feat(net)!: dynamic tracks serve fills for misses

dart/moq/lib/src/aliases.dart

@@ -100,7 +100,7 @@ typedef TrackProducer = MoqTrackProducer;
 /// A subscriber-requested track not yet accepted: accept it for a [TrackProducer] or abort it.
 typedef TrackRequest = MoqTrackRequest;
 
-/// A stream of uncached group requests for one track, for serving fetches on demand.
+/// A stream of the fills readers of one track need: runs of groups the cache lacks.
 typedef TrackDynamic = MoqTrackDynamic;
 
 /// A watch-only handle to whether a published track has subscribers; holding it keeps nothing open.
@@ -109,8 +109,8 @@ typedef TrackDemand = MoqTrackDemand;
 /// The read side of a raw track: yields groups in sequence order, skipping ahead if it falls behind.
 typedef TrackConsumer = MoqTrackConsumer;
 
-/// A request to produce one uncached group for a fetch consumer.
-typedef GroupRequest = MoqGroupRequest;
+/// A run of groups readers miss: accept each group you have and drop the rest.
+typedef Fill = MoqFill;
 
 /// The write side of a single group: append frames to it.
 typedef GroupProducer = MoqGroupProducer;

dart/moq/lib/src/durations.dart

@@ -35,11 +35,25 @@ extension BackoffDuration on MoqBackoff {
 
 /// Duration views over the subscription knobs.
 extension SubscriptionDuration on MoqSubscription {
-  /// Upper bound on buffering before a stalled group is skipped, or null for the default.
+  /// Upper bound on buffering before a stalled group is skipped, or null for the
+  /// publisher's max age alone.
   Duration? get maxDelay =>
-      maxDelayUs == null ? null : Duration(microseconds: maxDelayUs!);
+      maxDelayUs == null ? null : _saturatingMicros(maxDelayUs!);
 }
 
+/// Duration views over a fill.
+extension FillDuration on MoqFill {
+  /// The most tolerant age budget among its readers, or null for the publisher's max age alone.
+  Duration? get maxDelay {
+    final us = maxDelayUs();
+    return us == null ? null : _saturatingMicros(us);
+  }
+}
+
+/// A u64 past 2^63 - 1 microseconds, such as a peer's delay, reads back negative.
+Duration _saturatingMicros(int us) =>
+    Duration(microseconds: us < 0 ? 0x7FFFFFFFFFFFFFFF : us);
+
 /// Duration views over the publisher-side track settings.
 extension TrackInfoDuration on MoqTrackInfo {
   /// Maximum age of a non-latest group before the publisher evicts it, or null for the default.