C3 Context Design

C3 Context Level Exploration

⛔ CRITICAL GATE: Load Current Context First

STOP - Before ANY context-level work, execute:

cat .c3/README.md 2>/dev/null || echo "NO_CONTEXT_DOC"
cat .c3/settings.yaml 2>/dev/null || echo "NO_SETTINGS"
ls -d .c3/c3-*/  2>/dev/null || echo "NO_CONTAINERS"

Based on output:

• If "NO_CONTEXT_DOC" → Creating new context (fresh)
• If context exists → Read it completely before proposing changes
• If containers exist → Note them for reference

⚠️ DO NOT read ADRs unless user specifically asks:

• Context work focuses on current state, not historical decisions
• ADRs add unnecessary context → hallucination risk
• Only read: Context, Container READMEs (for inventory)

Why this gate exists: Context is the root of all C3 docs. Changes here cascade to ALL containers and components.

Self-check before proceeding:

• I executed the commands above
• I read existing context doc (if exists)
• I know what containers already exist

Overview

Context is the eagle-eye introduction to your architecture. Two core jobs:

1. What containers exist and what are they responsible for?
2. How do containers interact with each other?

Position: ROOT (c3-0) | Parent: None | Children: All Containers

📁 File Location: Context is .c3/README.md - NOT context/c3-0.md or any subfolder.

Announce: "I'm using the c3-context-design skill to explore Context-level impact."

The Principle

Upper layer defines WHAT. Lower layer implements HOW.

At Context level:

• I define WHAT containers exist and WHY
• Container implements my definitions (WHAT components exist)
• I do NOT define what's inside containers - that's Container's job

Integrity rule: Containers cannot exist without being listed in Context.

Include/Exclude

Litmus test: "Is this about WHY containers exist and HOW they relate to each other?"

Exploration Process

Phase 1: Analyze Change Impact

Already loaded context via Critical Gate. Now analyze:

Phase 2: Socratic Discovery

• Containers: "What would be separately deployed?"
• Protocols: "How do containers talk? What's the contract?"
• Boundary: "What's inside vs external?"
• Actors: "Who initiates interactions?"

Template

---
id: c3-0
c3-version: 3
title: [System Name] Overview
summary: >
  Bird's-eye view of the system, actors, and key interactions.
---

# [System Name] Overview

## Overview {#c3-0-overview}
[System purpose in 1-2 sentences]

## System Architecture {#c3-0-architecture}

` ` `mermaid
flowchart TB
    subgraph System["[System Name]"]
        C1[Container 1 c3-1]
        C2[Container 2 c3-2]
    end

    User((User)) --> C1
    C1 --> C2
` ` `

## Actors {#c3-0-actors}
| Actor | Type | Interacts Via |
|-------|------|---------------|

## Containers {#c3-0-containers}
| Container | ID | Archetype | Responsibility |
|-----------|-----|-----------|----------------|

## Container Interactions {#c3-0-interactions}
| From | To | Protocol | Purpose |
|------|-----|----------|---------|

## Cross-Cutting Concerns {#c3-0-cross-cutting}
- **Auth:** [approach]
- **Logging:** [approach]
- **Errors:** [approach]

Diagram Requirement

A container relationship diagram is REQUIRED at Context level.

Must show: containers, external systems, protocols, actors.

Use Mermaid only - no ASCII art.

⛔ Enforcement Harnesses

Harness 1: Template Fidelity

Rule: Output MUST match template structure exactly.

Required sections (in order):

1. Frontmatter (id, c3-version, title, summary)
2. Overview
3. System Architecture (with Mermaid diagram)
4. Actors
5. Containers
6. Container Interactions
7. Cross-Cutting Concerns

🚩 Red Flags:

• Sections missing or reordered
• ASCII diagram instead of Mermaid
• Missing frontmatter fields

Harness 2: Mermaid Only

Rule: ALL diagrams must use Mermaid syntax.

Verification Checklist

Before claiming completion, execute:

# Verify context doc exists
cat .c3/README.md | head -20

# Verify frontmatter
grep -E "^id:|^c3-version:|^title:" .c3/README.md

# Verify mermaid diagram exists
grep -c '```mermaid' .c3/README.md

• Critical gate executed (existing context loaded)
• Template sections present in correct order
• Mermaid diagram included (no ASCII)
• Frontmatter complete (id, c3-version, title, summary)
• All containers listed with responsibilities
• Interactions documented

📚 Reading Chain Output

At the end of context work, output a reading chain for affected containers.

Format:

## 📚 To Go Deeper

Context (c3-0) defines these containers:

**Containers to explore:**
├─ c3-1-{slug} - [responsibility, why it matters]
├─ c3-2-{slug} - [responsibility, why it matters]
└─ ...

**If this change affected protocols, also read:**
└─ c3-N-{slug} - [which protocol changed]

*Reading chain generated from containers listed in Context.*

Rules:

• List containers mentioned in Context's inventory
• Highlight which containers are affected by this change
• Never include ADRs unless user asked

Related

• references/core-principle.md - The C3 principle
• defaults.md - Context layer rules
• references/container-archetypes.md - Container types
• references/diagram-patterns.md - Diagram guidance