feat: make the cache pool backend configurable with CACHE_ADAPTER

[turegjorup]

Summary

The application cache pools (feeds.cache, feed.without.expire.cache, calendar.api.cache, auth.screen.cache, screen.status.cache, interactive_slide.cache) were hard-wired to cache.adapter.redis, forcing every installation to run Redis. This PR makes the backend selectable at runtime with a new CACHE_ADAPTER env var: redis (default, behavior unchanged), memcached, dbal, filesystem or apcu.

Why a factory instead of %env()% in cache.yaml

Symfony resolves a pool's adapter: option to a concrete service id at container compile time (CachePoolPass makes each pool a ChildDefinition of the adapter service), so the choice cannot be expressed with a runtime env placeholder. The pools now extend an abstract app.cache.adapter service backed by App\Cache\CacheAdapterFactory, which builds the selected adapter at runtime; CachePoolPass injects each pool's computed namespace and configured default_lifetime as the factory arguments. The custom parent mirrors the built-in cache.adapter.* wiring: lazy Redis/Memcached connections, pools attached to cache.default_clearer (wiped by cache:clear on deploy, as before) and reset: reset for long-running workers.

Backend notes

• redis (default) — unchanged; still uses REDIS_CACHE_DSN.
• memcached — shared like redis (MEMCACHED_CACHE_DSN, requires ext-memcached). Documented caveat: Memcached LRU-evicts under memory pressure, so long-lived entries (screen status, activation codes) can disappear early.
• dbal — shared cache in the application database; the cache_items table is auto-created on first write. A schema_filter hides it from doctrine:migrations:diff / schema:validate. TTL is honored on read (expired rows are deleted when encountered).
• filesystem — per-node under var/cache/<env>/pools; for single-server setups without Redis.
• apcu — per-PHP-process-pool; not shared with console crons or across nodes.

All backends honor default_lifetime and per-item TTLs (PSR-6 contract); an unknown CACHE_ADAPTER value fails fast with a message listing the valid options. array was deliberately not offered: a per-request cache breaks the screen activation flow (auth.screen.cache).

Files Changed

• src/Cache/CacheAdapterFactory.php (new) — runtime adapter factory
• config/services.yaml — factory wiring + abstract app.cache.adapter parent
• config/packages/cache.yaml — pools now extend app.cache.adapter
• config/packages/doctrine.yaml — schema_filter for cache_items
• .env — CACHE_ADAPTER + MEMCACHED_CACHE_DSN docs and defaults
• .env.test + deleted config/packages/test/cache.yaml — tests run with CACHE_ADAPTER=filesystem instead of per-pool overrides, removing the implicit Redis dependency from the three pools the old override file didn't cover
• tests/Cache/CacheAdapterFactoryTest.php (new) — unit tests incl. dbal roundtrip with table auto-creation (sqlite) and lazy redis/memcached creation
• CHANGELOG.md — Unreleased entry

Test Plan

• task test:api -- --filter CacheAdapterFactoryTest — 7 tests (APCu skipped where ext missing)
• task test:api -- --filter AuthenticationScreenTest — screen auth flow through factory-built filesystem pools: green
• Runtime switching on one compiled container: docker compose exec -e CACHE_ADAPTER=<redis|dbal|filesystem> phpfpm bin/console cache:pool:clear feeds.cache all succeed; -e CACHE_ADAPTER=bogus fails with Unknown CACHE_ADAPTER "bogus". Expected one of: "redis", "memcached", "dbal", "filesystem", "apcu".
• task code-analysis, task rector:check, task coding-standards:check, scripts/check-env-coverage.sh — green
• No API surface change (no src/Dto/src/State touched), so no spec regeneration needed

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