t386: pin the per-member drift baseline the fix's own tests left open

The two tests merged with #386 both start with the member already BUSY, so a
single global drift baseline passes them. This one sleeps the host while nothing
is busy and only then starts a turn, which fails without the per-member map.

fleetd/src/test/java/dev/ltms/fleet/health/FleetHealthMonitorTest.java

@@ -30,6 +30,7 @@ import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.ScheduledThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.BiConsumer;
 import java.util.function.LongSupplier;
 
@@ -277,6 +278,58 @@ class FleetHealthMonitorTest {
         }
     }
 
+    /**
+     * fleetd #386 follow-up, added on merge. The fix carries a PER-MEMBER drift baseline, so drift
+     * from a sleep that happened BEFORE a member went busy is never charged to that member. The
+     * two tests shipped with the fix both start with the member already BUSY, so a single global
+     * baseline passes them — this one fails without the per-member map.
+     *
+     * <p>Order matters: the host sleeps while nothing is busy, and only then does a member take a
+     * turn. Its stall clock must start at zero.
+     */
+    @Test void driftFromASleepBeforeAMemberWentBusyIsNotChargedToThatMember() {
+        Logger logger = (Logger) LoggerFactory.getLogger(FleetHealthMonitor.class);
+        ListAppender<ILoggingEvent> appender = new ListAppender<>();
+        appender.start();
+        logger.addAppender(appender);
+        try {
+            AtomicLong mono = new AtomicLong(0);
+            AtomicLong real = new AtomicLong(0);
+            AtomicReference<List<MemberSession>> roster = new AtomicReference<>(List.of());
+            FakeHerdr herdr = new FakeHerdr().withAgent("busy", "term_busy", "pane_busy", "tab_busy");
+            var scheduler = Executors.newSingleThreadScheduledExecutor();
+            AgentControl agents = new AgentControl(herdr);
+            FleetHealthMonitor monitor = new FleetHealthMonitor(agents, roster::get,
+                    new MessageService(agents, new Injector(agents), new Rendezvous(), new InMemoryReplyInbox()),
+                    scheduler, mono::get, real::get, 60, 600, (_, _) -> { });
+
+            monitor.tick();                                   // baseline, no members yet
+
+            // The host sleeps for 700s with nobody busy: the monotonic clock stands still.
+            real.set(TimeUnit.SECONDS.toNanos(700));
+            monitor.tick();
+
+            // Awake again. Only NOW does a member start a turn, with a fresh activity stamp taken
+            // from the monotonic clock. Both clocks advance together from here.
+            mono.set(TimeUnit.SECONDS.toNanos(10));
+            real.set(TimeUnit.SECONDS.toNanos(710));
+            roster.set(List.of(member("term_busy", MemberSession.State.BUSY,
+                    0, TimeUnit.SECONDS.toNanos(10))));
+            monitor.tick();
+
+            mono.set(TimeUnit.SECONDS.toNanos(20));
+            real.set(TimeUnit.SECONDS.toNanos(720));
+            monitor.tick();
+            monitor.stop();
+
+            assertEquals(0, appender.list.stream().filter(event -> event.getFormattedMessage()
+                            .contains("member=term_busy state=STALL_SUSPECTED")).count(),
+                    "the member has been busy for 10s, not 710s — the earlier sleep is not its stall");
+        } finally {
+            logger.detachAppender(appender);
+        }
+    }
+
     private static FleetHealthMonitor monitorWithClocks(FakeHerdr herdr, List<MemberSession> roster,
             java.util.concurrent.ScheduledExecutorService scheduler, LongSupplier clock,
             LongSupplier realtimeClock, long intervalSeconds, long workingSuspectAfterSeconds,