feat: add HIL diagnostics and meter health handling

tools/hil/discover.py

@@ -0,0 +1,21 @@
+#!/usr/bin/env python3
+from pathlib import Path
+
+from hil_common import main_guard, pio_command, run_checked
+
+
+def main() -> int:
+    print("Stable serial candidates (listing only; no device is opened):")
+    by_id = Path("/dev/serial/by-id")
+    candidates = sorted(by_id.iterdir()) if by_id.is_dir() else []
+    if not candidates:
+        print("  none")
+    for candidate in candidates:
+        print(f"  {candidate} -> {candidate.resolve()}")
+    print("\nPlatformIO discovery (metadata only):")
+    run_checked([pio_command(), "device", "list"])
+    return 0
+
+
+if __name__ == "__main__":
+    main_guard(main)