docs(ecosystem): complete hub stack consolidation (CUST-WP-0057)

Publish ecosystem architecture, event mapping, capability bridge, and async-base
decision docs; add cross-repo regression script; update extraction boundary and
bootstrap status; archive WP-0058 touch-ups.

docs/hub-ecosystem-async-base-decision.md

@@ -0,0 +1,32 @@
+# 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.