Review 1.2: keep SQL Server's error message out of the replication reason

When the distribution database could not be read, SQL Server's message
(which names the agent's login) was appended to Unavailable. That text is
the rules' "not measurable" reason and is returned unredacted by
/rule-states and /replication. It is now UnavailableDetail: shown on the
local instance page and [udeladt] in the API unless
ApiIncludesSensitiveEvidence. The agent list is also capped (TOP 500).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/SQLInsight.Collectors/Instance/ReplicationCollector.cs

@@ -14,7 +14,7 @@ public sealed class ReplicationCollector : Collector<ReplicationSnapshot>
     internal const string DistributionDatabaseSql = "SELECT TOP 1 name FROM sys.databases WHERE is_distributor = 1 AND state = 0";
 
     internal const string AgentsSql = """
-        SELECT a.name, a.publisher_db, h.runstatus, DATEADD(minute, DATEDIFF(minute, GETDATE(), GETUTCDATE()), h.time), h.delivery_latency,
+        SELECT TOP 500 a.name, a.publisher_db, h.runstatus, DATEADD(minute, DATEDIFF(minute, GETDATE(), GETUTCDATE()), h.time), h.delivery_latency,
                CAST(h.comments AS nvarchar(500))
         FROM dbo.MSdistribution_agents a
         OUTER APPLY (SELECT TOP 1 x.runstatus, x.time, x.delivery_latency, x.comments FROM dbo.MSdistribution_history x
@@ -58,7 +58,9 @@ public sealed class ReplicationCollector : Collector<ReplicationSnapshot>
             return new ReplicationSnapshot
             {
                 CapturedAt = context.Now, IsDistributor = true, DistributionDatabase = distribution,
-                Unavailable = NoRightsText + " (" + ex.Message.Split('\n')[0].Trim() + ")",
+                // The error message names the agent's login: kept apart from the reason, which rules and the API show as is.
+                Unavailable = NoRightsText,
+                UnavailableDetail = ex.Message.Split('\n')[0].Trim(),
             };
         }
         finally

src/SQLInsight.Core/Data/Replication.cs

@@ -32,6 +32,9 @@ public sealed record ReplicationSnapshot
     /// <summary>Why the distribution database could not be read (typically no SELECT rights); null when it could.</summary>
     public string? Unavailable { get; init; }
 
+    /// <summary>SQL Server's error message when it could not be read. Names the agent's login: sensitive (local UI only).</summary>
+    public string? UnavailableDetail { get; init; }
+
     public IReadOnlyList<DistributionAgent> Agents { get; init; } = [];
 
     /// <summary>Rows in MSrepl_errors the last 24 hours.</summary>

src/SQLInsight.Web/Api/ApiV1Endpoints.cs

@@ -572,6 +572,7 @@ public static class ApiV1Endpoints
             IsDistributor = r?.IsDistributor,
             r?.DistributionDatabase,
             r?.Unavailable,
+            UnavailableDetail = redact.Value(r?.UnavailableDetail),
             r?.ErrorsLastDay,
             Agents = (r?.Agents ?? []).Select(a => new { a.Name, a.PublisherDatabase, a.RunStatus, a.StatusText, a.LastRunAt, a.DeliveryLatencyMs, Comment = redact.Value(a.Comment) }),
         });

src/SQLInsight.Web/Components/Pages/Instance.razor

@@ -158,7 +158,7 @@ else
         <div class="card-head"><h2>Replikering</h2><span class="muted">distributionsdatabase @repl.DistributionDatabase</span></div>
         @if (repl.Unavailable is { } why)
         {
-            <p class="muted">@why</p>
+            <p class="muted">@why@(repl.UnavailableDetail is { } detail ? " (" + detail + ")" : "")</p>
         }
         else if (repl.Agents.Count == 0)
         {