improved perfs and event management

src/event_store.hpp

@@ -73,6 +73,15 @@ class EventStore {
   /// however large the captures are.
   std::vector<EventRecord> list() const;
 
+  /// Draws `record`'s preview again from its samples and returns the thumbnail's path, or an empty
+  /// string when the samples cannot be read.
+  ///
+  /// This is the repair for a preview that is missing or will not decode -- a write that failed, a
+  /// truncated file, a cache written by an older build. The `.npy` is the event, the `.bmp` is only a
+  /// picture of it, so a lost picture is recoverable and must not be shown as a blank row. It reads
+  /// the samples, so unlike `list()` it is **not** cheap: call it for the one event that needs it.
+  std::string redraw_preview(const EventRecord& record) const;
+
   /// Deletes one event's samples, sidecar and thumbnail.
   bool forget(const std::string& stem);