The source window has `winbar = " %f"` set by set_debug_chrome for the
filename chip. When open_bars does `:topleft split` / `:botright split`
from that window, the new bar windows inherit its winbar. The inherited
winbar renders an extra chrome row at the TOP of each bar window,
ABOVE our Row 0 separator — showing the scratch buffer's empty
filename, which reads as a phantom empty row sandwiched between our
separator and whatever sits above/below.
Explicitly `vim.wo[win].winbar = ""` in setup_bar_win first-thing, so
the bar shows only its own 3 rows (top sep / content / bottom sep)
with no inherited chrome.
swaits
53cc0802c3