feat: SAC 0.7.4 sidebar system stats block with UI toggle

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/services/system_stats.py

@@ -0,0 +1,115 @@
+"""Host and DB metrics for SAC sidebar (best-effort, no heavy queries)."""
+
+from __future__ import annotations
+
+import os
+import shutil
+import time
+from datetime import datetime, timedelta, timezone
+from pathlib import Path
+
+from sqlalchemy import func, select, text
+from sqlalchemy.orm import Session
+
+from app.models import Event, Problem
+
+
+def _disk_path() -> str:
+    explicit = os.environ.get("SAC_STATS_DISK_PATH", "").strip()
+    if explicit:
+        return explicit
+    return str(Path("/").resolve())
+
+
+def _read_cpu_percent() -> float | None:
+    try:
+        import psutil  # type: ignore[import-untyped]
+
+        return round(float(psutil.cpu_percent(interval=None)), 1)
+    except Exception:
+        return None
+
+
+def _read_memory() -> dict[str, float | int] | None:
+    try:
+        import psutil  # type: ignore[import-untyped]
+
+        vm = psutil.virtual_memory()
+        return {
+            "used_mb": int(vm.used / (1024 * 1024)),
+            "total_mb": int(vm.total / (1024 * 1024)),
+            "percent": round(float(vm.percent), 1),
+        }
+    except Exception:
+        return None
+
+
+def _read_disk(path: str) -> dict[str, float | int | str] | None:
+    try:
+        usage = shutil.disk_usage(path)
+        total = int(usage.total)
+        used = int(usage.used)
+        if total <= 0:
+            return None
+        return {
+            "path": path,
+            "used_gb": round(used / (1024**3), 1),
+            "total_gb": round(total / (1024**3), 1),
+            "percent": round(100.0 * used / total, 1),
+        }
+    except Exception:
+        return None
+
+
+def collect_system_stats(db: Session) -> dict:
+    collected_at = datetime.now(timezone.utc).isoformat()
+    disk_path = _disk_path()
+
+    db_status = "ok"
+    db_latency_ms: float | None = None
+    db_connections: int | None = None
+    t0 = time.perf_counter()
+    try:
+        db.execute(text("SELECT 1"))
+        db_latency_ms = round((time.perf_counter() - t0) * 1000, 1)
+        try:
+            db_connections = int(
+                db.scalar(
+                    text(
+                        "SELECT count(*) FROM pg_stat_activity "
+                        "WHERE datname = current_database() AND pid <> pg_backend_pid()"
+                    )
+                )
+                or 0
+            )
+        except Exception:
+            db_connections = None
+    except Exception:
+        db_status = "error"
+
+    since = datetime.now(timezone.utc) - timedelta(hours=1)
+    events_last_hour = 0
+    problems_open = 0
+    if db_status == "ok":
+        events_last_hour = int(
+            db.scalar(select(func.count()).select_from(Event).where(Event.received_at >= since)) or 0
+        )
+        problems_open = int(
+            db.scalar(select(func.count()).select_from(Problem).where(Problem.status == "open")) or 0
+        )
+
+    return {
+        "collected_at": collected_at,
+        "cpu_percent": _read_cpu_percent(),
+        "memory": _read_memory(),
+        "disk": _read_disk(disk_path),
+        "database": {
+            "status": db_status,
+            "latency_ms": db_latency_ms,
+            "active_connections": db_connections,
+        },
+        "app": {
+            "events_last_hour": events_last_hour,
+            "problems_open": problems_open,
+        },
+    }