Upgraded feedkit's handling of stream sources

sources/source.go

@@ -35,6 +35,9 @@ type PollSource interface {
 //
 // Run should block, producing events into `out` until ctx is cancelled or a fatal error occurs.
 // It MUST NOT close out (the scheduler/daemon owns the bus).
+//
+// Stream sources can classify exits by wrapping errors with StreamRetryable or
+// StreamFatal. Plain non-nil errors are treated as retryable by the scheduler.
 type StreamSource interface {
 	Input
 	Run(ctx context.Context, out chan<- event.Event) error