diff --git a/open-sse/translator/request/openai-to-gemini.ts b/open-sse/translator/request/openai-to-gemini.ts
index 14cc4d4e5e..cb1cedd713 100644
--- a/open-sse/translator/request/openai-to-gemini.ts
+++ b/open-sse/translator/request/openai-to-gemini.ts
@@ -464,12 +464,17 @@ function openaiToGeminiBase(
 
             // Gemini expects the signature on the functionCall part itself.
             // If we are in a mode where missing signatures cause 400s (and we couldn't find one),
-            // safely default to the bypass string to protect against 400s.
+            // safely default to the bypass string to protect against 400s. The bypass sentinel is
+            // an audit-trail risk (a magic validator-bypass string upstream could log/flag), so
+            // operators can disable it via ANTIGRAVITY_ALLOW_SIGNATURE_BYPASS=0 — real signatures
+            // are always preferred; the sentinel only fills the gap when none is available.
+            const signatureBypassEnabled =
+              toolNameOptions.supportsSignatureBypass &&
+              signaturelessToolCallMode !== "text" &&
+              process.env.ANTIGRAVITY_ALLOW_SIGNATURE_BYPASS !== "0";
             const finalSignature =
               embeddedThoughtSignature ||
-              (toolNameOptions.supportsSignatureBypass && signaturelessToolCallMode !== "text"
-                ? "skip_thought_signature_validator"
-                : undefined);
+              (signatureBypassEnabled ? "skip_thought_signature_validator" : undefined);
             parts.push({
               ...(finalSignature ? { thoughtSignature: finalSignature } : {}),
               functionCall: {
diff --git a/src/lib/oauth/providers/antigravity.ts b/src/lib/oauth/providers/antigravity.ts
index 8456938f82..f3790141c6 100644
--- a/src/lib/oauth/providers/antigravity.ts
+++ b/src/lib/oauth/providers/antigravity.ts
@@ -112,7 +112,12 @@ async function onboardAntigravityUser(
   tierId: string,
   metadata: Record<string, string>
 ): Promise<void> {
-  for (let i = 0; i < 10; i++) {
+  // Bounded onboarding: cap retries (was 10) and jitter the delay so a stuck
+  // loop cannot look like scripted automation to the upstream (ban-safety).
+  const MAX_ONBOARD_RETRIES = 3;
+  const BASE_RETRY_MS = 3000;
+  const JITTER_MS = 4000;
+  for (let i = 0; i < MAX_ONBOARD_RETRIES; i++) {
     try {
       const response = await fetchFirstOk(
         config.onboardUserEndpoints,
@@ -124,7 +129,7 @@ async function onboardAntigravityUser(
     } catch {
       return;
     }
-    await new Promise((resolve) => setTimeout(resolve, 5000));
+    await new Promise((resolve) => setTimeout(resolve, BASE_RETRY_MS + Math.random() * JITTER_MS));
   }
 }
 
diff --git a/tests/unit/translator-antigravity-signature-bypass.test.ts b/tests/unit/translator-antigravity-signature-bypass.test.ts
new file mode 100644
index 0000000000..f7a3853c86
--- /dev/null
+++ b/tests/unit/translator-antigravity-signature-bypass.test.ts
@@ -0,0 +1,62 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+
+const { openaiToAntigravityRequest } =
+  await import("../../open-sse/translator/request/openai-to-gemini.ts");
+
+const body = {
+  messages: [
+    { role: "user", content: "Use the terminal tool to echo hi." },
+    {
+      role: "assistant",
+      tool_calls: [
+        {
+          id: "call_1",
+          type: "function",
+          function: { name: "terminal", arguments: JSON.stringify({ command: "echo hi" }) },
+        },
+      ],
+    },
+    { role: "tool", tool_call_id: "call_1", name: "terminal", content: "hi" },
+  ],
+  tools: [
+    {
+      type: "function",
+      function: {
+        name: "terminal",
+        description: "Run a shell command",
+        parameters: { type: "object", properties: { command: { type: "string" } } },
+      },
+    },
+  ],
+};
+
+function modelParts(model: string, b: unknown) {
+  const envelope = openaiToAntigravityRequest(model, b, true) as {
+    request: { contents: Array<{ role: string; parts: Array<Record<string, unknown>> }> };
+  };
+  const modelMsg = envelope.request.contents.find((c) => c.role === "model");
+  assert.ok(modelMsg, "expected an assistant (model-role) message in the translation");
+  return modelMsg.parts;
+}
+
+test("antigravity multi-turn tool call carries the signature bypass sentinel by default", () => {
+  const parts = modelParts("gemini-3.1-pro-low", body);
+  const fc = parts.find((p) => p.functionCall);
+  assert.ok(fc, "expected a functionCall part");
+  assert.equal(fc.thoughtSignature, "skip_thought_signature_validator");
+});
+
+test("ANTIGRAVITY_ALLOW_SIGNATURE_BYPASS=0 disables the sentinel", () => {
+  const prev = process.env.ANTIGRAVITY_ALLOW_SIGNATURE_BYPASS;
+  process.env.ANTIGRAVITY_ALLOW_SIGNATURE_BYPASS = "0";
+  try {
+    const parts = modelParts("gemini-3.1-pro-low", body);
+    const fc = parts.find((p) => p.functionCall);
+    assert.ok(fc, "expected a functionCall part");
+    assert.equal(fc.thoughtSignature, undefined);
+  } finally {
+    if (prev === undefined) delete process.env.ANTIGRAVITY_ALLOW_SIGNATURE_BYPASS;
+    else process.env.ANTIGRAVITY_ALLOW_SIGNATURE_BYPASS = prev;
+  }
+});