fix(delegation): late-attached children take the parent's soft/hard stop kind; dedupe the fallback replay

_attach_child now mirrors a pending parent stop with the same split
interrupt() uses for its own fan-out (hard -> hard_interrupt, soft ->
interrupt), so a redirect is not turned into a cancel on a child that was
attached late. _restore_parent_cancellation collapses to re-attaching the
rejected unit's children: the replay is the attach step's job now.

Test fixture: _Batch gained origin_session_history_delivery on main after
the salvaged PR was written.

Co-authored-by: illidan <noequal666@gmail.com>

tools/delegate_tool_dispatch.py

@@ -375,19 +375,10 @@ def _dispatch_unit(unit: _Batch, unit_id: Optional[str], slot_key: Optional[str]
     )
 
 def _restore_parent_cancellation(unit: _Batch) -> None:
-    # Rejected children remain owned by the parent. Attach before replaying a
-    # cancellation that may have arrived while async admission had them detached.
-    parent = unit.parent_agent
+    """Rejected children stay owned by the parent: re-attach them (``_attach_child`` replays a stop that
+    arrived while async admission had them detached)."""
     for _, _, child in unit.children:
-        _attach_child(parent, child)
-    if getattr(parent, "_interrupt_requested", False) is True:
-        hard_stop = getattr(parent, "_hard_interrupt_requested", None)
-        for _, _, child in unit.children:
-            if hard_stop is not None and hard_stop.is_set():
-                _signal_child_stop(child, getattr(parent, "_interrupt_message", None))
-            else:
-                with _quiet("Failed to propagate interrupt to fallback child: %s"):
-                    child.interrupt(getattr(parent, "_interrupt_message", None))
+        _attach_child(unit.parent_agent, child)
 
 def _dispatch_background(batch: _Batch) -> str:
     """Dispatch the call as independent async units (see ``_units_of``) and return the tool result JSON. Every unit