TextBlock(const std::vector<std::string>& words, const std::vector<int16_t>& wordXpos,
+                     const std::vector<EpdFontFamily::Style>& wordStyles, const std::vector<uint8_t>& focusBoundary,
+                     const std::vector<uint16_t>& focusSuffixX, const BlockStyle& blockStyle)
+    : blockStyle(blockStyle) {
   // Focus annotations are optional: empty vectors mean no word in this block has a split.
   // When present, they must be sized in lockstep with words[].
-  const bool hasFocus = !wordFocusBoundary.empty();
-  if (words.size() != wordXpos.size() || words.size() != wordStyles.size() ||
-      (hasFocus && (words.size() != wordFocusBoundary.size() || words.size() != wordFocusSuffixX.size()))) {
-    LOG_ERR("TXB", "Render skipped: size mismatch (words=%u, xpos=%u, styles=%u, boundary=%u, suffixX=%u)\n",
-            (uint32_t)words.size(), (uint32_t)wordXpos.size(), (uint32_t)wordStyles.size(),
-            (uint32_t)wordFocusBoundary.size(), (uint32_t)wordFocusSuffixX.size());
+  const bool hasFocus = !focusBoundary.empty();
+  if (words.size() != wordXpos.size() || words.size() != wordStyles.size() || words.size() > 10000 ||
+      (hasFocus && (words.size() != focusBoundary.size() || words.size() != focusSuffixX.size()))) {
+    LOG_ERR("TXB", "Construction failed: size mismatch (words=%u, xpos=%u, styles=%u, boundary=%u, suffixX=%u)",
+            static_cast<uint32_t>(words.size()), static_cast<uint32_t>(wordXpos.size()),
+            static_cast<uint32_t>(wordStyles.size()), static_cast<uint32_t>(focusBoundary.size()),
+            static_cast<uint32_t>(focusSuffixX.size()));
+    isValid = false;
+    return;
+  }
+
+  numWords = static_cast<uint16_t>(words.size());
+  focusPresent = hasFocus;
+  if (numWords == 0) {
+    return;  // valid empty block, no arena
+  }
+
+  // Pass 1: total text size, one NUL per word. A line is at most a physical
+  // row of the page, so uint16_t offsets are ample; reject anything larger.
+  size_t totalText = 0;
+  for (const auto& w : words) totalText += w.size() + 1;
+  if (totalText > UINT16_MAX) {
+    LOG_ERR("TXB", "Construction failed: text size %u exceeds arena limit", static_cast<uint32_t>(totalText));
+    numWords = 0;
+    focusPresent = false;
+    isValid = false;
+    return;
+  }
+  textBytes = static_cast<uint16_t>(totalText);
+
+  const size_t size = arenaSize(numWords, focusPresent, textBytes);
+  arena = makeUniqueNoThrow<uint8_t[]>(size);
+  if (!arena) {
+    LOG_ERR("TXB", "OOM: arena %u bytes", static_cast<uint32_t>(size));
+    numWords = 0;
+    textBytes = 0;
+    focusPresent = false;
+    isValid = false;
+    return;
+  }
+  bindArenaPointers();
+
+  // Pass 2: fill. Mutable aliases of the const views bound above.
+  auto* textOff = const_cast<uint16_t*>(textOffArr);
+  auto* xpos = const_cast<int16_t*>(xposArr);
+  auto* styles = const_cast<uint8_t*>(stylesArr);
+  auto* text = const_cast<char*>(textArr);
+  uint16_t off = 0;
+  for (uint16_t i = 0; i < numWords; i++) {
+    textOff[i] = off;
+    xpos[i] = wordXpos[i];
+    styles[i] = static_cast<uint8_t>(wordStyles[i]);
+    memcpy(text + off, words[i].data(), words[i].size());
+    off += static_cast<uint16_t>(words[i].size());
+    text[off++] = '\0';
+  }
+  if (focusPresent) {
+    auto* suffixX = const_cast<uint16_t*>(focusSuffixXArr);
+    auto* boundary = const_cast<uint8_t*>(focusBoundaryArr);
+    for (uint16_t i = 0; i < numWords; i++) {
+      suffixX[i] = focusSuffixX[i];
+      boundary[i] = focusBoundary[i];
+    }
+  }
+}
+
+void TextBlock::render(const GfxRenderer& renderer, const int fontId, const int x, const int y) const {
+  if (!isValid) {
+    LOG_ERR("TXB", "Render skipped: invalid block");
     return;
   }
 
@@ -54,12 +149,13 @@ void TextBlock::render(const GfxRenderer& renderer, const int fontId, const int
     }
   };
 
-  for (size_t i = 0; i < words.size(); i++) {
-    const int wordX = wordXpos[i] + x;
-    const EpdFontFamily::Style currentStyle = wordStyles[i];
-    const auto baseDir = static_cast<BidiUtils::BidiBaseDir>(
-        BidiUtils::detectParagraphLevel(words[i].c_str(), blockStyle.isRtl ? 1 : 0));
-    const uint8_t boundary = hasFocus ? wordFocusBoundary[i] : 0;
+  for (uint16_t i = 0; i < numWords; i++) {
+    const char* word = wordText(i);
+    const int wordX = xposArr[i] + x;
+    const EpdFontFamily::Style currentStyle = wordStyle(i);
+    const auto baseDir =
+        static_cast<BidiUtils::BidiBaseDir>(BidiUtils::detectParagraphLevel(word, blockStyle.isRtl ? 1 : 0));
+    const uint8_t boundary = focusBoundary(i);
 
     // SUP/SUB shift the baseline passed to drawText; the glyph is also scaled 50% inside
     // drawText, so these offsets are chosen relative to the full-size ascender:
@@ -82,14 +178,15 @@ void TextBlock::render(const GfxRenderer& renderer, const int fontId, const int
       static_assert(sizeof(boldBuf) >= MAX_FOCUS_PREFIX_BYTES,
                     "boldBuf too small for max focus prefix (9 codepoints * 4 UTF-8 bytes + null)");
       const auto boldStyle = static_cast<EpdFontFamily::Style>(currentStyle | EpdFontFamily::BOLD);
-      const size_t boldLen = std::min<size_t>({static_cast<size_t>(boundary), words[i].size(), sizeof(boldBuf) - 1});
-      memcpy(boldBuf, words[i].c_str(), boldLen);
+      const size_t boldLen =
+          std::min<size_t>({static_cast<size_t>(boundary), static_cast<size_t>(wordTextLen(i)), sizeof(boldBuf) - 1});
+      memcpy(boldBuf, word, boldLen);
       boldBuf[boldLen] = '\0';
       renderer.drawText(fontId, wordX, wordY, boldBuf, true, boldStyle, baseDir);
-      const int suffixX = wordX + wordFocusSuffixX[i];
-      renderer.drawText(fontId, suffixX, wordY, words[i].c_str() + boldLen, true, currentStyle, baseDir);
+      const int suffixX = wordX + focusSuffixXArr[i];
+      renderer.drawText(fontId, suffixX, wordY, word + boldLen, true, currentStyle, baseDir);
     } else {
-      renderer.drawText(fontId, wordX, wordY, words[i].c_str(), true, currentStyle, baseDir);
+      renderer.drawText(fontId, wordX, wordY, word, true, currentStyle, baseDir);
     }
 
     if (scanning) {
@@ -97,18 +194,17 @@ void TextBlock::render(const GfxRenderer& renderer, const int fontId, const int
     }
 
     if (EpdFontFamily::hasTextDecoration(currentStyle)) {
-      const std::string& w = words[i];
       int lineStartX = wordX;
-      int lineWidth = renderer.getTextWidth(fontId, w.c_str(), currentStyle, baseDir);
+      int lineWidth = renderer.getTextWidth(fontId, word, currentStyle, baseDir);
 
       if ((currentStyle & (EpdFontFamily::SUP | EpdFontFamily::SUB)) != 0) {
         lineWidth = (lineWidth + 1) / 2;
       }
 
       // Do not decorate the synthetic em-space used for paragraph indentation.
-      if (w.size() >= 3 && static_cast<uint8_t>(w[0]) == 0xE2 && static_cast<uint8_t>(w[1]) == 0x80 &&
-          static_cast<uint8_t>(w[2]) == 0x83) {
-        const char* visibleText = w.c_str() + 3;
+      if (wordTextLen(i) >= 3 && static_cast<uint8_t>(word[0]) == 0xE2 && static_cast<uint8_t>(word[1]) == 0x80 &&
+          static_cast<uint8_t>(word[2]) == 0x83) {
+        const char* visibleText = word + 3;
         lineStartX += renderer.getTextAdvanceX(fontId, "\xe2\x80\x83", currentStyle);
         lineWidth = renderer.getTextWidth(fontId, visibleText, currentStyle, baseDir);
         if ((currentStyle & (EpdFontFamily::SUP | EpdFontFamily::SUB)) != 0) {
@@ -140,29 +236,23 @@ void TextBlock::render(const GfxRenderer& renderer, const int fontId, const int
 }
 
 bool TextBlock::serialize(HalFile& file) const {
-  // Focus annotations are optional; vectors are either empty (no splits in this block)
-  // or sized in lockstep with words[].
-  const bool hasFocus = !wordFocusBoundary.empty();
-  if (words.size() != wordXpos.size() || words.size() != wordStyles.size() ||
-      (hasFocus && (words.size() != wordFocusBoundary.size() || words.size() != wordFocusSuffixX.size()))) {
-    LOG_ERR("TXB", "Serialization failed: size mismatch (words=%u, xpos=%u, styles=%u, boundary=%u, suffixX=%u)\n",
-            static_cast<uint32_t>(words.size()), static_cast<uint32_t>(wordXpos.size()),
-            static_cast<uint32_t>(wordStyles.size()), static_cast<uint32_t>(wordFocusBoundary.size()),
-            static_cast<uint32_t>(wordFocusSuffixX.size()));
+  if (!isValid) {
+    LOG_ERR("TXB", "Serialization failed: invalid block");
     return false;
   }
 
-  // Word data
-  serialization::writePod(file, static_cast<uint16_t>(words.size()));
-  for (const auto& w : words) serialization::writeString(file, w);
-  for (auto x : wordXpos) serialization::writePod(file, x);
-  for (auto s : wordStyles) serialization::writePod(file, s);
-  // Focus block: 1-byte presence flag, followed by per-word vectors only when present.
-  // Saves 3 bytes/word when focus reading is disabled or no word on this line was split.
-  serialization::writePod(file, static_cast<uint8_t>(hasFocus ? 1 : 0));
-  if (hasFocus) {
-    for (auto b : wordFocusBoundary) serialization::writePod(file, b);
-    for (auto sx : wordFocusSuffixX) serialization::writePod(file, sx);
+  // Word data: scalars, then the arena verbatim -- its in-memory layout is
+  // exactly the on-disk layout (see TextBlock.h), so one write covers all
+  // per-word arrays and the text blob.
+  serialization::writePod(file, numWords);
+  serialization::writePod(file, static_cast<uint8_t>(focusPresent ? 1 : 0));
+  serialization::writePod(file, textBytes);
+  if (numWords > 0) {
+    const size_t size = arenaSize(numWords, focusPresent, textBytes);
+    if (file.write(arena.get(), size) != size) {
+      LOG_ERR("TXB", "Serialization failed: arena write (%u bytes)", static_cast<uint32_t>(size));
+      return false;
+    }
   }
 
   // Style (alignment + margins/padding/indent)
@@ -186,41 +276,64 @@ bool TextBlock::serialize(HalFile& file) const {
 
 std::unique_ptr<TextBlock> TextBlock::deserialize(HalFile& file) {
   uint16_t wc;
-  std::vector<std::string> words;
-  std::vector<int16_t> wordXpos;
-  std::vector<EpdFontFamily::Style> wordStyles;
-  std::vector<uint8_t> wordFocusBoundary;
-  std::vector<uint16_t> wordFocusSuffixX;
-  BlockStyle blockStyle;
-
-  // Word count
+  uint8_t hasFocus;
+  uint16_t textBytes;
   serialization::readPod(file, wc);
+  serialization::readPod(file, hasFocus);
+  serialization::readPod(file, textBytes);
 
-  // Sanity check: prevent allocation of unreasonably large vectors (max 10000 words per block)
+  // Sanity checks: cap the arena allocation and reject impossible geometry
+  // (every word carries at least its NUL terminator).
   if (wc > 10000) {
     LOG_ERR("TXB", "Deserialization failed: word count %u exceeds maximum", wc);
     return nullptr;
   }
+  if ((wc == 0 && textBytes != 0) || (wc > 0 && textBytes < wc)) {
+    LOG_ERR("TXB", "Deserialization failed: bad text size %u for %u words", textBytes, wc);
+    return nullptr;
+  }
 
-  // Word data
-  words.resize(wc);
-  wordXpos.resize(wc);
-  wordStyles.resize(wc);
-  for (auto& w : words) serialization::readString(file, w);
-  for (auto& x : wordXpos) serialization::readPod(file, x);
-  for (auto& s : wordStyles) serialization::readPod(file, s);
-  // Focus block: presence flag, then vectors only if present. Empty vectors when absent
-  // signal "no splits in this block" to render() (zero per-word RAM cost).
-  uint8_t hasFocus;
-  serialization::readPod(file, hasFocus);
-  if (hasFocus) {
-    wordFocusBoundary.resize(wc);
-    wordFocusSuffixX.resize(wc);
-    for (auto& b : wordFocusBoundary) serialization::readPod(file, b);
-    for (auto& sx : wordFocusSuffixX) serialization::readPod(file, sx);
+  std::unique_ptr<TextBlock> block(new (std::nothrow) TextBlock());
+  if (!block) {
+    LOG_ERR("TXB", "OOM: TextBlock");
+    return nullptr;
+  }
+  block->numWords = wc;
+  block->textBytes = textBytes;
+  block->focusPresent = hasFocus != 0;
+
+  if (wc > 0) {
+    const size_t size = arenaSize(wc, block->focusPresent, textBytes);
+    block->arena = makeUniqueNoThrow<uint8_t[]>(size);
+    if (!block->arena) {
+      LOG_ERR("TXB", "OOM: arena %u bytes", static_cast<uint32_t>(size));
+      return nullptr;
+    }
+    if (file.read(block->arena.get(), size) != size) {
+      LOG_ERR("TXB", "Deserialization failed: arena read (%u bytes)", static_cast<uint32_t>(size));
+      return nullptr;
+    }
+    block->bindArenaPointers();
+
+    // Validate offsets before anything dereferences wordText(): offset 0 first,
+    // strictly increasing, in bounds, and every word NUL-terminated (word i ends
+    // at the byte before offset i+1; the last word at the last text byte).
+    const uint16_t* textOff = block->textOffArr;
+    const char* text = block->textArr;
+    if (textOff[0] != 0 || text[textBytes - 1] != '\0') {
+      LOG_ERR("TXB", "Deserialization failed: corrupt text layout");
+      return nullptr;
+    }
+    for (uint16_t i = 1; i < wc; i++) {
+      if (textOff[i] <= textOff[i - 1] || textOff[i] >= textBytes || text[textOff[i] - 1] != '\0') {
+        LOG_ERR("TXB", "Deserialization failed: corrupt word offset %u", i);
+        return nullptr;
+      }
+    }
   }
 
   // Style (alignment + margins/padding/indent)
+  BlockStyle& blockStyle = block->blockStyle;
   serialization::readPod(file, blockStyle.alignment);
   serialization::readPod(file, blockStyle.textAlignDefined);
   serialization::readPod(file, blockStyle.marginTop);
@@ -236,7 +349,5 @@ std::unique_ptr<TextBlock> TextBlock::deserialize(HalFile& file) {
   serialization::readPod(file, blockStyle.isRtl);
   serialization::readPod(file, blockStyle.directionDefined);
 
-  return std::unique_ptr<TextBlock>(new TextBlock(std::move(words), std::move(wordXpos), std::move(wordStyles),
-                                                  std::move(wordFocusBoundary), std::move(wordFocusSuffixX),
-                                                  blockStyle));
+  return block;
 }

lib/Epub/Epub/blocks/TextBlock.h

@@ -9,42 +9,83 @@
 #include "Block.h"
 #include "BlockStyle.h"
 
-// Represents a line of text on a page
+// Represents a line of text on a page.
+//
+// All per-word data lives in ONE flat heap allocation (the arena) instead of
+// six parallel vectors: a resident page holds ~25-30 of these blocks, and the
+// vector-of-string layout cost ~250 throwing allocations per page load, which
+// was the primary driver of heap fragmentation on the ESP32-C3.
+//
+// Arena layout, in order (2-byte alignment holds by construction: all 16-bit
+// arrays come first and the arena base is allocator-aligned; RISC-V faults on
+// unaligned multi-byte access):
+//   uint16_t textOff[wordCount]        byte offset of word i's text in text[]
+//   int16_t  xpos[wordCount]
+//   uint16_t focusSuffixX[wordCount]   present only when focusPresent
+//   uint8_t  styles[wordCount]
+//   uint8_t  focusBoundary[wordCount]  present only when focusPresent
+//   char     text[textBytes]           all words back to back, NUL-terminated
+//
+// Each word is stored NUL-terminated so render() can hand `text + textOff[i]`
+// straight to C APIs (drawText) with no std::string materialization.
+//
+// Focus split semantics (unchanged from the vector layout): boundary N > 0
+// means the first N bytes of word i render bold, the remainder in the base
+// style. N is bounded to 9 codepoints (<= 36 UTF-8 bytes) by the clamp in
+// ParsedText::addWord. focusSuffixX is the pre-computed pixel offset from the
+// word start to the regular suffix. Both arrays are omitted from the arena
+// entirely when no word on the line has a split (zero per-word RAM cost when
+// focus reading is disabled).
 class TextBlock final : public Block {
  private:
-  std::vector<std::string> words;
-  std::vector<int16_t> wordXpos;
-  std::vector<EpdFontFamily::Style> wordStyles;
-  // Per-word focus boundary: N > 0 means the first N bytes of words[i] are rendered bold,
-  // the remainder in the base style. 0 means no split (whole word uses wordStyles[i]).
-  // N encodes the bold PREFIX length only — bounded to 9 codepoints (≤36 UTF-8 bytes) by
-  // FOCUS_READING_PERCENT's 1..9 clamp in ParsedText::addWord, so it always fits in uint8_t.
-  // Vector is empty when no focus splits exist anywhere in the block (zero per-word RAM cost
-  // when focus reading is disabled, or on lines that happen to contain no splittable words).
-  std::vector<uint8_t> wordFocusBoundary;
-  // Pre-computed pixel offset from word start to the regular suffix, stored when boundary > 0.
-  // Eliminates getTextAdvanceX from the render path. 0 when boundary == 0.
-  // Empty in lockstep with wordFocusBoundary.
-  std::vector<uint16_t> wordFocusSuffixX;
   BlockStyle blockStyle;
+  uint16_t numWords = 0;
+  uint16_t textBytes = 0;  // total size of the text region, including NULs
+  bool focusPresent = false;
+  bool isValid = true;
+  // The ONLY allocation: makeUniqueNoThrow, so OOM yields an invalid block
+  // instead of abort() (bare new is not nothrow with -fno-exceptions).
+  std::unique_ptr<uint8_t[]> arena;
+  // Typed views into the arena, bound once after the arena is filled. All
+  // 16-bit bases sit at even offsets, so direct dereference is alignment-safe.
+  const uint16_t* textOffArr = nullptr;
+  const int16_t* xposArr = nullptr;
+  const uint16_t* focusSuffixXArr = nullptr;  // null when !focusPresent
+  const uint8_t* stylesArr = nullptr;
+  const uint8_t* focusBoundaryArr = nullptr;  // null when !focusPresent
+  const char* textArr = nullptr;
+
+  TextBlock() = default;  // deserialize() fills the fields directly
+  static size_t arenaSize(uint16_t wordCount, bool hasFocus, uint16_t textBytes);
+  void bindArenaPointers();
 
  public:
-  explicit TextBlock(std::vector<std::string> words, std::vector<int16_t> word_xpos,
-                     std::vector<EpdFontFamily::Style> word_styles, std::vector<uint8_t> focus_boundary,
-                     std::vector<uint16_t> focus_suffix_x, const BlockStyle& blockStyle = BlockStyle())
-      : words(std::move(words)),
-        wordXpos(std::move(word_xpos)),
-        wordStyles(std::move(word_styles)),
-        wordFocusBoundary(std::move(focus_boundary)),
-        wordFocusSuffixX(std::move(focus_suffix_x)),
-        blockStyle(blockStyle) {}
+  // Flatten-on-construct: copies the layout-time vectors into the arena; the
+  // vectors die with the caller. On arena OOM the block is empty and valid()
+  // is false -- callers must check and fail the line instead of using it.
+  explicit TextBlock(const std::vector<std::string>& words, const std::vector<int16_t>& wordXpos,
+                     const std::vector<EpdFontFamily::Style>& wordStyles, const std::vector<uint8_t>& focusBoundary,
+                     const std::vector<uint16_t>& focusSuffixX, const BlockStyle& blockStyle = BlockStyle());
   ~TextBlock() override = default;
+  TextBlock(const TextBlock&) = delete;
+  TextBlock& operator=(const TextBlock&) = delete;
+
   void setBlockStyle(const BlockStyle& blockStyle) { this->blockStyle = blockStyle; }
   const BlockStyle& getBlockStyle() const { return blockStyle; }
-  const std::vector<std::string>& getWords() const { return words; }
-  bool isEmpty() override { return words.empty(); }
-  size_t wordCount() const { return words.size(); }
-  // given a renderer works out where to break the words into lines
+  bool isEmpty() override { return numWords == 0; }
+  bool valid() const { return isValid; }
+  uint16_t wordCount() const { return numWords; }
+  // NUL-terminated by construction; safe to pass to C APIs directly.
+  const char* wordText(const uint16_t i) const { return textArr + textOffArr[i]; }
+  uint16_t wordTextLen(const uint16_t i) const {
+    const uint16_t end = (i + 1 < numWords) ? textOffArr[i + 1] : textBytes;
+    return end - textOffArr[i] - 1;  // exclude the NUL
+  }
+  int16_t wordXpos(const uint16_t i) const { return xposArr[i]; }
+  EpdFontFamily::Style wordStyle(const uint16_t i) const { return static_cast<EpdFontFamily::Style>(stylesArr[i]); }
+  uint8_t focusBoundary(const uint16_t i) const { return focusPresent ? focusBoundaryArr[i] : 0; }
+  uint16_t focusSuffixX(const uint16_t i) const { return focusPresent ? focusSuffixXArr[i] : 0; }
+
   void render(const GfxRenderer& renderer, int fontId, int x, int y) const;
   BlockType getType() override { return TEXT_BLOCK; }
   bool serialize(HalFile& file) const;

lib/Epub/Epub/parsers/ChapterHtmlSlimParser.cpp

@@ -239,7 +239,16 @@ void ChapterHtmlSlimParser::startNewTextBlock(const BlockStyle& blockStyle) {
       // open. Merge those into the new style so the first child in a container inherits
       // the container's vertical spacing.
       const auto style = currentTextBlock->getBlockStyle();
-      currentTextBlock->setBlockStyle(style.getCombinedBlockStyle(blockStyle, BlockStyle::CombineAxis::Vertical));
+      BlockStyle incoming = blockStyle;
+      if (style.fromBrElement) {
+        // The empty block was created by a <br> section separator. Inject a full line of
+        // blank space before the following paragraph so the scene/section break is visible.
+        // This only fires when the <br> block stayed empty (i.e. no inline text was added).
+        const int16_t lineHeight = static_cast<int16_t>(renderer.getLineHeight(fontId) * lineCompression + 0.5f);
+        incoming.marginTop = static_cast<int16_t>(incoming.marginTop + lineHeight);
+      }
+
+      currentTextBlock->setBlockStyle(style.getCombinedBlockStyle(incoming, BlockStyle::CombineAxis::Vertical));
 
       flushPendingAnchor();
       return;
@@ -855,7 +864,14 @@ void XMLCALL ChapterHtmlSlimParser::startElement(void* userData, const XML_Char*
         // flush word preceding <br/> to currentTextBlock before calling startNewTextBlock
         self->flushPartWordBuffer();
       }
-      self->startNewTextBlock(self->blockStyleStack.back().withoutBottom());
+      // Tag the new block so startNewTextBlock can inject a full line-height gap if
+      // the block remains empty (i.e. <br> is a section separator between paragraphs).
+      // If the block gets text added before the next block opens it becomes non-empty,
+      // goes through makePages() normally, and the flag has no effect (inline <br> case).
+      BlockStyle brStyle =
+          self->currentTextBlock ? self->currentTextBlock->getBlockStyle() : self->blockStyleStack.back();
+      brStyle.fromBrElement = true;
+      self->startNewTextBlock(brStyle);
     } else {
       self->currentCssStyle = cssStyle;
       const auto accumulated = self->blockStyleStack.back().getCombinedBlockStyle(userAlignmentBlockStyle,

lib/I18n/translations/english.yaml

@@ -18,6 +18,7 @@ STR_NO_CHAPTERS: "No chapters"
 STR_END_OF_BOOK: "End of book"
 STR_EMPTY_CHAPTER: "Empty chapter"
 STR_INDEXING: "Indexing"
+STR_INDEX_FAILED: "Failed to index - invalid book"
 STR_MEMORY_ERROR: "Memory error"
 STR_PAGE_LOAD_ERROR: "Page load error"
 STR_EMPTY_FILE: "Empty file"

lib/I18n/translations/italian.yaml

@@ -383,3 +383,6 @@ STR_DISABLED: "Disattivato"
 STR_BOOKMARK_OPTION: "Segnalibro"
 STR_KOSYNC: "KOSync"
 STR_PWR_BTN_FOOTNOTE_BACK: "Rientro rapido dalle note"
+STR_EOB_CONTINUE_WITH: "Continua con"
+STR_EOB_HOME: "Home"
+STR_INDEX_FAILED: "Indicizzazione fallita - libro non valido"

lib/KOReaderSync/KOReaderCredentialStore.cpp

@@ -1,118 +1,43 @@
 #include "KOReaderCredentialStore.h"
 
-#include <HalStorage.h>
 #include <Logging.h>
 #include <MD5Builder.h>
 #include <ObfuscationUtils.h>
-#include <Serialization.h>
-
-#include "KOReaderJsonIO.h"
-
-// Initialize the static instance
-KOReaderCredentialStore KOReaderCredentialStore::instance;
 
 namespace {
-// File format version (for binary migration)
-constexpr uint8_t KOREADER_FILE_VERSION = 1;
-
-// File paths
-constexpr char KOREADER_FILE_BIN[] = "/.crosspoint/koreader.bin";
-constexpr char KOREADER_FILE_JSON[] = "/.crosspoint/koreader.json";
-constexpr char KOREADER_FILE_BAK[] = "/.crosspoint/koreader.bin.bak";
-
 // Default sync server URL
 constexpr char DEFAULT_SERVER_URL[] = "https://sync.koreader.rocks:443";
-
-// Legacy obfuscation key - "KOReader" in ASCII (only used for binary migration)
-constexpr uint8_t LEGACY_OBFUSCATION_KEY[] = {0x4B, 0x4F, 0x52, 0x65, 0x61, 0x64, 0x65, 0x72};
-constexpr size_t LEGACY_KEY_LENGTH = sizeof(LEGACY_OBFUSCATION_KEY);
-
-void legacyDeobfuscate(std::string& data) {
-  for (size_t i = 0; i < data.size(); i++) {
-    data[i] ^= LEGACY_OBFUSCATION_KEY[i % LEGACY_KEY_LENGTH];
-  }
-}
 }  // namespace
 
-bool KOReaderCredentialStore::saveToFile() const {
-  Storage.mkdir("/.crosspoint");
-  return KOReaderJsonIO::save(*this, KOREADER_FILE_JSON);
+void KOReaderCredentialStore::toJson(JsonDocument& doc) const {
+  doc["username"] = getUsername();
+  doc["password_obf"] = obfuscation::obfuscateToBase64(getPassword());
+  doc["serverUrl"] = getServerUrl();
+  doc["matchMethod"] = static_cast<uint8_t>(getMatchMethod());
 }
 
-bool KOReaderCredentialStore::loadFromFile() {
-  // Try JSON first
-  if (Storage.exists(KOREADER_FILE_JSON)) {
-    String json = Storage.readFile(KOREADER_FILE_JSON);
-    if (!json.isEmpty()) {
-      bool resave = false;
-      bool result = KOReaderJsonIO::load(*this, json.c_str(), &resave);
-      if (result && resave) {
-        saveToFile();
-        LOG_DBG("KRS", "Resaved KOReader credentials to update format");
-      }
-      return result;
-    }
-  }
+bool KOReaderCredentialStore::fromJson(JsonVariantConst doc) {
+  std::string user = doc["username"] | "";
 
-  // Fall back to binary migration
-  if (Storage.exists(KOREADER_FILE_BIN)) {
-    if (loadFromBinaryFile()) {
-      if (saveToFile()) {
-        Storage.rename(KOREADER_FILE_BIN, KOREADER_FILE_BAK);
-        LOG_DBG("KRS", "Migrated koreader.bin to koreader.json");
-        return true;
-      } else {
-        LOG_ERR("KRS", "Failed to save KOReader credentials during migration");
-        return false;
-      }
-    }
-  }
+  bool needsResave = false;
+  std::string pass = extractPassword(doc, needsResave);
 
-  LOG_DBG("KRS", "No credentials file found");
-  return false;
-}
+  setCredentials(user, pass);
+  setServerUrl(doc["serverUrl"] | "");
 
-bool KOReaderCredentialStore::loadFromBinaryFile() {
-  HalFile file;
-  if (!Storage.openFileForRead("KRS", KOREADER_FILE_BIN, file)) {
-    return false;
-  }
-
-  uint8_t version;
-  serialization::readPod(file, version);
-  if (version != KOREADER_FILE_VERSION) {
-    LOG_DBG("KRS", "Unknown file version: %u", version);
-    return false;
-  }
-
-  if (file.available()) {
-    serialization::readString(file, username);
+  uint8_t method = doc["matchMethod"] | (uint8_t)0;
+  if (method <= static_cast<uint8_t>(DocumentMatchMethod::BINARY)) {
+    setMatchMethod(static_cast<DocumentMatchMethod>(method));
   } else {
-    username.clear();
+    LOG_DBG("KRS", "Invalid matchMethod %u in JSON, resetting to FILENAME", method);
+    setMatchMethod(DocumentMatchMethod::FILENAME);
   }
 
-  if (file.available()) {
-    serialization::readString(file, password);
-    legacyDeobfuscate(password);
-  } else {
-    password.clear();
+  if (needsResave) {
+    LOG_DBG("KRS", "Resaved KOReader credentials to update format");
+    saveToFile();
   }
 
-  if (file.available()) {
-    serialization::readString(file, serverUrl);
-  } else {
-    serverUrl.clear();
-  }
-
-  if (file.available()) {
-    uint8_t method;
-    serialization::readPod(file, method);
-    matchMethod = static_cast<DocumentMatchMethod>(method);
-  } else {
-    matchMethod = DocumentMatchMethod::FILENAME;
-  }
-
-  LOG_DBG("KRS", "Loaded KOReader credentials from binary for user: %s", username.c_str());
   return true;
 }
 

lib/KOReaderSync/KOReaderCredentialStore.h

@@ -1,4 +1,7 @@
 #pragma once
+#include <ArduinoJson.h>
+#include <PersistableStore.h>
+
 #include <cstdint>
 #include <string>
 
@@ -14,9 +17,9 @@ enum class DocumentMatchMethod : uint8_t {
  * and base64-encoded before writing to JSON (not cryptographically secure,
  * but prevents casual reading and ties credentials to the specific device).
  */
-class KOReaderCredentialStore {
+
+class KOReaderCredentialStore : public PersistableStore<KOReaderCredentialStore> {
  private:
-  static KOReaderCredentialStore instance;
   std::string username;
   std::string password;
   std::string serverUrl;                                            // Custom sync server URL (empty = default)
@@ -24,20 +27,14 @@ class KOReaderCredentialStore {
 
   // Private constructor for singleton
   KOReaderCredentialStore() = default;
+  ~KOReaderCredentialStore() = default;
 
-  bool loadFromBinaryFile();
+  friend class PersistableStore<KOReaderCredentialStore>;
 
  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();
+  static const char* getFilePath() { return "/.crosspoint/koreader.json"; }
+  void toJson(JsonDocument& doc) const;
+  bool fromJson(JsonVariantConst doc);
 
   // Credential management
   void setCredentials(const std::string& user, const std::string& pass);

lib/KOReaderSync/KOReaderJsonIO.cpp

@@ -1,51 +0,0 @@
-#include "KOReaderJsonIO.h"
-
-#include <ArduinoJson.h>
-#include <HalStorage.h>
-#include <Logging.h>
-#include <ObfuscationUtils.h>
-
-#include "KOReaderCredentialStore.h"
-
-namespace KOReaderJsonIO {
-
-bool save(const KOReaderCredentialStore& store, const char* path) {
-  JsonDocument doc;
-  doc["username"] = store.getUsername();
-  doc["password_obf"] = obfuscation::obfuscateToBase64(store.getPassword());
-  doc["serverUrl"] = store.getServerUrl();
-  doc["matchMethod"] = static_cast<uint8_t>(store.getMatchMethod());
-
-  String json;
-  serializeJson(doc, json);
-  return Storage.writeFile(path, json);
-}
-
-bool load(KOReaderCredentialStore& store, const char* json, bool* needsResave) {
-  if (needsResave) *needsResave = false;
-  JsonDocument doc;
-  auto error = deserializeJson(doc, json);
-  if (error) {
-    LOG_ERR("KRS", "JSON parse error: %s", error.c_str());
-    return false;
-  }
-
-  std::string user = doc["username"] | std::string("");
-
-  bool ok = false;
-  std::string pass = obfuscation::deobfuscateFromBase64(doc["password_obf"] | "", &ok);
-  if (!ok || pass.empty()) {
-    pass = doc["password"] | std::string("");
-    if (!pass.empty() && needsResave) *needsResave = true;
-  }
-
-  store.setCredentials(user, pass);
-  store.setServerUrl(doc["serverUrl"] | std::string(""));
-
-  uint8_t method = doc["matchMethod"] | (uint8_t)0;
-  store.setMatchMethod(static_cast<DocumentMatchMethod>(method));
-
-  return true;
-}
-
-}  // namespace KOReaderJsonIO

lib/KOReaderSync/KOReaderJsonIO.h

@@ -1,8 +0,0 @@
-#pragma once
-
-class KOReaderCredentialStore;
-
-namespace KOReaderJsonIO {
-bool save(const KOReaderCredentialStore& store, const char* path);
-bool load(KOReaderCredentialStore& store, const char* json, bool* needsResave);
-}  // namespace KOReaderJsonIO

lib/Serialization/PersistableStore.cpp

@@ -0,0 +1,45 @@
+#include "PersistableStore.h"
+
+#include <HalStorage.h>
+#include <Logging.h>
+#include <ObfuscationUtils.h>
+
+bool PersistableStoreBase::writeDocToFile(const char* path, const JsonDocument& doc) {
+  Storage.mkdir("/.crosspoint");
+  String json;
+  serializeJson(doc, json);
+  if (!Storage.writeFile(path, json)) {
+    LOG_ERR("PERSIST", "Failed to write %s", path);
+    return false;
+  }
+  return true;
+}
+
+bool PersistableStoreBase::readDocFromFile(const char* path, JsonDocument& doc) {
+  if (!Storage.exists(path)) {
+    return false;  // Expected on first boot — not an error.
+  }
+  String json = Storage.readFile(path);
+  if (json.isEmpty()) {
+    LOG_ERR("PERSIST", "Failed to read %s (empty)", path);
+    return false;
+  }
+  auto error = deserializeJson(doc, json);
+  if (error) {
+    LOG_ERR("PERSIST", "JSON parse error in %s: %s", path, error.c_str());
+    return false;
+  }
+  return true;
+}
+
+std::string PersistableStoreBase::extractPassword(JsonVariantConst doc, bool& needsResave) {
+  bool ok = false;
+  std::string pass = obfuscation::deobfuscateFromBase64(doc["password_obf"] | "", &ok);
+  if (!ok) {
+    // Deobfuscation failed — fall back to legacy plaintext password.
+    pass = doc["password"] | "";
+    if (!pass.empty()) needsResave = true;
+  }
+  // A successfully decoded empty string is a legitimate value; preserve as-is.
+  return pass;
+}

lib/Serialization/PersistableStore.h

@@ -0,0 +1,82 @@
+#pragma once
+
+#include <Arduino.h>
+#include <ArduinoJson.h>
+
+#include <string>
+
+/**
+ * @brief Non-template core of PersistableStore.
+ *
+ * All ArduinoJson parse/serialize machinery is instantiated once here (in
+ * PersistableStore.cpp) instead of in every store's translation unit. GCC
+ * emits the JSON serializer/parser templates as local .isra clones per TU
+ * (~0.5KB each), so keeping serializeJson/deserializeJson out of the stores
+ * is what makes the abstraction flash-neutral.
+ */
+class PersistableStoreBase {
+ protected:
+  PersistableStoreBase() = default;
+  ~PersistableStoreBase() = default;
+
+  // Serializes doc and writes it to path (ensures /.crosspoint exists). Logs on failure.
+  static bool writeDocToFile(const char* path, const JsonDocument& doc);
+
+  // Reads path and parses it into doc. Returns false silently when the file
+  // does not exist (expected on first boot); logs on read/parse failure.
+  static bool readDocFromFile(const char* path, JsonDocument& doc);
+
+  /**
+   * Helper function for extracting an obfuscated password from a JSON value.
+   * Accepts JsonVariantConst so callers can pass either a whole JsonDocument
+   * or a JsonObject element (e.g. inside an array iteration).
+   * If the decoded password requires a resave (e.g. from plaintext fallback), `needsResave` is set to true.
+   */
+  static std::string extractPassword(JsonVariantConst doc, bool& needsResave);
+};
+
+/**
+ * @brief Base class for persistable singletons using CRTP.
+ *
+ * Derived classes must provide:
+ * - A private default constructor
+ * - friend class PersistableStore<Derived>;
+ * - static const char* getFilePath();
+ * - void toJson(JsonDocument& doc) const;
+ * - bool fromJson(JsonVariantConst doc);
+ *
+ * Note for implementers: read string values as `const char*` (e.g.
+ * `obj["name"] | ""`), never as `| std::string("")` — ArduinoJson's
+ * std::string converter drags a per-TU copy of the whole JSON serializer
+ * into flash via its serializeJson fallback.
+ */
+template <typename T>
+class PersistableStore : public PersistableStoreBase {
+ protected:
+  PersistableStore() = default;
+  ~PersistableStore() = default;
+
+ public:
+  // Delete copy constructor and assignment
+  PersistableStore(const PersistableStore&) = delete;
+  PersistableStore& operator=(const PersistableStore&) = delete;
+
+  static T& getInstance() {
+    static T instance;
+    return instance;
+  }
+
+  bool saveToFile() const {
+    JsonDocument doc;
+    static_cast<const T*>(this)->toJson(doc);
+    return writeDocToFile(T::getFilePath(), doc);
+  }
+
+  bool loadFromFile() {
+    JsonDocument doc;
+    if (!readDocFromFile(T::getFilePath(), doc)) {
+      return false;
+    }
+    return static_cast<T*>(this)->fromJson(doc.as<JsonVariantConst>());
+  }
+};