diff --git a/packages/evals/.gitignore b/packages/evals/.gitignore
index d67d472e2a..c4ff719702 100644
--- a/packages/evals/.gitignore
+++ b/packages/evals/.gitignore
@@ -1 +1,4 @@
 .browserbase/
+.trajectories/
+.rubric-cache/
+packages/
diff --git a/packages/evals/framework/codexCodeBridge.ts b/packages/evals/framework/codexCodeBridge.ts
index c50fb671b8..45a329cdf8 100644
--- a/packages/evals/framework/codexCodeBridge.ts
+++ b/packages/evals/framework/codexCodeBridge.ts
@@ -15,6 +15,7 @@
  */
 import http from "node:http";
 import type { AddressInfo } from "node:net";
+import { sanitizeErrorMessage } from "@browserbasehq/stagehand-integrations/harness";
 import type { AgentMount } from "../core/contracts/tool.js";
 import type { ExternalHarnessTaskPlan } from "./externalHarnessPlan.js";
 import type { EvalLogger } from "../logger.js";
@@ -55,18 +56,6 @@ function stringifyResult(value: unknown): string {
   }
 }
 
-/**
- * Snippet errors can embed connection URLs whose query strings carry
- * credentials (Browserbase connect URLs include signing keys). Redact
- * credential-bearing fragments before the message crosses the HTTP boundary
- * or reaches the logs; the rest stays intact so the agent can self-correct.
- */
-export function sanitizeErrorMessage(message: string): string {
-  return message
-    .replace(/([?&](?:signingKey|apiKey|api_key|token|key)=)[^&\s"']+/gi, "$1[redacted]")
-    .replace(/\b(sk-[A-Za-z0-9_-]{6})[A-Za-z0-9_-]+/g, "$1[redacted]");
-}
-
 export interface CodeBridge {
   port: number;
   close: () => Promise<void>;
diff --git a/packages/evals/package.json b/packages/evals/package.json
index c36f3a69d6..6de67da3ef 100644
--- a/packages/evals/package.json
+++ b/packages/evals/package.json
@@ -24,6 +24,7 @@
     "@braintrust/otel": "^0.2.1",
     "@browserbasehq/sdk": "catalog:",
     "@browserbasehq/stagehand": "workspace:*",
+    "@browserbasehq/stagehand-integrations": "workspace:*",
     "@openai/codex-sdk": "catalog:",
     "@opentelemetry/api": "catalog:",
     "@opentelemetry/exporter-trace-otlp-proto": "^0.220.0",
diff --git a/packages/integrations/claude-code/src/agent.ts b/packages/integrations/claude-code/src/agent.ts
index 6b7e07bca1..14f3d95f1e 100644
--- a/packages/integrations/claude-code/src/agent.ts
+++ b/packages/integrations/claude-code/src/agent.ts
@@ -3,10 +3,9 @@ import {
   FACADE_AGENT_INSTRUCTIONS,
   FACADE_TOOLS,
 } from "@browserbasehq/stagehand-integrations/facade";
+import { buildAllowlistedEnv } from "@browserbasehq/stagehand-integrations/harness";
 import { fileURLToPath } from "node:url";
 
-import { buildAllowlistedEnv } from "./env.ts";
-
 export const STAGEHAND_TOOL_NAMES = FACADE_TOOLS.map((tool) => `mcp__stagehand__${tool.name}`);
 
 async function main(): Promise<void> {
diff --git a/packages/integrations/claude-code/tests/agent.test.ts b/packages/integrations/claude-code/tests/agent.test.ts
index 83b5d07eec..4abd549b9f 100644
--- a/packages/integrations/claude-code/tests/agent.test.ts
+++ b/packages/integrations/claude-code/tests/agent.test.ts
@@ -1,8 +1,8 @@
 import { FACADE_TOOLS } from "@browserbasehq/stagehand-integrations/facade";
+import { buildAllowlistedEnv } from "@browserbasehq/stagehand-integrations/harness";
 import { describe, expect, it } from "vitest";
 
 import { STAGEHAND_TOOL_NAMES } from "../src/agent.ts";
-import { buildAllowlistedEnv } from "../src/env.ts";
 
 describe("claude-code stagehand example", () => {
   it("allows exactly the namespaced facade tools", () => {
diff --git a/packages/integrations/codex/src/agent.ts b/packages/integrations/codex/src/agent.ts
index c27eef56d7..fdb29a9f16 100644
--- a/packages/integrations/codex/src/agent.ts
+++ b/packages/integrations/codex/src/agent.ts
@@ -1,8 +1,7 @@
 import { Codex, type CodexOptions } from "@openai/codex-sdk";
+import { buildAllowlistedEnv } from "@browserbasehq/stagehand-integrations/harness";
 import { fileURLToPath } from "node:url";
 
-import { buildAllowlistedEnv } from "./env.ts";
-
 const serverPath = fileURLToPath(
   import.meta.resolve("@browserbasehq/stagehand-integrations/facade/stdio-server"),
 );
diff --git a/packages/integrations/codex/src/env.ts b/packages/integrations/codex/src/env.ts
deleted file mode 100644
index 849c34954b..0000000000
--- a/packages/integrations/codex/src/env.ts
+++ /dev/null
@@ -1,10 +0,0 @@
-/** Only STAGEHAND_* and BROWSERBASE_* host env vars cross into the server. */
-export function buildAllowlistedEnv(): Record<string, string> {
-  const env: Record<string, string> = {};
-  for (const [key, value] of Object.entries(process.env)) {
-    if (/^(STAGEHAND_|BROWSERBASE_)/.test(key) && value) {
-      env[key] = value;
-    }
-  }
-  return env;
-}
diff --git a/packages/integrations/codex/tests/agent.test.ts b/packages/integrations/codex/tests/agent.test.ts
index c506965f65..2358b534ef 100644
--- a/packages/integrations/codex/tests/agent.test.ts
+++ b/packages/integrations/codex/tests/agent.test.ts
@@ -1,7 +1,7 @@
+import { buildAllowlistedEnv } from "@browserbasehq/stagehand-integrations/harness";
 import { describe, expect, it } from "vitest";
 
 import { buildCodexConfig } from "../src/agent.ts";
-import { buildAllowlistedEnv } from "../src/env.ts";
 
 describe("codex stagehand example", () => {
   it("mounts the facade server in the config override", () => {
diff --git a/packages/integrations/core/package.json b/packages/integrations/core/package.json
index 895932a846..88d7715590 100644
--- a/packages/integrations/core/package.json
+++ b/packages/integrations/core/package.json
@@ -19,6 +19,10 @@
     },
     "./facade/stdio-server": {
       "import": "./dist/facade/stdio-server.mjs"
+    },
+    "./harness": {
+      "types": "./dist/harness/index.d.mts",
+      "import": "./dist/harness/index.mjs"
     }
   },
   "scripts": {
diff --git a/packages/integrations/core/src/facade/stdio-server.ts b/packages/integrations/core/src/facade/stdio-server.ts
index 3d0c782203..53b1bc5bac 100644
--- a/packages/integrations/core/src/facade/stdio-server.ts
+++ b/packages/integrations/core/src/facade/stdio-server.ts
@@ -10,6 +10,7 @@ import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
 import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
 import { CallToolRequestSchema, ListToolsRequestSchema } from "@modelcontextprotocol/sdk/types.js";
 import { closeCodeModeStdio } from "../codemode/stdio-lifecycle.js";
+import { sanitizeErrorMessage } from "../harness/redact.js";
 import { stagehandFacadeConfigFromEnv } from "./config.js";
 import {
   CodeModeRunInputSchema,
@@ -149,15 +150,6 @@ function stringifyResult(value: unknown): string {
   }
 }
 
-export function sanitizeErrorMessage(message: string): string {
-  return message
-    .replace(/([?&](?:signingKey|apiKey|api_key|token|key)=)[^&\s"']+/gi, "$1[redacted]")
-    .replace(/\b(sk-[A-Za-z0-9_-]{6})[A-Za-z0-9_-]+/g, "$1[redacted]")
-    .replace(/\b(bb_(?:live|test)_[A-Za-z0-9]{4})[A-Za-z0-9_-]+/g, "$1[redacted]")
-    .replace(/\bAIza[0-9A-Za-z_-]{30,}/g, "AIza[redacted]")
-    .replace(/\b(Bearer\s+)[A-Za-z0-9._~+/=-]{8,}/gi, "$1[redacted]");
-}
-
 async function shutdown(code: number): Promise<void> {
   if (closing) return;
   closing = true;
diff --git a/packages/integrations/core/src/harness/contract.ts b/packages/integrations/core/src/harness/contract.ts
new file mode 100644
index 0000000000..0a65299fe3
--- /dev/null
+++ b/packages/integrations/core/src/harness/contract.ts
@@ -0,0 +1,29 @@
+type LogLine = {
+  id?: string;
+  category?: string;
+  message: string;
+  level?: 0 | 1 | 2;
+  timestamp?: string;
+  auxiliary?: Record<
+    string,
+    {
+      value: string;
+      type: "object" | "string" | "html" | "integer" | "float" | "boolean";
+    }
+  >;
+};
+
+/** Logger surface required by agent harness adapters. */
+export type HarnessLogger = {
+  log(line: LogLine): void;
+  warn(line: LogLine): void;
+  error(line: LogLine): void;
+};
+
+/** Error raised when a harness adapter cannot complete its work. */
+export class HarnessAdapterError extends Error {
+  constructor(message: string, options?: { cause?: unknown }) {
+    super(message, options);
+    this.name = "HarnessAdapterError";
+  }
+}
diff --git a/packages/integrations/claude-code/src/env.ts b/packages/integrations/core/src/harness/env.ts
similarity index 93%
rename from packages/integrations/claude-code/src/env.ts
rename to packages/integrations/core/src/harness/env.ts
index 849c34954b..43069f433a 100644
--- a/packages/integrations/claude-code/src/env.ts
+++ b/packages/integrations/core/src/harness/env.ts
@@ -1,4 +1,4 @@
-/** Only STAGEHAND_* and BROWSERBASE_* host env vars cross into the server. */
+/** Only STAGEHAND_* and BROWSERBASE_* host env vars cross into harness processes. */
 export function buildAllowlistedEnv(): Record<string, string> {
   const env: Record<string, string> = {};
   for (const [key, value] of Object.entries(process.env)) {
diff --git a/packages/integrations/core/src/harness/index.ts b/packages/integrations/core/src/harness/index.ts
new file mode 100644
index 0000000000..75962aa097
--- /dev/null
+++ b/packages/integrations/core/src/harness/index.ts
@@ -0,0 +1,3 @@
+export * from "./contract.js";
+export * from "./env.js";
+export * from "./redact.js";
diff --git a/packages/integrations/core/src/harness/redact.ts b/packages/integrations/core/src/harness/redact.ts
new file mode 100644
index 0000000000..454f3a4d6b
--- /dev/null
+++ b/packages/integrations/core/src/harness/redact.ts
@@ -0,0 +1,19 @@
+export function sanitizeErrorMessage(message: string): string {
+  let sanitized = message;
+  // stdio-server and codexCodeBridge: credential-bearing URL query parameters.
+  sanitized = sanitized.replace(
+    /([?&](?:signingKey|apiKey|api_key|token|key)=)[^&\s"']+/gi,
+    "$1[redacted]",
+  );
+  // stdio-server and codexCodeBridge: OpenAI-style secret keys.
+  sanitized = sanitized.replace(/\b(sk-[A-Za-z0-9_-]{6})[A-Za-z0-9_-]+/g, "$1[redacted]");
+  // stdio-server: Browserbase live and test keys.
+  sanitized = sanitized.replace(
+    /\b(bb_(?:live|test)_[A-Za-z0-9]{4})[A-Za-z0-9_-]+/g,
+    "$1[redacted]",
+  );
+  // stdio-server: Google API keys.
+  sanitized = sanitized.replace(/\bAIza[0-9A-Za-z_-]{30,}/g, "AIza[redacted]");
+  // stdio-server: bearer authorization values.
+  return sanitized.replace(/\b(Bearer\s+)[A-Za-z0-9._~+/=-]{8,}/gi, "$1[redacted]");
+}
diff --git a/packages/integrations/core/tests/harness.test.ts b/packages/integrations/core/tests/harness.test.ts
new file mode 100644
index 0000000000..8ec2288c96
--- /dev/null
+++ b/packages/integrations/core/tests/harness.test.ts
@@ -0,0 +1,46 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { buildAllowlistedEnv, sanitizeErrorMessage } from "../src/harness/index.js";
+
+describe("harness contract", () => {
+  afterEach(() => {
+    vi.unstubAllEnvs();
+  });
+
+  it("redacts credential-bearing URL query parameters", () => {
+    expect(sanitizeErrorMessage("wss://example.test?signingKey=top-secret&foo=bar")).toBe(
+      "wss://example.test?signingKey=[redacted]&foo=bar",
+    );
+  });
+
+  it("redacts OpenAI-style secret keys", () => {
+    expect(sanitizeErrorMessage("key sk-abcdef1234567890")).toBe("key sk-abcdef[redacted]");
+  });
+
+  it("redacts Browserbase keys", () => {
+    expect(sanitizeErrorMessage("key bb_live_abcd1234567890")).toBe("key bb_live_abcd[redacted]");
+  });
+
+  it("redacts Google API keys", () => {
+    expect(sanitizeErrorMessage(`key AIza${"a".repeat(32)}`)).toBe("key AIza[redacted]");
+  });
+
+  it("redacts bearer authorization values", () => {
+    expect(sanitizeErrorMessage("Authorization: Bearer abcdefgh123456")).toBe(
+      "Authorization: Bearer [redacted]",
+    );
+  });
+
+  it("allows Stagehand and Browserbase env vars while excluding other and empty values", () => {
+    vi.stubEnv("STAGEHAND_MODEL", "model");
+    vi.stubEnv("BROWSERBASE_API_KEY", "browserbase-key");
+    vi.stubEnv("STAGEHAND_EMPTY", "");
+    vi.stubEnv("NOT_ALLOWLISTED_SECRET", "secret");
+
+    const env = buildAllowlistedEnv();
+
+    expect(env.STAGEHAND_MODEL).toBe("model");
+    expect(env.BROWSERBASE_API_KEY).toBe("browserbase-key");
+    expect(env).not.toHaveProperty("STAGEHAND_EMPTY");
+    expect(env).not.toHaveProperty("NOT_ALLOWLISTED_SECRET");
+  });
+});
diff --git a/packages/integrations/core/tsdown.config.ts b/packages/integrations/core/tsdown.config.ts
index d18c6ef4b6..2766e2babd 100644
--- a/packages/integrations/core/tsdown.config.ts
+++ b/packages/integrations/core/tsdown.config.ts
@@ -5,6 +5,7 @@ export default defineConfig({
     "codemode/stdio-server": "src/codemode/stdio-server.ts",
     "facade/index": "src/facade/index.ts",
     "facade/stdio-server": "src/facade/stdio-server.ts",
+    "harness/index": "src/harness/index.ts",
   },
   format: ["esm"],
   platform: "node",
diff --git a/packages/integrations/mastra/src/client.ts b/packages/integrations/mastra/src/client.ts
index aeff3baa56..8326585b7f 100644
--- a/packages/integrations/mastra/src/client.ts
+++ b/packages/integrations/mastra/src/client.ts
@@ -1,4 +1,5 @@
 import { MCPClient } from "@mastra/mcp";
+import { buildAllowlistedEnv } from "@browserbasehq/stagehand-integrations/harness";
 import { fileURLToPath } from "node:url";
 
 export type FacadeMCPClientOptions = {
@@ -9,17 +10,6 @@ export type FacadeMCPClientOptions = {
  * Starts the facade MCP server and returns its Mastra client.
  * Call `client.disconnect()` when finished to stop the child process and browser.
  */
-/** Only STAGEHAND_* and BROWSERBASE_* host env vars cross into the server. */
-export function buildAllowlistedEnv(): Record<string, string> {
-  const env: Record<string, string> = {};
-  for (const [key, value] of Object.entries(process.env)) {
-    if (/^(STAGEHAND_|BROWSERBASE_)/.test(key) && value) {
-      env[key] = value;
-    }
-  }
-  return env;
-}
-
 export function createFacadeMCPClient(options: FacadeMCPClientOptions = {}) {
   // Build @browserbasehq/stagehand-integrations first so this dist entrypoint exists.
   const serverPath = fileURLToPath(
diff --git a/packages/integrations/mastra/tests/client.test.ts b/packages/integrations/mastra/tests/client.test.ts
index 06eafadbd3..55f12d4637 100644
--- a/packages/integrations/mastra/tests/client.test.ts
+++ b/packages/integrations/mastra/tests/client.test.ts
@@ -1,7 +1,8 @@
 import { FACADE_TOOLS } from "@browserbasehq/stagehand-integrations/facade";
+import { buildAllowlistedEnv } from "@browserbasehq/stagehand-integrations/harness";
 import { afterEach, describe, expect, it } from "vitest";
 
-import { buildAllowlistedEnv, createFacadeMCPClient } from "../src/client.js";
+import { createFacadeMCPClient } from "../src/client.js";
 
 type FacadeClient = ReturnType<typeof createFacadeMCPClient>;
 
diff --git a/packages/integrations/vercel-ai/src/client.ts b/packages/integrations/vercel-ai/src/client.ts
index 35f18d6731..2e00bf23d4 100644
--- a/packages/integrations/vercel-ai/src/client.ts
+++ b/packages/integrations/vercel-ai/src/client.ts
@@ -1,22 +1,12 @@
 import { createMCPClient } from "@ai-sdk/mcp";
 import { Experimental_StdioMCPTransport } from "@ai-sdk/mcp/mcp-stdio";
+import { buildAllowlistedEnv } from "@browserbasehq/stagehand-integrations/harness";
 import { fileURLToPath } from "node:url";
 
 export type FacadeMCPClientOptions = {
   env?: Record<string, string>;
 };
 
-/** Only STAGEHAND_* and BROWSERBASE_* host env vars cross into the server. */
-export function buildAllowlistedEnv(): Record<string, string> {
-  const env: Record<string, string> = {};
-  for (const [key, value] of Object.entries(process.env)) {
-    if (/^(STAGEHAND_|BROWSERBASE_)/.test(key) && value) {
-      env[key] = value;
-    }
-  }
-  return env;
-}
-
 /**
  * Starts the stdio facade server as a child process and returns the AI SDK
  * MCP client connected to it. Call `client.close()` when finished to stop the
diff --git a/packages/integrations/vercel-ai/tests/client.test.ts b/packages/integrations/vercel-ai/tests/client.test.ts
index 8bfcf4d5bd..714cb51819 100644
--- a/packages/integrations/vercel-ai/tests/client.test.ts
+++ b/packages/integrations/vercel-ai/tests/client.test.ts
@@ -1,4 +1,5 @@
 import { afterEach, describe, expect, it } from "vitest";
+import { buildAllowlistedEnv } from "@browserbasehq/stagehand-integrations/harness";
 
 import { createFacadeMCPClient } from "../src/client.js";
 
@@ -53,7 +54,6 @@ describe("Stagehand facade MCP client", () => {
   it("allowlist excludes non-STAGEHAND/BROWSERBASE host vars", async () => {
     process.env.STAGEHAND_BROWSER = "local";
     process.env.NOT_ALLOWLISTED_SECRET = "must-not-cross";
-    const { buildAllowlistedEnv } = await import("../src/client.js");
     const env = buildAllowlistedEnv();
     expect(env.STAGEHAND_BROWSER).toBe("local");
     expect(env).not.toHaveProperty("NOT_ALLOWLISTED_SECRET");
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 647e3363eb..4810d60f8c 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -459,6 +459,9 @@ importers:
       '@browserbasehq/stagehand':
         specifier: workspace:*
         version: link:../sdk-ts
+      '@browserbasehq/stagehand-integrations':
+        specifier: workspace:*
+        version: link:../integrations/core
       '@openai/codex-sdk':
         specifier: 'catalog:'
         version: 0.147.0