feat(discord): add DiscordPlatformMessenger IPlatformMessenger implementation

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/GmRelay.DiscordBot/Infrastructure/Discord/DiscordPlatformMessenger.cs

@@ -0,0 +1,71 @@
+using GmRelay.DiscordBot.Rendering;
+using GmRelay.Shared.Platform;
+using GmRelay.Shared.Rendering;
+using NetCord;
+using NetCord.Rest;
+
+namespace GmRelay.DiscordBot.Infrastructure.Discord;
+
+public sealed class DiscordPlatformMessenger(RestClient restClient) : IPlatformMessenger
+{
+    public async Task<PlatformMessageRef> SendScheduleAsync(PlatformScheduleMessage message, CancellationToken ct)
+    {
+        var (embeds, actionRows) = DiscordSessionBatchRenderer.Render(message.View);
+
+        var channelId = ulong.Parse(message.Group.ExternalChannelId
+            ?? message.Group.ExternalGroupId);
+
+        var msg = await restClient.SendMessageAsync(
+            channelId,
+            new MessageProperties()
+                .WithEmbeds(embeds)
+                .WithComponents(actionRows));
+
+        return new PlatformMessageRef(
+            PlatformKind.Discord,
+            message.Group.ExternalGroupId,
+            null,
+            msg.Id.ToString());
+    }
+
+    public async Task UpdateScheduleAsync(PlatformScheduleMessage message, CancellationToken ct)
+    {
+        if (message.ExistingMessage is null)
+            return;
+
+        var (embeds, actionRows) = DiscordSessionBatchRenderer.Render(message.View);
+
+        var channelId = ulong.Parse(message.Group.ExternalChannelId
+            ?? message.Group.ExternalGroupId);
+        var messageId = ulong.Parse(message.ExistingMessage.ExternalMessageId);
+
+        await restClient.ModifyMessageAsync(
+            channelId,
+            messageId,
+            options =>
+            {
+                options.Embeds = embeds;
+                options.Components = actionRows;
+            });
+    }
+
+    public Task SendGroupMessageAsync(PlatformGroup group, string htmlText, CancellationToken ct)
+    {
+        return Task.CompletedTask;
+    }
+
+    public Task SendPrivateMessageAsync(PlatformPrivateMessage message, CancellationToken ct)
+    {
+        return Task.CompletedTask;
+    }
+
+    public Task AnswerInteractionAsync(PlatformInteractionReply reply, CancellationToken ct)
+    {
+        return Task.CompletedTask;
+    }
+
+    public Task SendCalendarFileAsync(PlatformCalendarFile file, CancellationToken ct)
+    {
+        return Task.CompletedTask;
+    }
+}

tests/GmRelay.Bot.Tests/Discord/DiscordPlatformMessengerTests.cs

@@ -0,0 +1,21 @@
+using GmRelay.DiscordBot.Infrastructure.Discord;
+using GmRelay.Shared.Platform;
+using GmRelay.Shared.Rendering;
+
+namespace GmRelay.Bot.Tests.Discord;
+
+public sealed class DiscordPlatformMessengerTests
+{
+    [Fact]
+    public void Constructor_ShouldAcceptRestClient()
+    {
+        var constructor = typeof(DiscordPlatformMessenger).GetConstructor(new[] { typeof(NetCord.Rest.RestClient) });
+        Assert.NotNull(constructor);
+    }
+
+    [Fact]
+    public void DiscordPlatformMessenger_ShouldImplementIPlatformMessenger()
+    {
+        Assert.True(typeof(IPlatformMessenger).IsAssignableFrom(typeof(DiscordPlatformMessenger)));
+    }
+}