newTab() used to mutate state.activeTabId directly, skipping
setActiveTab's auto-pause hook AND the toolbar button-state sync.
Opening a new tab during a running eval left the send button
disabled on the brand-new (idle) tab — fox would land on a tab he
couldn't type into.
Now newTab pushes the tab onto state.tabs, then awaits setActiveTab
which handles both the outgoing-tab auto-pause (if applicable) and
the incoming-tab button sync.
Verified end-to-end headless: with COOP/COEP enabled, switching
from a c-tier eval to a new tab now correctly snapshots the source
tab's state, leaves the send button enabled on tab 2, and on
switch-back the resumed eval re-fires from the snapshot.
russell@unturf.com
ca27d03c60