diff --git a/archreview/plans/R2-06-serverhistorian-failfast-plan.md.tasks.json b/archreview/plans/R2-06-serverhistorian-failfast-plan.md.tasks.json
index 49394bf0..9145edce 100644
--- a/archreview/plans/R2-06-serverhistorian-failfast-plan.md.tasks.json
+++ b/archreview/plans/R2-06-serverhistorian-failfast-plan.md.tasks.json
@@ -35,7 +35,7 @@
     {
       "id": "T5",
       "subject": "Wiring: AddValidatedOptions<ServerHistorianOptions, ServerHistorianOptionsValidator> in Program.cs hasDriver block + OptionsValidationException wiring test + residual alarm-only-mode startup warning",
-      "status": "pending",
+      "status": "completed",
       "blockedBy": [
         "T4"
       ]
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.Host/Program.cs b/src/Server/ZB.MOM.WW.OtOpcUa.Host/Program.cs
index 78e9707e..c5bfdff7 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.Host/Program.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.Host/Program.cs
@@ -117,11 +117,32 @@ if (hasDriver)
     // the read-side GatewayHistorianDataSource to stop owning + disposing its client (regressing the read
     // cutover), and a second channel to a co-located sidecar is cheap (the gateway pools the historian
     // sessions server-side).
+    // Fail-fast startup validation for the ServerHistorian section (archreview 06/S-11). A
+    // provably-crashing config — an enabled historian (or an enabled AlarmHistorian, which sources its
+    // gateway connection from THIS section) with an empty/malformed Endpoint — now fails host start with
+    // a named OptionsValidationException instead of a raw UriFormatException crash-loop out of the gateway
+    // client factory. Driver-block-only (mirrors OpcUaApplicationHostOptionsValidator below): admin-only
+    // nodes never build the historian singletons, so they must not be failed by a section they never
+    // consume. ApiKey/MaxTieClusterOverfetch stay warnings (they degrade, not crash) — see Validate().
+    builder.Services.AddValidatedOptions<ServerHistorianOptions, ServerHistorianOptionsValidator>(
+        builder.Configuration, ServerHistorianOptions.SectionName);
+
     var serverHistorianOptions = builder.Configuration
         .GetSection(ServerHistorianOptions.SectionName).Get<ServerHistorianOptions>()
         ?? new ServerHistorianOptions();
     foreach (var warning in serverHistorianOptions.Validate())
         Log.Warning("ServerHistorian misconfiguration detected at startup: {Warning}", warning);
+
+    // Residual "unusual but valid" corner (archreview 06/S-11): an alarm-history-only deployment
+    // (AlarmHistorian:Enabled=true while ServerHistorian:Enabled=false) legitimately sources its gateway
+    // connection from the disabled ServerHistorian section. That is allowed (the endpoint was already
+    // validated above), but log it so the mode is not a silent surprise: HistoryReads stay GoodNoData,
+    // and a wrong endpoint/key surfaces only as SQLite store-and-forward retry/dead-letter growth.
+    if (builder.Configuration.GetValue<bool>("AlarmHistorian:Enabled") && !serverHistorianOptions.Enabled)
+        Log.Warning(
+            "AlarmHistorian is enabled but ServerHistorian is disabled — the alarm-history sink is sourcing its " +
+            "gateway connection (endpoint/key/TLS) from the disabled ServerHistorian section; HistoryReads stay GoodNoData.");
+
     builder.Services.AddAlarmHistorian(
         builder.Configuration,
         (_, sp) => GatewayHistorian.CreateAlarmWriter(serverHistorianOptions, sp));