docs: Clarify atLeastOnceFlow filter

docs/src/main/paradox/dynamodb.md

@@ -301,6 +301,9 @@ A good alternative for advanced state management is to implement the handler as
 An Akka Streams `FlowWithContext` can be used instead of a handler for processing the envelopes, which is described in
 @ref:[Processing with Akka Streams](flow.md).
 
+In addition to the caveats described there a `DynamoDBProjection.atLeastOnceFlow` must not filter out envelopes. Always
+emit a `Done` element for each completed envelope, even if application processing was skipped for the envelope.
+
 ### Handler lifecycle
 
 You can override the `start` and `stop` methods of the @apidoc[Handler] or @apidoc[DynamoDBTransactHandler] to

docs/src/main/paradox/flow.md

@@ -20,7 +20,8 @@ from previously stored offset some envelopes may be processed more than once.
 There are a few caveats to be aware of:
 
 * If the flow filters out envelopes the corresponding offset will not be stored, and such an envelope
-  will be processed again if the projection is restarted and no later offset was stored.
+  will be processed again if the projection is restarted and no later offset was stored. Instead of filter it
+  is better to skip the processing but still emit the `Done` element.
 * The flow should not duplicate emitted envelopes (`mapConcat`) with same offset, because then it can result in
   that the first offset is stored and when the projection is restarted that offset is considered completed even
   though more of the duplicated envelopes were never processed.

docs/src/main/paradox/r2dbc.md

@@ -256,6 +256,9 @@ A good alternative for advanced state management is to implement the handler as
 An Akka Streams `FlowWithContext` can be used instead of a handler for processing the envelopes,
 which is described in @ref:[Processing with Akka Streams](flow.md).
 
+In addition to the caveats described there a `R2dbcProjection.atLeastOnceFlow` must not filter out envelopes. Always
+emit a `Done` element for each completed envelope, even if application processing was skipped for the envelope.
+
 ### Handler lifecycle
 
 You can override the `start` and `stop` methods of the `R2dbcHandler` to implement initialization
@@ -319,4 +322,4 @@ Scala
 :  @@snip [Example.scala](/akka-projection-r2dbc/src/test/scala/docs/home/projection/R2dbcProjectionDocExample.scala){#customConnectionFactory}
 
 Java
-:  @@snip [Example.java](/akka-projection-r2dbc/src/test/java/jdocs/home/projection/R2dbcProjectionDocExample.java){#customConnectionFactory}
+:  @@snip [Example.java](/akka-projection-r2dbc/src/test/java/jdocs/home/projection/R2dbcProjectionDocExample.java){#customConnectionFactory}