What

Define and apply a standard cross-reference convention for linking between
documents within a project and across ecosystem projects.

Why

Currently, cross-references between documents are ad-hoc — some use inline links,
some use footnotes, and cross-project references are mostly absent. A consistent
convention enables automated link validation and makes the documentation
interconnected rather than isolated per-project.

How

Intra-Project Cross-Reference Convention

Use blockquote format for outbound references within a project:

> **Cross-reference**:
> [Architecture Guide §3](./ARCHITECTURE.md#section-3) — Thread pool design
> [API Reference](./API_REFERENCE.md) — Public API details

Inter-Project Cross-Reference Convention

Use blockquote format with ecosystem-relative paths:

> **Ecosystem reference**:
> [common_system Result<T>](https://github.com/kcenon/common_system/blob/main/docs/API_REFERENCE.md#result-type) — Error handling base
> [thread_system Thread Pool](https://github.com/kcenon/thread_system/blob/main/docs/ARCHITECTURE.md#thread-pool) — Async execution

Cross-Reference Placement Rules

1. Place at the beginning of a section that depends on another document
2. Use blockquote (>) to visually distinguish from regular content
3. Include a brief description of why the reference is relevant
4. For architecture docs, include a Mermaid dependency diagram:

## Ecosystem Dependencies

```mermaid
graph TD
    A[common_system] --> B[thread_system]
    A --> C[container_system]
    B --> D[logger_system]
    B --> E[monitoring_system]
    D --> F[database_system]
    E --> F
    F --> G[network_system]
    G --> H[pacs_system]
```​

Implementation Steps

1. Create docs/CROSS_REFERENCE_GUIDE.md in common_system as the canonical convention
2. Add cross-references to ARCHITECTURE.md in each project (highest-value target)
3. Add ecosystem dependency diagrams to each project's README
4. Add inter-project references where APIs or patterns are shared

Acceptance Criteria

• docs/CROSS_REFERENCE_GUIDE.md exists in common_system
• All 8 ARCHITECTURE.md files have intra-project cross-references
• All 8 README.md files have ecosystem dependency Mermaid diagrams
• Inter-project references use the standard blockquote convention
• All cross-reference links are valid

Related

• Part of docs: Ecosystem documentation improvement — enterprise-level standardization #559 (Ecosystem documentation improvement)
• Depends on docs: Create SSOT documentation registry per project #563 (SSOT registry — provides document index for referencing)