c4-model

# C4 Model — Methodology Overlay (WHAT → HOW via Mermaid) **Sources (2026-08-12):** Simon Brown C4 https://c4model.com/ (Context, Container, Component, Code); Structurizr DSL https://github.com/structurizr/dsl (open-source DSL, paid cloud) + `structurizr-mcp` https://github.com/cubical6/structurizr-mcp + `go-structurizr`; C4-PlantUML https://github.com/plantuml-stdlib/C4-PlantUML; overarch https://github.com/soulspace-org/overarch (PlantUML/Structurizr generation); rendering **via Mermaid** `mermaid-js/mermaid` MIT per §44. > **Pack:** `architecture` core (`architect + ADR + TRD + threat-model + mermaid (+ C4 via mermaid)`) — `c4-model` teaches *what* to draw; `mermaid` renders it. See `docs/architecture/research-385-diagram.md` for C4 vs Mermaid vs PlantUML/Structurizr decision (Excalidraw/draw.io REJECT). ## When to use - Need system Context / Container / Component / Code views. ## Instructions 1. **Select level:** Context (system + actors) → Container (apps/data stores) → Component (modules) → Code (classes, optional). 2. **Render via Mermaid** (C4-inspired): `flowchart TD` with `subgraph` for boundaries, e.g.: ```mermaid flowchart TD user([User]) --> web[Web Container] web --> api[API Container] api --> db[(Database Container)] subgraph System Context user; web; api; db end ``` 3. **Advanced (optional):** For consistency checks across views, use Structurizr DSL (`structurizr-cli` + `workspace.dsl` → PlantUML/Mermaid) or C4-Pl...