Picking up some itsthisjutin ideas

lib/KOReaderSync/ChapterXPathForwardMapper.h

@@ -9,4 +9,13 @@ namespace ChapterXPathIndexerInternal {
 
 std::string findXPathForProgressInternal(const std::shared_ptr<Epub>& epub, int spineIndex, float intraSpineProgress);
 
+// Find the full-ancestry XPath for the paragraphIndex-th direct-body-child <p> element.
+// paragraphIndex is 1-based, matching the section paragraph LUT and KOReader XPath convention.
+// seekHint is an optional XHTML byte offset to start scanning from (0 = scan from beginning).
+// startParagraphCount is the number of body-child <p> elements already seen before seekHint
+// (i.e. the paragraphIndex of the LUT entry at the seek page, minus 1). Ignored when seekHint=0.
+// Returns empty string on failure; caller should fall back to findXPathForProgressInternal.
+std::string findXPathForParagraphInternal(const std::shared_ptr<Epub>& epub, int spineIndex, uint16_t paragraphIndex,
+                                          uint32_t seekHint = 0, uint16_t startParagraphCount = 0);
+
 }  // namespace ChapterXPathIndexerInternal