Publish typed values with bounded repeat timing

The shared publisher sends protocol publications through a small caller
transport. Retained values suppress equal payloads, while command
correlation and causation keep their evidence. Changed telemetry stays
non-retained at QoS 0 and supplies the latest five-minute or reconnect
snapshot at QoS 1. Repeats preserve observation times with fresh IDs.

All sends use the caller context and a five-second limit. The publisher
returns background failures to the runner without its own logging.

Issue: 40b314f