fix(discord): pace #info edits to stop per-channel rate-limit warnings

src/RustPlusBot.Discord/DiscordServiceCollectionExtensions.cs

@@ -33,6 +33,7 @@ public static IServiceCollection AddDiscordBot(this IServiceCollection services)
             }));
         services.AddSingleton<IUserDmSender, DiscordUserDmSender>();
         services.AddSingleton<RenderGate>();
+        services.AddSingleton<IChannelEditPacer, ChannelEditPacer>();
         services.AddSingleton<DiscordChannelMessenger>();
         services.AddHostedService<DiscordBotService>();
 

src/RustPlusBot.Discord/Posting/ChannelEditPacer.cs

@@ -0,0 +1,72 @@
+using System.Collections.Concurrent;
+using RustPlusBot.Abstractions.Time;
+
+namespace RustPlusBot.Discord.Posting;
+
+/// <summary>
+///     Per-channel edit pacer. Discord meters message edits per channel; the workspace refreshes several
+///     #info messages back-to-back on one tick, and a zero-gap burst exhausts that bucket, so Discord.Net
+///     preemptively waits on the tail edits and logs a rate-limit warning each time. This spreads the
+///     burst: successive edits to the same channel are held at least <c>minGap</c> apart. An edit to an
+///     idle channel (the common steady-state case) is not delayed at all.
+/// </summary>
+public sealed class ChannelEditPacer : IChannelEditPacer
+{
+    private readonly IClock _clock;
+    private readonly TimeSpan _minGap;
+
+    /// <summary>The earliest instant the next edit to each channel may be sent.</summary>
+    private readonly ConcurrentDictionary<ulong, DateTimeOffset> _nextAllowed = new();
+
+    /// <summary>Uses the default one-second spacing, comfortably under Discord's per-channel edit limit.</summary>
+    /// <param name="clock">Supplies the current time.</param>
+    public ChannelEditPacer(IClock clock) : this(clock, TimeSpan.FromSeconds(1))
+    {
+    }
+
+    /// <summary>Creates a pacer with an explicit minimum spacing between edits to a channel.</summary>
+    /// <param name="clock">Supplies the current time.</param>
+    /// <param name="minGap">The minimum spacing between successive edits to one channel; zero disables pacing.</param>
+    /// <exception cref="ArgumentOutOfRangeException">The gap is negative.</exception>
+    public ChannelEditPacer(IClock clock, TimeSpan minGap)
+    {
+        ArgumentNullException.ThrowIfNull(clock);
+        ArgumentOutOfRangeException.ThrowIfLessThan(minGap, TimeSpan.Zero);
+        _clock = clock;
+        _minGap = minGap;
+    }
+
+    /// <inheritdoc />
+    public async Task PaceAsync(ulong channelId, CancellationToken cancellationToken)
+    {
+        var wait = Reserve(channelId);
+        if (wait > TimeSpan.Zero)
+        {
+            await Task.Delay(wait, cancellationToken).ConfigureAwait(false);
+        }
+    }
+
+    /// <summary>
+    ///     Atomically reserves this call's edit slot for the channel and returns how long the caller must
+    ///     wait before sending it. Pure with respect to the clock, so the pacing decision is testable
+    ///     without real delays.
+    /// </summary>
+    /// <param name="channelId">The Discord channel the edit targets.</param>
+    /// <returns>The wait before the reserved slot; <see cref="TimeSpan.Zero" /> when the channel is idle.</returns>
+    public TimeSpan Reserve(ulong channelId)
+    {
+        var now = _clock.UtcNow;
+
+        // Reserve the slot after this one, starting from whichever is later: now, or the slot a
+        // concurrent/prior edit already claimed. The value returned is that next slot.
+        var nextAllowed = _nextAllowed.AddOrUpdate(
+            channelId,
+            now + _minGap,
+            (_, reserved) => (reserved > now ? reserved : now) + _minGap);
+
+        // This call's own slot is one gap before the slot it just reserved for the following edit.
+        var plannedSend = nextAllowed - _minGap;
+        var wait = plannedSend - now;
+        return wait > TimeSpan.Zero ? wait : TimeSpan.Zero;
+    }
+}

src/RustPlusBot.Discord/Posting/IChannelEditPacer.cs

@@ -0,0 +1,19 @@
+namespace RustPlusBot.Discord.Posting;
+
+/// <summary>
+///     Spaces out our own message edits to a channel so a burst never exhausts Discord's per-channel
+///     edit bucket (which otherwise makes Discord.Net preemptively throttle the tail of the burst and
+///     log a rate-limit warning). Shared process-wide, so every writer to a channel is paced against
+///     the same clock.
+/// </summary>
+public interface IChannelEditPacer
+{
+    /// <summary>
+    ///     Reserves the next edit slot for the channel and, if that slot is in the future, waits until it
+    ///     is due. Call immediately before editing; the first edit to an idle channel returns at once.
+    /// </summary>
+    /// <param name="channelId">The Discord channel the edit targets.</param>
+    /// <param name="cancellationToken">A cancellation token.</param>
+    /// <returns>A task that completes when the caller may send its edit.</returns>
+    Task PaceAsync(ulong channelId, CancellationToken cancellationToken);
+}

src/RustPlusBot.Features.Workspace/Reconciler/ServerInfoRefresher.cs

@@ -11,12 +11,14 @@ namespace RustPlusBot.Features.Workspace.Reconciler;
 /// <param name="renderers">All registered message renderers.</param>
 /// <param name="gate">Suppresses PATCHes for renders that did not change.</param>
 /// <param name="reconciler">The full reconcile, used to self-heal a missing or stale message.</param>
+/// <param name="pacer">Spaces this tick's edits so the burst does not exhaust the channel's edit bucket.</param>
 internal sealed class ServerInfoRefresher(
     IWorkspaceStore store,
     IWorkspaceGateway gateway,
     IEnumerable<IMessageRenderer> renderers,
     RenderGate gate,
-    IWorkspaceReconciler reconciler) : IServerInfoRefresher
+    IWorkspaceReconciler reconciler,
+    IChannelEditPacer pacer) : IServerInfoRefresher
 {
     /// <summary>The #info message keys this path refreshes, in declaration order.</summary>
     private static readonly string[] Keys =
@@ -69,6 +71,9 @@ public async Task RefreshAsync(ulong guildId, Guid serverId, CancellationToken c
 
             try
             {
+                // Space this edit from the previous one to the same channel so the tick's burst of #info
+                // edits does not exhaust Discord's per-channel edit bucket (an idle channel is not delayed).
+                await pacer.PaceAsync(record.DiscordChannelId, cancellationToken).ConfigureAwait(false);
                 await gateway
                     .EditMessageAsync(guildId, record.DiscordChannelId, record.DiscordMessageId, payload,
                         cancellationToken)

tests/RustPlusBot.Discord.Tests/Posting/ChannelEditPacerTests.cs

@@ -0,0 +1,84 @@
+using RustPlusBot.Abstractions.Time;
+using RustPlusBot.Discord.Posting;
+
+namespace RustPlusBot.Discord.Tests.Posting;
+
+public sealed class ChannelEditPacerTests
+{
+    private const ulong ChannelA = 500;
+    private const ulong ChannelB = 501;
+    private static readonly TimeSpan Gap = TimeSpan.FromSeconds(1);
+
+    [Fact]
+    public void A_negative_gap_is_rejected()
+    {
+        Assert.Throws<ArgumentOutOfRangeException>(() =>
+            new ChannelEditPacer(new TestClock(), TimeSpan.FromSeconds(-1)));
+    }
+
+    [Fact]
+    public void A_zero_gap_disables_pacing_without_throwing()
+    {
+        var pacer = new ChannelEditPacer(new TestClock(), TimeSpan.Zero);
+
+        Assert.Equal(TimeSpan.Zero, pacer.Reserve(ChannelA));
+        Assert.Equal(TimeSpan.Zero, pacer.Reserve(ChannelA));
+    }
+
+    [Fact]
+    public void First_edit_to_a_channel_waits_zero()
+    {
+        var pacer = new ChannelEditPacer(new TestClock(), Gap);
+
+        Assert.Equal(TimeSpan.Zero, pacer.Reserve(ChannelA));
+    }
+
+    [Fact]
+    public void Successive_edits_in_the_same_instant_are_staggered_by_the_gap()
+    {
+        var pacer = new ChannelEditPacer(new TestClock(), Gap);
+
+        Assert.Equal(TimeSpan.Zero, pacer.Reserve(ChannelA));
+        Assert.Equal(Gap, pacer.Reserve(ChannelA));
+        Assert.Equal(Gap * 2, pacer.Reserve(ChannelA));
+    }
+
+    [Fact]
+    public void An_edit_after_the_gap_has_elapsed_waits_zero()
+    {
+        var clock = new TestClock();
+        var pacer = new ChannelEditPacer(clock, Gap);
+
+        pacer.Reserve(ChannelA);
+        clock.UtcNow = clock.UtcNow.Add(Gap);
+
+        Assert.Equal(TimeSpan.Zero, pacer.Reserve(ChannelA));
+    }
+
+    [Fact]
+    public void An_edit_partway_through_the_gap_waits_only_the_remainder()
+    {
+        var clock = new TestClock();
+        var pacer = new ChannelEditPacer(clock, Gap);
+
+        pacer.Reserve(ChannelA);
+        clock.UtcNow = clock.UtcNow.Add(TimeSpan.FromMilliseconds(400));
+
+        Assert.Equal(TimeSpan.FromMilliseconds(600), pacer.Reserve(ChannelA));
+    }
+
+    [Fact]
+    public void Channels_are_paced_independently()
+    {
+        var pacer = new ChannelEditPacer(new TestClock(), Gap);
+
+        pacer.Reserve(ChannelA);
+
+        Assert.Equal(TimeSpan.Zero, pacer.Reserve(ChannelB));
+    }
+
+    private sealed class TestClock : IClock
+    {
+        public DateTimeOffset UtcNow { get; set; } = DateTimeOffset.UnixEpoch;
+    }
+}

tests/RustPlusBot.Features.Workspace.Tests/Reconciler/ServerInfoRefresherTests.cs

@@ -43,7 +43,7 @@ public async Task First_refresh_edits_the_message()
         var gateway = Substitute.For<IWorkspaceGateway>();
         var reconciler = Substitute.For<IWorkspaceReconciler>();
         var refresher = new ServerInfoRefresher(StoreWith(WorkspaceMessageKeys.ServerInfo), gateway, [renderer],
-            new RenderGate(), reconciler);
+            new RenderGate(), reconciler, Pacer());
 
         await refresher.RefreshAsync(GuildId, ServerId, default);
 
@@ -58,7 +58,7 @@ public async Task Unchanged_render_is_not_sent_twice()
         var gateway = Substitute.For<IWorkspaceGateway>();
         var reconciler = Substitute.For<IWorkspaceReconciler>();
         var refresher = new ServerInfoRefresher(StoreWith(WorkspaceMessageKeys.ServerInfo), gateway, [renderer],
-            new RenderGate(), reconciler);
+            new RenderGate(), reconciler, Pacer());
 
         await refresher.RefreshAsync(GuildId, ServerId, default);
         await refresher.RefreshAsync(GuildId, ServerId, default);
@@ -75,7 +75,7 @@ public async Task Changed_render_is_sent_again()
         var gateway = Substitute.For<IWorkspaceGateway>();
         var reconciler = Substitute.For<IWorkspaceReconciler>();
         var refresher = new ServerInfoRefresher(StoreWith(WorkspaceMessageKeys.ServerInfo), gateway, [renderer],
-            new RenderGate(), reconciler);
+            new RenderGate(), reconciler, Pacer());
 
         await refresher.RefreshAsync(GuildId, ServerId, default);
         renderer.Title = "v2";
@@ -95,7 +95,7 @@ public async Task Missing_message_row_escalates_to_full_reconcile()
             .Returns((ProvisionedMessage?)null);
         var gateway = Substitute.For<IWorkspaceGateway>();
         var reconciler = Substitute.For<IWorkspaceReconciler>();
-        var refresher = new ServerInfoRefresher(store, gateway, [renderer], new RenderGate(), reconciler);
+        var refresher = new ServerInfoRefresher(store, gateway, [renderer], new RenderGate(), reconciler, Pacer());
 
         await refresher.RefreshAsync(GuildId, ServerId, default);
 
@@ -122,7 +122,7 @@ public async Task Edit_failure_escalates_and_invalidates_the_gate()
         var reconciler = Substitute.For<IWorkspaceReconciler>();
         var gate = new RenderGate();
         var refresher = new ServerInfoRefresher(StoreWith(WorkspaceMessageKeys.ServerInfo), gateway, [renderer], gate,
-            reconciler);
+            reconciler, Pacer());
 
         await refresher.RefreshAsync(GuildId, ServerId, default);
 
@@ -141,7 +141,7 @@ public async Task Empty_payload_is_skipped_without_editing()
         var gateway = Substitute.For<IWorkspaceGateway>();
         var reconciler = Substitute.For<IWorkspaceReconciler>();
         var refresher = new ServerInfoRefresher(StoreWith(WorkspaceMessageKeys.ServerInfo), gateway, [renderer],
-            new RenderGate(), reconciler);
+            new RenderGate(), reconciler, Pacer());
 
         await refresher.RefreshAsync(GuildId, ServerId, default);
 
@@ -164,13 +164,50 @@ public async Task Refreshes_all_three_info_messages()
             WorkspaceMessageKeys.ServerTeam);
         var gateway = Substitute.For<IWorkspaceGateway>();
         var refresher = new ServerInfoRefresher(store, gateway, renderers, new RenderGate(),
-            Substitute.For<IWorkspaceReconciler>());
+            Substitute.For<IWorkspaceReconciler>(), Pacer());
 
         await refresher.RefreshAsync(GuildId, ServerId, default);
 
         Assert.All(renderers.Cast<StubRenderer>(), r => Assert.Equal(1, r.Calls));
     }
 
+    [Fact]
+    public async Task Each_edit_is_paced_before_it_is_sent()
+    {
+        var renderer = new StubRenderer(WorkspaceMessageKeys.ServerInfo, "v1");
+        var gateway = Substitute.For<IWorkspaceGateway>();
+        var pacer = Pacer();
+        var refresher = new ServerInfoRefresher(StoreWith(WorkspaceMessageKeys.ServerInfo), gateway, [renderer],
+            new RenderGate(), Substitute.For<IWorkspaceReconciler>(), pacer);
+
+        await refresher.RefreshAsync(GuildId, ServerId, default);
+
+        Received.InOrder(() =>
+        {
+            _ = pacer.PaceAsync(ChannelId, Arg.Any<CancellationToken>());
+            _ = gateway.EditMessageAsync(GuildId, ChannelId, MessageId, Arg.Any<MessagePayload>(),
+                Arg.Any<CancellationToken>());
+        });
+    }
+
+    [Fact]
+    public async Task A_skipped_unchanged_render_is_not_paced()
+    {
+        var renderer = new StubRenderer(WorkspaceMessageKeys.ServerInfo, "v1");
+        var gateway = Substitute.For<IWorkspaceGateway>();
+        var pacer = Pacer();
+        var refresher = new ServerInfoRefresher(StoreWith(WorkspaceMessageKeys.ServerInfo), gateway, [renderer],
+            new RenderGate(), Substitute.For<IWorkspaceReconciler>(), pacer);
+
+        await refresher.RefreshAsync(GuildId, ServerId, default);
+        await refresher.RefreshAsync(GuildId, ServerId, default);
+
+        // Second render is identical, so the gate suppresses the edit — and the pace with it.
+        await pacer.Received(1).PaceAsync(ChannelId, Arg.Any<CancellationToken>());
+    }
+
+    private static IChannelEditPacer Pacer() => Substitute.For<IChannelEditPacer>();
+
     private sealed class StubRenderer(string key, string title) : IMessageRenderer
     {
         public int Calls { get; private set; }