fn reset_temporary_condition_observations_after_restart(state: &AppState) -> Result<usize, AppError> {
    let mut changed = 0usize;
    for mut zone in state.db.list_zones()? {
        let Some(session) = zone.temporary_quick_thermostat.as_mut() else { continue; };
        if session.condition_started_at.is_none() && session.condition_last_observed_at.is_none() { continue; }
        session.condition_started_at = None;
        session.condition_last_observed_at = None;
        zone.updated_at = Utc::now();
        state.db.save_zone(&zone)?;
        changed += 1;
    }
    Ok(changed)
}

pub fn start(state: AppState) {
    // A continuous temperature hold cannot span controller downtime. Preserve the session
    // itself, but require fresh observations after every process restart (H11).
    if let Err(err) = reset_temporary_condition_observations_after_restart(&state) {
        tracing::warn!(error=?err, "cannot reset temporary thermostat observation continuity after restart");
    }
    let poll_state = state.clone();
    tokio::spawn(async move {
        sleep(Duration::from_millis(500)).await;
        loop {
            match poll_all(&poll_state).await {
                Ok(()) => {
                    if !poll_state.initial_device_sync_complete.swap(true, Ordering::AcqRel) {
                        tracing::info!("initial device state synchronized; thermostat control enabled");
                    }
                }
                Err(err) => tracing::error!(error=?err, "device poll cycle failed"),
            }
            let seconds = poll_state.settings.read().await.poll_interval_seconds.max(2);
            sleep(Duration::from_secs(seconds)).await;
        }
    });

    let control_state = state.clone();
    tokio::spawn(async move {
        sleep(Duration::from_secs(2)).await;
        loop {
            // A restart must never make decisions from the persisted, potentially stale
            // device snapshot. Wait for one full live poll before thermostat/schedule/automation
            // ownership can emit commands. Manual API/remote control remains available.
            if !control_state.initial_device_sync_complete.load(Ordering::Acquire) {
                sleep(Duration::from_millis(250)).await;
                continue;
            }
            if let Err(err) = control_zones(&control_state).await {
                tracing::error!(error=?err, "zone cycle failed");
            }
            if let Err(err) = run_automations(&control_state).await {
                tracing::error!(error=?err, "automation cycle failed");
            }
            let seconds = control_state.settings.read().await.zone_interval_seconds.max(2);
            let normal_delay = Duration::from_secs(seconds);
            let resume_delay = match next_zone_control_deadline_delay(&control_state) {
                Ok(value) => value,
                Err(err) => {
                    tracing::warn!(error=?err, "cannot calculate thermostat control deadline");
                    None
                }
            };
            let sleep_for = resume_delay.map(|delay| delay.min(normal_delay)).unwrap_or(normal_delay);
            tokio::select! {
                _ = sleep(sleep_for) => {},
                _ = control_state.zone_control_wakeup.notified() => {},
            }
        }
    });

    let maintenance_state = state;
    tokio::spawn(async move {
        sleep(Duration::from_secs(60)).await;
        loop {
            let settings = maintenance_state.settings.read().await.clone();
            // When InfluxDB is enabled, compact all locally retained legacy history before
            // transferring old buckets. Without Influx, compact only the configured retention window.
            let compaction_days = if settings.influxdb.enabled { 3650 } else { settings.history_retention_days.max(1) } as i64;
            if settings.history_compaction_enabled {
                match maintenance_state.db.compact_history(compaction_days) {
                    Ok(count) if count > 0 => tracing::info!(count, "history samples compacted"),
                    Ok(_) => {}
                    Err(err) => tracing::warn!(error=?err, "cannot compact history"),
                }
            }
            if settings.influxdb.enabled {
                match archive_old_history(&maintenance_state, settings.influxdb.history_threshold_days.max(1)).await {
                    Ok(count) if count > 0 => tracing::info!(count, "old local readings archived to InfluxDB and removed from SQLite"),
                    Ok(_) => {}
                    Err(err) => tracing::warn!(error=?err, "cannot archive old history to InfluxDB; SQLite copies were kept"),
                }
            } else {
                let retention_days = settings.history_retention_days.max(1) as i64;
                match maintenance_state.db.prune_readings(retention_days) {
                    Ok(count) if count > 0 => tracing::info!(count, retention_days, "old local readings pruned"),
                    Ok(_) => {}
                    Err(err) => tracing::warn!(error=?err, "cannot prune readings"),
                }
            }
            let event_retention_days = settings.event_log_retention_days.max(1) as i64;
            match maintenance_state.db.prune_events(event_retention_days) {
                Ok(count) if count > 0 => tracing::info!(count, event_retention_days, "old event log rows pruned"),
                Ok(_) => {}
                Err(err) => tracing::warn!(error=?err, "cannot prune event log"),
            }
            sleep(Duration::from_secs(6 * 60 * 60)).await;
        }
    });
}

async fn archive_old_history(state: &AppState, threshold_days: u32) -> Result<u64> {
    let cutoff = Utc::now() - chrono::Duration::days(threshold_days.max(1) as i64);
    let settings = state.settings.read().await.influxdb.clone();
    let mut moved = 0_u64;
    // Bound one maintenance pass so a very large legacy database never monopolizes the runtime.
    // Successful batches are deleted from SQLite, so the next pass naturally continues forward.
    for _ in 0..50 {
        let (devices, zones, ha) = state.db.history_before(cutoff, 1_000)?;
        if devices.is_empty() && zones.is_empty() && ha.is_empty() { break; }
        influxdb::write_batch(&state.http, &settings, &devices, &zones, &ha).await?;
        let deleted = state.db.delete_history_batch(&devices, &zones, &ha)?;
        moved += deleted;
        if deleted == 0 { break; }
    }
    Ok(moved)
}