refactor(ereader): delete the import-time Page monkey patch (R5)

ereader_layout.py defined _add_page_methods() and called it at import
time, attaching can_fit_line and available_width to the Page class if
they were absent. Page defines both, so the patch never fired - but the
two definitions of can_fit_line disagreed:

    Page          can_fit_line(baseline_spacing, ascent=0, descent=0)
    monkey patch  can_fit_line(line_height)

The patched version had no way to express descent, which is exactly the
clipping bug S2 fixed. Had Page.can_fit_line ever been renamed or moved,
this would have silently reinstated pre-S2 behaviour as a side effect of
importing a module in a different package.

Import-time patching of another module's class has no place here. If the
layout engine needs something from Page, it belongs on Page.

Tests pin the outcome: the module exposes no patcher, Page owns both
attributes, and can_fit_line still rejects a line whose descender would
hang past the content box.

894 passed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/layout/test_ereader_layout.py

@@ -899,5 +899,43 @@ class TestBidirectionalLayouter:
         assert next_pos == position  # No progress possible
 
 
+class TestNoPageMonkeyPatching:
+    """
+    R5: importing this module used to run _add_page_methods(), which attached
+    can_fit_line/available_width to Page if they were absent. They are not
+    absent, so it never fired - but its can_fit_line took (line_height) and
+    ignored descenders, while Page's takes (baseline_spacing, ascent, descent).
+    Had Page's ever been renamed, the import would have silently reinstated the
+    pre-S2 clipping bug from another package.
+    """
+
+    def test_module_does_not_patch_page(self):
+        import pyWebLayout.layout.ereader_layout as ereader_layout
+
+        assert not hasattr(ereader_layout, '_add_page_methods')
+
+    def test_page_owns_its_geometry_methods(self):
+        from pyWebLayout.concrete.page import Page
+
+        assert 'can_fit_line' in vars(Page)
+        assert 'available_width' in vars(Page)
+
+    def test_can_fit_line_still_accounts_for_descenders(self, sample_page_style):
+        """
+        The patched version took a single line_height and had no way to express
+        descent, so a descender hanging past the content box counted as fitting.
+        """
+        from pyWebLayout.concrete.page import Page
+
+        page = Page(size=(200, 100), style=sample_page_style)
+        content_y, content_h = page.content_rect[1], page.content_rect[3]
+        available = content_y + content_h - page._current_y_offset
+
+        assert page.can_fit_line(0, ascent=available, descent=0)
+        assert not page.can_fit_line(0, ascent=available, descent=1), \
+            "a descender past the content box must not be reported as fitting"
+        assert page.can_fit_line(0, ascent=available - 1, descent=1)
+
+
 if __name__ == "__main__":
     pytest.main([__file__, "-v"])