feat: a pulse whose width is wrong can be the trigger's event, so a glitch can be caught

src/condition.hpp

@@ -82,10 +82,18 @@ class EventDetector {
     return prev_ > cond_.level && v <= cond_.level;
   }
   double feed_edge(double value, double t) noexcept;
+  double feed_pulse(double value, double t) noexcept;
+  /// Whether a measured width satisfies `cond_.cmp`. `Within`/`Outside` take their two
+  /// bounds in either order, so a panel cannot make an empty band by typing the larger
+  /// figure into the first spin.
+  bool qualifies(double width_s) const noexcept;
 
   EventCondition cond_{};
   bool have_prev_ = false;
   double prev_ = 0.0;
+  bool in_pulse_ = false;      ///< PulseWidth: an opening edge has been seen.
+  bool pulse_up_ = false;      ///< PulseWidth: its polarity, so we know which edge closes it.
+  double pulse_start_s_ = 0.0;
 };
 
 }  // namespace udpscope