diff --git a/backend/app/version.py b/backend/app/version.py
index f3f8ca7..dceee1b 100644
--- a/backend/app/version.py
+++ b/backend/app/version.py
@@ -1,5 +1,5 @@
 """Единый источник версии SAC (API, health, логи, OpenAPI)."""
 
 APP_NAME = "Security Alert Center"
-APP_VERSION = "0.3.9"
+APP_VERSION = "0.4.0"
 APP_VERSION_LABEL = f"{APP_NAME} v.{APP_VERSION}"
diff --git a/frontend/src/components/HostAgentVersionUpgrade.vue b/frontend/src/components/HostAgentVersionUpgrade.vue
index 2826a77..af13d36 100644
--- a/frontend/src/components/HostAgentVersionUpgrade.vue
+++ b/frontend/src/components/HostAgentVersionUpgrade.vue
@@ -7,8 +7,12 @@
       v-if="showUpgrade"
       type="button"
       class="agent-version-upgrade"
-      :disabled="updating"
-      :title="upgradeTitle"
+      :class="{
+        'agent-version-upgrade--inactive': upgradeBlocked,
+        'agent-version-upgrade--updating': updating,
+      }"
+      :disabled="updating || upgradeBlocked"
+      :title="buttonTitle"
       @click.stop="emit('upgrade')"
     >
       <span class="agent-version-upgrade__arrow" aria-hidden="true">↑</span>
@@ -31,6 +35,8 @@ const props = defineProps<{
   host: HostSummary;
   git: AgentGitVersions | null | undefined;
   updating?: boolean;
+  /** Другой хост сейчас обновляется — стрелка видна, но неактивна (серая). */
+  upgradeBlocked?: boolean;
   outdatedHighlight?: boolean;
 }>();
 
@@ -40,9 +46,7 @@ const emit = defineEmits<{
 
 const gitTargetVersion = computed(() => gitTargetVersionForHost(props.host, props.git));
 
-const showUpgrade = computed(
-  () => !props.updating && isGitAgentUpgradeAvailable(props.host, props.git),
-);
+const showUpgrade = computed(() => isGitAgentUpgradeAvailable(props.host, props.git));
 
 const currentTitle = computed(() => {
   if (!props.host.product_version) return "";
@@ -56,6 +60,16 @@ const upgradeTitle = computed(() => {
   if (!gitTargetVersion.value) return "";
   return `Обновить агент до ${gitTargetVersion.value}`;
 });
+
+const buttonTitle = computed(() => {
+  if (props.updating) {
+    return "Обновление выполняется…";
+  }
+  if (props.upgradeBlocked) {
+    return "Дождитесь завершения обновления на другом хосте";
+  }
+  return upgradeTitle.value;
+});
 </script>
 
 <style scoped>
@@ -80,8 +94,7 @@ const upgradeTitle = computed(() => {
 }
 
 .agent-version-upgrade:disabled {
-  cursor: default;
-  opacity: 0.65;
+  cursor: not-allowed;
 }
 
 .agent-version-upgrade__arrow {
@@ -114,6 +127,18 @@ const upgradeTitle = computed(() => {
   background: rgba(63, 185, 80, 0.28);
 }
 
+.agent-version-upgrade--inactive .agent-version-upgrade__arrow,
+.agent-version-upgrade--updating .agent-version-upgrade__arrow {
+  background: rgba(139, 148, 158, 0.2);
+  color: #8b949e;
+}
+
+.agent-version-upgrade--inactive .agent-version-upgrade__target,
+.agent-version-upgrade--updating .agent-version-upgrade__target {
+  color: #8b949e;
+  text-decoration: none;
+}
+
 .agent-version-upgrade__busy {
   font-size: 0.85em;
 }
diff --git a/frontend/src/version.ts b/frontend/src/version.ts
index 0b4b5f1..0848572 100644
--- a/frontend/src/version.ts
+++ b/frontend/src/version.ts
@@ -1,4 +1,4 @@
 /** Fallback до загрузки /health; при релизе держите в sync с backend/app/version.py */
 export const APP_NAME = "Security Alert Center";
-export const APP_VERSION = "0.3.8";
+export const APP_VERSION = "0.4.0";
 export const APP_VERSION_LABEL = `${APP_NAME} v.${APP_VERSION}`;
diff --git a/frontend/src/views/HostsView.vue b/frontend/src/views/HostsView.vue
index 77ba59e..475321e 100644
--- a/frontend/src/views/HostsView.vue
+++ b/frontend/src/views/HostsView.vue
@@ -72,6 +72,7 @@
               :host="h"
               :git="data"
               :updating="upgradingHostId === h.id"
+              :upgrade-blocked="upgradingHostId != null && upgradingHostId !== h.id"
               :outdated-highlight="isVersionOutdated(h)"
               @upgrade="startAgentUpgrade(h)"
             />