Enhance documentation structure and clarify project domain; add new directories for architecture, contracts, and extensions; update roadmap and open questions with resolved decisions and clarification plans.

docs/ROADMAP.md

@@ -13,27 +13,33 @@ Goals:
 - Stabilize development environment and reproducible tooling.
 - Define domain language and baseline architecture docs.
 - Establish quality process (TDD/BDD + GitHub Flow).
+- Clarify the core-plus-extension project contract before implementation.
 
 Exit criteria:
 
 - Agreed glossary and architecture baseline.
 - Documented contribution and branch workflow.
 - CI skeleton in place for formatting, linting, and tests.
+- ADR for project revision lifecycle (draft/publish/supersede).
+- ADR for composable extension mechanism (shape, namespacing, discovery).
+- Initial repository layout includes dedicated locations for API contracts and extension schemas.
 
 ## Phase 1: Single-Node MVP (No Federation Yet)
 
 Goals:
 
 - User identity and basic authentication model.
-- Core DIY project entities (project, materials, steps, media, tags).
+- Core DIY project entities (project, materials, tools, steps, media, canonical links, tags).
 - Basic publishing lifecycle (draft, published, updated).
 - Search and browse within one instance.
+- Support extension payloads in project data model without requiring domain-specific first-party implementations.
 
 Exit criteria:
 
 - A user can publish and update a complete project end-to-end.
 - Project pages are discoverable and readable on one node.
 - Test coverage exists for core behavior paths.
+- At least one extension payload can be stored, validated, and rendered as non-breaking optional data.
 
 ## Phase 2: ActivityPub Foundation