diff --git a/Makefile b/Makefile
index 88d01fe4909..4ae6fc07ac7 100644
--- a/Makefile
+++ b/Makefile
@@ -525,14 +525,18 @@ workflowcheck: $(WORKFLOWCHECK)
 check: lint shell-check
 
 ##### Tests #####
+# verify-test-log reads the whole file, so a log left behind by an earlier run
+# would be judged as if it belonged to this one.
 clean-test-output:
 	@printf $(COLOR) "Delete test output..."
 	@rm -rf $(TEST_OUTPUT_ROOT)
+	@rm -f test.log
 	@go clean -testcache
 
 build-tests:
 	@printf $(COLOR) "Build tests..."
-	@CGO_ENABLED=$(CGO_ENABLED) go test $(TEST_TAG_FLAG) -exec="true" -count=0 $(TEST_DIRS)
+	@CGO_ENABLED=$(CGO_ENABLED) go test $(TEST_TAG_FLAG) -exec="true" -count=0 $(filter-out $(MIXED_BRAIN_TEST_ROOT)%,$(TEST_DIRS))
+	@cd $(MIXED_BRAIN_TEST_ROOT) && CGO_ENABLED=1 go test $(TEST_TAG_FLAG) -exec="true" -count=0 ./...
 
 unit-test: clean-test-output
 	@printf $(COLOR) "Run unit tests..."
diff --git a/cmd/tools/protogen/main.go b/cmd/tools/protogen/main.go
index cf2c00b2e6e..251f2a26adb 100644
--- a/cmd/tools/protogen/main.go
+++ b/cmd/tools/protogen/main.go
@@ -165,16 +165,65 @@ func newGenerator() (*generator, error) {
 	return &gen, nil
 }
 
+// removeExistingGenDirs clears out the previous run's output so a proto that
+// was deleted does not leave its Go behind.
+//
+// Only generated files go. A gen package sometimes needs a hand-written file
+// beside the generated ones, because a method has to be declared in the same
+// package as the type it is on, and wiping the directory deleted those without
+// saying so. Empty directories are then pruned, which is what removing a proto
+// used to rely on.
 func (g *generator) removeExistingGenDirs() error {
 	for _, dir := range g.chasmLibDirs {
 		genDir := filepath.Join(dir, "gen")
-		if err := os.RemoveAll(genDir); err != nil {
-			return fmt.Errorf("error removing directory %s: %w", genDir, err)
+		if !exists(genDir) {
+			continue
+		}
+		if err := filepath.Walk(genDir, func(path string, info os.FileInfo, err error) error {
+			if err != nil {
+				return err
+			}
+			if info.IsDir() || !strings.HasSuffix(info.Name(), ".pb.go") {
+				return nil
+			}
+			return os.Remove(path)
+		}); err != nil {
+			return fmt.Errorf("error removing generated files under %s: %w", genDir, err)
+		}
+		if err := pruneEmptyDirs(genDir); err != nil {
+			return fmt.Errorf("error pruning empty directories under %s: %w", genDir, err)
 		}
 	}
 	return nil
 }
 
+// pruneEmptyDirs removes dir and any descendant left with nothing in it,
+// deepest first.
+func pruneEmptyDirs(dir string) error {
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil
+		}
+		return err
+	}
+	for _, entry := range entries {
+		if entry.IsDir() {
+			if err := pruneEmptyDirs(filepath.Join(dir, entry.Name())); err != nil {
+				return err
+			}
+		}
+	}
+	remaining, err := os.ReadDir(dir)
+	if err != nil {
+		return err
+	}
+	if len(remaining) == 0 {
+		return os.Remove(dir)
+	}
+	return nil
+}
+
 func (g *generator) backupProtos() error {
 	if exists(g.protoOut) {
 		if err := os.Rename(g.protoOut, g.protoBackup); err != nil {
diff --git a/common/metrics/otel_metrics_handler_test.go b/common/metrics/otel_metrics_handler_test.go
index a2d0b34eb53..bf08a9460e1 100644
--- a/common/metrics/otel_metrics_handler_test.go
+++ b/common/metrics/otel_metrics_handler_test.go
@@ -193,9 +193,14 @@ func TestMeter(t *testing.T) {
 		cmpopts.SortSlices(func(x, y metricdata.Metrics) bool {
 			return x.Name < y.Name
 		}),
-		cmpopts.IgnoreFields(metricdata.DataPoint[int64]{}, "StartTime", "Time"),
-		cmpopts.IgnoreFields(metricdata.DataPoint[float64]{}, "StartTime", "Time"),
-		cmpopts.IgnoreFields(metricdata.HistogramDataPoint[int64]{}, "StartTime", "Time", "Bounds"),
+		// Exemplars are ignored rather than equated empty: the SDK hands back
+		// either a nil or an allocated-but-empty slice depending on whether
+		// its reservoir was ever touched, and equating empty globally would
+		// also hide a nil-versus-empty attribute set or data point.
+		cmpopts.IgnoreFields(metricdata.DataPoint[int64]{}, "StartTime", "Time", "Exemplars"),
+		cmpopts.IgnoreFields(metricdata.DataPoint[float64]{}, "StartTime", "Time", "Exemplars"),
+		cmpopts.IgnoreFields(
+			metricdata.HistogramDataPoint[int64]{}, "StartTime", "Time", "Bounds", "Exemplars"),
 	); diff != "" {
 		t.Errorf("mismatch (-want, +got):\n%s", diff)
 	}
@@ -264,7 +269,8 @@ func TestMeter_TimerInSeconds(t *testing.T) {
 		cmp.Comparer(func(a1, a2 attribute.Set) bool {
 			return a1.Equals(&a2)
 		}),
-		cmpopts.IgnoreFields(metricdata.HistogramDataPoint[float64]{}, "StartTime", "Time", "Bounds"),
+		cmpopts.IgnoreFields(
+			metricdata.HistogramDataPoint[float64]{}, "StartTime", "Time", "Bounds", "Exemplars"),
 	); diff != "" {
 		t.Errorf("mismatch (-want, +got):\n%s", diff)
 	}
diff --git a/service/history/hsm/hsmtest/sm.go b/service/history/hsm/hsmtest/sm.go
index d01aec19a01..0a5c72308cc 100644
--- a/service/history/hsm/hsmtest/sm.go
+++ b/service/history/hsm/hsmtest/sm.go
@@ -3,6 +3,7 @@ package hsmtest
 import (
 	"fmt"
 	"strings"
+	"sync/atomic"
 	"time"
 
 	"go.temporal.io/server/service/history/hsm"
@@ -41,10 +42,17 @@ func (d *Data) SetState(s State) {
 	d.state = s
 }
 
+// regenerated counts the timer tasks handed out. Timers with equal deadlines
+// are grouped into one state machine timer, and the wall clock does not tick
+// between two nodes of one walk on every platform, so each deadline is pushed
+// out by one more nanosecond than the last.
+var regenerated atomic.Int64
+
 func (d *Data) RegenerateTasks(node *hsm.Node) ([]hsm.Task, error) {
+	deadline := time.Now().Add(time.Hour + time.Duration(regenerated.Add(1)))
 	return []hsm.Task{
 		NewTask(
-			hsm.TaskAttributes{Deadline: time.Now().Add(time.Hour)},
+			hsm.TaskAttributes{Deadline: deadline},
 			false,
 		),
 		NewTask(