Avoid OOM diring HTML parsing by reducing max block size and freeing unneeded buffers

lib/Epub/Epub/ParsedText.cpp

@@ -355,12 +355,19 @@ void ParsedText::layoutAndExtractLines(
     }
   }
 
-  // Remove consumed words so size() reflects only remaining words
+  // Remove consumed words so size() reflects only remaining words, then
+  // release excess capacity.  Without shrink_to_fit the vector retains a
+  // large allocation from before the flush; the next paragraph fills it
+  // back up and eventually needs an even larger contiguous realloc.
   if (lineCount > 0) {
     const size_t consumed = lineBreakIndices[lineCount - 1];
     words.erase(words.begin(), words.begin() + consumed);
     wordStyles.erase(wordStyles.begin(), wordStyles.begin() + consumed);
     wordContinues.erase(wordContinues.begin(), wordContinues.begin() + consumed);
+    words.shrink_to_fit();
+    wordStyles.shrink_to_fit();
+    wordContinues.shrink_to_fit();
+    isContinuation_ = !includeLastLine;
   }
 }
 

lib/Epub/Epub/parsers/ChapterHtmlSlimParser.cpp

@@ -1207,11 +1207,12 @@ void XMLCALL ChapterHtmlSlimParser::characterData(void* userData, const XML_Char
     self->partWordBuffer[self->partWordBufferIndex++] = s[i];
   }
 
-  // If we have > 750 words buffered up, perform the layout and consume out all but the last line
-  // There should be enough here to build out 1-2 full pages and doing this will free up a lot of
-  // memory.
-  // Spotted when reading Intermezzo, there are some really long text blocks in there.
-  if (self->currentTextBlock->size() > 750) {
+  // Flush when words approach the doubling boundary that would require a
+  // large contiguous realloc.  96 fires before capacity reaches 128
+  // (the next doubling after 64), keeping the realloc below 1.5KB and
+  // releasing excess capacity via shrink_to_fit in layoutAndExtractLines.
+  // The original 750-word threshold was too late for low-heap devices.
+  if (self->currentTextBlock->size() > 96) {
     LOG_DBG("EHP", "Text block too long, splitting into multiple pages");
     const int horizontalInset = self->currentTextBlock->getBlockStyle().totalHorizontalInset();
     const uint16_t effectiveWidth = (horizontalInset < self->viewportWidth)