cleaned up ui added exporter

README.md

@@ -44,6 +44,7 @@ src/channel.*      ChannelBuffer (a ring pair as a plot::data::Series) and SlotS
 src/acquisition.*  the UDPStreamer client, the producer thread, frame decoding
 src/trigger.*      the trigger configuration and the producer-side state machine
 src/plot_host.*    the one plot::Figure, its rows' traces and cursors, the x link group
+src/export.*       the visible range as a table, and the .npy / .csv writers
 src/ui.*           the GTK4 window: toolbar, trigger panel, signal panel, plot box
 ```
 
@@ -188,8 +189,8 @@ assumed.
 pause/resume, the trigger toggle, the side-panel toggle and an overflow menu. Those
 four buttons are icons with tooltips; nine text buttons was a wall of words to read
 past every time you wanted the one you needed. The overflow menu holds **Fit to
-data**, **Cursors**, **Reset cursors** and the **Signal list** toggle — the things
-you set up once. The side column and the two panel toggles stay hidden until a
+data**, **Cursors**, **Reset cursors**, **Export visible range…** and the
+**Signal list** toggle — the things you set up once. The side column and the two panel toggles stay hidden until a
 CONFIG arrives — there is nothing to configure before the stream describes itself —
 and the first CONFIG reveals the signal panel (the trigger panel stays behind its
 own toggle).
@@ -239,7 +240,19 @@ latch, which the status line reports.
 
 The signal panel is one line per signal: a colour chip naming the trace it is drawn
 as, a checkbox that acquires it, its name, its unit, and a `⋯` menu holding the
-information popup and the gain/offset calibration popup. A `GtkSwitch` and two
+information popup and the gain/offset calibration popup.
+
+**The chip's colour belongs to the signal, not to the slot it landed in.** The
+palette is indexed by position in the signal list (`signal_color_index()`), so a
+signal dropped on two rows is the same colour in both and the chip names a trace
+unambiguously; indexing by trace slot made the same signal blue on row 1 and orange
+on row 2, and then the chip named neither. A signal that is on no plot — acquired or
+not — gets a **grey** chip rather than no chip, so every row of the panel is the same
+shape and the column of chips reads as a legend. Because `plot::Plot` fixes a trace's
+colour at `add_trace()`, the index is stored on the row (`Row::color_index`) and a
+colour change goes through a figure rebuild, which a drop already forces.
+
+A `GtkSwitch` and two
 always-visible buttons made a row about twice as tall (46 px against 26 px now),
 which is what turned a four-signal stream into a panel you have to scroll; Adwaita's
 button and list-row minimums, not the widgets themselves, set that height, so the
@@ -342,6 +355,30 @@ the widget keeps its context. A displayed event survives the rebuild because the
 pinned `[-pre, +post]` window is restated rather than re-derived from the live
 edge.
 
+**Export visible range…** (overflow menu) writes every signal bound to a visible row,
+over the shared x window, at the **stored** sample rate — never the LOD pyramid's
+buckets, which are the envelope the renderer drew rather than the acquisition. A
+signal on several rows is one column; the columns come out in channel order, so the
+file reads in the same order as the signal panel. The table has two time columns:
+`time` is the axis as displayed (stream seconds live, `[-pre, +post]` while an event
+is held) and `stream_time` is always the stream's own clock, so two exports taken in
+different modes line up.
+
+Two formats, picked by the extension the save dialog ends up with:
+
+| file | what it is |
+|---|---|
+| `.npy` | one NumPy structured array, `time`/`stream_time` as `<f8` and every signal as `<f4` — the width the ring stores, so the file invents no precision and is about half an all-`f8` one. `pd.DataFrame(np.load(path))` is the whole reader. |
+| `.csv` | the same table as text, `%.17g` for the times and `%.9g` for the values: the shortest widths that round-trip each type exactly. |
+
+Parquet (the original ask) would have meant linking Arrow — tens of megabytes of
+dependency for a feature whose output a three-line reader already handles.
+
+The table is collected when the menu item is clicked, not when the dialog is
+answered: a live view keeps scrolling while the file chooser is up. The live cut goes
+through `ScopeModel::live_window_locked()`, the same index range `publish_event()`
+uses, so an export and a capture of the same window hold the same samples.
+
 ## Review findings not (yet) implemented
 
 These are known deviations, found by a spec/code review, that are deliberate for