diff --git a/src/agents/pi-embedded-runner.test.ts b/src/agents/pi-embedded-runner.test.ts
index 4c29aa186..1ce3bc94d 100644
--- a/src/agents/pi-embedded-runner.test.ts
+++ b/src/agents/pi-embedded-runner.test.ts
@@ -1,6 +1,10 @@
+import type { AgentTool } from "@mariozechner/pi-agent-core";
+import { Type } from "@sinclair/typebox";
 import { describe, expect, it } from "vitest";
-
-import { buildEmbeddedSandboxInfo } from "./pi-embedded-runner.js";
+import {
+  buildEmbeddedSandboxInfo,
+  splitSdkTools,
+} from "./pi-embedded-runner.js";
 import type { SandboxContext } from "./sandbox.js";
 
 describe("buildEmbeddedSandboxInfo", () => {
@@ -45,3 +49,52 @@ describe("buildEmbeddedSandboxInfo", () => {
     });
   });
 });
+
+function createStubTool(name: string): AgentTool {
+  return {
+    name,
+    label: name,
+    description: "",
+    parameters: Type.Object({}),
+    execute: async () => ({ content: [], details: {} }),
+  };
+}
+
+describe("splitSdkTools", () => {
+  const tools = [
+    createStubTool("read"),
+    createStubTool("bash"),
+    createStubTool("edit"),
+    createStubTool("write"),
+    createStubTool("browser"),
+  ];
+
+  it("routes built-ins to custom tools when sandboxed", () => {
+    const { builtInTools, customTools } = splitSdkTools({
+      tools,
+      sandboxEnabled: true,
+    });
+    expect(builtInTools).toEqual([]);
+    expect(customTools.map((tool) => tool.name)).toEqual([
+      "read",
+      "bash",
+      "edit",
+      "write",
+      "browser",
+    ]);
+  });
+
+  it("keeps built-ins as SDK tools when not sandboxed", () => {
+    const { builtInTools, customTools } = splitSdkTools({
+      tools,
+      sandboxEnabled: false,
+    });
+    expect(builtInTools.map((tool) => tool.name)).toEqual([
+      "read",
+      "bash",
+      "edit",
+      "write",
+    ]);
+    expect(customTools.map((tool) => tool.name)).toEqual(["browser"]);
+  });
+});
diff --git a/src/agents/pi-embedded-runner.ts b/src/agents/pi-embedded-runner.ts
index 7913664c4..8720ee265 100644
--- a/src/agents/pi-embedded-runner.ts
+++ b/src/agents/pi-embedded-runner.ts
@@ -1,7 +1,11 @@
 import fs from "node:fs/promises";
 import os from "node:os";
 
-import type { AgentMessage, ThinkingLevel } from "@mariozechner/pi-agent-core";
+import type {
+  AgentMessage,
+  AgentTool,
+  ThinkingLevel,
+} from "@mariozechner/pi-agent-core";
 import type { Api, AssistantMessage, Model } from "@mariozechner/pi-ai";
 import {
   buildSystemPrompt,
@@ -12,6 +16,7 @@ import {
   SettingsManager,
   type Skill,
 } from "@mariozechner/pi-coding-agent";
+import type { TSchema } from "@sinclair/typebox";
 import { resolveHeartbeatPrompt } from "../auto-reply/heartbeat.js";
 import type {
   ReasoningLevel,
@@ -249,6 +254,33 @@ export function buildEmbeddedSandboxInfo(
   };
 }
 
+const BUILT_IN_TOOL_NAMES = new Set(["read", "bash", "edit", "write"]);
+
+type AnyAgentTool = AgentTool<TSchema, unknown>;
+
+export function splitSdkTools(options: {
+  tools: AnyAgentTool[];
+  sandboxEnabled: boolean;
+}): {
+  builtInTools: AnyAgentTool[];
+  customTools: ReturnType<typeof toToolDefinitions>;
+} {
+  // SDK rebuilds built-ins from cwd; route sandboxed versions as custom tools.
+  const { tools, sandboxEnabled } = options;
+  if (sandboxEnabled) {
+    return {
+      builtInTools: [],
+      customTools: toToolDefinitions(tools),
+    };
+  }
+  return {
+    builtInTools: tools.filter((tool) => BUILT_IN_TOOL_NAMES.has(tool.name)),
+    customTools: toToolDefinitions(
+      tools.filter((tool) => !BUILT_IN_TOOL_NAMES.has(tool.name)),
+    ),
+  };
+}
+
 export function queueEmbeddedPiMessage(
   sessionId: string,
   text: string,
@@ -528,11 +560,10 @@ export async function compactEmbeddedPiSession(params: {
           agentDir,
         );
 
-        const builtInToolNames = new Set(["read", "bash", "edit", "write"]);
-        const builtInTools = tools.filter((t) => builtInToolNames.has(t.name));
-        const customTools = toToolDefinitions(
-          tools.filter((t) => !builtInToolNames.has(t.name)),
-        );
+        const { builtInTools, customTools } = splitSdkTools({
+          tools,
+          sandboxEnabled: !!sandbox?.enabled,
+        });
 
         const { session } = await createAgentSession({
           cwd: resolvedWorkspace,
@@ -829,14 +860,10 @@ export async function runEmbeddedPiAgent(params: {
             agentDir,
           );
 
-          // Split tools into built-in (recognized by pi-coding-agent SDK) and custom (clawdbot-specific)
-          const builtInToolNames = new Set(["read", "bash", "edit", "write"]);
-          const builtInTools = tools.filter((t) =>
-            builtInToolNames.has(t.name),
-          );
-          const customTools = toToolDefinitions(
-            tools.filter((t) => !builtInToolNames.has(t.name)),
-          );
+          const { builtInTools, customTools } = splitSdkTools({
+            tools,
+            sandboxEnabled: !!sandbox?.enabled,
+          });
 
           const { session } = await createAgentSession({
             cwd: resolvedWorkspace,
diff --git a/src/agents/pi-embedded-subscribe.test.ts b/src/agents/pi-embedded-subscribe.test.ts
index 72e2541c5..b50e02d96 100644
--- a/src/agents/pi-embedded-subscribe.test.ts
+++ b/src/agents/pi-embedded-subscribe.test.ts
@@ -162,7 +162,9 @@ describe("subscribeEmbeddedPiSession", () => {
 
     expect(onBlockReply).toHaveBeenCalledTimes(1);
     const payload = onBlockReply.mock.calls[0][0];
-    expect(payload.text).toBe("_Reasoning:_\n_Because it helps_\n\nFinal answer");
+    expect(payload.text).toBe(
+      "_Reasoning:_\n_Because it helps_\n\nFinal answer",
+    );
   });
 
   it("emits block replies on text_end and does not duplicate on message_end", () => {