Fixes the bug where renaming a plain shell made its tab appear in every workstream. Optimistic tab overrides are now keyed per workstream (pendingByNode) and merged through mergePendingTabs, so a lingering override can no longer fabricate a phantom tab in another workstream. Also wires the plain-shell UI: the kind token, a close (x) affordance backed by the DELETE route, and a shell-aware disconnected screen. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>