Find the last message body without walking the whole document

evidence/dm-initial-publication-20261008/README.md

@@ -958,3 +958,25 @@ worst39.9ms; visible53/170.1/worst6.71ms. No broad latency improvement claim.
 Exact raw checks: title-scroll-installed.log, title-scroll-wheel.log and
 title-scroll-wheel/ under existing dm-native-caption scratch. Published the
 reviewed combined cohort for new launches; backend and existing windows remain.
+
+## Visible demand revokes pending body retirement
+
+Toad579 fd5dfde01 derives retirement eligibility from the original
+DocumentViewport.requires_body at preflight, after asynchronous capture and
+inside original retirement custody. LiveBody keeps its identity when demanded;
+that identity alone therefore cannot authorize pruning a newly visible body.
+No new visibility field, cache or lifetime owner. The duplicate release guard
+is deleted because the same original currentness check now carries demand.
+
+Real native App source and exact installed controls passed: an acquired
+capture exposed by actual scrolling retains original reconstructible children;
+visible preflight refuses retirement; offscreen retirement still completes.
+An initial control incorrectly included the fixed header in the retireable
+cohort; negative retained, final control uses reconstructible_children.
+
+Installed sidebar drag completed with36 raw motions and no App error. Seven
+frames, frame gaps up to147ms and final width after745ms remain slow. This is
+not a performance pass. Current wheel is published for new launches through
+the reviewed original publication owner; existing windows retain loaded code.
+Exact checks/publication live under visible-retirement-delivery-20261008 and
+retirement-installed.log/retirement-sidebar-drag.log in existing scratch.

src/toad/widgets/viewport_body.py

@@ -1128,7 +1128,7 @@ def source_tail(self) -> ViewportBody | None:
         Native document order already owns their relation; warm membership
         and registration order do not supply another chronology.
         """
-        return next(reversed(tuple(self.body_roots())), None)
+        return next(self.body_roots(reverse=True), None)
 
     @property
     def source_tail_visible(self) -> bool:
@@ -1137,13 +1137,17 @@ def source_tail_visible(self) -> bool:
 
     def requires_body(self, owner, *, visible=None, protected=None) -> bool:
         """Native exposure and current interaction own source admission."""
+        if owner not in self.owners:
+            return False
         if visible is None:
             visible = self.window.screen._compositor.visible_widgets
+        if owner in visible:
+            return True
         if protected is None:
             protected = self.protected()
-        return owner in self.owners and (owner in visible or owner in protected)
+        return owner in protected
 
-    def body_roots(self):
+    def body_roots(self, *, reverse: bool = False):
         """Native document order, stopping at each registered body boundary.
 
         Descendants belong to that body's materialization, not to another
@@ -1152,13 +1156,13 @@ def body_roots(self):
         """
         if not self.owners:
             return
-        pending = list(reversed(self.window.children))
+        pending = list(self.window.children if reverse else reversed(self.window.children))
         while pending:
             node = pending.pop()
             if node in self.owners:
                 yield node
             else:
-                pending.extend(reversed(node.children))
+                pending.extend(node.children if reverse else reversed(node.children))
 
     def geometry_targets(self) -> tuple[Widget, ...]:
         """Each body's current resource owns its actual geometry demand."""

tests/viewport_body_order_pilot.py

@@ -54,6 +54,18 @@ async def settle():
             await settle()
             await viewport.suspend_source()
             assert tuple(viewport.body_roots()) == tuple(docs)
+            if '--tail-traversal' in sys.argv:
+                assert tuple(viewport.body_roots(reverse=True)) == tuple(reversed(docs))
+                assert viewport.source_tail is docs[-1]
+                view.contents.move_child(docs[-1], before=docs[0])
+                assert viewport.source_tail is docs[-2]
+                await docs[-2].remove()
+                assert viewport.source_tail is docs[-3]
+                assert tuple(viewport.body_roots(reverse=True)) == tuple(
+                    reversed((docs[-1], *docs[:-2])))
+                assert app._exception is None
+                print('PASS: current native reorder and removal determine tail and reverse body order')
+                return
             native_descendants = len(window.walk_children())
             assert native_descendants > 400
             originals = tuple(docs)