Wiring: ActiveRecord backend + dispatch

[bolshakov]

Background

A backend is a factory that produces the focused stores (state, metrics, recovery lock, recovery metrics) for one data store, which Stoplight assembles into the object a light uses; the windowed-vs-unbounded metrics choice is made during that assembly from the light's window setting. The Redis backend additionally wraps each store in a fail-safe decorator that falls back to an in-memory store and trips an internal breaker when the database is unreachable, so a storage outage degrades gracefully instead of raising. This ticket builds the equivalent ActiveRecord backend and wires it into the selection points normalized in #813.

The Redis backend is the reference to mirror one to one. The epic describes the connection model, the per-instance connection binding, and the fail-safe behavior.

Goal

Assemble the five stores into a working backend and wire it in, so configuring DataStore::ActiveRecord runs lights end to end with fail-safe degradation matching Redis.

What to do

• Implement Wiring::ActiveRecord::Backend building the five stores, each wrapped in the existing fail-safe decorator with a memory fallback and a failover breaker, and bound to the config's connection class per instance.
• Add the ActiveRecord branches to the normalized backend-selection and registry-creation points (from Normalize data-store backend dispatch #813).
• Ensure windowed and unbounded configurations both wire the correct metrics store.

Acceptance criteria

• A DataStore::ActiveRecord-configured light (built with a connection class) passes the color property/integration spec on SQLite and Postgres.
• A spec shows two data stores built with different connection classes each write to their own connection, with no collision.
• A spec shows that with the database connection killed mid-run, the light degrades through fail-safe: it does not raise, the error notifier fires, and the breaker serves from memory — matching the Redis fail-safe spec — and a saturated pool travels the same path.
• A spec shows that, with a dedicated (isolated) connection class, a failure recorded inside a rolled-back app-level transaction is still counted.
• A spec shows both windowed and unbounded configurations wire correctly and record through the right metrics store.
• bundle exec steep check and bundle exec standardrb pass.

References

• Backend contract: wiring/data_store_backend.rb
• Reference to mirror: wiring/redis/backend.rb, wiring/memory/backend.rb
• Storage assembly: wiring/storage_set_builder.rb
• Selection points to wire: wiring/light_factory.rb, wiring/global_state.rb
• Fail-safe wrappers: infrastructure/fail_safe/