A send right after a view refreshes its page reader is not refused as a changed route

src/toad/transcript_preparation.py

@@ -7,6 +7,7 @@
 from collections.abc import Awaitable, Callable
 from dataclasses import dataclass, field, replace
 from itertools import islice
+from pathlib import Path
 from typing import TYPE_CHECKING, ClassVar
 from weakref import ReferenceType, ref
 
@@ -507,6 +508,10 @@ class ReplaceablePageSource(PreparedPageSource):
     @abstractmethod
     def replacement(self, through) -> ReplaceablePageSource: ...
 
+    def reads_from(self, root: str | Path) -> bool:
+        """Whether this reader reads a conversation from ``root``; a closed one reads none."""
+        return False
+
 
 class SavedHistory(ReplaceablePageSource):
     """Prepared pages for a snapshot; storage and work limits belong to the runtime.

src/toad/wire_history.py

@@ -439,15 +439,15 @@ async def execute(self, runtime, key):
 
 @dataclass(frozen=True)
 class ChannelDestination(BusDestination):
-    """A channel or inbox page: shown while its view still reads this conversation from this source."""
+    """A channel or inbox page: shown while its view still reads this conversation from this
+    root. A page reader the view replaces (a refresh, the next page) still shows it."""
 
-    source: WirePageBuffer
     view: CommsChatView
 
     def shown(self) -> bool:
         view = self.view
-        return view.is_attached and self.source is view.message_history.page_source and (
-            self.conversation == view.conversation)
+        return view.is_attached and self.conversation == view.conversation and (
+            view.message_history.page_source.reads_from(self.root))
 
     async def presented(self, sent: MessageReference) -> None:
         await self.view.show_sent(sent)
@@ -467,6 +467,9 @@ def __init__(self, *args, revision: ConversationObservation, **kwargs):
     def replacement(self, through) -> WirePageBuffer:
         return type(self)(self.loader, through, self.runtime, revision=self.revision)
 
+    def reads_from(self, root: str | Path) -> bool:
+        return self.loader.root == root
+
     def uses_observation(self, observation: Observation) -> bool:
         return observation.observes(self.loader.root)
 
@@ -502,7 +505,7 @@ def begin_submission(
         self, view: CommsChatView, owner: SubmissionOwner, submission: SubmittedText
     ) -> SubmissionStart:
         """A channel or inbox message queues behind the view's earlier ones; compose stays open."""
-        return owner.start_bus(submission, ChannelDestination(self.loader.root, self.loader.conversation, self, view))
+        return owner.start_bus(submission, ChannelDestination(self.loader.root, self.loader.conversation, view))
 
     def schedule_refresh(self, view: CommsChatView):
         history = view.message_history

tests/textual/test_stale_route_writes.py

@@ -19,8 +19,7 @@ async def test_a_view_that_changed_before_its_send_left_keeps_the_draft_editable
         messaging = workspace.comms.messaging
         before = messaging.bus.bus.revision()
         # Built for a conversation the view no longer shows: the view moved on before the send left.
-        stale = ChannelDestination(workspace.roots.wire, ChannelConversation(ChannelTarget("#elsewhere")),
-                                   view.message_history.page_source, view)
+        stale = ChannelDestination(workspace.roots.wire, ChannelConversation(ChannelTarget("#elsewhere")), view)
         await view.submissions.start_bus(OrdinaryInputSubmission("STALE_DRAFT"), stale).prepare()
         await ui.until(lambda: view.prompt.text == "STALE_DRAFT", why="the refused draft back in the composer")
         assert not view.submissions.delivering