A batch of view and instrument work, with the probes and docs for each.
- **Full screen per figure row**: a toggle on each row's top-right corner, revealed by
pointer proximity (`kMaximizeRevealPx` around its placed rect, per row, read from an
overlay-level motion controller so a revealed button under the pointer cannot flicker);
the plot menu offers the same as *Full screen this figure* / *Restore the layout*. The
arrangement is saved and restored through `RowState`, so nothing plotted moves. A layout
of one figure carries no toggle.
- **Second window**: `open_scope_window()` copies a figure (cells, width shares, signals in
their colours) or opens an empty one, with its own `RowSet` and `PlotArea`; the main
window's tick binds, acquires and repaints it, mirroring the time window and pin. Entries:
the plot menu's *Open this plot in a new window* and the overflow menu's *New scope window*.
- **Layout editor from the plot**: the plot menu gains *Edit the layout...* / *Done editing
the layout*, flipping the app's one toggle.
- **Measurements gate**: `MeasureOptions::gate` restricts a measurement to the held/pause
snapshot (live falls back to the live ring), persisted with the session and shown in the
measure dialog.
- **Crosshair axis badges**: a preference (`crosshair_axis_labels`, on by default) and the
plotter's badges where the lines meet the axes, in the axes' own formats; the plot menu
and the probe read them.
- **Event cache per configuration**: `EventStore` is keyed `<source>/<configuration>/`,
`retarget_event_store()` follows every configuration switch, and a pre-configuration cache
(loose files) is adopted into the configuration's folder on first start.
- **GTK4 lifecycle**: the main window's handlers move from the non-existent `"destroy"`
signal to `close-request`; scope windows are closed with it and the application quits
explicitly (the exit run's hang). The exit probe closes with `gtk_window_close()`.
- Probes: `[maximize-probe]` (single-figure rule and the corner reveal), `[scope-probe]`,
`[split-probe]` cell crosshair leg, `[prefs-probe]` store keying, `[configs]` store key,
`[rowmenu]` layout-editor entry; docs, help pages, README and AGENT.md updated.
Also fixes a probe-only use-after-free: `toggle_maximize_figure_row` replaces the figure
object, so the area must be re-pointed (the button's path does; the probe's raw call did not).
Martino Ferrari
bdf0ff7ddc