[WS-WORKSPACE] Workspace Runtime — artifact DSL projection, validation orchestration, publish, SSEHub fan-out, workspace-scoped notifications

[Aparnap2]

Priority: P1 | MVP Scope: Workspace Runtime with SSEHub fan-out

Context

The Workspace Runtime manages artifact creation, validation, publication, and real-time notification via SSEHub. It is the user-facing runtime that projects domain models into workspace artifacts.

Scope

• Artifact DSL projection (domain models → workspace artifacts)
• Validation orchestration (schema, business rules, cross-cutting concerns)
• Publish workflow (artifact lifecycle management)
• SSEHub fan-out for real-time workspace-scoped notifications
• Workspace-scoped notification delivery

Acceptance

• Artifacts are projected from domain models via DSL
• Validation orchestration catches schema and business rule violations
• Publish workflow manages artifact lifecycle (draft → review → published)
• SSEHub fans out notifications to workspace subscribers in real-time
• Notifications are workspace-scoped (tenant-aware)

Verification

• uv run pytest tests/v6/ — workspace runtime tests pass
• SSEHub fan-out delivers notifications to workspace subscribers
• Artifact validation catches known violation patterns