diff --git a/src/server/handlers/request/agent-stream.handler.test.ts b/src/server/handlers/request/agent-stream.handler.test.ts
index 1b5a6f62ea..c81fa9773f 100644
--- a/src/server/handlers/request/agent-stream.handler.test.ts
+++ b/src/server/handlers/request/agent-stream.handler.test.ts
@@ -531,7 +531,7 @@ describe("server/handlers/request/agent-stream.handler", () => {
     assertEquals(injectedToolSchema, inputSchema);
   });
 
-  it("passes runtime integration tool allowlists from forwarded props into the runtime agent config", async () => {
+  it("does not pass undeclared forwarded remote tool allowlists into the runtime agent config", async () => {
     let capturedAllowedTools: string[] | undefined;
 
     const handler = new AgentStreamHandler({
@@ -590,7 +590,70 @@ describe("server/handlers/request/agent-stream.handler", () => {
 
     assertExists(result.response);
     assertEquals(result.response.status, 200);
-    assertEquals(capturedAllowedTools, ["gmail:list-emails", "gmail:get-email"]);
+    assertEquals(capturedAllowedTools, undefined);
+  });
+
+  it("drops undeclared Studio runtime tool allowlists for untrusted clients", async () => {
+    let capturedAllowedTools: string[] | undefined;
+
+    const handler = new AgentStreamHandler({
+      ensureProjectDiscovery: async () => {},
+      getAgent: (id) => id === "assistant-1" ? createAgent("assistant-1") : undefined,
+      getAllAgentIds: () => ["assistant-1"],
+      sessionManager: new AgentRunSessionManager(),
+      createRuntime: (agent) => {
+        capturedAllowedTools = (agent.config as typeof agent.config & RuntimeRemoteToolConfig)
+          .__vfAllowedRemoteTools;
+
+        return {
+          stream: async (_messages, _context, callbacks) => {
+            callbacks?.onFinish?.({
+              text: "ok",
+              messages: [],
+              toolCalls: [],
+              status: "completed",
+              usage: {
+                promptTokens: 1,
+                completionTokens: 1,
+                totalTokens: 2,
+              },
+            });
+
+            return new ReadableStream<Uint8Array>({
+              start(controller) {
+                controller.close();
+              },
+            });
+          },
+        };
+      },
+    });
+
+    const body = createAgentStreamRequestBody({
+      forwardedProps: {
+        clientId: "external-client",
+        runtimeOverrides: {
+          allowedTools: ["studio_todo_write"],
+        },
+      },
+    });
+    const { jws, publicKeyPem } = await createControlPlaneSignature(body, { requestId: "run_1" });
+
+    const result = await handler.handle(
+      new Request("https://example.com/api/control-plane/runs/run_1/stream", {
+        method: "POST",
+        headers: {
+          "content-type": "application/json",
+          "x-veryfront-control-plane-jws": jws,
+        },
+        body,
+      }),
+      createCtx(publicKeyPem),
+    );
+
+    assertExists(result.response);
+    assertEquals(result.response.status, 200);
+    assertEquals(capturedAllowedTools, undefined);
   });
 
   it("auto-exposes Studio MCP tools for trusted Studio project-agent requests", async () => {
diff --git a/src/server/handlers/request/agent-stream.handler.ts b/src/server/handlers/request/agent-stream.handler.ts
index ad317731f9..e347500030 100644
--- a/src/server/handlers/request/agent-stream.handler.ts
+++ b/src/server/handlers/request/agent-stream.handler.ts
@@ -42,6 +42,7 @@ import {
   getInternalAgentStreamRequestSchema,
   type InternalAgentStreamRequest,
   type RuntimeAgentSourceContext,
+  type RuntimeRunAgentInput,
   toRuntimeRunAgentInput,
 } from "#veryfront/internal-agents/schema.ts";
 import { BaseHandler } from "../response/base.ts";
@@ -187,6 +188,75 @@ function getRequestedStudioToolNames(input: {
     .sort();
 }
 
+function sanitizeForwardedRuntimeAllowedTools(input: {
+  forwardedProps?: Record<string, unknown>;
+  availableToolNames: string[];
+  allowStudioRuntimeTools: boolean;
+}): Record<string, unknown> | undefined {
+  const forwardedProps = input.forwardedProps;
+  if (!isRecord(forwardedProps)) {
+    return forwardedProps;
+  }
+
+  const runtimeOverrides = isRecord(forwardedProps.runtimeOverrides)
+    ? forwardedProps.runtimeOverrides
+    : null;
+  if (!runtimeOverrides || !Object.hasOwn(runtimeOverrides, "allowedTools")) {
+    return forwardedProps;
+  }
+
+  const allowedTools = runtimeOverrides.allowedTools;
+  if (
+    !Array.isArray(allowedTools) || !allowedTools.every((toolName) => typeof toolName === "string")
+  ) {
+    return forwardedProps;
+  }
+
+  const availableToolNames = new Set(input.availableToolNames);
+  // Platform remote tools are gated separately by the child agent config in
+  // withVeryfrontPlatformRemoteTools. The Studio path is the one that consumes
+  // forwarded allowedTools, and Studio-only runtime tools are preserved only
+  // for trusted Studio clients that can already attach the Studio MCP surface.
+  const sanitizedAllowedTools = allowedTools.filter((toolName) =>
+    availableToolNames.has(toolName) ||
+    (input.allowStudioRuntimeTools && STUDIO_RUNTIME_REMOTE_TOOL_NAMES.has(toolName))
+  );
+  if (sanitizedAllowedTools.length === allowedTools.length) {
+    return forwardedProps;
+  }
+
+  const nextRuntimeOverrides: Record<string, unknown> = {
+    ...runtimeOverrides,
+    allowedTools: sanitizedAllowedTools,
+  };
+  if (sanitizedAllowedTools.length === 0) {
+    delete nextRuntimeOverrides.allowedTools;
+  }
+
+  const nextForwardedProps: Record<string, unknown> = {
+    ...forwardedProps,
+    runtimeOverrides: nextRuntimeOverrides,
+  };
+  if (Object.keys(nextRuntimeOverrides).length === 0) {
+    delete nextForwardedProps.runtimeOverrides;
+  }
+
+  return Object.keys(nextForwardedProps).length > 0 ? nextForwardedProps : undefined;
+}
+
+function sanitizeRuntimeRunAgentInput(input: RuntimeRunAgentInput): RuntimeRunAgentInput {
+  const clientProfile = resolveRuntimeClientProfile(input.forwardedProps);
+
+  return {
+    ...input,
+    forwardedProps: sanitizeForwardedRuntimeAllowedTools({
+      forwardedProps: input.forwardedProps,
+      availableToolNames: input.tools.map((tool) => tool.name),
+      allowStudioRuntimeTools: clientAllowsStudioMcp(clientProfile),
+    }),
+  };
+}
+
 function getVeryfrontApiMcpPolicy(agent: Agent): {
   allowAll: boolean;
   requestedToolNames: string[];
@@ -559,7 +629,7 @@ export class AgentStreamHandler extends BaseHandler {
               return this.respond(builder.json({ error: "Agent not found" }, 404));
             }
 
-            const runtimeInput = toRuntimeRunAgentInput(payload);
+            const runtimeInput = sanitizeRuntimeRunAgentInput(toRuntimeRunAgentInput(payload));
             const apiAuthToken = payload.credentials?.authToken || ctx.proxyToken ||
               getHostEnv("VERYFRONT_API_TOKEN") || "";
             const platformRuntimeAgent = await withVeryfrontPlatformRemoteTools({