docs(observability): component metrics are not all disabled by default Since v2.0, MetricSpec supports .auto_register(); those metrics export with no `metrics` block and are turned off with `enabled: false`. The blanket "disabled by default" claim on the Component Metrics page and the datasets reference is wrong for them.

docs(observability): the three cache metric families are registered alike but only the SQL cache records them generate_cache_metrics! registers the same instrument set for results, search_results and embeddings, and CacheMetrics::init() publishes every counter at zero, so a scrape carries all three prefixes in full. The metrics table documented the full set only for results_cache_*, leaving the other two families four series short, and it described the two stale-while-revalidate counters it did list for them as if they reported real activity. Every stale-serving and invalidation counter is incremented only through cache::metrics::sql_results::* and impl CacheMetrics for CachedQueryResult; the embeddings and search_results implementations are never reached from a production path, so those series stay at the zero they are published at. Reproduced against spiced v2.3.0: a /metrics scrape emits all 14 instruments for each of the three families, with the full reason/mode/outcome label cross-product at zero. Scoped per release: stale_rejections first shipped in v2.1.5, the other three in v2.3.0, so version-2.0.x and older are unchanged and the 2.1.x/2.2.x notes name only the counters those releases register.