diff --git a/packages/paperclip-runner/src/backends/codex-native-backend.ts b/packages/paperclip-runner/src/backends/codex-native-backend.ts
index 1653c75a6f..47a83bb5fe 100644
--- a/packages/paperclip-runner/src/backends/codex-native-backend.ts
+++ b/packages/paperclip-runner/src/backends/codex-native-backend.ts
@@ -92,6 +92,10 @@ function createTransportBackedNativeSessionBackend(
 ): NativeSessionBackend {
   const driverIdentity = transportDriverIdentity(input);
   const isCodex = input.provider.kind === "codex";
+  const supportsCollaborativePlanning =
+    isCodex ||
+    input.provider.kind === "opencode" ||
+    input.provider.kind === "acpx";
   if (
     input.provider.kind === "codex"
     && input.provider.approvalPolicy !== undefined
@@ -113,14 +117,18 @@ function createTransportBackedNativeSessionBackend(
     baseInstructions: nativeSystemInstructions(input),
     includeSkillInstructions: isCodex && "runtimeContext" in input,
     requestedCollaborationMode:
-      isCodex && "executionMode" in input ? input.executionMode : "default",
+      supportsCollaborativePlanning && "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.",
-        ...(isCodex && "executionMode" in input && input.executionMode === "plan"
+        ...(supportsCollaborativePlanning &&
+          "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.",
@@ -143,7 +151,9 @@ function createTransportBackedNativeSessionBackend(
     capabilities: isCodex
       ? {}
       : { steering: false, goals: false, threadLineage: false },
-    collaborationModes: isCodex ? ["default", "plan"] : ["default"],
+    collaborationModes: supportsCollaborativePlanning
+      ? ["default", "plan"]
+      : ["default"],
     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
index f31d0c3b4c..260751e5c0 100644
--- a/packages/paperclip-runner/src/backends/native-backend-factory.test.ts
+++ b/packages/paperclip-runner/src/backends/native-backend-factory.test.ts
@@ -1,6 +1,7 @@
 import { describe, expect, it } from "vitest";
 
 import type { NativeExecutionInput } from "../contracts/native-execution.js";
+import { FakeCodexTransport } from "../drivers/codex/codex-app-server-driver.test-support.js";
 import { createNativeSessionBackend } from "../index.js";
 import { createCodexNativeSessionBackend } from "./codex-native-backend.js";
 
@@ -126,6 +127,23 @@ function opencodeExecution(): NativeExecutionInput {
   };
 }
 
+function planningExecution(input: NativeExecutionInput): NativeExecutionInput {
+  return {
+    ...input,
+    schema: "paperclip.native-execution-input.v2",
+    task: { ...input.task, workMode: "planning" },
+    executionMode: "plan",
+    planningContext: {
+      documentId: null,
+      baseRevisionId: null,
+      baseRevisionNumber: 0,
+      markdown: "",
+      sha256: "empty-plan",
+      reviewContext: {},
+    },
+  };
+}
+
 function managedExecution(
   kind: "claude_managed" | "aws_agentcore",
 ): NativeExecutionInput {
@@ -251,10 +269,53 @@ describe("native backend factory", () => {
         resume: true,
         interruption: true,
         dynamicTools: true,
+        collaborationModes: ["default", "plan"],
       },
     });
   });
 
+  it.each([
+    ["OpenCode", opencodeExecution()],
+    ["ACPX Codex", acpxExecution("codex")],
+    ["ACPX Claude", acpxExecution("claude")],
+  ])(
+    "opens %s planning runs through the runner-managed plan contract",
+    async (_label, input) => {
+      const transport = new FakeCodexTransport();
+      const backend = createNativeSessionBackend(planningExecution(input), {
+        codexTransportFactory: () => transport,
+      });
+
+      await expect(backend.descriptor()).resolves.toMatchObject({
+        capabilities: { collaborationModes: ["default", "plan"] },
+      });
+      const session = await backend.openSession({
+        identity: {
+          runId: "run",
+          sessionId: "session",
+          companyId: "company",
+          issueId: "issue",
+          agentId: "agent",
+        },
+        workingDirectory: process.cwd(),
+      });
+
+      await expect(
+        session.startTurn({
+          message: { role: "user", text: "Author a plan." },
+          requestedCollaborationMode: "plan",
+        }),
+      ).resolves.toMatchObject({ effectiveCollaborationMode: "plan" });
+      expect(
+        transport.calls.find((call) => call.method === "thread/start")?.params,
+      ).toMatchObject({ permissions: "paperclip-runner-workspace-read-only" });
+      expect(
+        transport.calls.find((call) => call.method === "turn/start")?.params,
+      ).toMatchObject({ collaborationMode: { mode: "plan" } });
+      await session.close({ reason: "test complete" });
+    },
+  );
+
   it.each([
     [
       "claude_managed" as const,
@@ -337,6 +398,7 @@ describe("native backend factory", () => {
           resume: true,
           interruption: true,
           dynamicTools: true,
+          collaborationModes: ["default", "plan"],
         },
       });
     },