# Hub Ecosystem — Async SQLAlchemy Base Decision

**Updated:** 2026-07-09  
**Workplan:** `HUB-WP-0003-T04`  
**Decision:** Defer shared async base; hosts keep separate metadata

---

## Question

Should `hub_core.models.base` expose an async-compatible declarative base for
core-hub (async SQLAlchemy) while state-hub remains on sync sessions?

---

## Finding

- `state-hub` uses sync SQLAlchemy with FastAPI dependency-injected sessions.
- `core-hub` uses `sqlalchemy.ext.asyncio` with a separate `core_hub.db.Base`.
- Router factories in hub-core accept **host-injected models** — they do not
  require a shared metadata registry across runtimes.
- Merging bases would couple migration ownership and risk breaking State Hub's
  400+ test regression without benefit for the first consolidation slice.

---

## Decision

**Defer.** Each runtime keeps its own `Base` and Alembic history. hub-core
documents metadata isolation in `docs/metadata-isolation.md`. Revisit only if
a second async host needs to mount hub-core router factories with shared tables
in the same database instance.