Bring script headers onto the template and close safeguard gaps

Headers claimed protections the code never had, and several destructive paths had no
guard against a collapsed config value.

Tools/smart_long_test.sh

@@ -31,6 +31,29 @@
 #   NVMe any    :  5–10 min
 #
 # ==============================================================================================
+# DESIGN PRINCIPLES
+# ==============================================================================================
+#
+# Read-Only Diagnostic
+#   A SMART self-test is executed by the drive's own firmware and writes nothing to the
+#   filesystem. The array stays fully online and in use throughout; the only cost is
+#   background I/O contention while the drive read-scans itself.
+#
+# Full Scan, Not the Short Test
+#   The extended test reads every sector. The short test samples, and a bad sector in
+#   the unsampled region is exactly the kind of latent fault that only surfaces when
+#   something tries to read it — often during a rebuild, when redundancy is already gone.
+#
+# Per-Drive Isolation
+#   A drive that fails to start a test, does not support one, or reports an error never
+#   prevents the remaining drives from being tested. Partial coverage beats none.
+#
+# Report, Do Not Act
+#   Results are reported and notified; nothing is disabled, replaced or rebuilt on the
+#   basis of a failed test. Acting on a drive is a hardware decision with cost and
+#   downtime attached, and belongs to the operator.
+#
+# ==============================================================================================
 # OPERATIONAL SAFEGUARDS
 # ==============================================================================================
 #