feat(release): drive the installed entry from the packed tarballs

A throwaway consumer outside the repository declares every member as a file:
dependency, installs, and runs the installed executable with plain Node,
asserting the version it reports. That is the check a workspace link or a stale
lib/ in the checkout cannot pass for: it reads only what files selected.

The family declares its executable, so the vendored family — libraries a
consumer imports, with no executable — states that it has none instead of
carrying a probe that would prove nothing.

Both pack workflows run it after packing, still without credentials.

scripts/release/verify-packed-install.ts

@@ -0,0 +1,105 @@
+/**
+ * Install a packed release family into a throwaway consumer outside the
+ * repository and drive its installed executable with plain Node.
+ *
+ * Everything the packed tarballs need comes from the tarballs themselves: the
+ * consumer declares every member as a `file:` dependency, so the only registry
+ * traffic is for external dependencies. What this proves is that `files`
+ * selected a complete payload and that the published dependency ranges resolve
+ * — a workspace link or a stale `lib/` in the checkout cannot stand in for a
+ * missing file here
+ * ([rationale](../../.agents/notes/proposed/process/2026-08-10-npm-release-sequences.md)).
+ */
+
+import { spawnSync } from 'node:child_process'
+import { mkdtempSync, rmSync, writeFileSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join, resolve } from 'node:path'
+import { pathToFileURL } from 'node:url'
+import { parseArgs } from 'node:util'
+import { releaseFamily, tarballName, type ReleaseMember } from './families.ts'
+
+/**
+ * Environment for the installed artifact: no host Node hooks, no host DeepSeek
+ * Harness home, and no ambient npm user agent that would confuse npm.
+ * @param consumerRoot - the throwaway consumer directory.
+ * @returns The child environment.
+ */
+function consumerEnvironment(consumerRoot: string): NodeJS.ProcessEnv {
+  const environment = { ...process.env }
+  delete environment.npm_config_user_agent
+  delete environment.NPM_CONFIG_USER_AGENT
+  delete environment.NODE_OPTIONS
+  delete environment.NODE_PATH
+  environment.DSH_HOME = resolve(consumerRoot, '.dsh')
+  environment.DSH_AGENTS_HOME = resolve(consumerRoot, '.agents')
+  environment.DSH_TELEMETRY_DISABLED = '1'
+  return environment
+}
+
+/**
+ * Run a command in the consumer and fail the process on a non-zero exit.
+ * @param command - executable name.
+ * @param args - command arguments.
+ * @param cwd - working directory.
+ * @param env - child environment.
+ * @returns The captured stdout, trimmed.
+ */
+function run(command: string, args: readonly string[], cwd: string, env: NodeJS.ProcessEnv): string {
+  const result = spawnSync(command, [...args], { cwd, env, encoding: 'utf8' })
+  if (result.error !== undefined) throw result.error
+  if (result.status !== 0) {
+    throw new Error(`${command} ${args.join(' ')} exited with ${String(result.status)}:\n${result.stdout}\n${result.stderr}`)
+  }
+  return result.stdout.trim()
+}
+
+/** Install the family named by `--family` from `--from` and drive its entry. */
+function main(): void {
+  const { values } = parseArgs({
+    options: { family: { type: 'string' }, from: { type: 'string' } },
+    allowPositionals: false,
+  })
+  if (values.family === undefined || values.from === undefined) {
+    throw new Error('usage: verify-packed-install.ts --family <dsh|vendor> --from <packed directory>')
+  }
+
+  const family = releaseFamily(values.family)
+  const entry = family.installedEntry
+  const root = process.cwd()
+  const packed = resolve(root, values.from)
+  const members: ReleaseMember[] = family.members(root)
+
+  if (entry === undefined) {
+    console.log(`release verify-packed-install: family ${family.id} publishes no executable, nothing to drive`)
+    return
+  }
+
+  const consumerRoot = mkdtempSync(join(tmpdir(), `dsh-packed-${family.id}-`))
+  try {
+    const dependencies = Object.fromEntries(members.map(member =>
+      [member.name, pathToFileURL(join(packed, tarballName(member))).href]))
+    writeFileSync(join(consumerRoot, 'package.json'), `${JSON.stringify({
+      name: `dsh-packed-install-${family.id}`,
+      version: '0.0.0',
+      private: true,
+      dependencies,
+    }, null, 2)}\n`)
+
+    const environment = consumerEnvironment(consumerRoot)
+    console.log(`release verify-packed-install: installing ${String(members.length)} tarball(s) into ${consumerRoot}`)
+    run('npm', ['install', '--no-audit', '--no-fund', '--package-lock=false'], consumerRoot, environment)
+
+    const bin = join(consumerRoot, 'node_modules', ...entry.packageName.split('/'), entry.binPath)
+    const version = run(process.execPath, [bin, '--version'], consumerRoot, environment)
+    const expected = members.find(member => member.name === entry.packageName)?.version
+    if (version !== expected) {
+      throw new Error(`installed ${entry.packageName} --version reported ${JSON.stringify(version)}, expected ${String(expected)}`)
+    }
+    console.log(`release verify-packed-install: installed ${entry.packageName} reports ${version}`)
+  } finally {
+    rmSync(consumerRoot, { recursive: true, force: true })
+  }
+}
+
+main()