fix for reverse redering on restart

pyWebLayout/layout/ereader_layout.py

@@ -337,8 +337,17 @@ class BidirectionalLayouter:
             comparison = self._position_compare(actual_end, end_position)
 
             # Perfect match or close enough (within same block)
+            # BUT: ensure we actually moved backward (estimated_start < end_position)
             if comparison == 0:
-                return page, estimated_start
+                # Check if we actually found a valid previous page
+                if self._position_compare(estimated_start, end_position) < 0:
+                    return page, estimated_start
+                # If estimated_start >= end_position, we haven't moved backward
+                # Continue iterating to find a better position
+                elif iteration == 0:
+                    # On first iteration, if we can't find a previous position,
+                    # we're likely at or near the beginning
+                    break
 
             # Track best result so far
             distance = abs(actual_end.block_index - end_position.block_index)
@@ -357,7 +366,39 @@ class BidirectionalLayouter:
                 estimated_start.word_index = 0
 
         # If we exhausted iterations, return best result found
-        return best_page if best_page else page, best_start
+        # BUT: ensure we didn't return the same position (no backward progress)
+        final_page = best_page if best_page else page
+        final_start = best_start
+
+        # Safety check: if final_start >= end_position, we failed to move backward
+        # This can happen at the beginning of the document or when estimation failed
+        if self._position_compare(final_start, end_position) >= 0:
+            # Can't go further back - check if we're at the absolute beginning
+            if end_position.block_index == 0 and end_position.word_index == 0:
+                # Already at beginning, return as-is
+                return final_page, final_start
+
+            # Fallback strategy: try a more aggressive backward jump
+            # Start from several blocks before the current position
+            blocks_to_jump = max(1, min(5, end_position.block_index))
+            fallback_pos = RenderingPosition(
+                chapter_index=end_position.chapter_index,
+                block_index=max(0, end_position.block_index - blocks_to_jump),
+                word_index=0
+            )
+
+            # Render forward from the fallback position
+            fallback_page, fallback_end = self.render_page_forward(fallback_pos, font_scale)
+
+            # Verify the fallback actually moved us backward
+            if self._position_compare(fallback_pos, end_position) < 0:
+                return fallback_page, fallback_pos
+
+            # If even the fallback didn't work, we're likely at the beginning
+            # Return a page starting from the beginning
+            return self.render_page_forward(RenderingPosition(), font_scale)
+
+        return final_page, final_start
 
     def _scale_block_fonts(self, block: Block, font_scale: float) -> Block:
         """Apply font scaling to all fonts in a block"""

pyWebLayout/layout/page_buffer.py

@@ -420,12 +420,18 @@ class BufferedPageRenderer:
         cached_page = self.buffer.get_page(end_position)
         if cached_page:
             # Get previous position from reverse position map
-            prev_pos = self.buffer.reverse_position_map.get(end_position, end_position)
+            prev_pos = self.buffer.reverse_position_map.get(end_position)
 
-            # Start background rendering for previous pages
+            # Only use cache if we have the reverse position mapping
-            self.buffer.start_background_rendering(end_position, 'backward')
+            # Otherwise, we need to compute it
+            if prev_pos is not None:
+                # Start background rendering for previous pages
+                self.buffer.start_background_rendering(end_position, 'backward')
 
-            return cached_page, prev_pos
+                return cached_page, prev_pos
+
+            # Cache hit for the page, but we don't have the reverse position
+            # Fall through to compute it below
 
         # Render the page directly
         page, start_pos = self.layouter.render_page_backward(end_position, font_scale)