Implements P6.7 - Resource-pressure metrics + alerts. Adds a new
resource_pressure module that periodically collects system metrics:
- miroir_memory_pressure: reads cgroup v2 memory.current/memory.max,
returns 0=ok, 1=warn (>75%), 2=critical (>90%)
- miroir_cpu_throttled_seconds_total: reads cgroup cpu.stat
nr_throttled/throttled_time, reports cumulative throttled seconds
The collection runs on a 15-second interval in a background task and
updates metrics via the Metrics accessor methods.
PrometheusRule alerts were already present in
charts/miroir/templates/miroir-prometheusrule.yaml:
- MiroirMemoryPressure: fires when memory_pressure >= 2 for 5m
- MiroirRequestQueueBacklog: fires when queue_depth > 500 for 2m
- MiroirBackgroundJobBacklog: fires when background_queue_depth > 100 for 10m
- MiroirPeerDiscoveryGap: fires when peer_pod_count < deployment replicas
- MiroirNoLeader: fires when sum(miroir_leader) == 0 for 1m
Closes: miroir-m9q.7
6247cc6cd3