Updated local storage

README.md

@@ -46,6 +46,8 @@ 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/layout_store.* the per-source session layout file (TOML), written and read back
+src/event_series.hpp  an immutable captured event as a plot::data::Series
 src/ui.*           the GTK4 window: toolbar, trigger panel, signal panel, plot box
 ```
 
@@ -56,6 +58,41 @@ frame and the GUI thread takes once per frame around binding the traces.
 Samples cross the boundary through `plot::data::RingBuffer` (single producer,
 single consumer), never through the lock.
 
+## The session layout file
+
+What you arranged is remembered per data source, in
+`~/.config/udpscope/<host>_<port>.toml` (`$XDG_CONFIG_HOME` is honoured; the
+host's unsafe characters are replaced with `_`). The file holds the display
+window, the row layout and which signal each of a row's slots plots, and the
+per-signal gain and offset:
+
+```toml
+window_s = 2
+plots = 1
+
+[[plot]]
+signals = ["Ch1", "", "", ""]
+
+[[calibration]]
+name = "Ch1"
+gain = 2
+offset = 0.5
+```
+
+It is written (400 ms after the last change, and flushed on close) whenever the
+window, the layout, a drop or a calibration changes, and applied once, when the
+first CONFIG names the signals -- signal *names* are the identity, because a
+CONFIG renumbers and an enable/disable rebuilds the channel list. Signals the
+file plots are enabled on load, since a restored plot nobody acquires would come
+back blank. It is plain TOML and safe to edit; a malformed file loads whatever
+parsed rather than refusing to start. Writes go to a sibling temp file and are
+renamed over the target, so a crash mid-write leaves the old layout.
+
+The same reason the window control is a fixed-width label in the header bar
+(see the DPI/relayout notes in `ui.cpp`) is why the bar's `window` control does
+not expand: a header-bar child that expands is measured into the title's centre
+box, so the control stretched to the title and every window resize moved it.
+
 ## How the spec maps onto the code
 
 **One buffer of `N+1` slices, plus frozen event snapshots.** `ScopeModel`