Re-architect Sentinel as a zero-dependency Python package

Port the bash prototype to a structured, testable Python codebase while
preserving the same control loop and the seven detection signatures. The bash
implementation stays in src/ as the regression oracle.

Highlights:
- enodia_sentinel/ package (stdlib only — no runtime deps):
  - detectors/ : one pure function per signature, detect(state, cfg)->Alerts
  - system.py  : SystemState — one cached /proc + ss snapshot per sweep,
                 fully injectable so detectors are unit-testable
  - daemon.py  : sweep loop, in-process cooldown dedup, threaded snapshot
                 capture, and a SUID filesystem scan moved OFF the loop
                 thread onto a slow background cadence
  - snapshot.py: forensic text + JSON sidecar with per-signature IR guidance
  - config.py  : dataclass config via TOML + env overrides
  - netutil.py : public-IP / CIDR logic via stdlib ipaddress
- tests/ : 25 stdlib-unittest cases (no root, no /proc, no ss needed)
- TOML config, launcher wrapper, Makefile (pip-free install), hardened
  systemd unit (env-resolved ExecStart), updated PKGBUILD, rewritten README

Performance: per-sweep cost ~200 ms (shared cached state); the multi-second
SUID walk no longer blocks detection. scandir-based walk replaces os.walk.

Verified on Arch: all 7 detectors fire on red-team drills (reverse_shell,
ld_preload, deleted_exe, new_listener, new_suid confirmed live end-to-end),
no false positives on a clean sweep, 25/25 tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

enodia_sentinel/cli.py

@@ -0,0 +1,80 @@
+"""Command-line entry point.
+
+  enodia-sentinel run        # daemon loop (default; used by systemd)
+  enodia-sentinel check      # run every detector once, print alerts, exit
+  enodia-sentinel baseline   # (re)build listener/SUID baselines and exit
+"""
+from __future__ import annotations
+
+import argparse
+import signal
+import sys
+
+from . import __version__, detectors
+from .config import Config
+from .daemon import Sentinel
+from .system import SystemState, scan_suid_binaries
+
+
+def _cmd_run(cfg: Config) -> int:
+    sentinel = Sentinel(cfg)
+    signal.signal(signal.SIGTERM, sentinel.stop)
+    signal.signal(signal.SIGINT, sentinel.stop)
+    sentinel.run()
+    return 0
+
+
+def _cmd_baseline(cfg: Config) -> int:
+    sentinel = Sentinel(cfg)
+    sentinel.build_baselines()
+    print(f"Baselines written under {cfg.log_dir}")
+    return 0
+
+
+def _cmd_check(cfg: Config) -> int:
+    # One-shot: arm everything immediately, force the SUID scan.
+    sentinel = Sentinel(cfg)
+    sentinel.start_time = 0.0  # past the grace window
+    sentinel.load_baselines()
+    if not sentinel.listener_baseline:
+        sentinel.build_baselines()
+    alerts = sentinel.sweep(force_suid=True)
+    if not alerts:
+        print("No alerts.")
+        return 0
+    for a in sorted(alerts, key=lambda x: -x.severity):
+        print(f"[{a.severity}] {a.signature:<14} {a.detail}")
+    return 0
+
+
+def main(argv: list[str] | None = None) -> int:
+    parser = argparse.ArgumentParser(
+        prog="enodia-sentinel",
+        description="Host intrusion-detection daemon.",
+    )
+    parser.add_argument("--version", action="version",
+                        version=f"enodia-sentinel {__version__}")
+    parser.add_argument("-c", "--config", help="path to TOML config")
+    sub = parser.add_subparsers(dest="cmd")
+    sub.add_parser("run", help="run the daemon loop (default)")
+    sub.add_parser("check", help="run detectors once and print alerts")
+    sub.add_parser("baseline", help="rebuild listener/SUID baselines")
+    sub.add_parser("list-detectors", help="list available detectors")
+
+    args = parser.parse_args(argv)
+    cfg = Config.load(args.config)
+
+    if args.cmd == "list-detectors":
+        for det in detectors.REGISTRY:
+            mark = "on " if cfg.enabled(det.name) else "off"
+            print(f"  [{mark}] {det.name}")
+        return 0
+    if args.cmd == "baseline":
+        return _cmd_baseline(cfg)
+    if args.cmd == "check":
+        return _cmd_check(cfg)
+    return _cmd_run(cfg)
+
+
+if __name__ == "__main__":
+    sys.exit(main())