diff --git a/doc/skill-package-storage.md b/doc/skill-package-storage.md
index c5057926cac..dd2565425e1 100644
--- a/doc/skill-package-storage.md
+++ b/doc/skill-package-storage.md
@@ -131,6 +131,9 @@ pending delete/existence requests; incomplete cleanup retains the receipt for re
   verification budget per fill. This is a soft limit during a storage outage: cleanup preserves
   the last recoverable copy. Version projections retain the existing pin-aware cleanup.
   Abandoned package staging directories receive a one-hour crash grace.
+- Internal package caches, their files, and containing directories cannot be
+  imported as local skill sources. Fork the installed skill to retain its original
+  access restrictions.
 
 Each entrypoint still has a self-contained runtime tree, and remote staging can
 duplicate those trees. This change does not introduce a new runner transport format
diff --git a/server/src/__tests__/project-skill-sources.test.ts b/server/src/__tests__/project-skill-sources.test.ts
index 20838033e00..ed8e6c4f4d9 100644
--- a/server/src/__tests__/project-skill-sources.test.ts
+++ b/server/src/__tests__/project-skill-sources.test.ts
@@ -8,7 +8,7 @@ import os from 'node:os';
 import path from 'node:path';
 import { afterAll, beforeAll, describe, expect, it, vi } from 'vitest';
 import { and, eq, sql } from 'drizzle-orm';
-import { activityLog, agents, authUsers, companies, companyMemberships, companySkillSources, companySkillImportBudgets, companySkills, createDb, projects,
+import { activityLog, agents, authUsers, companies, companyMemberships, companySkillSources, companySkillImportBudgets, companySkills, companySkillVersions, createDb, projects,
   projectWorkspaces, projectSkillSources, projectAccessMembers } from '@paperclipai/db';
 import { startEmbeddedPostgresTestDatabase, getEmbeddedPostgresTestSupport } from './helpers/embedded-postgres.js';
 import { githubFixture } from './helpers/github-skills.js';
@@ -16,6 +16,7 @@ import { enqueueProjectSkillSource, detachProjectSkillSource, projectSkillSetupI
 import { adoptProjectSkillRepository, projectSkillRepositories, skillSourceSyncService } from '../services/skill-source-sync.js';
 import { skillSourceService, type SkillSourceContext } from '../services/skill-sources.js';
 import { companySkillService } from '../services/company-skills.js';
+import { skillPackagePaths } from '../services/skill-package-store.js';
 import { projectService } from '../services/projects.js';
 import { skillAccessService, withSkillActor } from '../services/skill-access.js';
 import type { AuthorizationActor } from '../services/authorization.js';
@@ -446,6 +447,7 @@ describe.skipIf(!support.supported)('automatic project skill sources', () => {
     const source = await skillSourceService(db).detail(companyId, binding!.sourceId!);
     const skillId = source.entries[0]!.skillId!;
     let privateSnapshotPath = '';
+    let privatePackagePath = '';
     const privateDerivatives: string[] = [];
     for (const user of ['alice', 'bob']) {
       await db.insert(authUsers).values({ id: user, name: user, email: `${user}@example.test`, createdAt: new Date(), updatedAt: new Date() });
@@ -459,6 +461,16 @@ describe.skipIf(!support.supported)('automatic project skill sources', () => {
       const [runtime] = await companySkillService(db).listRuntimeSkillEntries(companyId, { onlyKeys: new Set([skill.key]) });
       privateSnapshotPath = runtime!.source;
       await expect(companySkillService(db).importFromSource(companyId, runtime!.source)).rejects.toThrow(/Project-derived skill/);
+      const [version] = await db.select({ packageId: companySkillVersions.packageSnapshotId })
+        .from(companySkillVersions).where(eq(companySkillVersions.id, skill.currentVersionId!));
+      expect(version?.packageId).toBeTruthy();
+      privatePackagePath = skillPackagePaths(companyId, version!.packageId!).directory;
+      expect((await fs.stat(privatePackagePath)).isDirectory()).toBe(true);
+      for (const candidate of [privatePackagePath, path.join(privatePackagePath, 'private'), path.dirname(privatePackagePath)]) {
+        await expect(companySkillService(db).importFromSource(companyId, candidate)).rejects.toMatchObject({
+          status: 422, details: { code: 'skill_package_cache_import_denied' },
+        });
+      }
       const fork = await companySkillService(db).forkSkill(companyId, skillId, { slug: 'private-copy' });
       expect(fork.skill.accessSourceId).not.toBe(source.id);
       expect(fork.skill.accessSourceId).toBeTruthy();
@@ -475,6 +487,9 @@ describe.skipIf(!support.supported)('automatic project skill sources', () => {
       await expect(skillSourceService(db).branches(companyId, source.id, {}, { ...context, read: () => branchRead })).rejects.toThrow(/not found/);
       expect(branchRead).not.toHaveBeenCalled();
       await expect(companySkillService(db).importFromSource(companyId, privateSnapshotPath)).rejects.toThrow(/not found/);
+      await expect(companySkillService(db).importFromSource(companyId, privatePackagePath)).rejects.toMatchObject({
+        status: 422, details: { code: 'skill_package_cache_import_denied' },
+      });
       expect(await companySkillService(db).getById(companyId, skillId)).toBeNull();
       expect(await companySkillService(db).readFile(companyId, skillId, 'SKILL.md')).toBeNull();
       expect((await skillSourceService(db).list(companyId)).some(item => item.id === source.id)).toBe(false);
diff --git a/server/src/services/company-skills.ts b/server/src/services/company-skills.ts
index ad3820d3627..9ec8933b5ef 100644
--- a/server/src/services/company-skills.ts
+++ b/server/src/services/company-skills.ts
@@ -7,6 +7,7 @@ import { ensureSkillCacheDirectory, touchSkillVersionCache, withSkillVersionCach
 import { measureRunPhase } from "./execution-preparation-timing.js";
 import { verifyExistingBundledSkillRelease } from "./bundled-skill-release-validation.js";
 import { retainProjectSkillAccess, skillAccessService } from "./skill-access.js";
+import { assertLocalImportOutsideSkillPackageCache } from "./skill-local-import-boundary.js";
 import type { AuthorizationActor } from "./authorization.js";
 import { updateAgentConfigurationInTransaction } from "./agent-configuration-transaction.js";
 import { logger } from "../middleware/logger.js";
@@ -2992,6 +2993,7 @@ export function companySkillService(db: Db, options: { actor?: AuthorizationActo
         code: "skill_source_validation_failed",
       });
     }
+    await assertLocalImportOutsideSkillPackageCache(sourceRealPath, resolveManagedSkillsRoot(companyId));
     const projectRows = await projects.list(companyId);
     const configuredRoots = [
       resolveManagedSkillsRoot(companyId),
diff --git a/server/src/services/skill-local-import-boundary.test.ts b/server/src/services/skill-local-import-boundary.test.ts
new file mode 100644
index 00000000000..e049452fc07
--- /dev/null
+++ b/server/src/services/skill-local-import-boundary.test.ts
@@ -0,0 +1,42 @@
+import { promises as fs } from "node:fs";
+import os from "node:os";
+import path from "node:path";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { assertLocalImportOutsideSkillPackageCache } from "./skill-local-import-boundary.js";
+
+describe("local import package-cache boundary", () => {
+  let root: string;
+  let managed: string;
+  let cache: string;
+  beforeEach(async () => {
+    root = await fs.realpath(await fs.mkdtemp(path.join(os.tmpdir(), "skill-import-boundary-")));
+    managed = path.join(root, "skills", "company");
+    cache = path.join(managed, "__packages__");
+    await fs.mkdir(path.join(cache, "snapshot", "private"), { recursive: true });
+    await fs.writeFile(path.join(cache, "snapshot", "private", "SKILL.md"), "Private instructions");
+  });
+  afterEach(() => fs.rm(root, { recursive: true, force: true }));
+
+  it.each(["__packages__", "__packages__/snapshot", "__packages__/snapshot/private",
+    "__packages__/snapshot/private/SKILL.md", ".", ".."])('rejects cache or ancestor source "%s"', async source => {
+    await expect(assertLocalImportOutsideSkillPackageCache(await fs.realpath(path.join(managed, source)), managed))
+      .rejects.toMatchObject({ status: 422, details: { code: "skill_package_cache_import_denied" } });
+  });
+
+  it("rejects a symlink alias of the cache", async () => {
+    const alias = path.join(managed, "alias");
+    await fs.symlink(path.join(cache, "snapshot"), alias, "dir");
+    await expect(assertLocalImportOutsideSkillPackageCache(await fs.realpath(alias), managed)).rejects.toThrow("package caches");
+  });
+
+  it("rejects recursive ancestors before a concurrent fill can create the cache", async () => {
+    await fs.rm(cache, { recursive: true });
+    await expect(assertLocalImportOutsideSkillPackageCache(managed, managed)).rejects.toThrow("package caches");
+  });
+
+  it.each(["ordinary-skill", "__packages__-backup"])("allows unrelated sibling %s", async name => {
+    const source = path.join(managed, name);
+    await fs.mkdir(source);
+    await expect(assertLocalImportOutsideSkillPackageCache(await fs.realpath(source), managed)).resolves.toBeUndefined();
+  });
+});
diff --git a/server/src/services/skill-local-import-boundary.ts b/server/src/services/skill-local-import-boundary.ts
new file mode 100644
index 00000000000..ab5ad833486
--- /dev/null
+++ b/server/src/services/skill-local-import-boundary.ts
@@ -0,0 +1,22 @@
+import { promises as fs } from "node:fs";
+import path from "node:path";
+import { unprocessable } from "../errors.js";
+
+function contains(root: string, candidate: string) {
+  const relative = path.relative(root, candidate);
+  return relative === "" || (!path.isAbsolute(relative) && relative !== ".." && !relative.startsWith(`..${path.sep}`));
+}
+
+/** Package caches have package-level provenance, not local-import authority. */
+export async function assertLocalImportOutsideSkillPackageCache(sourceRealPath: string, managedSkillsRoot: string) {
+  const managedRoot = await fs.realpath(managedSkillsRoot).catch(() => null);
+  if (!managedRoot) return;
+  const reservedRoot = path.join(managedRoot, "__packages__");
+  const canonicalRoot = await fs.realpath(reservedRoot).catch(() => reservedRoot);
+  // Also reject ancestors before a cache exists: a concurrent fill must not
+  // become visible to a recursive import after its boundary check.
+  if ([reservedRoot, canonicalRoot].some(root => contains(root, sourceRealPath) || contains(sourceRealPath, root))) {
+    throw unprocessable("Skill package caches cannot be imported as local sources. Fork the installed skill to retain its access restrictions.",
+      { code: "skill_package_cache_import_denied" });
+  }
+}