feat: add dns-sync fmt command with semantic record sorting

src/DnsSync/Commands/FmtCommand.cs

@@ -0,0 +1,94 @@
+using DnsSync.Core;
+using DnsSync.Providers.Yaml;
+using Spectre.Console;
+using Spectre.Console.Cli;
+
+namespace DnsSync.Commands;
+
+public class FmtCommand : Command<FmtSettings>
+{
+    protected override int Execute(CommandContext context, FmtSettings settings, CancellationToken cancellationToken)
+    {
+        var directory = Path.GetFullPath(settings.Directory);
+
+        if (!System.IO.Directory.Exists(directory))
+        {
+            AnsiConsole.MarkupLine($"[red]✗[/] Directory not found: {Markup.Escape(directory)}");
+            return 1;
+        }
+
+        var files = System.IO.Directory.GetFiles(directory, "*.yaml")
+            .OrderBy(f => f)
+            .ToList();
+
+        if (files.Count == 0)
+        {
+            AnsiConsole.MarkupLine($"[yellow]~[/] No .yaml files found in {Markup.Escape(directory)}");
+            return 0;
+        }
+
+        var changed = 0;
+        var unchanged = 0;
+
+        foreach (var file in files)
+        {
+            var fileName = Path.GetFileNameWithoutExtension(file);
+            var zoneName = fileName + ".";
+            var original = File.ReadAllText(file);
+
+            IReadOnlyList<DnsRecord> records;
+            try
+            {
+                records = YamlProvider.ParseZoneYaml(original, zoneName);
+            }
+            catch (Exception ex)
+            {
+                AnsiConsole.MarkupLine($"  [red]✗[/] {Markup.Escape(fileName)}.yaml, parse error: {Markup.Escape(ex.Message)}");
+                continue;
+            }
+
+            var zone = new DnsZone { Name = zoneName, Records = records.ToList() };
+            var formatted = ZoneYamlSerializer.Serialize(zone);
+
+            if (formatted == original)
+            {
+                unchanged++;
+                continue;
+            }
+
+            changed++;
+
+            if (settings.Check)
+            {
+                AnsiConsole.MarkupLine($"  [yellow]~[/] {Markup.Escape(fileName)}.yaml would be reformatted");
+            }
+            else
+            {
+                File.WriteAllText(file, formatted);
+                AnsiConsole.MarkupLine($"  [green]✓[/] {Markup.Escape(fileName)}.yaml");
+            }
+        }
+
+        AnsiConsole.WriteLine();
+
+        if (settings.Check)
+        {
+            if (changed > 0)
+            {
+                AnsiConsole.MarkupLine($"[yellow]~[/] {changed} file(s) would be reformatted");
+                return 1;
+            }
+
+            AnsiConsole.MarkupLine($"[green]✓[/] All {unchanged} file(s) already formatted");
+            return 0;
+        }
+
+        if (changed > 0)
+            AnsiConsole.MarkupLine($"[green]✓[/] Reformatted [bold]{changed}[/] file(s)");
+
+        if (unchanged > 0)
+            AnsiConsole.MarkupLine($"[dim]{unchanged} file(s) already formatted[/]");
+
+        return 0;
+    }
+}

src/DnsSync/Commands/FmtSettings.cs

@@ -0,0 +1,16 @@
+using System.ComponentModel;
+using Spectre.Console.Cli;
+
+namespace DnsSync.Commands;
+
+public class FmtSettings : CommandSettings
+{
+    [CommandArgument(0, "[DIRECTORY]")]
+    [Description("Directory containing zone YAML files (default: ./zones)")]
+    [DefaultValue("./zones")]
+    public string Directory { get; set; } = "./zones";
+
+    [CommandOption("--check")]
+    [Description("Check formatting without writing changes (exit 1 if files would change)")]
+    public bool Check { get; set; }
+}

src/DnsSync/Program.cs

@@ -154,6 +154,11 @@
         .WithExample(["diff", "--from", "cloudflare", "--to", "route53", "--config", "config.yaml"])
         .WithExample(["diff", "--from", "cloudflare", "--to", "porkbun", "--zone", "example.com.", "--config", "config.yaml"]);
 
+    config.AddCommand<FmtCommand>("fmt")
+        .WithDescription("Reformat zone YAML files to canonical sorted style")
+        .WithExample(["fmt"])
+        .WithExample(["fmt", "./zones", "--check"]);
+
     config.AddCommand<DriftCommand>("drift")
         .WithDescription("Detect DNS record drift from desired state without applying changes")
         .WithExample(["drift", "--config", "config.yaml"])

src/DnsSync/Providers/Yaml/ZoneYamlSerializer.cs

@@ -10,6 +10,37 @@ namespace DnsSync.Providers.Yaml;
 /// </summary>
 public static class ZoneYamlSerializer
 {
+    private static readonly Dictionary<string, int> RecordTypeOrder = new(StringComparer.OrdinalIgnoreCase)
+    {
+        ["SOA"] = 0,
+        ["NS"] = 1,
+        ["A"] = 2,
+        ["AAAA"] = 3,
+        ["CNAME"] = 4,
+        ["MX"] = 5,
+        ["TXT"] = 6,
+        ["SRV"] = 7,
+        ["CAA"] = 8,
+    };
+
+    private static int GetTypeOrder(string type) =>
+        RecordTypeOrder.TryGetValue(type, out var order) ? order : 100;
+
+    /// <summary>
+    /// Returns a sorted copy of the record with MX values ordered by preference ascending.
+    /// Non-MX records are returned as-is.
+    /// </summary>
+    private static DnsRecord SortRecordValues(DnsRecord record)
+    {
+        if (record is MxRecord mx && mx.Values.Count > 1)
+        {
+            var sorted = mx.Values.OrderBy(v => v.Preference).ThenBy(v => v.Exchange, StringComparer.OrdinalIgnoreCase).ToList();
+            return new MxRecord { Name = mx.Name, Type = mx.Type, Ttl = mx.Ttl, Values = sorted };
+        }
+
+        return record;
+    }
+
     public static string Serialize(DnsZone zone, string? providerName = null)
     {
         var sb = new StringBuilder();
@@ -18,15 +49,20 @@ public static string Serialize(DnsZone zone, string? providerName = null)
         sb.AppendLine($"# Imported {fromClause}by dns-sync on {DateTime.UtcNow:yyyy-MM-dd}");
         sb.AppendLine();
 
-        // Group records by subdomain key for output
+        // Group records by subdomain key, apex first then alphabetical
         var bySubdomain = zone.Records
             .GroupBy(r => SubdomainKey(r.Name, zone.Name))
-            .OrderBy(g => g.Key == "" ? "\0" : g.Key); // apex first
+            .OrderBy(g => g.Key == "" ? "\0" : g.Key); // apex first, then alphabetical
 
         foreach (var group in bySubdomain)
         {
             var key = group.Key;
-            var records = group.ToList();
+            // Sort records within each subdomain: semantic type order, then alphabetical
+            var records = group
+                .Select(SortRecordValues)
+                .OrderBy(r => GetTypeOrder(r.Type))
+                .ThenBy(r => r.Type, StringComparer.OrdinalIgnoreCase)
+                .ToList();
             var yamlKey = key == "" ? "''" : key;
 
             if (records.Count == 1)