diff --git a/translator/tocwconfig/sampleConfig/opentelemetry/combined_v1_v2_eks_config.yaml b/translator/tocwconfig/sampleConfig/opentelemetry/combined_v1_v2_eks_config.yaml
index 64f2cfd821..d4f71d6466 100644
--- a/translator/tocwconfig/sampleConfig/opentelemetry/combined_v1_v2_eks_config.yaml
+++ b/translator/tocwconfig/sampleConfig/opentelemetry/combined_v1_v2_eks_config.yaml
@@ -642,6 +642,7 @@ processors:
             - k8s.pod.name
             - k8s.namespace.name
             - k8s.container.name
+            - runtime_tag
     groupbyattrs/files:
         keys:
             - log.file.name
@@ -1129,15 +1130,9 @@ processors:
     transform/cw_k8s_ci_v0_neuron_promote:
         error_mode: ignore
         metric_statements:
-            - context: datapoint
+            - context: resource
               statements:
-                - set(resource.attributes["k8s.pod.name"], attributes["k8s.pod.name"]) where attributes["k8s.pod.name"] != nil
-                - set(resource.attributes["k8s.namespace.name"], attributes["k8s.namespace.name"]) where attributes["k8s.namespace.name"] != nil
-                - set(resource.attributes["k8s.container.name"], attributes["k8s.container.name"]) where attributes["k8s.container.name"] != nil
-                - set(resource.attributes["aws.neuron.runtime.tag"], attributes["runtime_tag"]) where attributes["runtime_tag"] != nil
-                - delete_key(attributes, "k8s.pod.name") where attributes["k8s.pod.name"] != nil
-                - delete_key(attributes, "k8s.namespace.name") where attributes["k8s.namespace.name"] != nil
-                - delete_key(attributes, "k8s.container.name") where attributes["k8s.container.name"] != nil
+                - set(attributes["aws.neuron.runtime.tag"], attributes["runtime_tag"]) where attributes["runtime_tag"] != nil
                 - delete_key(attributes, "runtime_tag") where attributes["runtime_tag"] != nil
     transform/cw_k8s_ci_v0_promote_node_name:
         error_mode: ignore
diff --git a/translator/tocwconfig/sampleConfig/opentelemetry/container_insights_node_config.yaml b/translator/tocwconfig/sampleConfig/opentelemetry/container_insights_node_config.yaml
index 9d1a005ce8..109a7e9546 100644
--- a/translator/tocwconfig/sampleConfig/opentelemetry/container_insights_node_config.yaml
+++ b/translator/tocwconfig/sampleConfig/opentelemetry/container_insights_node_config.yaml
@@ -209,6 +209,7 @@ processors:
             - k8s.pod.name
             - k8s.namespace.name
             - k8s.container.name
+            - runtime_tag
     k8sattributes/cw_k8s_ci_v0_node:
         auth_type: serviceAccount
         exclude:
@@ -765,15 +766,9 @@ processors:
     transform/cw_k8s_ci_v0_neuron_promote:
         error_mode: ignore
         metric_statements:
-            - context: datapoint
+            - context: resource
               statements:
-                - set(resource.attributes["k8s.pod.name"], attributes["k8s.pod.name"]) where attributes["k8s.pod.name"] != nil
-                - set(resource.attributes["k8s.namespace.name"], attributes["k8s.namespace.name"]) where attributes["k8s.namespace.name"] != nil
-                - set(resource.attributes["k8s.container.name"], attributes["k8s.container.name"]) where attributes["k8s.container.name"] != nil
-                - set(resource.attributes["aws.neuron.runtime.tag"], attributes["runtime_tag"]) where attributes["runtime_tag"] != nil
-                - delete_key(attributes, "k8s.pod.name") where attributes["k8s.pod.name"] != nil
-                - delete_key(attributes, "k8s.namespace.name") where attributes["k8s.namespace.name"] != nil
-                - delete_key(attributes, "k8s.container.name") where attributes["k8s.container.name"] != nil
+                - set(attributes["aws.neuron.runtime.tag"], attributes["runtime_tag"]) where attributes["runtime_tag"] != nil
                 - delete_key(attributes, "runtime_tag") where attributes["runtime_tag"] != nil
     transform/cw_k8s_ci_v0_node_logs_set_log_destination:
         error_mode: ignore
diff --git a/translator/tocwconfig/sampleConfig/opentelemetry/default_otel_config_aks.yaml b/translator/tocwconfig/sampleConfig/opentelemetry/default_otel_config_aks.yaml
index 08c01102f6..36bce8c16c 100644
--- a/translator/tocwconfig/sampleConfig/opentelemetry/default_otel_config_aks.yaml
+++ b/translator/tocwconfig/sampleConfig/opentelemetry/default_otel_config_aks.yaml
@@ -281,6 +281,7 @@ processors:
             - k8s.pod.name
             - k8s.namespace.name
             - k8s.container.name
+            - runtime_tag
     k8sattributes/cw_k8s_ci_v0_node:
         auth_type: serviceAccount
         exclude:
@@ -763,15 +764,9 @@ processors:
     transform/cw_k8s_ci_v0_neuron_promote:
         error_mode: ignore
         metric_statements:
-            - context: datapoint
+            - context: resource
               statements:
-                - set(resource.attributes["k8s.pod.name"], attributes["k8s.pod.name"]) where attributes["k8s.pod.name"] != nil
-                - set(resource.attributes["k8s.namespace.name"], attributes["k8s.namespace.name"]) where attributes["k8s.namespace.name"] != nil
-                - set(resource.attributes["k8s.container.name"], attributes["k8s.container.name"]) where attributes["k8s.container.name"] != nil
-                - set(resource.attributes["aws.neuron.runtime.tag"], attributes["runtime_tag"]) where attributes["runtime_tag"] != nil
-                - delete_key(attributes, "k8s.pod.name") where attributes["k8s.pod.name"] != nil
-                - delete_key(attributes, "k8s.namespace.name") where attributes["k8s.namespace.name"] != nil
-                - delete_key(attributes, "k8s.container.name") where attributes["k8s.container.name"] != nil
+                - set(attributes["aws.neuron.runtime.tag"], attributes["runtime_tag"]) where attributes["runtime_tag"] != nil
                 - delete_key(attributes, "runtime_tag") where attributes["runtime_tag"] != nil
     transform/cw_k8s_ci_v0_promote_node_name:
         error_mode: ignore
diff --git a/translator/tocwconfig/sampleConfig/opentelemetry/default_otel_config_gke.yaml b/translator/tocwconfig/sampleConfig/opentelemetry/default_otel_config_gke.yaml
index f9d782e291..3d28332843 100644
--- a/translator/tocwconfig/sampleConfig/opentelemetry/default_otel_config_gke.yaml
+++ b/translator/tocwconfig/sampleConfig/opentelemetry/default_otel_config_gke.yaml
@@ -281,6 +281,7 @@ processors:
             - k8s.pod.name
             - k8s.namespace.name
             - k8s.container.name
+            - runtime_tag
     k8sattributes/cw_k8s_ci_v0_node:
         auth_type: serviceAccount
         exclude:
@@ -762,15 +763,9 @@ processors:
     transform/cw_k8s_ci_v0_neuron_promote:
         error_mode: ignore
         metric_statements:
-            - context: datapoint
+            - context: resource
               statements:
-                - set(resource.attributes["k8s.pod.name"], attributes["k8s.pod.name"]) where attributes["k8s.pod.name"] != nil
-                - set(resource.attributes["k8s.namespace.name"], attributes["k8s.namespace.name"]) where attributes["k8s.namespace.name"] != nil
-                - set(resource.attributes["k8s.container.name"], attributes["k8s.container.name"]) where attributes["k8s.container.name"] != nil
-                - set(resource.attributes["aws.neuron.runtime.tag"], attributes["runtime_tag"]) where attributes["runtime_tag"] != nil
-                - delete_key(attributes, "k8s.pod.name") where attributes["k8s.pod.name"] != nil
-                - delete_key(attributes, "k8s.namespace.name") where attributes["k8s.namespace.name"] != nil
-                - delete_key(attributes, "k8s.container.name") where attributes["k8s.container.name"] != nil
+                - set(attributes["aws.neuron.runtime.tag"], attributes["runtime_tag"]) where attributes["runtime_tag"] != nil
                 - delete_key(attributes, "runtime_tag") where attributes["runtime_tag"] != nil
     transform/cw_k8s_ci_v0_promote_node_name:
         error_mode: ignore
diff --git a/translator/translate/otel/pipeline/opentelemetry/containerinsights/neuron.yaml b/translator/translate/otel/pipeline/opentelemetry/containerinsights/neuron.yaml
index beeed7e846..cd7970b39a 100644
--- a/translator/translate/otel/pipeline/opentelemetry/containerinsights/neuron.yaml
+++ b/translator/translate/otel/pipeline/opentelemetry/containerinsights/neuron.yaml
@@ -89,18 +89,13 @@ processors:
     - k8s.pod.name
     - k8s.namespace.name
     - k8s.container.name
+    - runtime_tag
   transform/cw_k8s_ci_v0_neuron_promote:
     error_mode: ignore
     metric_statements:
-    - context: datapoint
+    - context: resource
       statements:
-      - set(resource.attributes["k8s.pod.name"], attributes["k8s.pod.name"]) where attributes["k8s.pod.name"] != nil
-      - set(resource.attributes["k8s.namespace.name"], attributes["k8s.namespace.name"]) where attributes["k8s.namespace.name"] != nil
-      - set(resource.attributes["k8s.container.name"], attributes["k8s.container.name"]) where attributes["k8s.container.name"] != nil
-      - set(resource.attributes["aws.neuron.runtime.tag"], attributes["runtime_tag"]) where attributes["runtime_tag"] != nil
-      - delete_key(attributes, "k8s.pod.name") where attributes["k8s.pod.name"] != nil
-      - delete_key(attributes, "k8s.namespace.name") where attributes["k8s.namespace.name"] != nil
-      - delete_key(attributes, "k8s.container.name") where attributes["k8s.container.name"] != nil
+      - set(attributes["aws.neuron.runtime.tag"], attributes["runtime_tag"]) where attributes["runtime_tag"] != nil
       - delete_key(attributes, "runtime_tag") where attributes["runtime_tag"] != nil
   transform/cw_k8s_ci_v0_neuron_hw_attrs:
     error_mode: ignore
diff --git a/translator/translate/otel/pipeline/opentelemetry/containerinsights/neuron_multiruntime_test.go b/translator/translate/otel/pipeline/opentelemetry/containerinsights/neuron_multiruntime_test.go
new file mode 100644
index 0000000000..e9ea43662a
--- /dev/null
+++ b/translator/translate/otel/pipeline/opentelemetry/containerinsights/neuron_multiruntime_test.go
@@ -0,0 +1,337 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: MIT
+
+// Per-core Neuron attribution on multi-runtime nodes.
+//
+// Invariant: when several Neuron runtimes share a node, every (core, runtime)
+// reading must reach the exporter under its own identity. neuron-monitor reports
+// every core from every runtime -- the owning pair real, the rest zero -- so
+// runtime_tag is the only attribute separating a core's real reading from another
+// runtime's zero for that same core. Stop separating them and two datapoints share
+// an identity, the last write wins, and for one core that is a plausible-looking 0.
+//
+// These run the shipped neuron.yaml -- groupbyattrs then the promote transform,
+// rendered from the embedded template rather than restated, so a config change that
+// breaks the invariant fails here. TestNeuronMultiRuntimeCollapsedConfigLosesData
+// runs a config that violates it, proving the assertions discriminate.
+
+package containerinsights
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"sort"
+	"testing"
+	"text/template"
+
+	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/groupbyattrsprocessor"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/transformprocessor"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"go.opentelemetry.io/collector/component"
+	"go.opentelemetry.io/collector/confmap"
+	"go.opentelemetry.io/collector/consumer"
+	"go.opentelemetry.io/collector/consumer/consumertest"
+	"go.opentelemetry.io/collector/pdata/pmetric"
+	"go.opentelemetry.io/collector/processor"
+	"go.opentelemetry.io/collector/processor/processortest"
+	"gopkg.in/yaml.v3"
+)
+
+const (
+	neuronGroupByAttrs = "groupbyattrs/cw_k8s_ci_v0_neuron"
+	neuronPromote      = "transform/cw_k8s_ci_v0_neuron_promote"
+
+	testPod       = "neuron-burn-abcde-12345"
+	testNamespace = "default"
+	testContainer = "burn"
+	tagA          = "burn-core0"
+	tagB          = "burn-core1"
+)
+
+// renderedNeuronProcessors returns the processors block of the shipped neuron.yaml.
+func renderedNeuronProcessors(t *testing.T) map[string]any {
+	t.Helper()
+	tmpl, err := template.New("neuron").Parse(neuronYAML)
+	require.NoError(t, err)
+	var buf bytes.Buffer
+	require.NoError(t, tmpl.Execute(&buf, templateData{
+		ClusterName:        "test-cluster",
+		Region:             "us-west-2",
+		CollectionInterval: "30s",
+		ScrapeTimeout:      "10s",
+		NodeName:           "test-node",
+		HostIP:             "127.0.0.1",
+	}))
+
+	var parsed map[string]any
+	require.NoError(t, yaml.Unmarshal(buf.Bytes(), &parsed))
+	processors, ok := parsed["processors"].(map[string]any)
+	require.True(t, ok, "neuron.yaml has no processors block")
+	return processors
+}
+
+func processorConfig(t *testing.T, processors map[string]any, name string) map[string]any {
+	t.Helper()
+	raw, ok := processors[name]
+	require.True(t, ok, "neuron.yaml is missing %s", name)
+	cfg, ok := raw.(map[string]any)
+	require.True(t, ok, "%s is not a mapping", name)
+	return cfg
+}
+
+// buildChain wires groupbyattrs -> promote -> sink from the given configs.
+func buildChain(t *testing.T, gbaCfg, promoteCfg map[string]any) (processor.Metrics, *consumertest.MetricsSink) {
+	t.Helper()
+	sink := new(consumertest.MetricsSink)
+
+	promote := newProcessor(t, transformprocessor.NewFactory(), "transform", promoteCfg, sink)
+	gba := newProcessor(t, groupbyattrsprocessor.NewFactory(), "groupbyattrs", gbaCfg, promote)
+	return gba, sink
+}
+
+func newProcessor(
+	t *testing.T, factory processor.Factory, typ string, cfg map[string]any, next consumer.Metrics,
+) processor.Metrics {
+	t.Helper()
+	c := factory.CreateDefaultConfig()
+	require.NoError(t, confmap.NewFromStringMap(cfg).Unmarshal(c))
+	p, err := factory.CreateMetrics(
+		context.Background(), processortest.NewNopSettings(component.MustNewType(typ)), c, next)
+	require.NoError(t, err)
+	require.NoError(t, p.Start(context.Background(), componenttestNopHost{}))
+	return p
+}
+
+type componenttestNopHost struct{}
+
+func (componenttestNopHost) GetExtensions() map[component.ID]component.Component { return nil }
+
+// multiRuntimeMetrics is what neuron-monitor emits for 2 cores x 2 runtimes on one
+// node: the owning pair real, the other zero. Pod identity is identical across all
+// four -- one pod holding both cores, which occurs in practice and is the
+// collapse-prone case, since pod identity alone cannot separate the datapoints.
+func multiRuntimeMetrics() pmetric.Metrics {
+	md := pmetric.NewMetrics()
+	sm := md.ResourceMetrics().AppendEmpty().ScopeMetrics().AppendEmpty()
+	m := sm.Metrics().AppendEmpty()
+	m.SetName("neuroncore_utilization_ratio")
+	dps := m.SetEmptyGauge().DataPoints()
+
+	add := func(core, tag string, value float64) {
+		dp := dps.AppendEmpty()
+		dp.SetDoubleValue(value)
+		a := dp.Attributes()
+		a.PutStr("neuroncore", core)
+		a.PutStr("runtime_tag", tag)
+		a.PutStr("k8s.pod.name", testPod)
+		a.PutStr("k8s.namespace.name", testNamespace)
+		a.PutStr("k8s.container.name", testContainer)
+	}
+	add("0", tagA, 75.1)
+	add("1", tagA, 0)
+	add("0", tagB, 0)
+	add("1", tagB, 75.3)
+	return md
+}
+
+// observed flattens the sink into "core=<n> tag=<t> value=<v>" triples, reading the
+// tag from the RESOURCE (where the promote puts it) and the core from the datapoint.
+func observed(t *testing.T, sink *consumertest.MetricsSink) []string {
+	t.Helper()
+	var out []string
+	for _, md := range sink.AllMetrics() {
+		for i := 0; i < md.ResourceMetrics().Len(); i++ {
+			rm := md.ResourceMetrics().At(i)
+			tag := "<none>"
+			if v, ok := rm.Resource().Attributes().Get("aws.neuron.runtime.tag"); ok {
+				tag = v.Str()
+			}
+			for j := 0; j < rm.ScopeMetrics().Len(); j++ {
+				ms := rm.ScopeMetrics().At(j).Metrics()
+				for k := 0; k < ms.Len(); k++ {
+					dps := ms.At(k).Gauge().DataPoints()
+					for d := 0; d < dps.Len(); d++ {
+						dp := dps.At(d)
+						core, _ := dp.Attributes().Get("neuroncore")
+						out = append(out, fmt.Sprintf("core=%s tag=%s value=%.1f",
+							core.Str(), tag, dp.DoubleValue()))
+					}
+				}
+			}
+		}
+	}
+	sort.Strings(out)
+	return out
+}
+
+func consume(t *testing.T, chain processor.Metrics, md pmetric.Metrics) {
+	t.Helper()
+	require.NoError(t, chain.ConsumeMetrics(context.Background(), md))
+}
+
+// TestNeuronMultiRuntimeKeepsEveryCorePerRuntime requires all four (core, runtime)
+// readings to survive the shipped config with their real values.
+func TestNeuronMultiRuntimeKeepsEveryCorePerRuntime(t *testing.T) {
+	processors := renderedNeuronProcessors(t)
+	chain, sink := buildChain(t,
+		processorConfig(t, processors, neuronGroupByAttrs),
+		processorConfig(t, processors, neuronPromote))
+	consume(t, chain, multiRuntimeMetrics())
+
+	assert.Equal(t, []string{
+		"core=0 tag=burn-core0 value=75.1",
+		"core=0 tag=burn-core1 value=0.0",
+		"core=1 tag=burn-core0 value=0.0",
+		"core=1 tag=burn-core1 value=75.3",
+	}, observed(t, sink),
+		"both busy cores must survive with their own runtime tag; a missing 75.x "+
+			"reading means one runtime's datapoint was shadowed by another's zero")
+}
+
+// TestNeuronMultiRuntimeSeparatesRuntimesIntoResources pins the mechanism: one
+// ResourceMetrics per runtime is what stops the datapoints colliding.
+func TestNeuronMultiRuntimeSeparatesRuntimesIntoResources(t *testing.T) {
+	processors := renderedNeuronProcessors(t)
+	chain, sink := buildChain(t,
+		processorConfig(t, processors, neuronGroupByAttrs),
+		processorConfig(t, processors, neuronPromote))
+	consume(t, chain, multiRuntimeMetrics())
+
+	tags := map[string]int{}
+	total := 0
+	for _, md := range sink.AllMetrics() {
+		for i := 0; i < md.ResourceMetrics().Len(); i++ {
+			rm := md.ResourceMetrics().At(i)
+			v, ok := rm.Resource().Attributes().Get("aws.neuron.runtime.tag")
+			require.True(t, ok, "resource is missing aws.neuron.runtime.tag")
+			tags[v.Str()]++
+			total++
+		}
+	}
+	assert.Equal(t, 2, total, "expected one ResourceMetrics per runtime")
+	assert.Equal(t, map[string]int{tagA: 1, tagB: 1}, tags)
+}
+
+// TestNeuronMultiRuntimePromotesPodIdentity requires pod identity to land on the
+// resource and NOT remain on the datapoint. groupbyattrs moves its grouping keys
+// rather than copying them, so nothing downstream needs to re-promote them.
+func TestNeuronMultiRuntimePromotesPodIdentity(t *testing.T) {
+	processors := renderedNeuronProcessors(t)
+	chain, sink := buildChain(t,
+		processorConfig(t, processors, neuronGroupByAttrs),
+		processorConfig(t, processors, neuronPromote))
+	consume(t, chain, multiRuntimeMetrics())
+
+	for _, md := range sink.AllMetrics() {
+		for i := 0; i < md.ResourceMetrics().Len(); i++ {
+			rm := md.ResourceMetrics().At(i)
+			for _, kv := range []struct{ key, want string }{
+				{"k8s.pod.name", testPod},
+				{"k8s.namespace.name", testNamespace},
+				{"k8s.container.name", testContainer},
+			} {
+				v, ok := rm.Resource().Attributes().Get(kv.key)
+				require.True(t, ok, "resource is missing %s", kv.key)
+				assert.Equal(t, kv.want, v.Str())
+			}
+
+			for j := 0; j < rm.ScopeMetrics().Len(); j++ {
+				ms := rm.ScopeMetrics().At(j).Metrics()
+				for k := 0; k < ms.Len(); k++ {
+					dps := ms.At(k).Gauge().DataPoints()
+					for d := 0; d < dps.Len(); d++ {
+						attrs := dps.At(d).Attributes()
+						for _, key := range []string{
+							"k8s.pod.name", "k8s.namespace.name", "k8s.container.name", "runtime_tag",
+						} {
+							_, present := attrs.Get(key)
+							assert.False(t, present,
+								"%s must be moved off the datapoint, not left on it", key)
+						}
+					}
+				}
+			}
+		}
+	}
+}
+
+// TestNeuronMultiRuntimeCollapsedConfigLosesData is the negative control: it runs a
+// config that drops the runtime dimension and asserts the loss, so the tests above
+// are known to discriminate rather than merely pass. If it ever starts passing, the
+// collapse has stopped reproducing and those assertions prove nothing.
+//
+// The collapse needs both halves. groupbyattrs omits the runtime_tag key, so the
+// runtimes are not split into separate resources; the promote then runs in
+// `context: datapoint` while writing resource.attributes, which are
+// per-ResourceMetrics -- so the statement executes once per datapoint and the last
+// write wins -- and deletes runtime_tag from the datapoint. This is the shape the
+// agent shipped with.
+func TestNeuronMultiRuntimeCollapsedConfigLosesData(t *testing.T) {
+	collapsedGBA := map[string]any{
+		"keys": []any{"k8s.pod.name", "k8s.namespace.name", "k8s.container.name"},
+	}
+	collapsedPromote := map[string]any{
+		"error_mode": "ignore",
+		"metric_statements": []any{
+			map[string]any{
+				"context": "datapoint",
+				"statements": []any{
+					`set(resource.attributes["k8s.pod.name"], attributes["k8s.pod.name"]) where attributes["k8s.pod.name"] != nil`,
+					`set(resource.attributes["k8s.namespace.name"], attributes["k8s.namespace.name"]) where attributes["k8s.namespace.name"] != nil`,
+					`set(resource.attributes["k8s.container.name"], attributes["k8s.container.name"]) where attributes["k8s.container.name"] != nil`,
+					`set(resource.attributes["aws.neuron.runtime.tag"], attributes["runtime_tag"]) where attributes["runtime_tag"] != nil`,
+					`delete_key(attributes, "k8s.pod.name") where attributes["k8s.pod.name"] != nil`,
+					`delete_key(attributes, "k8s.namespace.name") where attributes["k8s.namespace.name"] != nil`,
+					`delete_key(attributes, "k8s.container.name") where attributes["k8s.container.name"] != nil`,
+					`delete_key(attributes, "runtime_tag") where attributes["runtime_tag"] != nil`,
+				},
+			},
+		},
+	}
+
+	chain, sink := buildChain(t, collapsedGBA, collapsedPromote)
+	consume(t, chain, multiRuntimeMetrics())
+	got := observed(t, sink)
+
+	// One resource, one surviving tag: the four datapoints keep only two identities.
+	assert.Len(t, got, 4, "the pre-fix chain still emits four datapoints")
+	tags := map[string]struct{}{}
+	for _, md := range sink.AllMetrics() {
+		for i := 0; i < md.ResourceMetrics().Len(); i++ {
+			if v, ok := md.ResourceMetrics().At(i).Resource().Attributes().Get("aws.neuron.runtime.tag"); ok {
+				tags[v.Str()] = struct{}{}
+			}
+		}
+	}
+	assert.Len(t, tags, 1,
+		"pre-fix, all runtimes collapse onto ONE resource tag; got %v", tags)
+
+	// With one tag on the resource, (core, tag) is no longer unique: each core
+	// appears twice, once with its real value and once with another runtime's zero.
+	// Downstream that is a duplicate identity and one value is lost.
+	perCore := map[string][]float64{}
+	for _, md := range sink.AllMetrics() {
+		for i := 0; i < md.ResourceMetrics().Len(); i++ {
+			rm := md.ResourceMetrics().At(i)
+			for j := 0; j < rm.ScopeMetrics().Len(); j++ {
+				ms := rm.ScopeMetrics().At(j).Metrics()
+				for k := 0; k < ms.Len(); k++ {
+					dps := ms.At(k).Gauge().DataPoints()
+					for d := 0; d < dps.Len(); d++ {
+						dp := dps.At(d)
+						core, _ := dp.Attributes().Get("neuroncore")
+						perCore[core.Str()] = append(perCore[core.Str()], dp.DoubleValue())
+					}
+				}
+			}
+		}
+	}
+	for core, values := range perCore {
+		assert.Len(t, values, 2,
+			"pre-fix, core %s carries two datapoints under one identity %v — whichever "+
+				"arrives last wins, and for one core that is a legitimate-looking 0",
+			core, values)
+	}
+}