diff --git a/doc/sandbox-work-folders.md b/doc/sandbox-work-folders.md
index 16ace68e16..b3055a5de0 100644
--- a/doc/sandbox-work-folders.md
+++ b/doc/sandbox-work-folders.md
@@ -41,6 +41,9 @@ links before locating their runtime so task-local launch paths remain valid.
 Sandbox runs use the operating-system user's home directory. Both legacy
 adapters and the native runner enter the same host-owned lifecycle before
 dispatch. Local execution keeps its existing workspace and home behavior.
+Legacy ACP proxies use a private host staging directory while agent sessions start
+in the sandbox home. Native runner launches carry the validated scoped paths
+through runnerd to ACPX; CLI configuration remains in its private runtime directories.
 Warm sandbox task bindings persist independently of the experimental isolated
 workspace setting. Only the active host run can establish that binding; the
 setting still controls user-configurable worktree operations.
diff --git a/packages/adapter-utils/src/acpx-engine/execute.ts b/packages/adapter-utils/src/acpx-engine/execute.ts
index c1de4487a3..04ec8e5879 100644
--- a/packages/adapter-utils/src/acpx-engine/execute.ts
+++ b/packages/adapter-utils/src/acpx-engine/execute.ts
@@ -22,6 +22,7 @@ import {
   prepareAdapterExecutionTargetRuntime,
   readAdapterExecutionTarget,
   resolveAdapterExecutionTargetTimeout,
+  resolveAdapterExecutionTargetCwd,
   resolveReferencedSourceIgnore,
   runAdapterExecutionTargetShellCommand,
   startAdapterExecutionTargetPaperclipBridge,
@@ -1698,9 +1699,21 @@ async function buildRuntime(input: {
   const workspaceWorktreePath = asString(workspaceContext.worktreePath, "");
   const agentHome = asString(workspaceContext.agentHome, "");
   const configuredCwd = asString(config.cwd, "");
+  const executionTarget = readAdapterExecutionTarget({
+    executionTarget: input.ctx.executionTarget,
+    legacyRemoteExecution: input.ctx.executionTransport?.remoteExecution,
+  });
+  const stateDir = path.resolve(asString(config.stateDir, "") || defaultStateDir(agent.companyId, agent.id));
+  const workFolderHome = executionTarget?.kind === "remote" && executionTarget.transport === "sandbox"
+    ? executionTarget.workFolderHome
+    : undefined;
   const useConfiguredInsteadOfAgentHome = workspaceSource === "agent_home" && configuredCwd.length > 0;
   const effectiveWorkspaceCwd = useConfiguredInsteadOfAgentHome ? "" : workspaceCwd;
-  const cwd = effectiveWorkspaceCwd || configuredCwd || process.cwd();
+  // Scoped workspaces exist only in the sandbox. The ACP proxy and staging
+  // metadata need a host directory; never materialize the remote repo on it.
+  const cwd = workFolderHome
+    ? path.join(stateDir, "work-folder-proxy")
+    : effectiveWorkspaceCwd || configuredCwd || process.cwd();
   // Referenced (additional) projects to stage into the sandbox alongside the
   // anchor workspace, read from the workspace realization record. The list is
   // empty unless run prep resolved referenced projects — gated upstream by the
@@ -1771,10 +1784,7 @@ async function buildRuntime(input: {
         (value): value is Record<string, unknown> => typeof value === "object" && value !== null,
       )
     : [];
-  const executionTarget = readAdapterExecutionTarget({
-    executionTarget: input.ctx.executionTarget,
-    legacyRemoteExecution: input.ctx.executionTransport?.remoteExecution,
-  });
+
   const remoteExecutionIdentity = adapterExecutionTargetSessionIdentity(executionTarget);
   const effectiveExecutionCwd =
     remoteExecutionIdentity && typeof remoteExecutionIdentity.remoteCwd === "string"
@@ -1838,7 +1848,6 @@ async function buildRuntime(input: {
     asNumber(config.timeoutSec, DEFAULT_ACP_ENGINE_TIMEOUT_SEC),
   );
   const timeoutSec = timeoutResolution.timeoutSec;
-  const stateDir = path.resolve(asString(config.stateDir, "") || defaultStateDir(agent.companyId, agent.id));
   await fs.mkdir(stateDir, { recursive: true });
 
   const envConfig = parseObject(config.env);
@@ -2061,7 +2070,7 @@ async function buildRuntime(input: {
   // diverge from the cwd that fed the fingerprint.
   const sessionCwd =
     useRemoteProcessSession && executionTarget?.kind === "remote"
-      ? executionTarget.remoteCwd
+      ? resolveAdapterExecutionTargetCwd(executionTarget, undefined, cwd)
       : cwd;
   // The 17 fields the session fingerprint hashes. Company, agent, and task
   // identifiers are NOT here; they scope the outer session key only (see
diff --git a/packages/adapter-utils/src/acpx-engine/startup-characterization.test.ts b/packages/adapter-utils/src/acpx-engine/startup-characterization.test.ts
index 9367f933e8..8684bd71ef 100644
--- a/packages/adapter-utils/src/acpx-engine/startup-characterization.test.ts
+++ b/packages/adapter-utils/src/acpx-engine/startup-characterization.test.ts
@@ -487,6 +487,30 @@ describe("ACPX engine startup characterization", () => {
       expect(sessionInputs[0]?.cwd).toBe(remoteCwd);
     });
 
+    it("keeps sandbox work folders remote while spawning the ACP proxy on the host", async () => {
+      const { root, stateDir, executionTarget } = await setupRemoteSandbox();
+      const home = path.join(root, "sandbox-home");
+      const primary = path.join(home, "repos", "primary");
+      await fs.mkdir(primary, { recursive: true });
+      await fs.writeFile(path.join(primary, "keep.txt"), "sandbox work");
+      const mkdir = vi.spyOn(fs, "mkdir");
+      const { sessionInputs, runtimeOptions } = await runExecutor(
+        { agent: "custom", agentCommand: "node ./fake-acp.js", stateDir, cwd: primary },
+        {
+          authToken: "real-run-jwt",
+          context: { paperclipWorkspace: { cwd: primary, source: "project" } },
+          executionTarget: { ...executionTarget, remoteCwd: primary, workFolderHome: home },
+        },
+      );
+      expect(mkdir.mock.calls.some(([directory]) => directory === primary)).toBe(false);
+      expect(sessionInputs[0]?.cwd).toBe(home);
+      expect(runtimeOptions[0]?.spawnCwd).toBe(path.join(stateDir, "work-folder-proxy"));
+      await expect(fs.readFile(path.join(primary, "keep.txt"), "utf8")).resolves.toBe("sandbox work");
+      expect(vi.mocked(prepareAdapterExecutionTargetRuntime).mock.calls[0]![0].workspaceLocalDir)
+        .toBe(path.join(stateDir, "work-folder-proxy"));
+      mkdir.mockRestore();
+    });
+
     it("threads a managed-home asset through the same seam after the workspace", async () => {
       const { root, stateDir, localCwd, executionTarget } = await setupRemoteSandbox();
       const managedHomeDir = path.join(root, "managed-home");
diff --git a/packages/paperclip-runner/src/control-plane/durable-prp-control-plane.test.ts b/packages/paperclip-runner/src/control-plane/durable-prp-control-plane.test.ts
index d5a5fed36b..1b91749b3e 100644
--- a/packages/paperclip-runner/src/control-plane/durable-prp-control-plane.test.ts
+++ b/packages/paperclip-runner/src/control-plane/durable-prp-control-plane.test.ts
@@ -387,6 +387,46 @@ it("preserves only bounded GitHub credential projection at the runner spawn boun
   expect(launches[0]!.environment.DATABASE_URL).toBeUndefined();
 });
 
+it.each(["codex", "claude", "pi"] as const)("carries scoped HOME through the runner launch boundary to the %s ACPX environment", async (agent) => {
+  const root = mkdtempSync(resolve(tmpdir(), "runner-scoped-home-"));
+  const home = resolve(root, "sandbox-home");
+  const scoped = {
+    HOME: home,
+    PAPERCLIP_RUNNER_EXTERNAL_SANDBOX: "1",
+    PAPERCLIP_TASK_DIR: resolve(home, "task"),
+    PAPERCLIP_AGENT_DIR: resolve(home, "agent"),
+    PAPERCLIP_USER_DIR: resolve(home, "user"),
+    PAPERCLIP_PROJECT_DIR: resolve(home, "project"),
+    PAPERCLIP_REPOS_DIR: resolve(home, "repos"),
+    PAPERCLIP_PRIMARY_REPO: resolve(home, "repos", "primary"),
+    PAPERCLIP_WORKSPACE_CWD: resolve(home, "repos", "primary"),
+    AGENT_HOME: resolve(home, "agent"),
+  };
+  const launches: RunnerProcessLaunchSpec[] = [];
+  try {
+    spawnRunner({
+      connection: { mode: "connect", connectUrl: "ws://127.0.0.1:43127" },
+      stateDirectory: root, identity, ticket: "bootstrap-ticket",
+      maxOutboxBytes: 256 * 1024, p0ReserveBytes: 64 * 1024,
+      runnerVersion: expectedRunnerVersion, runnerDigest: expectedRunnerDigest,
+      environment: { ...scoped, DATABASE_URL: "must-not-cross" },
+      processLauncher: (spec) => {
+        launches.push(spec);
+        return {
+          child: { pid: 42, exitCode: null, signalCode: null, kill: () => true },
+          completion: Promise.resolve({ code: 0, signal: null, stdout: "", stderr: "" }),
+        };
+      },
+    });
+    expect(launches[0]!.environment).toMatchObject(scoped);
+    expect(launches[0]!.environment.DATABASE_URL).toBeUndefined();
+    const { createSanitizedAcpxSpawnInput } = await import("../drivers/acpx/environment.js");
+    expect(createSanitizedAcpxSpawnInput(launches[0]!.environment, agent).env).toMatchObject(scoped);
+  } finally {
+    rmSync(root, { recursive: true, force: true });
+  }
+});
+
 it("preserves the controller-selected ACPX provider package root", () => {
   const launches: RunnerProcessLaunchSpec[] = [];
   spawnRunner({
diff --git a/packages/paperclip-runner/src/control-plane/durable-prp-control-plane.ts b/packages/paperclip-runner/src/control-plane/durable-prp-control-plane.ts
index ffdefe9e0d..1277a09050 100644
--- a/packages/paperclip-runner/src/control-plane/durable-prp-control-plane.ts
+++ b/packages/paperclip-runner/src/control-plane/durable-prp-control-plane.ts
@@ -28,6 +28,7 @@ import { dirname, resolve } from "node:path";
 import type { Duplex } from "node:stream";
 import { fileURLToPath } from "node:url";
 
+import { externalWorkFolderEnvironment } from "../work-folder-environment.js";
 import { githubCredentialEnvironment } from "../github-credential-environment.js";
 import {
   validatePrpEvent,
@@ -2060,7 +2061,7 @@ function runnerEnvironment(
       const value = explicitSource[key];
       if (value !== undefined) environment[key] = value;
     }
-    Object.assign(environment, githubCredentialEnvironment(explicitSource));
+    Object.assign(environment, githubCredentialEnvironment(explicitSource), externalWorkFolderEnvironment(explicitSource));
   }
   return environment;
 }