fix: key singleton mutex on config folder (#2946)

* fix: key singleton mutex on config folder

* update changelog

---------

Co-authored-by: Jason Dove <1695733+jasongdove@users.noreply.github.com>

CHANGELOG.md

@@ -12,6 +12,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
   - Playlists ignored this setting in earlier builds
 - Always randomize start points for all collections the first time they are used
   - Previously, only collections scheduled during the first day of a playout build had their start points randomized
+- Allow multiple ETV instances when multiple config folders are used
 
 ## [26.6.0] - 2026-07-09
 ### Added

ErsatzTV/Program.cs

@@ -1,6 +1,8 @@
 using System.Diagnostics;
 using System.Globalization;
 using System.Runtime.InteropServices;
+using System.Security.Cryptography;
+using System.Text;
 using Destructurama;
 using ErsatzTV.Core;
 using ErsatzTV.Services.Validators;
@@ -47,9 +49,14 @@ public class Program
 
     public static async Task<int> Main(string[] args)
     {
+        // Keyed on the config folder, not a constant, so an instance running against an
+        // isolated ETV_CONFIG_FOLDER (a staging copy) can coexist with the primary one.
+        string singletonId = Convert.ToHexString(
+            SHA256.HashData(Encoding.UTF8.GetBytes(FileSystemLayout.AppDataFolder)))[..16];
+
         using var _ = new Mutex(
             true,
-            "Global\\ErsatzTV.Singleton.74360cd8985c4d1fb6bc9e81887206fe",
+            $"Global\\ErsatzTV.Singleton.{singletonId}",
             out bool createdNew);
         if (!createdNew)
         {