diff --git a/next.config.mjs b/next.config.mjs
index ac7197503ce..d99ccd3ad53 100644
--- a/next.config.mjs
+++ b/next.config.mjs
@@ -223,6 +223,11 @@ const nextConfig = {
     "pino-pretty",
     "thread-stream",
     "pino-abstract-transport",
+    // `ws` must stay external so server-side WebSocket executors keep the real
+    // native masking implementation and optional helpers in the runtime bundle.
+    "ws",
+    "bufferutil",
+    "utf-8-validate",
     "better-sqlite3",
     // sqlite-vec ships a native vec0.so loaded at runtime via createRequire().
     // Turbopack otherwise tries to bundle the .so and fails with "Unknown module
diff --git a/src/sse/handlers/chat.ts b/src/sse/handlers/chat.ts
index 0bee6caa424..f333db3d0ee 100644
--- a/src/sse/handlers/chat.ts
+++ b/src/sse/handlers/chat.ts
@@ -96,6 +96,7 @@ import { enforceApiKeyPolicy } from "../../shared/utils/apiKeyPolicy";
 import { hasProviderQuotaBypassScope } from "../../shared/constants/apiKeyPolicyScopes";
 import { cloneLogPayload } from "@/lib/logPayloads";
 import { handleInternalUsageCommand } from "@/lib/usage/internalUsageCommand";
+import { shouldPersistUnavailableStateForComboFailure } from "../services/unavailableStatePolicy";
 import {
   applyTaskAwareRouting,
   getTaskRoutingConfig,
@@ -1742,11 +1743,12 @@ async function handleSingleModelChat(
             model,
             providerProfile,
             {
-              persistUnavailableState: !(
-                isCombo &&
-                result.status === 429 &&
-                (failureKind === "rate_limit" || failureKind === "transient")
-              ),
+              persistUnavailableState: shouldPersistUnavailableStateForComboFailure({
+                isCombo,
+                provider,
+                status: result.status,
+                failureKind,
+              }),
               isCombo,
             }
           );
diff --git a/src/sse/services/unavailableStatePolicy.ts b/src/sse/services/unavailableStatePolicy.ts
new file mode 100644
index 00000000000..80dbaff80b1
--- /dev/null
+++ b/src/sse/services/unavailableStatePolicy.ts
@@ -0,0 +1,22 @@
+/**
+ * Policy for whether a combo fallback should persist connection unavailability.
+ *
+ * Combo-managed transient 429s stay in-memory for Antigravity because that path
+ * has dedicated quota handling. Other providers should persist the cooldown so
+ * the same connection is skipped on later requests, not just within the current
+ * combo attempt.
+ */
+export function shouldPersistUnavailableStateForComboFailure(options: {
+  isCombo?: boolean;
+  provider?: string | null;
+  status: number;
+  failureKind?: string | null;
+}): boolean {
+  const isAntigravityComboTransient429 =
+    options.isCombo === true &&
+    options.provider === "antigravity" &&
+    options.status === 429 &&
+    (options.failureKind === "rate_limit" || options.failureKind === "transient");
+
+  return !isAntigravityComboTransient429;
+}
diff --git a/tests/unit/next-config.test.ts b/tests/unit/next-config.test.ts
index 29821fa4ec1..d2a8753d010 100644
--- a/tests/unit/next-config.test.ts
+++ b/tests/unit/next-config.test.ts
@@ -101,6 +101,9 @@ test("next config declares Turbopack aliases, runtime assets and server external
 
   for (const packageName of [
     "thread-stream",
+    "ws",
+    "bufferutil",
+    "utf-8-validate",
     "better-sqlite3",
     // sqlite-vec ships a native vec0.so loaded at runtime; without externalizing it
     // the Turbopack build fails with "Unknown module type" on the .so (issue #3066).
diff --git a/tests/unit/unavailable-state-policy.test.ts b/tests/unit/unavailable-state-policy.test.ts
new file mode 100644
index 00000000000..438833f320d
--- /dev/null
+++ b/tests/unit/unavailable-state-policy.test.ts
@@ -0,0 +1,38 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+
+import { shouldPersistUnavailableStateForComboFailure } from "../../src/sse/services/unavailableStatePolicy.ts";
+
+test("combo transient 429 persists for non-Antigravity providers", () => {
+  assert.equal(
+    shouldPersistUnavailableStateForComboFailure({
+      isCombo: true,
+      provider: "openai",
+      status: 429,
+      failureKind: "transient",
+    }),
+    true
+  );
+
+  assert.equal(
+    shouldPersistUnavailableStateForComboFailure({
+      isCombo: true,
+      provider: "anthropic",
+      status: 429,
+      failureKind: "rate_limit",
+    }),
+    true
+  );
+});
+
+test("combo transient 429 stays in-memory for Antigravity", () => {
+  assert.equal(
+    shouldPersistUnavailableStateForComboFailure({
+      isCombo: true,
+      provider: "antigravity",
+      status: 429,
+      failureKind: "transient",
+    }),
+    false
+  );
+});