fix(ereader): keep resume position when a block spans a page (S11)

render_page_forward discarded new_pos on the failure path, but a block that
only partially fitted has still advanced the position: paragraph_layouter
reports the word it stopped at, and _layout_paragraph_on_page packs it into
new_pos. Dropping it told the caller no progress was made, so navigation
dead-ended on any paragraph larger than a single page - the reader saw "end of
document" mid-book.

A 2877-word paragraph at 800x600 rendered 26 lines and reported the start
position back; it now paginates across 12 pages.

Also guard the navigation loop: EreaderManager.next_page treats no-progress as
end-of-document, which is only correct at the actual end. Anywhere else it now
logs the offending block index and skips that block, so a future layout bug
costs one block rather than the rest of the book.

pyWebLayout/layout/ereader_layout.py

@@ -344,7 +344,14 @@ class BidirectionalLayouter:
                 scaled_block, page, current_pos, font_scale)
 
             if not success:
-                # Block doesn't fit, we're done with this page
+                # The block did not fit in its entirety. It may still have been
+                # laid out partially - a paragraph larger than one page places as
+                # many lines as fit and reports the word it stopped at. Keeping
+                # that resume point is what allows the next page to continue;
+                # discarding it tells the caller no progress was made, which
+                # dead-ends navigation on the block forever.
+                if self._position_compare(new_pos, current_pos) > 0:
+                    current_pos = new_pos
                 break
 
             # Add inter-block spacing after successfully laying out a block

pyWebLayout/layout/ereader_manager.py

@@ -9,6 +9,7 @@ into a unified, easy-to-use API.
 from __future__ import annotations
 from typing import List, Dict, Optional, Tuple, Any, Callable
 import json
+import logging
 from pathlib import Path
 
 from .ereader_layout import RenderingPosition, ChapterNavigator, ChapterInfo
@@ -20,6 +21,8 @@ from pyWebLayout.style.page_style import PageStyle
 from pyWebLayout.style.fonts import BundledFont
 from pyWebLayout.layout.document_layouter import image_layouter
 
+logger = logging.getLogger(__name__)
+
 
 class BookmarkManager:
     """
@@ -417,6 +420,21 @@ class EreaderLayoutManager:
             self._notify_position_changed()
             return self.get_current_page()
 
+        # No progress. That is the correct answer only at the end of the
+        # document; anywhere else a block has failed to lay out and would trap
+        # the reader on this page. Skipping the block costs one block, not the
+        # rest of the book.
+        if self.current_position.block_index < len(self.blocks):
+            logger.error(
+                "Block %d made no layout progress; skipping it. This is a layout "
+                "bug - the block placed nothing and reported no resume point.",
+                self.current_position.block_index)
+            self.current_position = RenderingPosition(
+                chapter_index=self.current_position.chapter_index,
+                block_index=self.current_position.block_index + 1)
+            self._notify_position_changed()
+            return self.get_current_page()
+
         return None  # At end of document
 
     def previous_page(self) -> Optional[Page]: