fix(plant): alert hygiene — watchdog gate, trend smoothing, UPS [#344]

Three live-fire defects: unconditional 30-min watchdog page, tsys6 flap
false-positive, Tripp Lite runtime-low gap. TDD: 4 new regression tests.
On-box ha core check passed before commit.

Meat + verification: https://projects.knownelement.com/issues/344#note-4966

tests/test_sdlc.sh

@@ -47,5 +47,23 @@ echo "=== secrets ==="
 t "no private keys in tree" \
   "! grep -rInE 'BEGIN (RSA |OPENSSH |EC |DSA )?PRIVATE KEY' --exclude-dir=.git --exclude-dir=docs ."
 
+echo "=== alert hygiene: push only when something is wrong (2026-09-06 live-fire) ==="
+# The 30-min sweep used to page every cycle even when the fleet was all-OK
+# (48 pages/day of noise). Notify must sit behind the dead>0 + 4h-cooldown gate.
+t "plant watchdog notify gated (dead-only + cooldown input)" \
+  "grep -q 'pfv_plant_watchdog_last_notify' configuration.yaml && grep -q 'notify_gate' automations.yaml"
+
+# tsys6 DRAC ambient quantizes to whole degrees C and flaps ~2F; the raw-fed
+# trend sensor tripped TEMP RISING FAST with zero real climb (2026-09-06 05:02 CDT).
+t "trend sensors fed from smoothed sources" \
+  "grep -q 'time_simple_moving_average' packages/plant_snmp.yaml && sed -n '/^binary_sensor:/,/^utility_meter:/p' packages/plant_snmp.yaml | grep -q 'entity_id: sensor.pfv_tsys6_drac_ambient_smoothed'"
+
+# Tripp Lite had runtime sensors but no runtime-low alert — half the plant's
+# shutdown window was unmonitored.
+t "runtime-low covers Tripp Lite" \
+  "sed -n '/id: pfv_plant_ups_runtime_low/,/^  mode:/p' automations.yaml | grep -q 'sensor.pfv_tripp_lite_runtime_minutes'"
+t "runtime-low status check maps per-UPS" \
+  "sed -n '/id: pfv_plant_ups_runtime_low/,/^  mode:/p' automations.yaml | grep -q 'status_map'"
+
 echo "=== SDLC SUITE: $FAIL failures ==="
 exit "$FAIL"