**The blank scope window in trigger mode.** A held event pins the main window to
`[-pre, +post]`, and the tick mirrors that pin onto every scope window. It passed
`pinned_range().min/max` to `pin_event_window()`, which takes **spans** (`pre, post`): `min` is
signed, so `pre` came out negative and the group range became `[+pre, +post]` — an inverted x
window. The plotter then had nothing to draw: no trace, no x-axis labels, an empty plot that
looked like a broken window. `RowSet::pin_display_range(x0, x1)` states the pin as the range a
mirroring view actually has, and the tick uses it; live mode was never affected, which is why the
defect only showed under the trigger.
Also restores the scope-window `rebuild_if_dirty()` in the tick, which a reproduction experiment
had left commented out (`REPRO-TEMP`) and a later commit carried: a window opened empty and filled
by a drop kept the figure it was built with.
Probe: `[scope-probe] pin_mirror=1 main=[..] scope=[..] x=[..]` pins the main window, reads the
scope's pin and plot x range a frame later, and reads `0` for an inverted or mismatched pin.
Docs: probe readings and the trigger/pinning invariant (range vs spans).
Martino Ferrari
ecdbf4f0e1