feat(infra): add fleet health probe + crontab (#559, FLEET-006)

- scripts/fleet_health_probe.sh: SSH, disk, memory, process checks
- infrastructure/cron/fleet-health.crontab: 5-minute cron schedule
- Thresholds: disk<90%, mem<90%, critical processes monitored

scripts/fleet_health_probe.sh

@@ -0,0 +1,83 @@
+#!/usr/bin/env bash
+# fleet_health_probe.sh — Automated health checks for Timmy Foundation fleet
+# Refs: timmy-home #559, FLEET-006
+# Runs every 5 min via cron. Checks: SSH reachability, disk < 90%, memory < 90%, critical processes.
+set -euo pipefail
+
+LOG_DIR="/var/log/timmy"
+ALERT_LOG="${LOG_DIR}/fleet_health.log"
+HEARTBEAT_DIR="/var/lib/timmy/heartbeats"
+mkdir -p "$LOG_DIR" "$HEARTBEAT_DIR"
+
+# Configurable thresholds
+DISK_THRESHOLD=90
+MEM_THRESHOLD=90
+
+# Hosts to probe (space-separated SSH hosts)
+FLEET_HOSTS="${FLEET_HOSTS:-143.198.27.163 104.131.15.18}"
+
+# Critical processes that must be running locally
+CRITICAL_PROCESSES="${CRITICAL_PROCESSES:-act_runner}"
+
+log() {
+    echo "[$(date -Iseconds)] $1" | tee -a "$ALERT_LOG"
+}
+
+alert() {
+    log "ALERT: $1"
+}
+
+ok() {
+    log "OK: $1"
+}
+
+status=0
+
+# --- SSH Reachability ---
+for host in $FLEET_HOSTS; do
+    if nc -z -w 5 "$host" 22 >/dev/null 2>&1 || timeout 5 bash -c "</dev/tcp/${host}/22" 2>/dev/null; then
+        ok "SSH reachable: $host"
+    else
+        alert "SSH unreachable: $host"
+        status=1
+    fi
+done
+
+# --- Disk Usage ---
+disk_usage=$(df / | awk 'NR==2 {print $5}' | tr -d '%')
+if [[ "$disk_usage" -lt "$DISK_THRESHOLD" ]]; then
+    ok "Disk usage: ${disk_usage}%"
+else
+    alert "Disk usage critical: ${disk_usage}%"
+    status=1
+fi
+
+# --- Memory Usage ---
+mem_usage=$(free | awk '/Mem:/ {printf("%.0f", $3/$2 * 100.0)}')
+if [[ "$mem_usage" -lt "$MEM_THRESHOLD" ]]; then
+    ok "Memory usage: ${mem_usage}%"
+else
+    alert "Memory usage critical: ${mem_usage}%"
+    status=1
+fi
+
+# --- Critical Processes ---
+for proc in $CRITICAL_PROCESSES; do
+    if pgrep -f "$proc" >/dev/null 2>&1; then
+        ok "Process alive: $proc"
+    else
+        alert "Process missing: $proc"
+        status=1
+    fi
+done
+
+# --- Heartbeat Touch ---
+touch "${HEARTBEAT_DIR}/fleet_health.last"
+
+if [[ "$status" -eq 0 ]]; then
+    log "Fleet health probe passed."
+else
+    log "Fleet health probe FAILED."
+fi
+
+exit "$status"