swarm-bao: give the store's collector an explicit self-telemetry port

8890, so it stops claiming the hive collector's 8888 in the shared netns.
Extends the module-eval port case to all three tiers.

nix/host-modules/swarm-bao.nix

@@ -1295,6 +1295,29 @@ in
         Two spellings present as a healthy-looking 401.
       '';
     };
+
+    otel.telemetryPort = lib.mkOption {
+      type = lib.types.port;
+      default = 8890;
+      description = ''
+        Port the collector inside the store's container serves its **own**
+        metrics on — queue depth, refused and dropped samples, exporter
+        failures. How you find out that telemetry is being lost, so it is
+        worth keeping rather than switching off.
+
+        ⚠️ **Deliberately neither 8888 nor 8889.** 8888 is the collector
+        binary's built-in default, which the hive tier
+        ({option}`services.hyperhive.otel.telemetryPort`) already binds, and
+        8889 is the swarm tier's
+        ({option}`services.hyperhive.swarm.otel.telemetryPort`). This
+        container runs with `privateNetwork = false`, so all three share the
+        host's network namespace whenever they are co-located — and unlike
+        the OTLP ports this one appears nowhere in either config when it is
+        left undeclared, so nothing that compares configured ports can see
+        the clash. The second collector to start simply dies with
+        `bind: address already in use`.
+      '';
+    };
   };
 
   # ⚠️ Gated on `deploy.bao.enable`, and that is load-bearing rather than
@@ -2373,6 +2396,25 @@ in
                   exporters = [ "otlphttp" ];
                 };
 
+                # Moves this collector's self-metrics off the built-in
+                # default of `localhost:8888`, which the hive tier holds —
+                # this container shares the host's netns, so leaving the
+                # default in place is the hive collector failing to bind.
+                #
+                # ⚠️ `metrics.address` is the spelling that looks right and
+                # is REJECTED by this collector version:
+                # `'migration.MetricsConfigV030' has invalid keys:
+                # address`. `readers` is the schema it accepts, and the
+                # difference is a startup failure rather than a warning.
+                service.telemetry.metrics.readers = [
+                  {
+                    pull.exporter.prometheus = {
+                      host = "127.0.0.1";
+                      port = cfg.otel.telemetryPort;
+                    };
+                  }
+                ];
+
                 # An extension configured but not listed here is INERT — the
                 # receiver's `storage: file_storage` above would name a
                 # component the collector never starts, and the exporter's

nix/module-eval/hive-otel.nix

@@ -54,6 +54,23 @@ let
     # one carries none.
     swarm.otel.scrapeTargets.plain = "127.0.0.1:9999";
   };
+
+  # Also duplicated from bao-otel-collector.nix, where it is the fixture for
+  # the store standing beside a HIVE collector. That co-location is exactly
+  # the topology the port case below needs: two collectors, one netns, and
+  # nothing but their self-telemetry ports keeping them apart.
+  # `clientSecretFile` is what ../host-modules/otel.nix's identity assertion
+  # demands of any hive with the tier on.
+  baoWithHiveOtel = hive {
+    deploy.bao.enable = true;
+    otel.enable = true;
+    otel.clientSecretFile = "/var/lib/hive-otel-oidc/client.secret";
+  };
+
+  # The collector INSIDE the store's container — neither the host's nor the
+  # swarm tier's.
+  baoForwarderSettings =
+    machine: machine.containers.swarm-bao.config.services.opentelemetry-collector.settings;
   cases = [
     {
       # The tier in the middle. Its OTLP receiver takes both signals on one
@@ -133,17 +150,28 @@ let
         && u.startLimitIntervalSec or 0 > u.serviceConfig.RestartSec * u.startLimitBurst;
     }
     {
-      # Both collectors share a network namespace whenever they are
-      # co-located, and this port appears in no config the port-collision
-      # assertion can read — so equal defaults mean the second to start dies
-      # at `bind()`. Pinned as a case rather than an assertion: enforcing it
-      # belongs with the other port checks, not here.
-      name = "the two collector tiers do not claim the same self-telemetry port";
+      # Collectors share a network namespace whenever they are co-located,
+      # and this port appears in no config the port-collision assertion can
+      # read — so equal defaults mean the second to start dies at `bind()`.
+      # Pinned as a case rather than an assertion: enforcing it belongs with
+      # the other port checks, not here.
+      #
+      # THREE tiers, because the store's container grew a collector of its
+      # own and this case could not see it: an UNDECLARED port is not an
+      # absent one, it is the binary's 8888, which is the hive tier's. That
+      # is why `portOf` falls back to 8888 rather than throwing — a tier that
+      # declares nothing has to fail this case loudly, not evaluate away.
+      name = "no two collector tiers claim the same self-telemetry port";
       ok =
         let
-          portOf = s: (lib.head s.service.telemetry.metrics.readers).pull.exporter.prometheus.port;
+          portOf =
+            s:
+            (lib.head (s.service.telemetry.metrics.readers or [ { } ])).pull.exporter.prometheus.port or 8888;
+          hivePort = portOf hiveOtelSettings;
+          swarmPort = portOf (otelSettings baoWithCollector);
+          baoPort = portOf (baoForwarderSettings baoWithHiveOtel);
         in
-        portOf hiveOtelSettings != portOf (otelSettings baoWithCollector);
+        hivePort != swarmPort && hivePort != baoPort && swarmPort != baoPort;
     }
   ];
 in