Add audit logs.

API/ROLAC.API/Services/Logging/SystemLogQueue.cs

@@ -0,0 +1,32 @@
+using System.Threading.Channels;
+using ROLAC.API.Entities.Logging;
+
+namespace ROLAC.API.Services.Logging;
+
+/// <summary>
+/// A singleton, bounded in-memory queue decoupling log producers (the ILogger hot path, the
+/// audit interceptor, singleton services) from the single background DB writer. Enqueue is a
+/// non-blocking <c>TryWrite</c>; when full the OLDEST entry is dropped (DropWrite) rather than
+/// blocking a request thread or throwing — logging must never throw or stall business code.
+/// Carries both SystemLog and AuditLog rows via a small union envelope.
+/// </summary>
+public sealed class SystemLogQueue
+{
+    private readonly Channel<LogEnvelope> _channel =
+        Channel.CreateBounded<LogEnvelope>(new BoundedChannelOptions(capacity: 4096)
+        {
+            FullMode = BoundedChannelFullMode.DropWrite,
+            SingleReader = true,
+            SingleWriter = false,
+        });
+
+    public bool TryEnqueue(SystemLog log) => _channel.Writer.TryWrite(new LogEnvelope(log, null));
+
+    public bool TryEnqueue(AuditLog log) => _channel.Writer.TryWrite(new LogEnvelope(null, log));
+
+    public IAsyncEnumerable<LogEnvelope> ReadAllAsync(CancellationToken cancellationToken) =>
+        _channel.Reader.ReadAllAsync(cancellationToken);
+}
+
+/// <summary>Either a SystemLog or an AuditLog — exactly one is non-null.</summary>
+public sealed record LogEnvelope(SystemLog? System, AuditLog? Audit);