fix(deploy): staleness batch logs one Warning per batch, not one per instance

Claude-Session: https://claude.ai/code/session_01Y5ef34iUUMjmwnMpL9xgmB

src/ZB.MOM.WW.ScadaBridge.DeploymentManager/DeploymentService.cs

@@ -1708,6 +1708,11 @@ public class DeploymentService
         // older schema) still yields the frozen-hash staleness result, with a
         // null diff.
         var deployedRevisionHash = ComputeDeployedHash(snapshot, instanceId, out var deployedConfig);
+
+        // Deliberately outside ComputeDeployedHash's JsonException catch: DiffService
+        // compares already-deserialized POCOs and does no JSON work of its own, so it
+        // cannot raise the exception that catch exists for. A DiffService that ever
+        // starts parsing JSON must revisit this.
         var diff = deployedConfig == null
             ? null
             : _diffService.ComputeDiff(
@@ -1832,6 +1837,16 @@ public class DeploymentService
         var deployedHashes = await _repository.GetDeployedRevisionHashesAsync(cancellationToken);
         var session = _flatteningPipeline.CreateSession();
 
+        // Failures are summarised into ONE Warning at the end rather than logged
+        // per instance: this runs for the whole fleet on a cache-TTL cadence, so a
+        // single broken shared template fanning out to N instances would otherwise
+        // emit N Warning lines every minute, forever. The per-instance detail stays
+        // at Debug for whoever is actually diagnosing it.
+        var evaluated = 0;
+        var failedCount = 0;
+        var firstFailureInstanceId = 0;
+        string? firstFailureError = null;
+
         foreach (var instanceId in instanceIds.Distinct())
         {
             cancellationToken.ThrowIfCancellationRequested();
@@ -1839,15 +1854,24 @@ public class DeploymentService
             if (!deployedHashes.TryGetValue(instanceId, out var deployedHash))
                 continue;
 
+            evaluated++;
+
             // Read-only path: hash only, so skip the Roslyn compile — the deploy
             // gate remains the authoritative compile.
             var currentResult = await _flatteningPipeline.FlattenAndValidateAsync(
                 instanceId, cancellationToken, validateScripts: false, session);
             if (currentResult.IsFailure)
             {
-                _logger.LogWarning(
+                _logger.LogDebug(
                     "Could not evaluate staleness of instance {InstanceId}: {Error}",
                     instanceId, currentResult.Error);
+                if (failedCount == 0)
+                {
+                    firstFailureInstanceId = instanceId;
+                    firstFailureError = currentResult.Error;
+                }
+
+                failedCount++;
                 staleness[instanceId] = null;
                 continue;
             }
@@ -1870,6 +1894,14 @@ public class DeploymentService
                 !string.Equals(normalizedDeployedHash, currentHash, StringComparison.Ordinal);
         }
 
+        if (failedCount > 0)
+        {
+            _logger.LogWarning(
+                "Could not evaluate staleness of {FailedCount} of {EvaluatedCount} instances; " +
+                "first failure: instance {InstanceId}: {Error}",
+                failedCount, evaluated, firstFailureInstanceId, firstFailureError);
+        }
+
         return staleness;
     }