Expand REQ-HOST-3 with per-component appsettings.json sections, each mapped
to a dedicated options class owned by the component. Convention: components
define their own options class, Host binds via Options pattern, components
read via IOptions<T>. Options classes live in component projects, not Commons.
Cluster Infrastructure: add min-nr-of-members=1 requirement for single-node
operation after failover. Add graceful shutdown / CoordinatedShutdown section
for fast singleton handover during planned maintenance.
Site Runtime: add explicit supervision strategies per actor type (Resume for
coordinators, Stop for short-lived execution actors). Stagger Instance Actor
startup to prevent reconnection storms. Add Tell-vs-Ask usage guidance per
Akka.NET best practices (Tell for hot path, Ask for system boundaries only).
Data Connection Layer: add Connection Actor Model section documenting the
Become/Stash pattern for connection lifecycle state machine.
Health Monitoring: add dead letter count as a monitored metric.
Host: add REQ-HOST-8a for dead letter monitoring (subscribe to EventStream,
log at Warning level, report as health metric).
