Land two design documents from planning sessions: - DESIGN-storage-primitives.md (files module, workspace, capability negotiation, vector columns) - DESIGN-extension-composability.md (slots/contributes manifest fields, lib.require relaxation, SDK helpers) Expand ROADMAP.md with detailed v0.8.x-v1.0 plan: storage primitives, reference extensions, sidecar tier, stable release gate criteria. Merge design decisions from both planning docs. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>