feat: crash recovery, service_failed monitoring, broker health fields, command expiry sweep

- Add GET /api/clients/crashed endpoint (process_status=crashed or stale heartbeat)
- Add restart_app command action with same lifecycle + lockout as reboot_host
- Scheduler: crash auto-recovery loop (CRASH_RECOVERY_ENABLED flag, lockout, MQTT publish)
- Scheduler: unconditional command expiry sweep per poll cycle (sweep_expired_commands)
- Listener: subscribe to infoscreen/+/service_failed; persist service_failed_at + unit
- Listener: extract broker_connection block from health payload; persist reconnect_count + last_disconnect_at
- DB migration b1c2d3e4f5a6: service_failed_at, service_failed_unit, mqtt_reconnect_count, mqtt_last_disconnect_at on clients
- Add GET /api/clients/service_failed and POST /api/clients/<uuid>/clear_service_failed
- Monitoring overview API: include mqtt_reconnect_count + mqtt_last_disconnect_at per client
- Frontend: orange service-failed alert panel (hidden when empty, auto-refresh, quittieren action)
- Frontend: MQTT reconnect count + last disconnect in client detail panel
- MQTT auth hardening: listener/scheduler/server use env credentials; broker enforces allow_anonymous false
- Client command lifecycle foundation: ClientCommand model, reboot_host/shutdown_host, full ACK lifecycle
- Docs: TECH-CHANGELOG, DEV-CHANGELOG, MQTT_EVENT_PAYLOAD_GUIDE, copilot-instructions updated
- Add implementation-plans/, RESTART_VALIDATION_CHECKLIST.md, TODO.md

implementation-plans/reboot-kickoff-summary.md

@@ -0,0 +1,54 @@
+## Reboot Reliability Kickoff Summary
+
+### Objective
+Ship a reliable, observable restart and shutdown workflow for Raspberry Pi 5 clients, with safe escalation and clear operator outcomes.
+
+### What Is Included
+1. Asynchronous command lifecycle with idempotent command_id handling.
+2. Monitoring-first state visibility from queued to terminal outcomes.
+3. Client acknowledgements for accepted, execution_started, completed, and failed.
+4. Pi 5 USB-SATA SSD timeout baseline and tuning rules.
+5. Capability-tier recovery with optional managed PoE escalation.
+
+### What Is Not Included
+1. Full maintenance module in client-management.
+2. Required managed power-switch integration.
+3. Production Wake-on-LAN rollout.
+
+### Team Split
+1. Platform team: API command lifecycle, safety controls, listener ack ingestion.
+2. Web team: lifecycle-aware UX and command status display.
+3. Client team: strict validation, dedupe, ack sequence, secure execution helper, reboot continuity.
+
+### Ownership Matrix
+| Team | Primary Plan File | Main Deliverables |
+| --- | --- | --- |
+| Platform team | implementation-plans/reboot-implementation-handoff-share.md | Command lifecycle backend, policy enforcement, listener ack mapping, safety lockout and escalation |
+| Web team | implementation-plans/reboot-implementation-handoff-share.md | Lifecycle UI states, bulk safety UX, capability visibility, command status polling |
+| Client team | implementation-plans/reboot-implementation-handoff-client-team.md | Command validation, dedupe persistence, ack sequence, secure execution helper, reboot continuity |
+| Project coordination | implementation-plans/reboot-kickoff-summary.md | Phase sequencing, canary gates, rollback thresholds, cross-team sign-off tracking |
+
+### Baseline Operational Defaults
+1. Safety lockout: 3 reboot commands per client in rolling 15 minutes.
+2. Escalation cooldown: 60 seconds.
+3. Reconnect target on Pi 5 SSD: 90 seconds baseline, 150 seconds cold-boot ceiling.
+4. Rollback canary trigger: failed plus timed_out above 5 percent.
+
+### Frozen Contract Snapshot
+1. Canonical command topic: infoscreen/{client_uuid}/commands.
+2. Canonical ack topic: infoscreen/{client_uuid}/commands/ack.
+3. Transitional compatibility topics during migration:
+- infoscreen/{client_uuid}/command
+- infoscreen/{client_uuid}/command/ack
+4. Command schema version: 1.0.
+5. Allowed command actions: reboot_host, shutdown_host.
+6. Allowed ack status values: accepted, execution_started, completed, failed.
+7. Validation snippets:
+- implementation-plans/reboot-command-payload-schemas.md
+- implementation-plans/reboot-command-payload-schemas.json
+
+### Immediate Next Steps
+1. Continue implementation in parallel by team against frozen contract.
+2. Client team validates dedupe and expiry handling on canonical topics.
+3. Platform team verifies ack-state transitions for accepted, execution_started, completed, failed.
+4. Execute one-group canary and validate timing plus failure drills.