On macOS a fullscreen transition hides the traffic lights and pins the
left titlebar cluster to the window edge. `usePanelTitlebar` reserved the
strip's left inset by measuring that cluster, but only re-measured on
ResizeObserver callbacks and window `resize`: the `resize` fires before the
window-state IPC lands (so it measures the OLD cluster position) and the
cluster's move afterwards is a pure translate with no size delta, so nothing
re-runs. The SESSIONS | BOTS strip kept a stale gap (or, sidebar expanded,
a zero reservation with the toggle button sitting on top of the first tab)
until a sidebar toggle or reload (#108641).
Subscribe to the same `$connection` fields wiring.tsx derives
`--titlebar-controls-left` from (isFullscreen, windowButtonPosition) and
re-measure after a double rAF so the read lands after the clusters
repaint; unrelated connection updates do not re-commit a stale read.
Co-authored-by: KoNit-K <124019182+KoNit-K@users.noreply.github.com>
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