feat: implement set-based invoice payment calculations and enhance email logging configuration

Fuchs/Services/ProcessWebComService.cs

@@ -74,8 +74,8 @@ public class ProcessWebComService : IComService
             FuchsTelemetry.EmailsFailed.Add(1, new KeyValuePair<string, object?>("reason", "invalid-email"));
             act?.SetStatus(ActivityStatusCode.Error, "invalid-email");
             // Every attempt is audit-logged, including this early rejection (previously it returned unlogged).
-            await WriteAuditLogAsync(reference, "", "", default, false,
-                [$"Invalid recipient email address: '{email}'"]);
+            await WriteAuditLogAsync(reference, "", BuildAuditConfig(subject, email, name, cc, attachments?.Keys),
+                default, false, [$"Invalid recipient email address: '{email}'"]);
             return false;
         }
 
@@ -86,7 +86,8 @@ public class ProcessWebComService : IComService
             _logger.LogInformation(
                 "[ComService DISABLED] Would send email ref={Reference} subject='{Subject}' to={Email}",
                 reference, subject, email);
-            await WriteAuditLogAsync(reference, "", "", default, false, ["Service disabled – email not sent"]);
+            await WriteAuditLogAsync(reference, "", BuildAuditConfig(subject, email, name, cc, attachments?.Keys),
+                default, false, ["Service disabled – email not sent"]);
             FuchsTelemetry.EmailsFailed.Add(1, new KeyValuePair<string, object?>("reason", "disabled"));
             return false;
         }
@@ -153,7 +154,8 @@ public class ProcessWebComService : IComService
         _logger.LogInformation("SendEmailAsync ref={Reference} success={Success} in {Ms} ms",
             reference, success, sw.ElapsedMilliseconds);
 
-        await WriteAuditLogAsync(reference, messageId, "", success ? DateTime.UtcNow : default, success, errors);
+        await WriteAuditLogAsync(reference, messageId, BuildAuditConfig(subject, email, name, cc, attachments?.Keys),
+            success ? DateTime.UtcNow : default, success, errors);
         return success;
     }
 
@@ -308,6 +310,30 @@ public class ProcessWebComService : IComService
         }
     }
 
+    /// <summary>
+    /// Serialises the audit <c>config</c> stored in <c>fds__emaillog.config</c>: who the mail went
+    /// to, its subject and the attachment <em>names</em> — never the body or attachment bytes.
+    /// The shape (<c>subject</c>/<c>from</c>/<c>to[]</c>/<c>cc[]</c>/<c>bcc[]</c>/<c>attachments[]</c>,
+    /// addresses as <c>"Name" &lt;email&gt;</c>) is the one the legacy mailer wrote and that
+    /// <c>[dbo].[fds_wgd_lastEmails]</c> reads back with <c>OPENJSON</c>; an empty string here
+    /// made that dashboard widget fail for every row the new service logged.
+    /// Pure so the contract can be unit-tested without a database.
+    /// </summary>
+    internal static string BuildAuditConfig(string subject, string email, string? name, string? cc,
+        IEnumerable<string>? attachmentNames) =>
+        JsonConvert.SerializeObject(new
+        {
+            subject     = subject ?? "",
+            from        = "",
+            to          = new[] { FormatAddress(email, name) },
+            cc          = string.IsNullOrWhiteSpace(cc) ? Array.Empty<string>() : new[] { cc.Trim() },
+            bcc         = Array.Empty<string>(),
+            attachments = (attachmentNames ?? []).ToArray()
+        });
+
+    private static string FormatAddress(string email, string? name) =>
+        string.IsNullOrWhiteSpace(name) ? (email ?? "") : $"\"{name.Trim()}\" <{email}>";
+
     /// <summary>
     /// Builds the parameter list for <c>[dbo].[fds__logEmail]</c>. <c>fds__emaillog</c> declares
     /// <c>config</c> and <c>DateSent</c> as NOT NULL, so neither may be sent as NULL: