fix(epub): decode percent-encoded internal asset paths so assets render correctly (#2249)

## Summary

* **What is the goal of this PR?** 
* Fix EPUBs where internal file references are written in URL-style
escaped form, like spaces appearing as `%20`, so the reader can find the
right files instead of treating those references as missing.
* **What changes are included?**
* Added a small shared helper that converts those escaped EPUB-internal
paths back into their normal filenames before we try to look them up.
* Applied that cleanup step across the EPUB parsing flow wherever we
resolve internal references, including cover images, manifest items, TOC
links, spine entries, and inline HTML images.
* Kept the change narrowly focused on EPUB-internal asset resolution
rather than changing broader URL or networking behavior.

## Additional Context

* The user-facing bug here is that some books package their internal
filenames in an escaped form, so a file like `Chapter 1.xhtml` may be
referenced more like `Chapter%201.xhtml`. The reader was treating that
escaped text as the literal filename, which means otherwise-valid books
could lose images, covers, or chapter targets because the lookup no
longer matched the real file inside the EPUB.
* Risk is intentionally low. The helper only rewrites valid `%XX` escape
sequences and leaves malformed input alone, so it should improve
compatibility with escaped filenames without broadening the parser’s
behavior in unrelated cases.

## Local Testing Performed
* This was tested on my device with the user-provided optimized epub
that was not rendering images within the text prior to this fix (cover
image and chapter headers were rendering fine):

[orv_main_baseline.epub.zip](https://github.com/user-attachments/files/28529545/orv_main_baseline.epub.zip)
* This was also tested by the user with a local build and the affected
epub and confirmed to be working

## Steps for Testing
* Try to open the affected epub (linked above) or any epub that has
similar percent-encoding on a build prior to this fix.
* Apply this fix, clear book cache, and re-open the affected book.
* Images should render properly.
---

### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _**< YES >**_

lib/Epub/Epub.cpp

@@ -118,7 +118,7 @@ bool Epub::parseContentOpf(BookMetadataCache::BookMetadata& bookMetadata, const
       }
 
       if (!imageRef.empty()) {
-        bookMetadata.coverItemHref = FsHelpers::normalisePath(coverPageBase + imageRef);
+        bookMetadata.coverItemHref = FsHelpers::normalisePath(FsHelpers::decodeUriEscapes(coverPageBase + imageRef));
         LOG_DBG("EBP", "Found cover image from guide: %s", bookMetadata.coverItemHref.c_str());
       }
     }

lib/Epub/Epub/BookMetadataCache.cpp

@@ -9,7 +9,7 @@
 #include "FsHelpers.h"
 
 namespace {
-constexpr uint8_t BOOK_CACHE_VERSION = 6;
+constexpr uint8_t BOOK_CACHE_VERSION = 7;
 constexpr char bookBinFile[] = "/book.bin";
 constexpr char tmpSpineBinFile[] = "/spine.bin.tmp";
 constexpr char tmpTocBinFile[] = "/toc.bin.tmp";

lib/Epub/Epub/parsers/ChapterHtmlSlimParser.cpp

@@ -445,7 +445,7 @@ void XMLCALL ChapterHtmlSlimParser::startElement(void* userData, const XML_Char*
 
         {
           // Resolve the image path relative to the HTML file
-          std::string resolvedPath = FsHelpers::normalisePath(self->contentBase + src);
+          std::string resolvedPath = FsHelpers::normalisePath(FsHelpers::decodeUriEscapes(self->contentBase + src));
 
           if (ImageDecoderFactory::isFormatSupported(resolvedPath)) {
             // Create a unique filename for the cached image

lib/Epub/Epub/parsers/ContentOpfParser.cpp

@@ -186,7 +186,7 @@ void XMLCALL ContentOpfParser::startElement(void* userData, const XML_Char* name
       if (strcmp(atts[i], "id") == 0) {
         itemId = atts[i + 1];
       } else if (strcmp(atts[i], "href") == 0) {
-        href = FsHelpers::normalisePath(self->baseContentPath + atts[i + 1]);
+        href = FsHelpers::normalisePath(FsHelpers::decodeUriEscapes(self->baseContentPath + atts[i + 1]));
       } else if (strcmp(atts[i], "media-type") == 0) {
         mediaType = atts[i + 1];
       } else if (strcmp(atts[i], "properties") == 0) {
@@ -315,7 +315,7 @@ void XMLCALL ContentOpfParser::startElement(void* userData, const XML_Char* name
       if (strcmp(atts[i], "type") == 0) {
         type = atts[i + 1];
       } else if (strcmp(atts[i], "href") == 0) {
-        guideHref = FsHelpers::normalisePath(self->baseContentPath + atts[i + 1]);
+        guideHref = FsHelpers::normalisePath(FsHelpers::decodeUriEscapes(self->baseContentPath + atts[i + 1]));
       }
     }
     if (!guideHref.empty()) {

lib/Epub/Epub/parsers/TocNavParser.cpp

@@ -126,13 +126,14 @@ void XMLCALL TocNavParser::endElement(void* userData, const XML_Char* name) {
   if (strcmp(name, "a") == 0 && self->state == IN_ANCHOR) {
     // Create TOC entry when closing anchor tag (we have all data now)
     if (!self->currentLabel.empty() && !self->currentHref.empty()) {
-      std::string href = FsHelpers::normalisePath(self->baseContentPath + self->currentHref);
+      const std::string rawTarget = self->baseContentPath + self->currentHref;
+      const size_t pos = rawTarget.find('#');
+      const std::string rawPath = pos == std::string::npos ? rawTarget : rawTarget.substr(0, pos);
+      std::string href = FsHelpers::normalisePath(FsHelpers::decodeUriEscapes(rawPath));
       std::string anchor;
 
-      const size_t pos = href.find('#');
       if (pos != std::string::npos) {
-        anchor = href.substr(pos + 1);
-        href = href.substr(0, pos);
+        anchor = FsHelpers::decodeUriEscapes(rawTarget.substr(pos + 1));
       }
 
       if (self->cache) {

lib/Epub/Epub/parsers/TocNcxParser.cpp

@@ -145,13 +145,14 @@ void XMLCALL TocNcxParser::endElement(void* userData, const XML_Char* name) {
     // This is the safest place to push the data, assuming <navLabel> always comes before <content>.
     // NCX spec says navLabel comes before content.
     if (!self->currentLabel.empty() && !self->currentSrc.empty()) {
-      std::string href = FsHelpers::normalisePath(self->baseContentPath + self->currentSrc);
+      const std::string rawTarget = self->baseContentPath + self->currentSrc;
+      const size_t pos = rawTarget.find('#');
+      const std::string rawPath = pos == std::string::npos ? rawTarget : rawTarget.substr(0, pos);
+      std::string href = FsHelpers::normalisePath(FsHelpers::decodeUriEscapes(rawPath));
       std::string anchor;
 
-      const size_t pos = href.find('#');
       if (pos != std::string::npos) {
-        anchor = href.substr(pos + 1);
-        href = href.substr(0, pos);
+        anchor = FsHelpers::decodeUriEscapes(rawTarget.substr(pos + 1));
       }
 
       if (self->cache) {

lib/FsHelpers/FsHelpers.cpp

@@ -7,6 +7,34 @@
 
 namespace FsHelpers {
 
+namespace {
+bool isHexDigit(const char c) { return (c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F'); }
+
+uint8_t hexValue(const char c) {
+  if (c >= '0' && c <= '9') return static_cast<uint8_t>(c - '0');
+  if (c >= 'a' && c <= 'f') return static_cast<uint8_t>(10 + (c - 'a'));
+  return static_cast<uint8_t>(10 + (c - 'A'));
+}
+}  // namespace
+
+std::string decodeUriEscapes(const std::string& path) {
+  std::string decoded;
+  decoded.reserve(path.size());
+
+  for (size_t i = 0; i < path.size(); i++) {
+    if (path[i] == '%' && i + 2 < path.size() && isHexDigit(path[i + 1]) && isHexDigit(path[i + 2])) {
+      const uint8_t value = static_cast<uint8_t>((hexValue(path[i + 1]) << 4) | hexValue(path[i + 2]));
+      decoded += static_cast<char>(value);
+      i += 2;
+      continue;
+    }
+
+    decoded += path[i];
+  }
+
+  return decoded;
+}
+
 std::string normalisePath(const std::string& path) {
   std::vector<std::string> components;
   std::string component;

lib/FsHelpers/FsHelpers.h

@@ -7,6 +7,8 @@
 
 namespace FsHelpers {
 
+std::string decodeUriEscapes(const std::string& path);
+
 std::string normalisePath(const std::string& path);
 
 void sortFileList(std::vector<std::string>& strs);