diff --git a/packages/paperclip-runner/src/drivers/runtime-context-materializer.test.ts b/packages/paperclip-runner/src/drivers/runtime-context-materializer.test.ts
index a39009de562..28f43f7b211 100644
--- a/packages/paperclip-runner/src/drivers/runtime-context-materializer.test.ts
+++ b/packages/paperclip-runner/src/drivers/runtime-context-materializer.test.ts
@@ -106,23 +106,23 @@ describe("runtime context materialization", () => {
     }
   });
 
-  it("materializes a configured API key into the isolated Codex home", async () => {
+  it("does not materialize an API key into the isolated Codex home", async () => {
     const root = await mkdtemp(join(tmpdir(), "paperclip-runtime-context-api-key-"));
     roots.push(root);
-    const sourceCodexHome = join(root, "source-codex-home");
     const codexHome = join(root, "codex-home");
-    await mkdir(sourceCodexHome, { recursive: true });
-    await writeFile(join(sourceCodexHome, "auth.json"), JSON.stringify({ OPENAI_API_KEY: "host-key-must-not-win" }), { mode: 0o600 });
+    await mkdir(codexHome, { recursive: true });
+    await writeFile(
+      join(codexHome, "auth.json"),
+      JSON.stringify({ OPENAI_API_KEY: "stale-persisted-key" }),
+      { mode: 0o600 },
+    );
 
     await prepareIsolatedCodexHome({
       context: null,
       codexHome,
-      sourceCodexHome,
-      apiKey: "configured-agent-key",
     });
 
-    await expect(readFile(join(codexHome, "auth.json"), "utf8")).resolves.toBe(JSON.stringify({ OPENAI_API_KEY: "configured-agent-key" }));
-    expect((await stat(join(codexHome, "auth.json"))).mode & 0o777).toBe(0o600);
+    await expect(stat(join(codexHome, "auth.json"))).rejects.toThrow();
   });
 
   it("reconciles changed and empty assignments without following unexpected symlinks", async () => {
diff --git a/packages/paperclip-runner/src/drivers/runtime-context-materializer.ts b/packages/paperclip-runner/src/drivers/runtime-context-materializer.ts
index 02889d8d339..8e8cb53be94 100644
--- a/packages/paperclip-runner/src/drivers/runtime-context-materializer.ts
+++ b/packages/paperclip-runner/src/drivers/runtime-context-materializer.ts
@@ -51,7 +51,7 @@ export async function materializeNativeRuntimeSkills(context: NativeRuntimeConte
   }
 }
 
-export async function prepareIsolatedCodexHome(input: { context: NativeRuntimeContextSnapshot | null; codexHome: string; sourceCodexHome?: string | null; nativeMcp?: NativeMcpLaunchBinding | null; apiKey?: string | null }): Promise<void> {
+export async function prepareIsolatedCodexHome(input: { context: NativeRuntimeContextSnapshot | null; codexHome: string; sourceCodexHome?: string | null; nativeMcp?: NativeMcpLaunchBinding | null }): Promise<void> {
   await mkdir(input.codexHome, { recursive: true, mode: 0o700 });
   await chmod(input.codexHome, 0o700);
   await materializeNativeRuntimeSkills(input.context, join(input.codexHome, "skills"));
@@ -64,24 +64,13 @@ export async function prepareIsolatedCodexHome(input: { context: NativeRuntimeCo
       "",
     ].join("\n"), { mode: 0o600 });
   }
-  const apiKey = input.apiKey;
-  if (apiKey?.trim()) {
-    // Codex app-server intentionally receives a small allowlisted process
-    // environment and does not inherit OPENAI_API_KEY. Materialize an
-    // API-key-only credential in the per-session Codex home instead. That
-    // home is excluded from durable backup credentials and removed with the
-    // isolated runner state.
-    const target = join(input.codexHome, "auth.json");
-    await rm(target, { force: true });
-    await writeFile(target, JSON.stringify({ OPENAI_API_KEY: apiKey }), { mode: 0o600 });
-    await chmod(target, 0o600);
-    return;
-  }
+  const targetAuth = join(input.codexHome, "auth.json");
+  await rm(targetAuth, { force: true });
   const sourceHome = input.sourceCodexHome?.trim();
   if (!sourceHome) return;
   const sourceAuth = join(sourceHome, "auth.json");
   const stat = await lstat(sourceAuth).catch(() => null);
   if (!stat?.isFile() || stat.isSymbolicLink()) return;
-  await copyFile(sourceAuth, join(input.codexHome, "auth.json"));
-  await chmod(join(input.codexHome, "auth.json"), 0o600);
+  await copyFile(sourceAuth, targetAuth);
+  await chmod(targetAuth, 0o600);
 }
diff --git a/packages/paperclip-runner/src/live/runnerd-codex-transport.test.ts b/packages/paperclip-runner/src/live/runnerd-codex-transport.test.ts
index 70d6a728ebb..f7ac3bace5d 100644
--- a/packages/paperclip-runner/src/live/runnerd-codex-transport.test.ts
+++ b/packages/paperclip-runner/src/live/runnerd-codex-transport.test.ts
@@ -88,6 +88,38 @@ it("preserves OpenCode runtime bindings when a durable runner is respawned", ()
   });
 });
 
+it("passes the configured Codex API key only through the provider process environment", () => {
+  const environment = createCapabilityRunnerdProviderEnvironment({
+    provider: "codex",
+    options: {
+      provider: "codex",
+      environment: {
+        PATH: "/bin",
+        OPENAI_API_KEY: "configured-provider-key",
+        PAPERCLIP_API_KEY: "must-not-reach-provider",
+      },
+    },
+    identity: {
+      runnerInstanceId: "runner-1",
+      environmentLeaseId: "lease-1",
+      runId: "run-1",
+      normalizedSessionId: "session-1",
+      turnId: "turn-1",
+      itemId: "item-1",
+    },
+    codexHome: "/isolated/codex-home",
+    runtimeContextPath: "/isolated/runtime-context.json",
+    hasRuntimeContext: false,
+  });
+  expect(environment).toMatchObject({
+    PATH: "/bin",
+    HOME: "/isolated/codex-home",
+    CODEX_HOME: "/isolated/codex-home",
+    OPENAI_API_KEY: "configured-provider-key",
+  });
+  expect(environment.PAPERCLIP_API_KEY).toBeUndefined();
+});
+
 it.each(["opencode", "acpx"] as const)(
   "advertises runner-managed planning through the %s provider boundary",
   async (provider) => {
diff --git a/packages/paperclip-runner/src/live/runnerd-codex-transport.ts b/packages/paperclip-runner/src/live/runnerd-codex-transport.ts
index faf1d70ffec..c423871a9ba 100644
--- a/packages/paperclip-runner/src/live/runnerd-codex-transport.ts
+++ b/packages/paperclip-runner/src/live/runnerd-codex-transport.ts
@@ -846,11 +846,14 @@ export function createCapabilityRunnerdProviderEnvironment(input: {
   if (input.provider === "aws_agentcore") {
     return createSanitizedAwsAgentCoreEnvironment(input.options.environment);
   }
-  return createSanitizedCodexEnvironment({
+  const environment = createSanitizedCodexEnvironment({
     ...input.options.environment,
     HOME: input.codexHome,
     CODEX_HOME: input.codexHome,
   });
+  const apiKey = input.options.environment?.OPENAI_API_KEY;
+  if (apiKey?.trim()) environment.OPENAI_API_KEY = apiKey;
+  return environment;
 }
 
 export function resolveSourceCodexHome(
@@ -1376,7 +1379,6 @@ class DurablePrpCodexTransport implements CodexAppServerTransport {
         sourceCodexHome:
           this.options.sourceCodexHome ??
           resolveSourceCodexHome(this.options.environment),
-        apiKey: this.options.environment?.OPENAI_API_KEY,
         nativeMcp: nativeMcpLaunchBinding(this.options.environment),
       });
     }
@@ -1699,7 +1701,6 @@ class DurablePrpCodexTransport implements CodexAppServerTransport {
         sourceCodexHome:
           this.options.sourceCodexHome ??
           resolveSourceCodexHome(this.options.environment),
-        apiKey: this.options.environment?.OPENAI_API_KEY,
         nativeMcp: nativeMcpLaunchBinding(this.options.environment),
       });
     }