diff --git a/.circleci/config.yml b/.circleci/config.yml
index 98b50a9260..038645c377 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -287,6 +287,12 @@ jobs:
             go vet ./...
             go vet -C tools ./...
 
+      # The third-party notices link the licence text this bundle copies into
+      # docs/assets/landing, which is generated rather than tracked.
+      - run:
+          name: Build the landing-page diagram
+          command: make docs-landing-assets
+
       - run:
           name: Check documentation links
           command: python3 scripts/check-doc-links.py
@@ -416,7 +422,10 @@ jobs:
       - install-fmpy
 
       # One scripts/race-shard.sh shard per node: internal/exec/runtime alone peaks near
-      # 6.5 GB under -race, so it shares its 8 GB node only sequentially (tests/wasm, tools).
+      # 8.5 GB under -race, so it shares its 8 GB node only sequentially (tests/wasm, tools).
+      # The race detector's memory is per process and the corpus-wide exploration alone
+      # accounts for half of that peak, so the package runs as two processes: the
+      # exploration, then everything else (4 GB each).
       - run:
           name: Run Go race tests
           command: |
@@ -429,10 +438,14 @@ jobs:
             shard=${shards[$CIRCLE_NODE_INDEX]}
             pkgs=$(scripts/race-shard.sh "$shard")
             echo "shard $shard:"; echo "$pkgs"
-            go test -v -race -pgo=off -timeout 30m $pkgs
             if [ "$shard" = runtime ]; then
+              exploration='^TestExploreWithIsExploreOverTheConformanceCorpus$'
+              go test -v -race -pgo=off -timeout 30m -run "$exploration" $pkgs
+              go test -v -race -pgo=off -timeout 30m -skip "$exploration" $pkgs
               go test -v -race -pgo=off -timeout 30m ./tests/wasm
               go test -C tools -v -race -pgo=off -timeout 30m ./...
+            else
+              go test -v -race -pgo=off -timeout 30m $pkgs
             fi
           no_output_timeout: 30m
           environment:
diff --git a/internal/exec/runtime/sweep_queue_test.go b/internal/exec/runtime/sweep_queue_test.go
index cbe618a584..f56384b2fb 100644
--- a/internal/exec/runtime/sweep_queue_test.go
+++ b/internal/exec/runtime/sweep_queue_test.go
@@ -210,11 +210,32 @@ func TestRunSweepWithKeepsEachRowsWritesToItself(t *testing.T) {
 	}
 }
 
+// metDeadline is a context whose deadline is met when the test says so rather than when a
+// clock does, so a slow machine cannot meet it before every job has taken its first row.
+type metDeadline struct {
+	context.Context
+	done chan struct{}
+	once sync.Once
+}
+
+func (d *metDeadline) Done() <-chan struct{} { return d.done }
+
+func (d *metDeadline) Err() error {
+	select {
+	case <-d.done:
+		return context.DeadlineExceeded
+	default:
+		return nil
+	}
+}
+
+func (d *metDeadline) meet() { d.once.Do(func() { close(d.done) }) }
+
 // A deadline met mid-sweep ends the sweep with context.DeadlineExceeded and no table: no row
 // starts once the deadline is visible, the rows in flight finish and are discarded — an
 // absence, never a partial answer — as one job reports when it meets the deadline between
-// two rows. The rows the jobs take first wait out the deadline, so on any job count the
-// rows started are exactly the jobs' first ones.
+// two rows. The rows the jobs take first wait out the deadline, which the last of them to
+// start meets, so on any job count the rows started are exactly the jobs' first ones.
 func TestRunSweepWithStopsAtTheDeadline(t *testing.T) {
 	fresh, scope := sweepJobsFixture(t)
 	first := firstOf(t, fresh)
@@ -225,13 +246,15 @@ func TestRunSweepWithStopsAtTheDeadline(t *testing.T) {
 	}
 	double := sweepCalcRun(sym, scope)
 	for _, jobs := range []int{1, sweepJobs} {
-		stop, cancel := context.WithTimeout(context.Background(), 20*time.Millisecond)
+		stop := &metDeadline{Context: context.Background(), done: make(chan struct{})}
 		var started, finished, late atomic.Int64
 		waiting := func(ctx *Context, bindings []SweepBinding) (SweepRunResult, error) {
-			started.Add(1)
 			if stop.Err() != nil {
 				late.Add(1)
 			}
+			if started.Add(1) == int64(jobs) {
+				stop.meet()
+			}
 			if bindings[0].Value.Const.Int <= int64(sweepJobs) {
 				<-stop.Done()
 			}
@@ -240,7 +263,6 @@ func TestRunSweepWithStopsAtTheDeadline(t *testing.T) {
 			return result, err
 		}
 		table, err := RunSweepWith(stop, SweepWorkers{First: firstOf(t, fresh), Jobs: jobs, Fresh: fresh}, "test::Fib", plan, 0, waiting)
-		cancel()
 		if !errors.Is(err, context.DeadlineExceeded) || len(table.Rows) != 0 || table.Target != "" {
 			t.Fatalf("on %d jobs: table of %d rows and %v, want no table and context.DeadlineExceeded", jobs, len(table.Rows), err)
 		}