observabilitylisted

Write and review Swift code that makes an app observable: emit the right signal (log, signpost, metric, diagnostic) at the right level, keep user data out of the logs, and get the data back from production in a form you can actually read - symbolicated, aggregated, and attributed to the right release. Review process: 1. Establish the signal model (three pillars, unified logging architecture, levels and persistence, dev vs production visibility) using `references/fundamentals.md`. 1. Confirm each emission uses the right signal via the decision tree below; reroute if it does not (print where a Logger belongs, a log where a signpost belongs, a hand-rolled timer where MetricKit already measures). 1. Validate `Logger` usage (subsystem/category structure, level choice, privacy annotations, interpolation performance, wrapper design) using `references/logger-api.md`. 1. Validate log retrieval workflows (Console.app, `log` CLI predicates, logging profiles, sysdiagnose) using `references/log-cli-and-console.md`. 1. Validate in-app log access and support-log export using `references/oslogstore.md`. 1. Validate signpost instrumentation (`OSSignposter`, IDs, intervals, points of interest, Instruments wiring) using `references/signposts.md`. 1. Validate cross-flow correlation (activities, correlation IDs) using `references/activity-tracing.md`. 1. Validate MetricKit adoption (subscription timing, payload handling, histograms, diagnostics, the iOS 27 `MetricManager` API) using `references