Document Architectural Decisions with ADRs

[GDYendell]

Architecture Decision Records Analysis and Progress

Summary

Analysis of FastCS git history and PRs identified 10 significant architectural decisions that merit ADRs. These decisions span major refactorings from 2024-2025 that fundamentally shaped the FastCS architecture.

Current Progress

Completed ADRs (3/10):

• ✅ ADR-0003: Backend-to-Transport Refactoring (PR Refactor developer API with transports and app launcher #67, Nov 2024)
• ✅ ADR-0004: Handler to AttributeIO/AttributeIORef Pattern (PR Replace Handler with AttributeIO / AttributeIORef #218, Oct 2025)
• ✅ ADR-0005: ControllerAPI Abstraction Layer (PR Create ControllerAPI class to decouple transport from Controller #87, Mar 2025)
• ✅ ADR-0003: Backend-to-Transport Refactoring (Nov 2024, PR Refactor developer API with transports and app launcher #67)
• ✅ ADR-0005: ControllerAPI Abstraction Layer (Mar 2025, PR Create ControllerAPI class to decouple transport from Controller #87)
• ✅ADR-0006: Controller Initialization on Main Event Loop (Aug 2024, PR Enable controller initialisation on main event loop #49)
• ✅ADR-0007: SubController Removal (Oct 2025, PR Remove SubController #222)
• ✅ADR-0008: SubControllerVector Implementation (Nov 2025)
• ✅ ADR-0004: Handler to AttributeIO/AttributeIORef Pattern (Oct 2025, PR Replace Handler with AttributeIO / AttributeIORef #218)
• ✅ADR-0009: Transport Consolidation (Sep 2025)
• ✅ADR-0010: Background Thread Removal (Jan 2025)
• ✅ADR-0011: Transport Dependencies as Optional Extras (Sep 2025)
• ❌ ADR-0012: Logging Framework with Tracer Support (Oct 2025)

Key Architectural Themes

The completed ADRs reveal consistent architectural principles:

1. Composition over Inheritance: Backend → Transport plugins, removal of SubController
2. Separation of Concerns: ControllerAPI, AttributeIO/AttributeIORef split
3. Encapsulation: Static views, read-only APIs, breaking circular dependencies
4. Memory Efficiency: Shared instances (AttributeIO) with lightweight refs
5. Type Safety: Generic types, validation at initialization
6. Plugin Architecture: Transports, AttributeIOs as composable components

Notes

• Existing ADR infrastructure at docs/explanations/decisions/
• Template: COPYME
• Format follows Michael Nygard's ADR pattern
• All ADRs reference specific PRs and commits with dates and impact metrics