feat: add ResetCommandsOnStartup flag to clear stale global commands

Adds an opt-in DiscordOptions.ResetCommandsOnStartup toggle. When enabled,
DiscordBotService deletes all global application commands on ready before
registering the current command set per guild, so leftover commands from a
bot that previously used the same Discord application can be cleared.

Documents the one-shot usage in docs/development/running-locally.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: HandyS11

docs/development/running-locally.md

@@ -25,6 +25,21 @@
 
 A missing or empty `Discord:Token` makes the host fail fast at startup with a clear `OptionsValidationException`.
 
+## Clearing stale slash commands
+
+If the Discord application was previously used by another bot, leftover **global** commands can
+appear in every guild alongside this bot's commands. Run once with `Discord:ResetCommandsOnStartup`
+enabled to delete all global commands at startup before the current commands are registered:
+
+```bash
+dotnet run --project src/RustPlusBot.Host -- --Discord:ResetCommandsOnStartup=true
+```
+
+The flag also reads from the `Discord__ResetCommandsOnStartup` environment variable or a
+`"Discord": { "ResetCommandsOnStartup": true }` entry in configuration. It is a one-shot: once the
+stale global commands are gone, leave it off for normal runs. Per-guild commands are already
+overwritten on every startup, so a normal run after the reset leaves only the current command set.
+
 ## Provisioning the workspace
 
 1. Invite the bot with the **Manage Channels**, **Manage Roles**, **Manage Messages**, and

src/RustPlusBot.Discord/DiscordBotService.cs

@@ -68,6 +68,13 @@ private async Task OnReadyAsync()
             return;
         }
 
+        if (_options.ResetCommandsOnStartup)
+        {
+            await client.Rest.DeleteAllGlobalCommandsAsync().ConfigureAwait(false);
+            logger.LogWarning(
+                "ResetCommandsOnStartup is enabled: deleted all global application commands before registration.");
+        }
+
         foreach (var guild in client.Guilds)
         {
             await interactions.RegisterCommandsToGuildAsync(guild.Id).ConfigureAwait(false);

src/RustPlusBot.Discord/DiscordOptions.cs

@@ -5,4 +5,11 @@ public sealed class DiscordOptions
 {
     /// <summary>The bot token.</summary>
     public string Token { get; set; } = string.Empty;
+
+    /// <summary>
+    /// When <see langword="true"/>, deletes all global application commands on startup before
+    /// registering the bot's commands. Use as a one-shot to clear stale commands left by another
+    /// bot that previously used this application, then leave disabled for normal runs.
+    /// </summary>
+    public bool ResetCommandsOnStartup { get; set; }
 }