fix/simplify: rebuild with cascade

Author: DaveSkender

src/_common/Observables/IStreamHub.cs

@@ -95,7 +95,7 @@ public interface IStreamHub<in TIn, TOut>
     /// All periods (inclusive) after this DateTime will be removed.
     /// </param>
     /// <param name="notify">
-    /// Send delete point to subscribers.
+    /// Notify subscribers of the delete point.
     /// </param>
     void RemoveRange(DateTime fromTimestamp, bool notify);
 
@@ -104,11 +104,11 @@ public interface IStreamHub<in TIn, TOut>
     /// </summary>
     /// <remarks>
     /// For observers, if your intention is to rebuild from a provider,
-    /// use alternate <see cref="IStreamObserver{T}.Rebuild(int,int?)"/>.
+    /// use alternate <see cref="IStreamObserver{T}.Rebuild(int)"/>.
     /// </remarks>
     /// <param name="fromIndex">From index, inclusive</param>
     /// <param name="notify">
-    /// Send delete point to subscribers.
+    /// Notify subscribers of the delete position.
     /// </param>
     void RemoveRange(int fromIndex, bool notify);
 

src/_common/Observables/IStreamObserver.cs

@@ -31,8 +31,13 @@ public interface IStreamObserver<in T>
     /// <param name="item">
     /// The current notification information.
     /// </param>
-    /// <param name="indexHint">Provider index hint</param>
-    void OnAdd(T item, int? indexHint);
+    /// <param name="notify">
+    /// Notify subsribers of the new item.
+    /// </param>
+    /// <param name="indexHint">
+    /// Provider index hint, if known.
+    /// </param>
+    void OnAdd(T item, bool notify, int? indexHint);
 
     /// <summary>
     /// Provides the observer with starting point in timeline
@@ -113,8 +118,5 @@ public interface IStreamObserver<in T>
     /// All periods (inclusive) after this index position
     /// will be removed and recalculated.
     /// </param>
-    /// <param name="provIndex">
-    /// Matching provider index, if known.
-    /// </param>
-    void Rebuild(int fromIndex, int? provIndex = null);
+    void Rebuild(int fromIndex);
 }

src/_common/Observables/StreamHub.Observable.cs

@@ -75,7 +75,7 @@ private void NotifyObserversOnAdd(TOut item, int? indexHint)
         // send to subscribers
         foreach (IStreamObserver<TOut> o in _observers.ToArray())
         {
-            o.OnAdd(item, indexHint);
+            o.OnAdd(item, notify: true, indexHint);
         }
     }
 

src/_common/Observables/StreamHub.Observer.cs

@@ -12,11 +12,11 @@ public abstract partial class StreamHub<TIn, TOut> : IStreamObserver<TIn>
 
     // observer methods
 
-    public virtual void OnAdd(TIn item, int? indexHint)
+    public virtual void OnAdd(TIn item, bool notify, int? indexHint)
     {
         // pass-thru, usually
         (TOut result, int index) = ToIndicator(item, indexHint);
-        AppendCache(result, index);
+        AppendCache(result, notify);
     }
 
     public void OnChange(DateTime fromTimestamp)