feat(all): add resilient server recovery and talent upgrades

go/internal/server/lifecycle/gate_test.go

@@ -0,0 +1,31 @@
+package lifecycle
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+func TestDrainRejectsNewRequestsAndWaitsForAdmittedRequest(t *testing.T) {
+	gate := NewGate()
+	done, ok := gate.BeginRequest()
+	if !ok || !gate.Ready() {
+		t.Fatal("ready gate rejected request")
+	}
+	gate.Drain()
+	if gate.Ready() {
+		t.Fatal("draining gate remained ready")
+	}
+	if _, ok := gate.BeginRequest(); ok {
+		t.Fatal("draining gate admitted new request")
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), 20*time.Millisecond)
+	defer cancel()
+	if err := gate.Wait(ctx); err == nil {
+		t.Fatal("drain completed before admitted request")
+	}
+	done()
+	if err := gate.Wait(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+}