fix(swarm-otel): reserve the swarm tier's component names from hive names

The collector names components `<kind>/<owner>` — a hive name for the
per-hive pipelines, the literal `swarm` for the swarm tier's own. Both
land in one attrset via `//`, so a hive named `swarm` replaced the swarm
tier's parts and lost its own: its receiver kept accepting pushes into a
pipeline that routed nowhere, and its samples lost the `hive` stamp that
makes attribution unforgeable. Zero failed assertions.

The reserved name is now bound once and interpolated at each swarm-tier
use, so the guard checks the same string the config emits rather than a
copy of it. A second swarm-tier pipeline joins the list and inherits the
check without touching the assertion.

nix/host-modules/swarm-otel.nix

@@ -43,6 +43,21 @@ let
 
   autheliaCfg = hyperhiveCfg.swarm.authelia;
 
+  # The collector names its components `<kind>/<owner>`, where `<owner>` is a
+  # hive name for the per-hive pipelines and this literal for the swarm tier's
+  # own. The two share one namespace and are merged with `//`, so a hive named
+  # this would silently REPLACE the swarm tier's parts — and lose its own
+  # pipeline in the process, while its receiver keeps accepting pushes.
+  #
+  # Bound once and interpolated at every swarm-tier use below, so the assertion
+  # that reserves it is checking the same string the config emits. A literal
+  # repeated at each site would let the guard and the config drift apart, which
+  # is the failure this guard exists to prevent.
+  swarmTierName = "swarm";
+  # Every `<owner>` this module claims for itself. One entry today; a second
+  # swarm-tier pipeline would be added here and inherit the check for free.
+  reservedOwners = [ swarmTierName ];
+
   # `attrNames` is sorted, so this is a function of the hive SET and not of
   # the order anyone wrote it in.
   #
@@ -286,6 +301,33 @@ in
           List the swarm's hives.
         '';
       }
+      {
+        # A hive whose name is one this module claims for itself collides in
+        # the collector's component namespace, and `//` resolves it silently:
+        # the swarm tier's parts win, that hive's `metrics/<name>` pipeline
+        # disappears, and its `resource/<name>` stamp goes with it — so the
+        # hive still connects and pushes into nothing, unlabelled.
+        #
+        # Checked rather than documented for the same reason the port range
+        # is: the names are all known at evaluation time, and the runtime
+        # symptom is a hive that looks healthy and reports no metrics, with
+        # nothing in any log naming the cause.
+        assertion = !lib.any (h: lib.elem h reservedOwners) (lib.attrNames hyperhiveCfg.swarm.hives);
+        message = ''
+          services.hyperhive.swarm.hives contains ${
+            lib.concatMapStringsSep ", " (h: "'${h}'") (
+              lib.filter (h: lib.elem h reservedOwners) (lib.attrNames hyperhiveCfg.swarm.hives)
+            )
+          }, which the swarm collector reserves for its own pipelines.
+
+          The collector names components `<kind>/<owner>` and uses the hive
+          name as the owner, so such a hive would silently replace the
+          swarm tier's parts and lose its own — it would keep accepting
+          pushes into a pipeline that routes nowhere.
+
+          Rename the hive. Reserved: ${lib.concatMapStringsSep ", " (n: "'${n}'") reservedOwners}.
+        '';
+      }
       {
         # A hive proves who it is with a token this provider mints, so
         # there is no version of this collector that runs without one.
@@ -512,9 +554,9 @@ in
                 # not have. Keeping it out of them makes the absence
                 # structural rather than something to remember to strip.
                 // lib.optionalAttrs (cfg.scrapeTargets != { }) {
-                  "metrics/swarm" = {
+                  "metrics/${swarmTierName}" = {
                     receivers = [ "prometheus" ];
-                    processors = [ "resource/swarm" ];
+                    processors = [ "resource/${swarmTierName}" ];
                     exporters = exporterNames;
                   };
                 };
@@ -602,8 +644,10 @@ in
                 # an invented one (a sentinel, the local hive's name) would be
                 # queried as though it meant something.
                 // lib.optionalAttrs (cfg.scrapeTargets != { }) {
-                  "resource/swarm".attributes = [
+                  "resource/${swarmTierName}".attributes = [
                     {
+                      # The metric LABEL, a different namespace from the
+                      # component name above — deliberately not interpolated.
                       key = "swarm";
                       value = swarmDisplayName;
                       action = "upsert";