Northwind 커머스 옵트인 + netscript CLI로 스캐폴딩된 비공개 Assistant/MCP 쇼케이스

# Showcase Archetype Implementation Plan

## 1. CLI Entry Point: `netscript init <name> --from showcase`

Add an opt-in flag to the existing `init` command. Default behavior (no `--from`) must remain untouched.

```ts
// packages/cli/src/commands/init.ts
export async function init(name: string, opts: { from?: string }) {
  if (opts.from === 'showcase') {
    return scaffoldShowcase(name);
  }
  return scaffoldDefault(name); // unchanged
}
```

Document a `showcase:setup` recipe in `docs/recipes/showcase.md` covering:
- Prerequisites (Node, pnpm, Postgres for Prisma)
- `netscript init my-app --from showcase`
- `pnpm showcase:setup` (migrations, seed, dev server)
- Sign-in flow and MCP/chat entry points

## 2. Commerce App Composition

Reuse existing Utility pages and plugin wiring. New domain modules:

- `orders`, `customers`, `products`, `line_items` — Prisma models with realistic dated seed data (spread across the last 90 days, deterministic).
- Typed oRPC reads: `orders.list`, `orders.byId`, `customers.list`, `products.list` with shared Zod schemas.
- Prisma persistence layer with a thin repository per aggregate.

## 3. Durable Worker Progress + Saga

- Worker writes progress rows (`worker_progress`) keyed by `(job_id, step)` — idempotent upserts.
- Order detail page renders saga state: `order → payment → shipping`, each with `pending | active | done | failed` and timestamps.
- Real webhook ingress at `/api/webhooks/:provider` with signature verification and idempotency keys.
- Activity feed stream-linked to the order via SSE, replaying from the last seen offset.

## 4. Authenticated Private Chat / MCP

- Session-scoped chat with ownership checks on every read/write.
- Finite catch-up: client requests `since=<offset>`, server returns bounded batch + `next_offset`.
- Exact-offset resume: no gaps, no duplicates; offsets are monotonic per conversation.
- Native transcript replay: server can replay full transcript for a conversation the caller owns.
- No-key provider setup: local echo/stub provider so the app runs without API keys.
- Canonical sign-in: single auth entry point reused by chat and MCP.

## 5. Byte-Identical Default Init Proof

- Snapshot the default scaffold output (all 220 files, including the agent bundle) into `test/fixtures/default-init/`.
- Test compares byte-for-byte with **no exclusions, no normalization** (no line-ending or whitespace normalization).
- Any drift fails CI with a diff.

## 6. Gate Run

Execute in order:
1. Root check tasks
2. Type check
3. Architecture/quality gate
4. Lint/format ratchet
5. Export doc-lint
6. Publish dry-run
7. Fresh `scaffold.showcase` through all local gates

## 7. Focused Tests + Negative Controls

- Unit tests for saga transitions, offset resume, ownership checks.
- Stub scenarios for webhook ingress and worker progress.
- Mounted chat browser regression (Playwright) covering catch-up + replay.
- Negative controls:
  - **Missing shipping persistence** → saga must fail loudly, not silently pass.
  - **Empty-conversation deadlock** → catch-up on empty conversation returns immediately with `next_offset=0`.
  - **Cold evidence-directory failure** → missing evidence dir surfaces a clear error, not a hang.

## 8. Cardinality Debt Register

Record in `docs/debt/cardinality.md`:

| Item | Owner | Cost | Stop condition | Closure gate |
|------|-------|------|----------------|--------------|
| Per-order activity fan-out | @backend | O(n) reads per order | >100 events/order | Paginated activity API |
| Chat offset storage | @platform | 1 row per conversation | >10k conversations | Move to append-only log |
| Webhook idempotency table growth | @backend | Unbounded | >1M rows | TTL + archival job |

Each entry requires owner, cost estimate, stop condition, and closure gate before merge.