diff --git a/src/mcp/register.ts b/src/mcp/register.ts
index 9d87967..5fd219c 100644
--- a/src/mcp/register.ts
+++ b/src/mcp/register.ts
@@ -1,17 +1,33 @@
 import type * as VSCode from "vscode";
 import { resolvePatchloomStatus } from "../binary/patchloom.js";
-import { getPatchloomLog } from "../logging/outputChannel.js";
+import { getPatchloomLog, getPatchloomRuntimeConfig } from "../logging/outputChannel.js";
+import { isAllowedPatchloomEnvKey } from "../util.js";
 
 /** Plain descriptor used to construct vscode.McpStdioServerDefinition at register time. */
 export interface McpServerBinaryDescriptor {
   readonly label: string;
   readonly command: string;
   readonly args: readonly string[];
+  readonly env?: Record<string, string>;
+}
+
+function patchloomOnlyEnv(extra: Record<string, string> | undefined): Record<string, string> {
+  const env: Record<string, string> = {};
+  if (extra === undefined) {
+    return env;
+  }
+  for (const [key, value] of Object.entries(extra)) {
+    if (isAllowedPatchloomEnvKey(key)) {
+      env[key] = value;
+    }
+  }
+  return env;
 }
 
 /** Pure helper for native MCP definitions (no vscode). Empty when binary unknown. */
 export function mcpServerDefinitionsForBinary(
-  binaryPath: string | undefined
+  binaryPath: string | undefined,
+  env?: Record<string, string>
 ): readonly McpServerBinaryDescriptor[] {
   if (!binaryPath) {
     return [];
@@ -20,12 +36,18 @@ export function mcpServerDefinitionsForBinary(
     {
       label: "Patchloom MCP",
       command: binaryPath,
-      args: ["mcp-server"]
+      args: ["mcp-server"],
+      env: patchloomOnlyEnv(env)
     }
   ];
 }
 
-type McpStdioServerDefinitionCtor = new (...args: readonly unknown[]) => unknown;
+type McpStdioServerDefinitionCtor = new (
+  label: string,
+  command: string,
+  args: string[],
+  env: Record<string, string>
+) => unknown;
 
 interface VsCodeLmWithMcp {
   registerMcpServerDefinitionProvider?(
@@ -52,23 +74,16 @@ function mcpStdioCtor(vscode: VsCodeWithMcpApi): McpStdioServerDefinitionCtor |
   return typeof ctor === "function" ? ctor : undefined;
 }
 
-function createMcpStdioServerDefinition(
+export function createMcpStdioServerDefinition(
   Ctor: McpStdioServerDefinitionCtor,
   descriptor: McpServerBinaryDescriptor
 ): unknown | undefined {
   const args = [...descriptor.args];
+  const env = descriptor.env ?? {};
   try {
-    return new Ctor({
-      label: descriptor.label,
-      command: descriptor.command,
-      args
-    });
+    return new Ctor(descriptor.label, descriptor.command, args, env);
   } catch {
-    try {
-      return new Ctor(descriptor.label, descriptor.command, args);
-    } catch {
-      return undefined;
-    }
+    return undefined;
   }
 }
 
@@ -102,8 +117,9 @@ export async function registerMcpServerProviderWithBinary(context: VSCode.Extens
     const disposable = vscode.lm.registerMcpServerDefinitionProvider("patchloom", {
       onDidChangeMcpServerDefinitions: emitter.event,
       provideMcpServerDefinitions: async () => {
+        const runtime = await getPatchloomRuntimeConfig();
         const definitions: unknown[] = [];
-        for (const descriptor of mcpServerDefinitionsForBinary(resolvedBinaryPath)) {
+        for (const descriptor of mcpServerDefinitionsForBinary(resolvedBinaryPath, runtime.extraEnv)) {
           const definition = createMcpStdioServerDefinition(Ctor, descriptor);
           if (definition !== undefined) {
             definitions.push(definition);
diff --git a/test/unit/mcpRegister.test.ts b/test/unit/mcpRegister.test.ts
index 44e3242..e274013 100644
--- a/test/unit/mcpRegister.test.ts
+++ b/test/unit/mcpRegister.test.ts
@@ -1,6 +1,18 @@
 import assert from "node:assert/strict";
 import test from "node:test";
-import { mcpServerDefinitionsForBinary } from "../../src/mcp/register.js";
+import {
+  createMcpStdioServerDefinition,
+  mcpServerDefinitionsForBinary
+} from "../../src/mcp/register.js";
+
+class FakeStdio {
+  constructor(
+    public label: string,
+    public command: string,
+    public args: string[],
+    public env: Record<string, string> = {}
+  ) {}
+}
 
 test("mcpServerDefinitionsForBinary returns empty when binary is undefined", () => {
   assert.deepEqual(mcpServerDefinitionsForBinary(undefined), []);
@@ -12,6 +24,37 @@ test("mcpServerDefinitionsForBinary returns one stdio definition for a path", ()
   assert.deepEqual(defs[0], {
     label: "Patchloom MCP",
     command: "/opt/patchloom",
-    args: ["mcp-server"]
+    args: ["mcp-server"],
+    env: {}
   });
 });
+
+test("mcpServerDefinitionsForBinary includes filtered PATCHLOOM env", () => {
+  const defs = mcpServerDefinitionsForBinary("/opt/patchloom", {
+    PATCHLOOM_MCP_SURFACE: "core",
+    PATH: "/tmp/evil"
+  });
+  assert.deepEqual(defs[0]?.env, { PATCHLOOM_MCP_SURFACE: "core" });
+});
+
+test("createMcpStdioServerDefinition constructs positionally so command is the binary", () => {
+  const instance = createMcpStdioServerDefinition(FakeStdio, {
+    label: "Patchloom MCP",
+    command: "/opt/patchloom",
+    args: ["mcp-server"]
+  }) as FakeStdio;
+  assert.equal(instance.command, "/opt/patchloom");
+  assert.equal(instance.label, "Patchloom MCP");
+  assert.deepEqual(instance.args, ["mcp-server"]);
+  assert.deepEqual(instance.env, {});
+});
+
+test("createMcpStdioServerDefinition forwards PATCHLOOM env", () => {
+  const instance = createMcpStdioServerDefinition(FakeStdio, {
+    label: "Patchloom MCP",
+    command: "/opt/patchloom",
+    args: ["mcp-server"],
+    env: { PATCHLOOM_MCP_SURFACE: "core" }
+  }) as FakeStdio;
+  assert.equal(instance.env.PATCHLOOM_MCP_SURFACE, "core");
+});