feat: add everything-claude-code sync document

harper-best-practices/ECC-SYNC.md

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+# Syncing to everything-claude-code (ECC)
+
+This document describes how to keep the [everything-claude-code](https://github.com/anthropics/everything-claude-code) Harper skill and rules up to date when changes are made here.
+
+## Repository Layout
+
+```
+harperfast/skills/harper-best-practices/
+├── SKILL.md       # High-level skill description + quick reference
+├── AGENTS.md      # Full compiled guide (all rules expanded inline)
+└── rules/         # Individual rule files
+    ├── adding-tables-with-schemas.md
+    ├── automatic-apis.md
+    └── ...
+
+everything-claude-code/
+├── skills/harper-best-practices/
+│   └── SKILL.md   # Combined SKILL.md + AGENTS.md content (see below)
+└── rules/harper/
+    ├── adding-tables-with-schemas.md
+    ├── automatic-apis.md
+    └── ...
+```
+
+## Syncing the Rules
+
+The individual rule files map directly. To sync all rules:
+
+```bash
+cp -r harperfast/skills/harper-best-practices/rules/ everything-claude-code/rules/harper/
+```
+
+After copying, verify that the rules referenced in the ECC SKILL.md still match the updated content.
+
+## Syncing the Skill File
+
+ECC does not use a separate AGENTS.md. Instead, the full content from `AGENTS.md` is merged inline into `skills/harper-best-practices/SKILL.md`. The harperfast `SKILL.md` (high-level overview + quick reference) acts as the structure, and the harperfast `AGENTS.md` (expanded rule details) fills in the body.
+
+### Structure of the ECC SKILL.md
+
+| Section                                       | Source                                                                                |
+| --------------------------------------------- | ------------------------------------------------------------------------------------- |
+| Frontmatter (`name`, `description`, `origin`) | harperfast `SKILL.md` frontmatter, with `origin: ECC` instead of `license`/`metadata` |
+| `## When to Use`                              | harperfast `SKILL.md`                                                                 |
+| `## Steps`                                    | harperfast `SKILL.md` (`## How It Works` renamed to `## Steps`)                       |
+| `## Rule Categories by Priority` table        | harperfast `SKILL.md`                                                                 |
+| `## Rule Details` — all expanded sections     | harperfast `AGENTS.md` content, with heading levels adjusted (see below)              |
+
+### Heading Level Adjustments
+
+The ECC SKILL.md uses different heading levels than AGENTS.md because the content is nested under `## Rule Details`:
+
+| AGENTS.md                            | ECC SKILL.md                                          |
+| ------------------------------------ | ----------------------------------------------------- |
+| `## 1. Schema & Data Design`         | `### 1. Schema & Data Design`                         |
+| `### 1.1 Adding Tables with Schemas` | `#### 1.1 [Adding Tables...](../../rules/harper/...)` |
+| `#### When to Use`                   | `##### When to Use`                                   |
+| `#### How It Works`                  | `##### How It Works`                                  |
+| `#### Example`                       | `##### Example`                                       |
+
+Rule section headings in ECC also include a markdown link to the corresponding rule file, e.g.:
+
+```markdown
+#### 1.1 [Adding Tables with Schemas](../../rules/harper/adding-tables-with-schemas.md)
+```
+
+### Syncing Process
+
+When `AGENTS.md` is updated:
+
+1. **Identify changed sections** by diffing `AGENTS.md` against the expanded rule content in the ECC SKILL.md (sections `### 1.` through `### 4.`).
+2. **Apply content changes** to the corresponding section in the ECC SKILL.md, respecting the heading level and naming conventions above.
+3. **Do not copy structure verbatim** — the ECC file omits the Table of Contents, the `---` separators between top-level sections map to the ECC structure, and section headings include rule file links.
+
+When `SKILL.md` (the overview/quick reference) is updated:
+
+1. Update the `## When to Use`, `## Steps`, and `## Rule Categories by Priority` sections in the ECC SKILL.md to match.
+2. The `## Quick Reference` and `## How to Use` sections in harperfast `SKILL.md` have **no equivalent** in the ECC file — they are replaced by the full inline content.