1.0.0-alpha9: backend cache instrumentation The first content release built on the alpha7 collector contract. Surfaces backend cache health (Memcache, Redis, APCu, database, file backends) per request and correlates it with CWV metrics on a new admin panel. - CacheInstrumentor request-scoped service holds per-request counters with per-bin breakdown for hottest-miss tracking. - InstrumentedCacheBackend wraps any CacheBackendInterface and records hit/miss/timing on get and getMultiple. - InstrumentedCacheFactory decorates cache_factory so every bin (including those added by contrib) gets the wrapper. - BackendCacheCollector implements Shape 2 (async-decoration) and Shape 4 (panel-contribution). Renders a Backend cache correlation panel showing CWV metrics bucketed by miss count. Opt-in via backend_cache_instrumentation_enabled (default FALSE). Default installs pay zero overhead; enabled installs pay roughly 5 microseconds per cache get. Validates the one-collector-per-minor-release cadence the alpha7 contract was designed around. Subsequent 1.x minor releases add render-tree (1.1), database (1.2), runtime health (1.3), external services (1.4) on the same contract. See ROADMAP.md and docs/collector-contract.md for the trajectory.