diff --git a/package.json b/package.json
index 795cf6b..367bf51 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@first-tree-ai/context-tree",
-  "version": "0.1.7",
+  "version": "0.1.8",
   "description": "Durable, structured project context for coding agents: a CLI plus framework-neutral skills.",
   "type": "module",
   "license": "Apache-2.0",
diff --git a/scripts/package-e2e.mjs b/scripts/package-e2e.mjs
index ad64dc2..162c062 100644
--- a/scripts/package-e2e.mjs
+++ b/scripts/package-e2e.mjs
@@ -136,12 +136,35 @@ try {
     "a local install must not write skills to the home directory",
   );
 
-  // A global install does, which is the documented path.
-  const globalPostinstall = spawnSync(process.execPath, [join(installedPackage, "scripts/postinstall.mjs")], {
+  // Nor does a global install of a package that depends on this one: npm sets npm_config_global
+  // for its dependencies too, and this copy is nested inside the consumer, which is that layout.
+  const nestedPostinstall = spawnSync(process.execPath, [join(installedPackage, "scripts/postinstall.mjs")], {
     cwd: consumerRoot,
     encoding: "utf8",
     env: { ...npmEnvironment, npm_config_global: "true" },
   });
+  assert.equal(nestedPostinstall.status, 0, "postinstall must never fail an install");
+  assert.match(nestedPostinstall.stdout, /run `context-tree install`/u);
+  assert.equal(
+    existsSync(join(temporaryRoot, ".claude", "skills")),
+    false,
+    "a global install of a dependent package must not write skills to the home directory",
+  );
+
+  // A direct global install does. Installing for real is what proves it, because the layout npm
+  // produces is the whole basis of the distinction.
+  const globalPrefix = join(temporaryRoot, "global-prefix");
+  execFileSync("npm", ["install", "-g", "--prefix", globalPrefix, "--no-audit", "--no-fund", tarball], {
+    cwd: temporaryRoot,
+    env: npmEnvironment,
+    stdio: "pipe",
+  });
+  const globallyInstalled = join(globalPrefix, "lib/node_modules/@first-tree-ai/context-tree");
+  const globalPostinstall = spawnSync(process.execPath, [join(globallyInstalled, "scripts/postinstall.mjs")], {
+    cwd: temporaryRoot,
+    encoding: "utf8",
+    env: { ...npmEnvironment, npm_config_global: "true" },
+  });
   assert.equal(globalPostinstall.status, 0, "postinstall must never fail an install");
   assert.match(globalPostinstall.stdout, /installed 6 skills for claude/u);
   for (const skill of SKILLS) {
diff --git a/scripts/postinstall.mjs b/scripts/postinstall.mjs
index f021f81..74e7443 100644
--- a/scripts/postinstall.mjs
+++ b/scripts/postinstall.mjs
@@ -5,20 +5,32 @@
 // A failure must never fail `npm install`: the CLI is still usable, and
 // `context-tree install` can be run by hand afterwards.
 //
-// Only a global install writes to the home directory. Adding this package as a local
-// dependency — including this repository's own `pnpm install` — must not silently
-// modify the developer's agent configuration, so it just prints the command.
+// Only a direct global install writes to the home directory; anything else just prints the
+// command, so installing this package as a dependency never touches a developer's own agents.
 
 import { spawnSync } from "node:child_process";
-import { dirname, resolve } from "node:path";
+import { existsSync } from "node:fs";
+import { basename, dirname, join, resolve } from "node:path";
 import { fileURLToPath } from "node:url";
 
-if (process.env.npm_config_global !== "true") {
+const packageRoot = resolve(dirname(fileURLToPath(import.meta.url)), "..");
+
+// npm sets npm_config_global for a global install's dependencies too, so the flag alone does not
+// identify the install target. A dependency copy sits inside the owning package's node_modules; a
+// directly installed one sits in npm's own prefix, which is not a package.
+function ownedByAnotherPackage(directory) {
+  const parent = dirname(directory);
+  if (parent === directory) return false;
+  if (basename(directory) === "node_modules") return existsSync(join(parent, "package.json"));
+  return ownedByAnotherPackage(parent);
+}
+
+if (process.env.npm_config_global !== "true" || ownedByAnotherPackage(packageRoot)) {
   process.stdout.write("Context Tree: run `context-tree install` to add the skills to your agent.\n");
   process.exit(0);
 }
 
-const cli = resolve(dirname(fileURLToPath(import.meta.url)), "..", "dist", "cli", "index.mjs");
+const cli = join(packageRoot, "dist", "cli", "index.mjs");
 const result = spawnSync(process.execPath, [cli, "install"], { encoding: "utf8" });
 
 if (result.error !== undefined || result.status !== 0) {