diff --git a/packages/paperclip-runner/src/drivers/acpx/installation-integrity.ts b/packages/paperclip-runner/src/drivers/acpx/installation-integrity.ts
index e96722c9759..9017824a5a1 100644
--- a/packages/paperclip-runner/src/drivers/acpx/installation-integrity.ts
+++ b/packages/paperclip-runner/src/drivers/acpx/installation-integrity.ts
@@ -30,6 +30,7 @@ import {
 import type { Readable, Writable } from "node:stream";
 
 import { resolveQualifiedAcpxProfile, type QualifiedAcpxProfile } from "./qualified-profiles.js";
+import { resolveInstalledProviderAuthority } from "./installed-provider-authority.js";
 import {
   VERIFIED_RUNTIME_EXECUTABLE_ENV,
   verifiedRuntimeExecutableHandoff,
@@ -645,11 +646,13 @@ export async function verifyQualifiedAcpxInstallation(
 ): Promise<VerifiedAcpxInstallation> {
   // Keep the selected package authority available when its bundled provider
   // wrapper delegates platform installation to the published server manifest.
-  if ((profile.agent === "codex" || profile.agent === "claude") && resolvePackageJson === defaultPackageJsonResolver && process.env.PAPERCLIP_ACPX_PROVIDER_PACKAGE_ROOT !== undefined) {
-    resolvePackageJson = createAcpxPackageJsonResolver(
-      process.env.PAPERCLIP_ACPX_PROVIDER_PACKAGE_ROOT,
-      process.env.PAPERCLIP_ACPX_PROVIDER_PACKAGE_MANIFEST,
-    );
+  if ((profile.agent === "codex" || profile.agent === "claude") && resolvePackageJson === defaultPackageJsonResolver) {
+    const boundRoot = process.env.PAPERCLIP_ACPX_PROVIDER_PACKAGE_ROOT;
+    const authority = boundRoot === undefined ? resolveInstalledProviderAuthority(import.meta.url) : {
+      root: boundRoot,
+      manifest: process.env.PAPERCLIP_ACPX_PROVIDER_PACKAGE_MANIFEST,
+    };
+    if (authority) resolvePackageJson = createAcpxPackageJsonResolver(authority.root, authority.manifest);
   }
   const builtin = profile.agent === "grok";
   if (builtin && (profile.agentServerPackage !== "builtin:grok-acp" || profile.agentServerVersion !== "1" || profile.agentRuntimePackage !== "native:grok" || profile.agentRuntimeVersion !== "1.0.13")) {
diff --git a/packages/paperclip-runner/src/drivers/acpx/installed-provider-authority.test.ts b/packages/paperclip-runner/src/drivers/acpx/installed-provider-authority.test.ts
new file mode 100644
index 00000000000..c1274972577
--- /dev/null
+++ b/packages/paperclip-runner/src/drivers/acpx/installed-provider-authority.test.ts
@@ -0,0 +1,60 @@
+import { mkdtemp, mkdir, writeFile, symlink, rm, realpath } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { pathToFileURL } from "node:url";
+import { afterEach, describe, expect, it } from "vitest";
+import { resolveInstalledProviderAuthority } from "./installed-provider-authority.js";
+
+const roots: string[] = [];
+afterEach(async () => { await Promise.all(roots.splice(0).map(root => rm(root, { recursive: true, force: true }))); });
+async function fixture(name = "@paperclipai/server") {
+  const root = await realpath(await mkdtemp(join(tmpdir(), "installed-acpx-authority-")));
+  roots.push(root);
+  const directory = join(root, "dist/vendor/paperclip-runner/drivers/acpx");
+  await mkdir(directory, { recursive: true });
+  const module = join(directory, "installation-integrity.js");
+  await writeFile(module, "export {};\n");
+  const manifest = join(root, "package.json");
+  await writeFile(manifest, JSON.stringify({ name }));
+  return { root, module, manifest };
+}
+
+describe("installed provider authority", () => {
+  it("derives the owning server only from the normal installed verifier layout", async () => {
+    const f = await fixture();
+    expect(resolveInstalledProviderAuthority(pathToFileURL(f.module).href)).toEqual({ root: f.root, manifest: f.manifest });
+    expect(resolveInstalledProviderAuthority(pathToFileURL(join(f.root, "src/drivers/acpx/installation-integrity.ts")).href)).toBeUndefined();
+    expect(resolveInstalledProviderAuthority(pathToFileURL(join(f.root, "dist/drivers/acpx/installation-integrity.js")).href)).toBeUndefined();
+  });
+
+  it("rejects a substituted package owner", async () => {
+    const f = await fixture("unrelated-package");
+    expect(() => resolveInstalledProviderAuthority(pathToFileURL(f.module).href)).toThrow("owning server package");
+  });
+
+  it("rejects a symlinked manifest before adopting its declarations", async () => {
+    const f = await fixture();
+    const other = join(f.root, "other.json");
+    await writeFile(other, JSON.stringify({ name: "@paperclipai/server" }));
+    await rm(f.manifest);
+    await symlink(other, f.manifest);
+    expect(() => resolveInstalledProviderAuthority(pathToFileURL(f.module).href)).toThrow();
+  });
+
+  it("rejects a redirected verifier directory", async () => {
+    const f = await fixture();
+    const old = join(f.root, "dist/vendor/paperclip-runner/drivers/acpx");
+    const other = join(f.root, "other");
+    await mkdir(other);
+    await writeFile(join(other, "installation-integrity.js"), "export {};\n");
+    await rm(old, { recursive: true });
+    await symlink(other, old);
+    expect(() => resolveInstalledProviderAuthority(pathToFileURL(f.module).href)).toThrow("package layout");
+  });
+
+  it.each(["", " ".repeat(256 * 1024 + 1)])("rejects unbounded or empty owner metadata", async contents => {
+    const f = await fixture();
+    await writeFile(f.manifest, contents);
+    expect(() => resolveInstalledProviderAuthority(pathToFileURL(f.module).href)).toThrow("bounded regular file");
+  });
+});
diff --git a/packages/paperclip-runner/src/drivers/acpx/installed-provider-authority.ts b/packages/paperclip-runner/src/drivers/acpx/installed-provider-authority.ts
new file mode 100644
index 00000000000..fd0979295c4
--- /dev/null
+++ b/packages/paperclip-runner/src/drivers/acpx/installed-provider-authority.ts
@@ -0,0 +1,51 @@
+import { closeSync, constants, fstatSync, lstatSync, openSync, readFileSync, realpathSync } from "node:fs";
+import { isAbsolute, join, resolve } from "node:path";
+import { fileURLToPath } from "node:url";
+
+export function resolveInstalledProviderAuthority(moduleUrl: string): { root: string; manifest: string } | undefined {
+  const url = new URL(moduleUrl);
+  if (url.protocol !== "file:") return undefined;
+  const modulePath = fileURLToPath(url);
+  const suffix = "/dist/vendor/paperclip-runner/drivers/acpx/installation-integrity.js";
+  if (!modulePath.endsWith(suffix)) return undefined;
+  const root = modulePath.slice(0, -suffix.length);
+  if (!isAbsolute(root) || resolve(root) !== root || realpathSync(root) !== root) {
+    throw new Error("Installed ACPX server authority must be a canonical package directory");
+  }
+  for (const relative of ["", "dist", "dist/vendor", "dist/vendor/paperclip-runner", "dist/vendor/paperclip-runner/drivers", "dist/vendor/paperclip-runner/drivers/acpx"]) {
+    const path = join(root, relative);
+    const metadata = lstatSync(path);
+    if (!metadata.isDirectory() || metadata.isSymbolicLink() || realpathSync(path) !== path) {
+      throw new Error("Installed ACPX server authority escapes its package layout");
+    }
+  }
+  const moduleMetadata = lstatSync(modulePath);
+  if (!moduleMetadata.isFile() || moduleMetadata.isSymbolicLink() || realpathSync(modulePath) !== modulePath) {
+    throw new Error("Installed ACPX verifier must remain in its package layout");
+  }
+  const manifest = join(root, "package.json");
+  const fd = openSync(manifest, constants.O_RDONLY | constants.O_NOFOLLOW);
+  try {
+    const before = fstatSync(fd, { bigint: true });
+    if (!before.isFile() || before.size < 1n || before.size > 256n * 1024n) {
+      throw new Error("Installed ACPX server manifest must be a bounded regular file");
+    }
+    const bytes = readFileSync(fd);
+    const after = fstatSync(fd, { bigint: true });
+    const named = lstatSync(manifest, { bigint: true });
+    if (before.dev !== after.dev || before.ino !== after.ino || before.size !== after.size
+      || before.mtimeNs !== after.mtimeNs || before.ctimeNs !== after.ctimeNs
+      || named.dev !== before.dev || named.ino !== before.ino || named.isSymbolicLink()
+      || bytes.length !== Number(before.size) || realpathSync(manifest) !== manifest) {
+      throw new Error("Installed ACPX server manifest changed during admission");
+    }
+    const value = JSON.parse(bytes.toString("utf8"));
+    if (!value || typeof value !== "object" || Array.isArray(value)
+      || !Object.hasOwn(value, "name") || value.name !== "@paperclipai/server") {
+      throw new Error("Installed ACPX verifier requires the owning server package");
+    }
+  } finally {
+    closeSync(fd);
+  }
+  return { root, manifest };
+}