TerminalView kills its child process on any logical-tree detach unless
BeginReparent() suppressed it, and RebuildOverviewGrid() detaches every
existing pane whenever one is added - so opening a second interactive
session killed the first. Focus-mode tab switches had the same defect.
PtyTerminalSession now puts the control in permanent reparent mode after
launch (teardown stays explicit via ConPtyPaneViewModel.Dispose -> Kill),
and the new ConPtyPaneHost reparents each pane's single long-lived view
across grid rebuilds and tab switches instead of letting the DataTemplate
instantiate a dead replacement.
mika kuns
aac84e48b7