GHSA-2rx9-3g3h-c2jv

## Summary

A crafted lockfile alias could reach several install-time filesystem joins. With `--trust-lockfile` or a frozen lockfile, traversal segments could create links outside the intended project or `node_modules` boundary. This patch validates dependency names and every virtual-store slot before creating directories, links, bins, or hoisted entries.

## Security boundary

- A shared safe-join helper rejects traversal, absolute, platform-specific, and reserved dependency names before filesystem materialization. - Direct and transitive dependency links, package links, bin destinations, and public/private hoist destinations use the same containment rule. - Global virtual-store slots validate the complete slot path, including version-derived components, before directory creation. - Snapshot slots and package names are checked before store initialization and before the current-lockfile fast path, closing the warm-install bypass. - Rejections preserve `ERR_PNPM_INVALID_DEPENDENCY_NAME`.

## Exploit replay

Before the patch, `pacquet install --frozen-lockfile --trust-lockfile` accepted a `../../escaped-link` dependency key and created a symlink outside the project. With this patch, the same lockfile is rejected before materialization and no outside link is created.

## Files changed

- `pacquet/crates/package-manager/src/safe_join_modules_dir.rs` defines the shared containment rule. - Install, symlink, bin, hoist, virtual-store, and frozen-lockfile paths call that helper before filesystem materialization. - The corresponding `tests.rs` files cover every sink, including warm installs and global virtual-store slots.

## Commands run

```text $ cargo test --locked -p pacquet-package-manager --lib PASS: 434 tests $ cargo clippy --locked -p pacquet-package-manager --all-targets -- --deny warnings PASS $ cargo fmt --all -- --check PASS ```

## Validation

- Full pacquet package-manager suite: 434 passed. - Focused regressions cover direct and transitive aliases, bins, hoists, package names, global virtual-store version traversal, and a poisoned prior-install slot. - `cargo clippy -p pacquet-package-manager --all-targets -- -D warnings`: passed. - `cargo fmt --all -- --check` and `git diff --check`: passed.

## Compatibility

Valid unscoped and scoped dependency aliases continue to work. The reproduced escape was specific to pacquet, so this branch does not change the TypeScript CLI or the lockfile format.

--- Written by an agent (Codex, GPT-5).