diff --git a/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Kpi/KpiMetricAggregation.cs b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Kpi/KpiMetricAggregation.cs
index df661750..a463a875 100644
--- a/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Kpi/KpiMetricAggregation.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Kpi/KpiMetricAggregation.cs
@@ -42,10 +42,10 @@ public enum KpiRollupAggregation
 /// Keying by <c>(source, metric)</c> — not metric alone — is deliberate:
 /// <c>deliveredLastInterval</c> is emitted by both
 /// <see cref="KpiSources.NotificationOutbox"/> and <see cref="KpiSources.SiteCallAudit"/>,
-/// so a metric name is not globally unique. Every metric string is taken from the
-/// emitting source verbatim (shared <see cref="KpiMetrics"/> constants where they exist,
-/// otherwise the source's own private literal), so this catalog stays a faithful mirror
-/// of what actually lands in <c>KpiSample.Metric</c>.
+/// so a metric name is not globally unique. Every catalogued metric string is now a shared
+/// <see cref="KpiMetrics"/> constant — the emitting source consumes the same constant — so an
+/// emitter rename is a <strong>compile error</strong>, not a silent Gauge downgrade (R4), and
+/// this catalog stays a faithful mirror of what actually lands in <c>KpiSample.Metric</c>.
 /// </para>
 /// <para>
 /// The catalog stores only the <see cref="KpiRollupAggregation.Rate"/> pairs; anything
@@ -57,12 +57,6 @@ public enum KpiRollupAggregation
 /// </remarks>
 public static class KpiMetricAggregationCatalog
 {
-    // Metric literals for the sources that keep their names private (no shared
-    // KpiMetrics constant exists for these). Charted metrics use the KpiMetrics catalog.
-    private const string SiteCallAuditDeliveredLastInterval = "deliveredLastInterval";
-    private const string SiteHealthAlarmEvalErrors = "alarmEvalErrors";
-    private const string SiteHealthEventLogWriteFailures = "eventLogWriteFailures";
-
     /// <summary>
     /// The <c>(source, metric)</c> pairs classified as <see cref="KpiRollupAggregation.Rate"/>
     /// (sum-per-hour). Every other emitted metric is a <see cref="KpiRollupAggregation.Gauge"/>.
@@ -99,11 +93,11 @@ public static class KpiMetricAggregationCatalog
     {
         (KpiSources.NotificationOutbox, KpiMetrics.NotificationOutbox.DeliveredLastInterval),
         (KpiSources.SiteCallAudit, KpiMetrics.SiteCallAudit.FailedLastInterval),
-        (KpiSources.SiteCallAudit, SiteCallAuditDeliveredLastInterval),
+        (KpiSources.SiteCallAudit, KpiMetrics.SiteCallAudit.DeliveredLastInterval),
         (KpiSources.SiteHealth, KpiMetrics.SiteHealth.ScriptErrors),
-        (KpiSources.SiteHealth, SiteHealthAlarmEvalErrors),
+        (KpiSources.SiteHealth, KpiMetrics.SiteHealth.AlarmEvalErrors),
         (KpiSources.SiteHealth, KpiMetrics.SiteHealth.DeadLetters),
-        (KpiSources.SiteHealth, SiteHealthEventLogWriteFailures),
+        (KpiSources.SiteHealth, KpiMetrics.SiteHealth.EventLogWriteFailures),
     };
 
     /// <summary>
diff --git a/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Kpi/KpiMetrics.cs b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Kpi/KpiMetrics.cs
index d2230812..ffedf771 100644
--- a/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Kpi/KpiMetrics.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Kpi/KpiMetrics.cs
@@ -18,11 +18,16 @@ namespace ZB.MOM.WW.ScadaBridge.Commons.Types.Kpi;
 /// <strong>not</strong> a rename — changing any value would orphan historical samples.
 /// </para>
 /// <para>
-/// Only the metrics a trend page actually charts are catalogued here. Sources may emit
-/// additional internal metrics (e.g. the Notification Outbox <c>stuckCount</c> /
-/// <c>oldestPendingAgeSeconds</c>, the Site Call Audit <c>deliveredLastInterval</c> /
-/// <c>stuck</c> / <c>oldestPendingAgeSeconds</c>, and the bulk of the Site Health catalog)
-/// that no page references; those stay private to their source until a page charts them.
+/// This catalog now carries two kinds of metric: those a trend page charts, <em>and</em>
+/// those the <see cref="KpiMetricAggregationCatalog"/> classifies for the hourly rollup fold
+/// (e.g. <c>SiteCallAudit/deliveredLastInterval</c>, <c>SiteHealth/alarmEvalErrors</c>,
+/// <c>SiteHealth/eventLogWriteFailures</c>) even if no page charts them yet. The C4/R4 lesson
+/// is that <strong>any metric named in two places needs one shared symbol</strong>: a private
+/// literal on the emitter plus a matching private literal in the catalog drifts silently on a
+/// rename. Sources may still keep genuinely single-use internal metrics (e.g. the Notification
+/// Outbox <c>stuckCount</c> / <c>oldestPendingAgeSeconds</c>, the Site Call Audit <c>stuck</c> /
+/// <c>oldestPendingAgeSeconds</c>, and the bulk of the Site Health catalog) private until a page
+/// or the catalog references them.
 /// Constants are grouped by source via nested static classes mirroring
 /// <see cref="KpiSources"/>.
 /// </para>
@@ -65,6 +70,11 @@ public static class KpiMetrics
 
         /// <summary>Cached calls that failed permanently in the last KPI interval.</summary>
         public const string FailedLastInterval = "failedLastInterval";
+
+        /// <summary>Cached calls delivered in the last KPI interval. Not charted by a trend
+        /// page today, but named in the rollup aggregation catalog as a Rate metric — so it
+        /// is a shared symbol to keep the emitter and catalog in lock-step (R4).</summary>
+        public const string DeliveredLastInterval = "deliveredLastInterval";
     }
 
     /// <summary>
@@ -98,6 +108,16 @@ public static class KpiMetrics
         /// <summary>Script-execution error count reported by the site.</summary>
         public const string ScriptErrors = "scriptErrors";
 
+        /// <summary>Alarm-evaluation error count reported by the site. Named in the rollup
+        /// aggregation catalog as a Rate metric — shared symbol so an emitter rename is a
+        /// compile error, not a silent Gauge downgrade (R4).</summary>
+        public const string AlarmEvalErrors = "alarmEvalErrors";
+
+        /// <summary>Event-log write-failure count reported by the site. Named in the rollup
+        /// aggregation catalog as a Rate metric — shared symbol so an emitter rename is a
+        /// compile error, not a silent Gauge downgrade (R4).</summary>
+        public const string EventLogWriteFailures = "eventLogWriteFailures";
+
         /// <summary>Summed store-and-forward buffer depth across all buffers.</summary>
         public const string SfBufferDepth = "sfBufferDepth";
     }
diff --git a/src/ZB.MOM.WW.ScadaBridge.HealthMonitoring/Kpi/SiteHealthKpiSampleSource.cs b/src/ZB.MOM.WW.ScadaBridge.HealthMonitoring/Kpi/SiteHealthKpiSampleSource.cs
index 1c2701ca..501cb967 100644
--- a/src/ZB.MOM.WW.ScadaBridge.HealthMonitoring/Kpi/SiteHealthKpiSampleSource.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.HealthMonitoring/Kpi/SiteHealthKpiSampleSource.cs
@@ -40,7 +40,7 @@ public sealed class SiteHealthKpiSampleSource : IKpiSampleSource
     private const string MetricConnectionsUp = "connectionsUp";
     private const string MetricConnectionsDown = KpiMetrics.SiteHealth.ConnectionsDown;
     private const string MetricScriptErrors = KpiMetrics.SiteHealth.ScriptErrors;
-    private const string MetricAlarmEvalErrors = "alarmEvalErrors";
+    private const string MetricAlarmEvalErrors = KpiMetrics.SiteHealth.AlarmEvalErrors;
     private const string MetricSfBufferDepth = KpiMetrics.SiteHealth.SfBufferDepth;
     private const string MetricDeadLetters = KpiMetrics.SiteHealth.DeadLetters;
     private const string MetricParkedMessages = "parkedMessages";
@@ -48,7 +48,7 @@ public sealed class SiteHealthKpiSampleSource : IKpiSampleSource
     private const string MetricEnabledInstances = "enabledInstances";
     private const string MetricDisabledInstances = "disabledInstances";
     private const string MetricAuditBacklogPending = "auditBacklogPending";
-    private const string MetricEventLogWriteFailures = "eventLogWriteFailures";
+    private const string MetricEventLogWriteFailures = KpiMetrics.SiteHealth.EventLogWriteFailures;
 
     private readonly ICentralHealthAggregator _aggregator;
 
diff --git a/src/ZB.MOM.WW.ScadaBridge.SiteCallAudit/Kpi/SiteCallAuditKpiSampleSource.cs b/src/ZB.MOM.WW.ScadaBridge.SiteCallAudit/Kpi/SiteCallAuditKpiSampleSource.cs
index bfab3778..f7a2d994 100644
--- a/src/ZB.MOM.WW.ScadaBridge.SiteCallAudit/Kpi/SiteCallAuditKpiSampleSource.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.SiteCallAudit/Kpi/SiteCallAuditKpiSampleSource.cs
@@ -42,7 +42,7 @@ public sealed class SiteCallAuditKpiSampleSource : IKpiSampleSource
     private const string MetricBuffered = KpiMetrics.SiteCallAudit.Buffered;
     private const string MetricParked = KpiMetrics.SiteCallAudit.Parked;
     private const string MetricFailedLastInterval = KpiMetrics.SiteCallAudit.FailedLastInterval;
-    private const string MetricDeliveredLastInterval = "deliveredLastInterval";
+    private const string MetricDeliveredLastInterval = KpiMetrics.SiteCallAudit.DeliveredLastInterval;
     private const string MetricStuck = "stuck";
     private const string MetricOldestPendingAgeSeconds = "oldestPendingAgeSeconds";
 
diff --git a/tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Kpi/KpiMetricAggregationTests.cs b/tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Kpi/KpiMetricAggregationTests.cs
index 7bbae2bf..a3cb9b08 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Kpi/KpiMetricAggregationTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Kpi/KpiMetricAggregationTests.cs
@@ -148,4 +148,22 @@ public class KpiMetricAggregationTests
             KpiRollupAggregation.Rate,
             KpiMetricAggregationCatalog.Resolve(KpiSources.SiteCallAudit, "deliveredLastInterval"));
     }
+
+    // ---- Task 8: catalog metric literals promoted to shared KpiMetrics constants (R4) ----
+
+    [Fact]
+    public void PromotedMetricConstants_LockHistoricalPersistedValues()
+    {
+        // Persisted data contract — these are symbol promotions, NOT renames.
+        Assert.Equal("deliveredLastInterval", KpiMetrics.SiteCallAudit.DeliveredLastInterval);
+        Assert.Equal("alarmEvalErrors", KpiMetrics.SiteHealth.AlarmEvalErrors);
+        Assert.Equal("eventLogWriteFailures", KpiMetrics.SiteHealth.EventLogWriteFailures);
+    }
+
+    [Theory]
+    [InlineData(KpiSources.SiteCallAudit, KpiMetrics.SiteCallAudit.DeliveredLastInterval)]
+    [InlineData(KpiSources.SiteHealth, KpiMetrics.SiteHealth.AlarmEvalErrors)]
+    [InlineData(KpiSources.SiteHealth, KpiMetrics.SiteHealth.EventLogWriteFailures)]
+    public void Resolve_PromotedRatePairs_StillClassifyAsRate(string source, string metric)
+        => Assert.Equal(KpiRollupAggregation.Rate, KpiMetricAggregationCatalog.Resolve(source, metric));
 }