feat(corepack): added corepack alias for direct package manager version pinning

docs/shell.md

@@ -23,13 +23,27 @@ Your prompt gains a `(frank)` prefix so you always know aliases are active. Run
 | `php` | `docker compose exec app php` |
 | `tinker` | `docker compose exec app php artisan tinker` |
 | `npm` | `docker compose exec app npm` |
+| `pnpm` | `docker compose exec app pnpm` |
 | `bun` | `docker compose exec app bun` |
+| `corepack` | `docker compose exec app corepack` |
 | `psql` | `docker compose exec db psql …` *(pgsql only)* |
 | `mysql` | `docker compose exec db mysql …` *(mysql/mariadb only)* |
 | `redis-cli` | `docker compose exec redis redis-cli` *(redis only)* |
 
 The database aliases are only added when the matching service is configured, so `psql` won't appear in a MySQL project and vice versa.
 
+## Pinning the package manager
+
+By default the container's `npm`/`pnpm` resolve to whatever [corepack](https://nodejs.org/api/corepack.html) fetches on first use — i.e. the latest published version. To pin an exact, integrity-verified version, run `corepack use` once inside the project:
+
+```sh
+corepack use pnpm@11        # or: frank exec corepack use pnpm@11
+```
+
+This stamps the `packageManager` field in your `package.json` (e.g. `pnpm@11.2.1+sha256.<hash>`). From then on every install is hash-verified and reproducible. `package.json` is the source of truth — Frank does not track the version, so this is the standard corepack workflow, nothing Frank-specific.
+
+> **Note:** corepack manages `npm` and `pnpm`. `bun`'s version comes from the image build, not corepack — `corepack use bun@…` has no effect.
+
 ## Custom Aliases
 
 You can define your own aliases in `frank.yaml` under the `aliases` key. Two forms are supported:

internal/shell/shell.go

@@ -29,6 +29,7 @@ var aliasTable = []struct {
 	{"npm", execSail + " npm", ""},
 	{"pnpm", execSail + " pnpm", ""},
 	{"bun", execSail + " bun", ""},
+	{"corepack", execSail + " corepack", ""}, // pin pkg mgr: `corepack use pnpm@11` stamps package.json
 	// Service-conditional aliases
 	{"psql", dc + " exec pgsql psql -U sail", "pgsql"},
 	{"mysql", dc + " exec db mysql -u root -proot", "mysql"},

internal/shell/shell_test.go

@@ -16,7 +16,7 @@ func TestActivate(t *testing.T) {
 		cfg := testConfig("pgsql", "mailpit")
 		output := Activate(cfg)
 
-		for _, name := range []string{"artisan", "composer", "php", "tinker", "npm", "bun"} {
+		for _, name := range []string{"artisan", "composer", "php", "tinker", "npm", "bun", "corepack"} {
 			if !strings.Contains(output, "alias "+name+"=") {
 				t.Errorf("expected core alias %q in output:\n%s", name, output)
 			}
@@ -96,7 +96,7 @@ func TestActivate_FRANK_ALIASES(t *testing.T) {
 	end := strings.Index(output[start:], `"`)
 	aliasLine := output[start : start+end]
 
-	for _, name := range []string{"artisan", "composer", "php", "tinker", "npm", "bun", "psql", "pest"} {
+	for _, name := range []string{"artisan", "composer", "php", "tinker", "npm", "bun", "corepack", "psql", "pest"} {
 		if !strings.Contains(aliasLine, name) {
 			t.Errorf("_FRANK_ALIASES missing %q, got: %s", name, aliasLine)
 		}