fix: stop test fixtures from deleting the repository's dependencies

Four fixtures linked the installed dependencies into a throwaway root with a
single directory symlink at <fixture>/node_modules, then ran pnpm inside that
root. pnpm does not recognise the modules directory it finds there and purges
it; with CI=true it does so without a prompt. The purge followed the symlink and
deleted the repository's own node_modules mid-run, so a test suite uninstalled
the workspace it was running in. That is what produced the cascading,
file-unrelated failures a full test:unit run reported, and it happened twice
while running the suites for the adapter re-review.

scripts/lib/fixture-node-modules.ts replaces all four sites: node_modules is a
real directory whose entries are individual symlinks, so a recursive delete
unlinks the fixture's own links instead of walking through one link into the
shared tree. Resolution is unchanged.

tests/unit/fixture-node-modules.test.ts performs the exact recursive delete pnpm
performs and asserts the source tree survives, and check:adapter-inventory now
fails on any reintroduction of the directory-symlink form — verified by putting
the old line back and watching the gate reject it.

A full tests/unit + tests/integration run now leaves the dependencies intact.
removal-fixture, supply-chain and security-followup-archive, the three suites
that had to be excluded before, pass in that run.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/unit/ci-artifact-contract.test.ts

@@ -19,6 +19,7 @@ import {
   validateCiArtifact,
 } from "../../scripts/lib/ci-artifact-validator.ts";
 import { writeCiGateLogAtomic } from "../../scripts/lib/ci-gate-log.ts";
+import { linkFixtureNodeModules } from "../../scripts/lib/fixture-node-modules.ts";
 import { captureCiCandidateArchive, verifyCiCandidateArchive } from "../../scripts/lib/ci-candidate-archive.ts";
 import {
   CANDIDATE_ARCHIVE_USAGE,
@@ -2131,7 +2132,7 @@ async function ensureProviderBaseFixture(): Promise<string> {
     recursive: true,
   });
   await rm(path.join(root, "artifacts/release"), { recursive: true, force: true });
-  await symlink(path.join(sourceRoot, "node_modules"), path.join(root, "node_modules"), "dir");
+  await linkFixtureNodeModules(root, sourceRoot);
   const git = spawnSync("git", ["show", "-s", "--format=%H%n%ct", "HEAD"], {
     cwd: sourceRoot,
     encoding: "utf8",

tests/unit/fixture-node-modules.test.ts

@@ -0,0 +1,89 @@
+import { mkdtemp, mkdir, readdir, readFile, rm, stat, writeFile } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import path from "node:path";
+
+import { describe, expect, it } from "vitest";
+
+import { linkFixtureNodeModules } from "../../scripts/lib/fixture-node-modules.ts";
+
+/**
+ * A removal or provider fixture runs `pnpm` inside a throwaway copy of the
+ * repository. pnpm does not recognise the modules directory it finds there and
+ * purges it, and with `CI=true` it does so without a prompt. When
+ * `<fixture>/node_modules` was a single directory symlink, that purge followed
+ * the link and deleted the repository's own installed dependencies mid-run —
+ * a test suite uninstalling the workspace it was running in.
+ */
+describe("fixture node_modules linking", () => {
+  async function sourceTree() {
+    const source = await mkdtemp(path.join(tmpdir(), "fixture-source-"));
+    const modules = path.join(source, "node_modules");
+    await mkdir(path.join(modules, "left", "lib"), { recursive: true });
+    await mkdir(path.join(modules, "@scope", "right"), { recursive: true });
+    await mkdir(path.join(modules, ".bin"), { recursive: true });
+    await writeFile(path.join(modules, "left", "lib", "index.js"), "export default 1;\n");
+    await writeFile(path.join(modules, "@scope", "right", "package.json"), "{}\n");
+    await writeFile(path.join(modules, ".modules.yaml"), "{}\n");
+    return source;
+  }
+
+  it("survives a recursive delete of the fixture's node_modules", async () => {
+    const source = await sourceTree();
+    const fixture = await mkdtemp(path.join(tmpdir(), "fixture-root-"));
+    try {
+      await linkFixtureNodeModules(fixture, source);
+
+      // The fixture resolves the same packages...
+      expect(
+        await readFile(
+          path.join(fixture, "node_modules/left/lib/index.js"),
+          "utf8",
+        ),
+      ).toContain("export default 1;");
+      expect(
+        (await readdir(path.join(fixture, "node_modules"))).sort(),
+      ).toEqual([".bin", ".modules.yaml", "@scope", "left"]);
+
+      // ...and this is exactly what pnpm's purge does.
+      await rm(path.join(fixture, "node_modules"), {
+        recursive: true,
+        force: true,
+      });
+
+      // The repository's real dependencies are untouched.
+      expect(
+        await readFile(
+          path.join(source, "node_modules/left/lib/index.js"),
+          "utf8",
+        ),
+      ).toContain("export default 1;");
+      expect(
+        await stat(path.join(source, "node_modules/@scope/right/package.json")),
+      ).toBeDefined();
+      expect(
+        (await readdir(path.join(source, "node_modules"))).sort(),
+      ).toEqual([".bin", ".modules.yaml", "@scope", "left"]);
+    } finally {
+      await rm(source, { recursive: true, force: true });
+      await rm(fixture, { recursive: true, force: true });
+    }
+  });
+
+  it("creates node_modules as a real directory, never a symlink", async () => {
+    const source = await sourceTree();
+    const fixture = await mkdtemp(path.join(tmpdir(), "fixture-root-"));
+    try {
+      await linkFixtureNodeModules(fixture, source);
+      const { lstat } = await import("node:fs/promises");
+      const entry = await lstat(path.join(fixture, "node_modules"));
+      expect(entry.isSymbolicLink()).toBe(false);
+      expect(entry.isDirectory()).toBe(true);
+      expect(
+        (await lstat(path.join(fixture, "node_modules/left"))).isSymbolicLink(),
+      ).toBe(true);
+    } finally {
+      await rm(source, { recursive: true, force: true });
+      await rm(fixture, { recursive: true, force: true });
+    }
+  });
+});