module-eval: pin the severity mapping's direction and the panel

The direction is the part a reviewer cannot check by looking, so it is
asserted at both ends of the table and in both tiers' groups: an inverted
mapping still maps every value to something, and a case that only asks
whether a severity parser exists passes on the exact defect. The reader
that turns a rendered operator list back into a PRIORITY -> name function
lives in lib.nix, since both tiers need it.

The panel is asserted on its query rather than its title, because a panel
that keeps the title and loses the expression renders an empty graph that
looks exactly like zero prioless lines.

nix/module-eval/grafana.nix

@@ -217,6 +217,32 @@ let
           grafanaRemoteAuthelia.services.hyperhive.swarm.statusPublish.tokenEndpoint
           == "https://auth.example.invalid/api/oidc/token";
     }
+    {
+      # The standing check on the collector's PRIORITY mapping — whether a line
+      # ever reaches the log store carrying no severity. It is shipped config
+      # rather than something an operator imports by hand, which also means it
+      # can be deleted by hand. Read out of the dashboard the provisioner
+      # actually ships (`dashboardDir` in ../host-modules/swarm-grafana.nix
+      # names this file), and asserted on the QUERY rather than the title,
+      # because a panel that keeps its title and loses its expression renders
+      # an empty graph that looks exactly like zero prioless lines.
+      name = "the logs dashboard still counts lines that arrive with no severity";
+      ok =
+        let
+          board = builtins.fromJSON (
+            builtins.readFile ../host-modules/swarm-grafana/dashboards/logstore.json
+          );
+          exprs = lib.concatMap (p: map (t: t.expr or "") (p.targets or [ ])) board.panels;
+          counts = lib.filter (e: lib.hasInfix "severity_text" e && lib.hasInfix "stats count()" e) exprs;
+        in
+        # Both arms of the split: lines that HAD a priority and arrived without
+        # a severity anyway (the regression line, which must reach zero), and
+        # lines that never had one to map — Claude Code's own OTLP telemetry,
+        # which no mapping can reach. Folded into one number the second would
+        # keep the panel off zero forever and hide the first.
+        lib.any (e: lib.hasInfix "PRIORITY:*" e) counts
+        && lib.any (e: lib.hasInfix "PRIORITY:\"\"" e) counts;
+    }
   ];
 in
 runGroup "grafana" cases