diff --git a/packages/paperclip-runner/src/backends/codex-native-backend.ts b/packages/paperclip-runner/src/backends/codex-native-backend.ts
new file mode 100644
index 0000000000..ee137a7c85
--- /dev/null
+++ b/packages/paperclip-runner/src/backends/codex-native-backend.ts
@@ -0,0 +1,84 @@
+import { createCodexTaskEnvelope } from "../contracts/codex.js";
+import type { NativeExecutionInput } from "../contracts/native-execution.js";
+import type {
+  NativeSessionBackend,
+  PersistedNativeSession,
+} from "../contracts/native-session-backend.js";
+import type { CodexAppServerTransport } from "../drivers/codex/app-server-transport.js";
+import { CodexAppServerDriver } from "../drivers/codex/codex-app-server-driver.js";
+import { HarnessDriverBackend } from "./harness-driver-backend.js";
+import { nativeSystemInstructions, nativeTaskConstraints } from "./runtime-context.js";
+
+export interface CodexNativeSessionBackendOptions {
+  runnerInstanceId?: string;
+  onSpawn?: (meta: {
+    pid: number;
+    processGroupId: number | null;
+    startedAt: string;
+  }) => Promise<void>;
+  transportFactory?: (context?: {
+    providerRecoveryPolicy?: PersistedNativeSession["providerRecoveryPolicy"];
+  }) => CodexAppServerTransport;
+  dynamicTools?: readonly Readonly<Record<string, unknown>>[];
+  dynamicToolHandler?: (call: {
+    tool: string;
+    callId: string;
+    threadId: string;
+    turnId: string;
+    arguments: unknown;
+  }) => Promise<unknown>;
+}
+
+/**
+ * Constructs the first production-native provider boundary. Other provider
+ * contracts may already be persisted, but their runtime implementations are
+ * deliberately shipped in separate provider slices.
+ */
+export function createCodexNativeSessionBackend(
+  input: NativeExecutionInput,
+  options: CodexNativeSessionBackendOptions = {},
+): NativeSessionBackend {
+  if (input.provider.kind !== "codex") {
+    throw new Error("Codex native backend requires provider kind codex");
+  }
+
+  return new HarnessDriverBackend(new CodexAppServerDriver({
+    ...(input.provider.model ? { model: input.provider.model } : {}),
+    approvalPolicy: input.provider.approvalPolicy ?? "never",
+    baseInstructions: nativeSystemInstructions(input),
+    includeSkillInstructions: "runtimeContext" in input,
+    requestedCollaborationMode:
+      "executionMode" in input ? input.executionMode : "default",
+    taskEnvelope: createCodexTaskEnvelope({
+      objective: input.completionContract.contract.objective,
+      contractRevision: input.completionContract.contract.revision,
+      criteria: input.completionContract.contract.criteria,
+      constraints: [
+        "Work only inside the supplied working directory.",
+        ...("executionMode" in input && input.executionMode === "plan"
+          ? [
+              "Use native plan collaboration mode and do not modify workspace files.",
+              "Treat the supplied Paperclip planning context as the canonical pinned base revision.",
+              "Complete one structured provider plan item; Paperclip will synchronize it after completion.",
+              "Keep the final response to a short synchronization summary instead of repeating the full plan.",
+            ]
+          : []),
+        ...nativeTaskConstraints(input),
+        "Return one semantic completion result.",
+      ],
+    }),
+    runnerInstanceId:
+      options.runnerInstanceId ?? `paperclip-native-${input.binding.runId}`,
+    onSpawn: options.onSpawn,
+    transportFactory: options.transportFactory,
+    dynamicTools: options.dynamicTools,
+    dynamicToolHandler: options.dynamicToolHandler,
+    driverIdentity: {
+      kind: "codex_app_server",
+      displayName: "Codex app-server",
+      version: "codex-v2",
+    },
+    collaborationModes: ["default", "plan"],
+    requireProviderSessionIdentity: options.transportFactory !== undefined,
+  }));
+}
diff --git a/packages/paperclip-runner/src/backends/native-backend-factory.test.ts b/packages/paperclip-runner/src/backends/native-backend-factory.test.ts
new file mode 100644
index 0000000000..57a644b341
--- /dev/null
+++ b/packages/paperclip-runner/src/backends/native-backend-factory.test.ts
@@ -0,0 +1,95 @@
+import { describe, expect, it } from "vitest";
+
+import type { NativeExecutionInput } from "../contracts/native-execution.js";
+import { createNativeSessionBackend } from "../index.js";
+import { createCodexNativeSessionBackend } from "./codex-native-backend.js";
+
+function execution(
+  provider: NativeExecutionInput["provider"] = {
+    kind: "codex",
+    model: null,
+    approvalPolicy: "never",
+  },
+): NativeExecutionInput {
+  return {
+    schema: "paperclip.native-execution-input.v1",
+    binding: {
+      companyId: "company",
+      runId: "run",
+      issueId: "issue",
+      agentId: "agent",
+      executionWorkspaceId: "workspace",
+    },
+    task: {
+      identifier: "PAP-1",
+      title: "Exercise Codex native routing",
+      description: null,
+      prompt: "Complete the task.",
+      workMode: "standard",
+    },
+    workspace: {
+      cwd: "/workspace",
+      repoUrl: null,
+      repoRef: null,
+      branchName: null,
+    },
+    session: {
+      normalizedSessionId: "session",
+      driverKind: "codex_app_server",
+      protocolVersion: 1,
+      lifecyclePolicy: { mode: "per_turn", idleTimeoutMs: null },
+    },
+    provider,
+    completionContract: {
+      id: "contract",
+      sha256: "sha256",
+      schemaVersion: "1",
+      contract: {
+        revision: "revision",
+        objective: "Complete the task.",
+        criteria: [],
+      },
+    },
+    interactionResponses: [],
+    credentialBindings: [],
+  };
+}
+
+describe("native backend factory", () => {
+  it("constructs the Codex backend without starting its transport", async () => {
+    const backend = createNativeSessionBackend(execution(), {
+      codexTransportFactory: () => {
+        throw new Error("descriptor must not launch the transport");
+      },
+    });
+
+    await expect(backend.descriptor()).resolves.toMatchObject({
+      kind: "runner",
+      name: "codex_app_server",
+      version: "codex-v2",
+      capabilities: {
+        collaborationModes: ["default", "plan"],
+      },
+    });
+  });
+
+  it("fails closed when a deferred provider reaches the factory", () => {
+    expect(() =>
+      createNativeSessionBackend(execution({
+        kind: "opencode",
+        model: "openrouter/model",
+      })),
+    ).toThrow(
+      "Native backend for opencode is not included in the Codex-first runner",
+    );
+  });
+
+  it("guards the provider-specific constructor as a second boundary", () => {
+    expect(() =>
+      createCodexNativeSessionBackend(execution({
+        kind: "opencode",
+        model: "openrouter/model",
+      })),
+    ).toThrow("Codex native backend requires provider kind codex");
+  });
+});
diff --git a/packages/paperclip-runner/src/backends/native-backend-factory.ts b/packages/paperclip-runner/src/backends/native-backend-factory.ts
new file mode 100644
index 0000000000..0ce8ebe458
--- /dev/null
+++ b/packages/paperclip-runner/src/backends/native-backend-factory.ts
@@ -0,0 +1,41 @@
+import type { NativeExecutionInput } from "../contracts/native-execution.js";
+import type {
+  NativeSessionBackend,
+  PersistedNativeSession,
+} from "../contracts/native-session-backend.js";
+import type { CodexAppServerTransport } from "../drivers/codex/app-server-transport.js";
+import {
+  createCodexNativeSessionBackend,
+  type CodexNativeSessionBackendOptions,
+} from "./codex-native-backend.js";
+
+export interface NativeBackendFactoryOptions
+  extends Omit<CodexNativeSessionBackendOptions, "transportFactory"> {
+  codexTransportFactory?: (context?: {
+    providerRecoveryPolicy?: PersistedNativeSession["providerRecoveryPolicy"];
+  }) => CodexAppServerTransport;
+}
+
+/**
+ * Selects only provider implementations included in this release slice.
+ * Persisted contracts for future providers do not make those providers
+ * executable before their independently reviewed runtime ships.
+ */
+export function createNativeSessionBackend(
+  input: NativeExecutionInput,
+  options: NativeBackendFactoryOptions = {},
+): NativeSessionBackend {
+  if (input.provider.kind !== "codex") {
+    throw new Error(
+      `Native backend for ${input.provider.kind} is not included in the Codex-first runner`,
+    );
+  }
+
+  return createCodexNativeSessionBackend(input, {
+    runnerInstanceId: options.runnerInstanceId,
+    onSpawn: options.onSpawn,
+    dynamicTools: options.dynamicTools,
+    dynamicToolHandler: options.dynamicToolHandler,
+    transportFactory: options.codexTransportFactory,
+  });
+}
diff --git a/packages/paperclip-runner/src/index.ts b/packages/paperclip-runner/src/index.ts
index a25d3f32ac..c7c9d706e3 100644
--- a/packages/paperclip-runner/src/index.ts
+++ b/packages/paperclip-runner/src/index.ts
@@ -11,6 +11,10 @@ export * from "./contracts/question-set.js";
 export * from "./contracts/runtime-context.js";
 export * from "./contracts/types.js";
 export * from "./backends/harness-driver-backend.js";
+export {
+  createNativeSessionBackend,
+  type NativeBackendFactoryOptions,
+} from "./backends/native-backend-factory.js";
 export * from "./native-session-runtime.js";
 export {
   DurablePrpControlPlane,