test(relay): drill bursts across a two-relay cluster on impaired links

quest/m1/README.md

@@ -58,7 +58,6 @@ blocks. The quests that gated m0 lines moved under them.
 - [Subscribe ranges](/quest/m1/subscribe-ranges/README.md) - a lite-07 SUBSCRIBE asks for past and live ranges in either order and replaces FETCH; relays fill misses by range, including over moq-transport
 - [Live media time](/quest/m1/subscribe-live-time.md) - re-scoped against `set_live`: a lite-07 SUBSCRIBE_OK carries the publisher's current media time only if a reader still needs it
 - [Cross-relay bursts re-run](/quest/m1/cross-relay-bursts.md) - condition: the #4349 reporter re-runs their A/B/C comparison against current cdn.moq.pro
-- [Two-relay drill on impaired links](/quest/m1/cross-relay-drill.md) - a bursty small-group track crosses two clustered relays over lossy, delayed, flow-limited QUIC without unanswered FETCHes or `Old` stalls
 - [Untimed lite-07](/quest/m1/lite-untimed.md) - lite-07 carries an untimed track in both languages; lite-05/06 write send time
 - [Finalize moq-lite-07](/quest/m1/lite07-finalize.md) - when the maintainer cuts it, lite-07 negotiates as `moq-lite-07` and the next release ships it
 - [Late lower groups](/quest/m1/lite-late-lower-group.md) - a moq-lite subscriber with a floor receives a group created below the first served one, as moq-transport does

quest/m1/cross-relay-bursts.md

@@ -26,10 +26,15 @@ used and against `main`:
   route-flap drops (about 70 of 560 groups) reproduce only on 0.15.6 and are
   gone on moq-net 0.3.8 and later, most likely by #4387.
 - **Not reproduced.** Unanswered FETCHes and the 30 s `Stream(Old)` stalls
-  showed up on no build. The mock models neither loss nor flow control, so
-  [Two-relay drill on impaired links](/quest/m1/cross-relay-drill.md) covers
-  that gap. Several 30 s timers of that era have since been removed or
-  shortened (#4606, #4741).
+  showed up on no build, nor in the real-QUIC drill
+  `rs/moq-relay/tests/drills.rs::bursts_cross_a_cluster` (bursts of 30
+  across two clustered relays, every hop with 5% loss, delay, a 100 kbit/s
+  bottleneck that each burst overflows, and 16-stream QUIC credit): every
+  group arrives within about 3.5 s, and the occasional live `Old` reset is recovered by FETCH. Several
+  30 s timers of that era have since been removed or shortened (#4606, #4741).
+- **Queueing.** FETCHes beyond a session's stream credit wait for it, one
+  cross-relay round trip per slot, so with tight credit a gap's FETCH can
+  outlast a 2 s deadline without being lost.
 - **Expected.** Across relays a burst arrives newest-first, as the lite draft
   specifies; fetching on every gap at once multiplies FETCHes.
 
@@ -39,5 +44,4 @@ used and against `main`:
 
 ## Related
 
-- [Two-relay drill on impaired links](/quest/m1/cross-relay-drill.md) - looks for the unreproduced FETCH and `Old` stalls without waiting on the reporter
 - [Routes and announces](/quest/m1/cluster-routing/routes.md) - owns the stale and flapping announcements from the same report

rs/moq-net/src/lite/subscriber.rs

@@ -4445,8 +4445,6 @@ impl<S: crate::transport::poll::Session> kio::Task for FetchServeRun<S> {
 
 			match &mut self.state {
 				FetchRunState::Open { request } => {
-					tracing::info!(broadcast = %self.serve.subscriber.log_path(&self.serve.path), track = %self.serve.name, group = self.group, "fetch started");
-
 					// A peer that sent GOAWAY told us to stop opening streams on this session.
 					if self.serve.subscriber.going_away.is_set() {
 						request.take().expect("request pending").reject(Error::GoingAway);
@@ -4468,6 +4466,10 @@ impl<S: crate::transport::poll::Session> kio::Task for FetchServeRun<S> {
 						}
 					};
 
+					// Only once the stream opens: the open parks on stream credit and
+					// re-polls this state, so logging before it repeats per poll.
+					tracing::info!(broadcast = %self.serve.subscriber.log_path(&self.serve.path), track = %self.serve.name, group = self.group, "fetch started");
+
 					let request = request.take().expect("request pending");
 
 					// A peer that predates lite-06 addresses whole groups only, so ask for