Enable eager native scrollback rebuild mode while assistant text is actively streaming so reflowed Markdown rows do not leave stale duplicated tails in WSL/Windows Terminal scrollback.\n\nFixes #1615
- Added a post-dispatch refresh hook to recompute foreground tool render mode after key turn/tool events.
- Computed whether any non-background pending tool is active and toggled eager native scrollback rebuild accordingly.
- Added a regression test confirming eager rebuild is enabled while foreground tools are pending and disabled when none remain.