diff --git a/packages/paperclip-runner/src/backends/codex-acpx-native-backend.ts b/packages/paperclip-runner/src/backends/codex-acpx-native-backend.ts
new file mode 100644
index 0000000000..caedc8996e
--- /dev/null
+++ b/packages/paperclip-runner/src/backends/codex-acpx-native-backend.ts
@@ -0,0 +1,71 @@
+import type { NativeExecutionInput } from "../contracts/native-execution.js";
+import type { NativeSessionBackend } from "../contracts/native-session-backend.js";
+import {
+  CodexAcpxDriver,
+  type CodexAcpxDriverOptions,
+} from "../drivers/acpx/codex-acpx-driver.js";
+import { resolveQualifiedAcpxProfile } from "../drivers/acpx/qualified-profiles.js";
+import { HarnessDriverBackend } from "./harness-driver-backend.js";
+import {
+  nativeSystemInstructions,
+  nativeTaskConstraints,
+} from "./runtime-context.js";
+
+export interface CodexAcpxNativeSessionBackendOptions extends Omit<
+  CodexAcpxDriverOptions,
+  "model" | "permissionMode" | "systemInstructions"
+> {}
+
+/**
+ * Constructs the qualified Codex ACPX backend. Other ACPX agents remain
+ * unavailable until their runtime, policy, and conformance slices ship.
+ */
+export function createCodexAcpxNativeSessionBackend(
+  input: NativeExecutionInput,
+  options: CodexAcpxNativeSessionBackendOptions,
+): NativeSessionBackend {
+  if (input.provider.kind !== "acpx" || input.provider.agent !== "codex") {
+    throw new Error(
+      "Codex ACPX backend requires provider kind acpx with agent codex",
+    );
+  }
+  const qualifiedProfile = resolveQualifiedAcpxProfile(
+    "codex",
+    input.provider.model,
+  );
+  for (const field of [
+    "driverKind",
+    "protocolVersion",
+    "acpxVersion",
+    "agent",
+    "agentProfileVersion",
+    "agentServerPackage",
+    "agentServerVersion",
+    "agentRuntimePackage",
+    "agentRuntimeVersion",
+    "commandDigest",
+  ] as const) {
+    if (input.provider.profile[field] !== qualifiedProfile[field]) {
+      throw new Error(
+        `Persisted Codex ACPX profile does not match the qualified ${field}`,
+      );
+    }
+  }
+
+  const constraints = nativeTaskConstraints(input);
+  const systemInstructions = [
+    nativeSystemInstructions(input),
+    "",
+    "Paperclip Runner constraints:",
+    ...constraints.map((constraint) => `- ${constraint}`),
+  ].join("\n");
+
+  return new HarnessDriverBackend(
+    new CodexAcpxDriver({
+      ...options,
+      model: input.provider.model,
+      permissionMode: input.provider.permissionMode ?? "approve-reads",
+      systemInstructions,
+    }),
+  );
+}
diff --git a/packages/paperclip-runner/src/backends/native-backend-factory.test.ts b/packages/paperclip-runner/src/backends/native-backend-factory.test.ts
index 57a644b341..004193d6b4 100644
--- a/packages/paperclip-runner/src/backends/native-backend-factory.test.ts
+++ b/packages/paperclip-runner/src/backends/native-backend-factory.test.ts
@@ -55,6 +55,44 @@ function execution(
   };
 }
 
+function acpxExecution(agent: "codex" | "pi" = "codex"): NativeExecutionInput {
+  return {
+    ...execution(),
+    session: {
+      normalizedSessionId: "session",
+      driverKind: "acpx_runtime",
+      protocolVersion: 1,
+      lifecyclePolicy: { mode: "per_turn", idleTimeoutMs: null },
+    },
+    provider: {
+      kind: "acpx",
+      agent,
+      model:
+        agent === "codex"
+          ? "gpt-5.6-sol"
+          : "openrouter/deepseek/deepseek-v4-flash-0731",
+      permissionPolicy: "interactive",
+      profile: {
+        driverKind: "acpx_runtime",
+        protocolVersion: 1,
+        acpxVersion: "0.13.1",
+        agent,
+        agentProfileVersion: 1,
+        agentServerPackage:
+          agent === "codex" ? "@agentclientprotocol/codex-acp" : "pi-acp",
+        agentServerVersion: agent === "codex" ? "1.6.2" : "0.0.33",
+        agentRuntimePackage:
+          agent === "codex" ? null : "@earendil-works/pi-coding-agent",
+        agentRuntimeVersion: agent === "codex" ? null : "0.84.2",
+        commandDigest:
+          agent === "codex"
+            ? "sha256:94049b3e3c3aee87de62703786e4fa81d031d7bd979f99bdf516d84f28791a79"
+            : "sha256:8c696f38296d53d0061fa11534570c5ddd951b63532aed30e0f1fcc676dc169f",
+      },
+    },
+  };
+}
+
 describe("native backend factory", () => {
   it("constructs the Codex backend without starting its transport", async () => {
     const backend = createNativeSessionBackend(execution(), {
@@ -75,21 +113,65 @@ describe("native backend factory", () => {
 
   it("fails closed when a deferred provider reaches the factory", () => {
     expect(() =>
-      createNativeSessionBackend(execution({
-        kind: "opencode",
-        model: "openrouter/model",
-      })),
+      createNativeSessionBackend(
+        execution({
+          kind: "opencode",
+          model: "openrouter/model",
+        }),
+      ),
     ).toThrow(
       "Native backend for opencode is not included in the Codex-first runner",
     );
   });
 
+  it("constructs the qualified Codex ACPX backend without starting ACPX", async () => {
+    const backend = createNativeSessionBackend(acpxExecution(), {
+      acpxRuntimeDirectory: "/runtime",
+    });
+
+    await expect(backend.descriptor()).resolves.toMatchObject({
+      kind: "runner",
+      name: "acpx_runtime",
+      version: "0.13.1",
+      capabilities: {
+        resume: false,
+        interruption: true,
+        dynamicTools: true,
+      },
+    });
+  });
+
+  it("requires an explicit runtime root and keeps other ACPX agents disabled", () => {
+    expect(() => createNativeSessionBackend(acpxExecution())).toThrow(
+      "requires an instance runtime directory",
+    );
+    expect(() =>
+      createNativeSessionBackend(acpxExecution("pi"), {
+        acpxRuntimeDirectory: "/runtime",
+      }),
+    ).toThrow("ACPX backend for pi is not included");
+  });
+
+  it("rejects a Codex ACPX snapshot that drifts from its qualified profile", () => {
+    const input = acpxExecution();
+    if (input.provider.kind !== "acpx") throw new Error("invalid fixture");
+    input.provider.profile.commandDigest = `sha256:${"a".repeat(64)}`;
+
+    expect(() =>
+      createNativeSessionBackend(input, {
+        acpxRuntimeDirectory: "/runtime",
+      }),
+    ).toThrow("does not match the qualified commandDigest");
+  });
+
   it("guards the provider-specific constructor as a second boundary", () => {
     expect(() =>
-      createCodexNativeSessionBackend(execution({
-        kind: "opencode",
-        model: "openrouter/model",
-      })),
+      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
index 0ce8ebe458..8148034ade 100644
--- a/packages/paperclip-runner/src/backends/native-backend-factory.ts
+++ b/packages/paperclip-runner/src/backends/native-backend-factory.ts
@@ -8,12 +8,22 @@ import {
   createCodexNativeSessionBackend,
   type CodexNativeSessionBackendOptions,
 } from "./codex-native-backend.js";
+import {
+  createCodexAcpxNativeSessionBackend,
+  type CodexAcpxNativeSessionBackendOptions,
+} from "./codex-acpx-native-backend.js";
 
-export interface NativeBackendFactoryOptions
-  extends Omit<CodexNativeSessionBackendOptions, "transportFactory"> {
+export interface NativeBackendFactoryOptions extends Omit<
+  CodexNativeSessionBackendOptions,
+  "transportFactory"
+> {
   codexTransportFactory?: (context?: {
     providerRecoveryPolicy?: PersistedNativeSession["providerRecoveryPolicy"];
   }) => CodexAppServerTransport;
+  acpxRuntimeDirectory?: string;
+  acpxEnvironment?: NodeJS.ProcessEnv;
+  acpxManagedCodexCredentialSourcePath?: string;
+  acpxDynamicToolHandler?: CodexAcpxNativeSessionBackendOptions["dynamicToolHandler"];
 }
 
 /**
@@ -25,6 +35,26 @@ export function createNativeSessionBackend(
   input: NativeExecutionInput,
   options: NativeBackendFactoryOptions = {},
 ): NativeSessionBackend {
+  if (input.provider.kind === "acpx") {
+    if (input.provider.agent !== "codex") {
+      throw new Error(
+        `Native ACPX backend for ${input.provider.agent} is not included in the Codex-first runner`,
+      );
+    }
+    if (!options.acpxRuntimeDirectory?.trim()) {
+      throw new Error(
+        "Codex ACPX backend requires an instance runtime directory",
+      );
+    }
+    return createCodexAcpxNativeSessionBackend(input, {
+      runtimeDirectory: options.acpxRuntimeDirectory,
+      environment: options.acpxEnvironment,
+      managedCodexCredentialSourcePath:
+        options.acpxManagedCodexCredentialSourcePath,
+      dynamicTools: options.dynamicTools,
+      dynamicToolHandler: options.acpxDynamicToolHandler,
+    });
+  }
   if (input.provider.kind !== "codex") {
     throw new Error(
       `Native backend for ${input.provider.kind} is not included in the Codex-first runner`,