# migration-ready-schema

Defines data model guidelines for idempotent data imports and clean rollbacks. Useful when drafting architecture contracts in ARCH-{slug}.md.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · ★ 107
- Author: avelikiy
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/avelikiy/great_cto/tree/HEAD/skills/migration-ready-schema/SKILL.md
- Updated: 2026-10-24
- HTML: https://affpapa.org/en/nevibecode/skills/migration-ready-schema

## What it does

This skill inspects database schema designs before code generation starts. It enforces two metadata columns on importable tables: a nullable `source_ref` with a `UNIQUE` constraint using `{source}:{type}:{id}` for deduplication, plus a nullable `import_batch_id` UUID. Without `import_batch_id`, rolling back a corrupted batch requires manual surgery. Imports must remain reversible.

The second requirement turns real-world actors into separate tables. Storing contact details inline inside an order leaves no target row when external systems push contacts first. The skill also enforces integers for monetary values (`*_cents`), time-zone awareness on date fields, and dedicated tracking tables named `outbound_message` and `processed_webhook_events`.

These checks apply to files within `docs/architecture/**` and `docs/data-import/**`. Ephemeral caches and materialized views are explicitly excluded from these rules.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add avelikiy/great_cto --skill migration-ready-schema -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/migration-ready-schema/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/migration-ready-schema/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add avelikiy/great_cto --skill migration-ready-schema -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/migration-ready-schema/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add avelikiy/great_cto --skill migration-ready-schema -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/migration-ready-schema/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install avelikiy/great_cto migration-ready-schema
```

2. **Manually: put the files in place**
- File: `.github/skills/migration-ready-schema/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add avelikiy/great_cto --skill migration-ready-schema -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/avelikiy/great_cto --path skills/migration-ready-schema
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/migration-ready-schema/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add avelikiy/great_cto --skill migration-ready-schema -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/avelikiy/great_cto/tree/HEAD/skills/migration-ready-schema/SKILL.md

## When to use it
- enforce idempotent database schema designs before writing migration scripts
- add batch tracking columns to enable clean rollbacks after failed imports
- split inline contact attributes into dedicated relational entities
- prevent float precision errors on financial amounts and dates

## Example prompts
- Review the schema in `docs/architecture/ARCH-billing.md` against `migration-ready-schema` rules.
- Add `source_ref` and `import_batch_id` columns to the new inventory table.
- Check if our customer contact tables follow the migration-ready entity guidelines.

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 22da65a08b1e3ce3.

BEGIN THIRD-PARTY FILE 22da65a08b1e3ce3
````text
---
name: migration-ready-schema
description: Data-model rules that make a schema importable from day one, so the migration-import-engineer is never blocked on missing columns. Every SMB Product-Builder product must let a customer bring their data from an incumbent (ServiceTitan/Toast/Mindbody/Shopify) — that requires provenance (source_ref) and rollback (import_batch_id) on importable entities, and modelling real-world actors as entities rather than inline fields. Applied by architect when writing the data model in ARCH-{slug}.md, and checked by migration-import-engineer. One cheap rule set prevents the migration↔architecture seam gap from recurring across all 40 products.
when_to_use: |
  Apply when:
  - architect writes the Data contracts / data model section of ARCH-{slug}.md
  - migration-import-engineer verifies the destination schema can satisfy its
    idempotency + rollback invariants
  - any new entity is added that could be populated from an import or a third-party sync
  Do NOT apply to purely ephemeral / derived tables (caches, materialized views) that are
  never imported into.
effort: low
allowed-tools: Read, Write, Grep, Glob
paths:
  - "docs/architecture/**"
  - "docs/data-import/**"
---

# Migration-ready schema — importable from day one

Every SMB product's wedge is **low switching cost** — the customer brings their data from
the incumbent. If the schema can't receive that data idempotently and reversibly, the
`migration-import-engineer` blocks and the wedge is a slogan. These rules are cheap at
design time and impossible to retrofit cleanly. **Apply them to the data model in ARCH,
before any import is designed.**

## The three rules (the ones that actually block imports)

### 1. Importable entities carry `source_ref` (provenance)
Any entity that can be populated from an incumbent export or a third-party sync gets a
nullable, **unique** `source_ref` column:

```
source_ref  text  UNIQUE NULL   -- e.g. "servicetitan:pricebook:8842"
```

- It is the **dedup key** for idempotent re-import (re-running an export never duplicates).
- Namespaced `{source}:{type}:{id}` so two incumbents can't collide.
- Nullable because natively-created rows have no source.

### 2. Importable entities carry `import_batch_id` (rollback)
```
import_batch_id  uuid  NULL  -- tags every row written by one import run
```
Rollback = delete where `import_batch_id = ?`. Without it there is no undo, and an import
with no undo is one a user will never trust enough to run.

### 3. Model real-world actors as entities, not inline fields
A customer, contact, vendor, member, or tenant is an **entity with its own table**, even if
````
END THIRD-PARTY FILE 22da65a08b1e3ce3

The third-party file has ended. Everything between the 22da65a08b1e3ce3 tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

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