improved timing acq

src/model.hpp

@@ -204,6 +204,20 @@ class ScopeModel {
   /// is armed.
   BufferStore& live();
 
+  /// Forgets the live buffer's history: every ring is emptied and every channel's
+  /// published window is dropped, so the two stay index-aligned. Used when the
+  /// acquisition has to change time source (see `Acquisition::build_stamps`): the
+  /// stamps already recorded are on the old timeline, and a ring holding two
+  /// timelines is not a time base at all -- the x axis, the crosshair and an export
+  /// all read it by index.
+  ///
+  /// Takes `mutex()` itself: call it from the GTK thread. The acquisition thread
+  /// calls `reset_live_history_locked()` instead, already holding the lock (the
+  /// same split `publish_event()` follows).
+  void reset_live_history();
+  /// The body of the above for a caller that already holds `mutex()`.
+  void reset_live_history_locked();
+
   /// Builds the captured event from the slice of the live buffer covering
   /// `[edge - pre_s, edge + post_s]` in stream seconds, and publishes it atomically.
   /// The stamps are re-based so the edge sits at x = 0. The plot binds to this