Panel sizes are reconciled against the window on every resize, with the preview holding a 360x200 floor that panels yield to before it gives.
Measured preview pane: 760px window 192 -> 433, 560px window 2 -> 516. Windows at or above 1280px are unchanged.
- fitPanels owns the who-yields decision for both axes
- panel caps are window-relative, replacing a flat 600px inspector cap
- below 860 the sidebar rails, below 700 the inspector collapses too
- auto-collapse is derived render state and never writes leftCollapsed
(localStorage) or rightCollapsed (synced into the shareable URL)
- the rail and header toggles act on the effective state, so neither is a
dead click that silently persists a collapse the user never asked for
