A supply nobody could read is unknown, not empty

plugins/printers/api/asset_routes.py

@@ -2109,7 +2109,9 @@ def _annotate_supply(supply, vendor_name, modelnumberid):
     Waste cartridge direction depends on vendor, so classification lives in
     the supply_parts helper. Part numbers come from the modelsupplies table.
     """
-    level = supply.get('level', 0)
+    # .get('level') with no default: a supply with no reading carries None, and
+    # a 0 default would put back the very substitution this reports around.
+    level = supply.get('level')
     name = supply.get('name', 'Unknown')
     supplytype = derivesupplytype(name)
     color = derivecolor(name, supply.get('color'))
@@ -2117,6 +2119,7 @@ def _annotate_supply(supply, vendor_name, modelnumberid):
     return {
         'name': name,
         'level': level,
+        'lastseen': supply.get('lastseen'),
         'color': color,
         'supplytype': supplytype,
         'status': cls['status'],
@@ -2160,6 +2163,7 @@ def _get_low_supplies_data():
 
     results = []
     total_checked = 0
+    unknown_printers = 0
 
     for printer, asset, comm, vendor, model in unique_printers:
         supplies = service.getsuppliesbyip_cached(comm.ipaddress)
@@ -2178,13 +2182,24 @@ def _get_low_supplies_data():
         # shown it. The whole report exists to answer "what needs replacing".
         annotated = []
         has_low = False
+        has_unknown = False
         for s in supplies:
             item = _annotate_supply(s, vendor_name, modelnumberid)
             if item['status'] == 'ok':
                 continue
+            # A supply nobody could read is not a supply that needs replacing,
+            # so it does not join the list of things to act on. It is counted
+            # instead: a printer that has gone quiet should be visible as that,
+            # not disappear from the report and not masquerade as empty.
+            if item['status'] == 'unknown':
+                has_unknown = True
+                continue
             has_low = True
             annotated.append(item)
 
+        if has_unknown:
+            unknown_printers += 1
+
         if has_low:
             # location name for the report row
             # Via the relationship, the way the printers list does it. The
@@ -2222,7 +2237,12 @@ def _get_low_supplies_data():
         'summary': {
             'total_checked': total_checked,
             'low': low_count,
-            'critical': critical_count
+            'critical': critical_count,
+            # Printers with at least one unreadable supply. They are NOT in
+            # 'printers' above - nothing about them needs ordering - but a
+            # count that only ever went up when a cartridge ran low would hide
+            # a fleet quietly going dark.
+            'unknown': unknown_printers
         }
     }