Storage & infrastructure adapters (OSS-selectable backends)

[JSONbored]

Part of #975.

Context

The hosted service uses managed cloud primitives (relational DB, key-value store, object storage, vector index, work queue, distributed lock). Self-hosters need OSS-friendly equivalents, selected by configuration, with no managed cloud dependency.

Deliverables

• Adapter interfaces for: relational store, key-value store, object store, vector index (optional / retrieval), work queue, and distributed lock.
• At least one OSS implementation per adapter, e.g.: SQLite/Postgres · Redis or filesystem · S3-compatible (MinIO) or filesystem · a local vector store or disabled · in-process or Redis queue · advisory/Redis lock.
• Config-selected backend per adapter; schema bootstrap/migrations for the relational store.
• Hosted service keeps its managed adapters unchanged.

Acceptance criteria

• docker compose up provisions working defaults using only OSS infra (no managed cloud services required).
• Switching a backend is a config change; no core logic changes.

Notes

• Vector/retrieval is optional — the stack must run fully with it disabled.

Sub-issues

• selfhost(infra): PgBouncer connection pooler #1200 — PgBouncer connection pooler
• selfhost(queue): worker concurrency control (QUEUE_CONCURRENCY) #1201 — worker concurrency control (QUEUE_CONCURRENCY)