Resolves #330.

Mirrors pnpm v11's `@pnpm/bins.resolver`, `@pnpm/bins.linker`, and `@zkochan/cmd-shim` (resolved at pnpm `4750fd370c` and cmd-shim `0d79ca9534`):

- New `pacquet-cmd-shim` crate parses the `bin` field of a package manifest into commands. Both `bin: string | object` and the `directories.bin` glob fallback are supported, with the same path-traversal and URL-safe-name guards as upstream. Conflict resolution follows `pkgOwnsBin` + lexical compare.
- Shim generator writes all three flavors per bin: Unix `/bin/sh` (byte-compatible with pnpm's `generateShShim`), Windows `.cmd` (CRLF, `%~dp0` paths), and PowerShell `.ps1` (`$basedir`/`$exe` header with Windows/POSIX-pwsh detection). Mirrors `generateCmdShim` and `generatePwshShim` minus the unused `nodePath`/`prependToPath`/`progArgs` branches.
- All filesystem IO behind per-capability DI traits — `FsReadHead`, `FsReadFile`, `FsReadString`, `FsReadDir`, `FsWalkFiles`, `FsCreateDirAll`, `FsWrite`, `FsSetExecutable`, `FsEnsureExecutableBits` — following the pattern documented in [#332](#332 (comment)). `FsWrite` is a thin shim over `std::fs::write` and is **not atomic**; a future atomic-write capability can build on it without renaming. Production callers turbofish the unit-struct provider `::<RealApi>`; tests inject unit-struct fakes to cover IO error paths real fs can't trigger portably. Generic param is named `Api` (not `Fs`) so the same provider can grow non-fs capabilities without a rename.
- New `LinkVirtualStoreBins` step walks each virtual-store slot and links its child packages' bins into the slot's own `node_modules/.bin`, matching `linkBinsOfDependencies` in pnpm's `building/during-install`. Slot iteration, per-slot child reads, and shim writes parallelised on rayon.
- `SymlinkDirectDependencies` and `InstallWithoutLockfile` call the bin linker after the symlink layout is in place. Direct-dep linking and the symlink loop are exposed as free `link_direct_dep_bins` / `symlink_direct_deps_into_node_modules` functions so they're unit-testable without the mock-registry scaffold.

Tests port the relevant `bins/resolver` and `bins/linker` cases from pnpm (`directories.bin` discovery, scoped bin names, dangerous locations, idempotent shim skip, conflict resolution) and add fakes-injected coverage for the IO error variants.

**Not in this PR**: hoisted-bin precedence and lifecycle-script-created bins. Both depend on subsystems pacquet hasn't built yet — hoisting (`hoistPattern` / `publicHoistPattern` resolution + the lift step) and lifecycle scripts (`exec/lifecycle/` runner + `allowBuilds` plumbing). The bin-linking side already does the right thing for both (shims are paths, so they pick up files generated post-extract; the precedence rule is a small addition once hoisting tags candidates as hoisted). Tracked separately in  with full porting coordinates.



## Performance

When the bin-linking step landed it added ~7% to the warm-cache Frozen Lockfile install ([benchmark](#333 (comment))). Closing that gap took a sequence of changes that mirror how pnpm v11 avoids the same costs in its own `linkBinsOfDependencies` ([4750fd370c](https://github.com/pnpm/pnpm/blob/4750fd370c/building/during-install/src/index.ts#L258-L309)):

- **Bundled manifests in `index.db`.** `extract_tarball_entries` captures the parsed `package.json`, picks the subset pnpm caches via a port of `normalizeBundledManifest` (`name`, `version`, `bin`, `directories`, `dependencies`, lifecycle `scripts`, …), and stuffs it into `PackageFilesIndex.manifest`. `prefetch_cas_paths` surfaces it back as a `HashMap<cache_key, Arc<Value>>` so the bin linker doesn't have to re-read `package.json` per child off disk.
- **msgpackr-records encoder learns `serde_json::Value`.** The encoder previously errored with `ManifestNotSupported` if anything ever set `manifest`; now it records-encodes nested JSON objects (slot-allocated per distinct key set) so `useRecords: true` readers see them as JS `Object`s rather than `Map`s — necessary for pnpm's `manifest.bin` / `manifest.directories?.bin` property accesses to resolve.
- **`Arc<Value>` for `PackageBinSource.manifest`.** The lockfile-driven bin-link path produces `slots × children` clones of the parsed manifest (~6k on the integrated-benchmark fixture). Sharing via `Arc` turns each push into a refcount bump.
- **`hasBin` filter via lockfile.** `LinkVirtualStoreBins` now takes the lockfile `packages:` section, pre-computes an `Option<HashSet<PackageKey>>` of `hasBin: true` keys at install start, and skips snapshot children that aren't in the set *before* any path-building or manifest lookup. ~95% of a real lockfile's packages don't declare a bin, so this short-circuits the bulk of the per-slot work. `None` is reserved for the pathological case where the lockfile lacks a `packages:` section (fall back to processing every child); `Some(empty)` is authoritative — lockfile says no package has a bin, every slot short-circuits. Mirrors pnpm's filter at `building/during-install/src/index.ts:283`.
- **Lockfile-driven slot iteration.** `run_lockfile_driven` walks `snapshots` directly and builds slot paths lexically. The previous `run_with_readdir` path enumerated every slot via `Api::read_dir(virtual_store_dir)` and probed each slot's own package directory with a wasted `read_dir` (~1267 wasted `open(O_DIRECTORY) + close` per warm install). The readdir-driven path survives as a fallback for `install_without_lockfile` and retains the existence probe there (small N, no virtual-store invariant from `create_virtual_dir_by_snapshot` to lean on).
- **Parallel prefetch decode.** `StoreIndex::get_many_raw` returns undecoded row bytes; the SQLite mutex releases before `prefetch_cas_paths` fans the msgpackr decode + integrity check across rayon.

Latest CI benchmark on this branch ([job 75462998251](https://github.com/pnpm/pacquet/actions/runs/25701679172/job/75462998251)):

| Scenario | pacquet@HEAD | pacquet@main | Relative |
|---|---|---|---|
| Frozen Lockfile | 2.074s ± 102ms | 2.026s ± 70ms | +2.4% (within noise) |
| Frozen Lockfile (Hot Cache) | **479.6ms ± 38ms** | **535.8ms ± 37ms** | **~10% faster than main** |

The follow-up #417 splits manifests into a dedicated `package_manifests` SQLite table so the unfiltered `package_index` prefetch payload stays at its original size and the manifest fetch becomes a targeted SELECT against just the `hasBin: true` subset.

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Co-authored-by: Zoltan Kochan <z@kochan.io>