Retry S3 link registry fetch on transient errors in match command (#3229)

Co-authored-by: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

Author: Mpdreamz

src/services/Elastic.Documentation.Assembler/ContentSources/RepositoryBuildMatchingService.cs

@@ -8,6 +8,7 @@
 using Elastic.Documentation.Configuration.Assembler;
 using Elastic.Documentation.Diagnostics;
 using Elastic.Documentation.LinkIndex;
+using Elastic.Documentation.Links;
 using Elastic.Documentation.Services;
 using Microsoft.Extensions.Logging;
 using Nullean.ScopedFileSystem;
@@ -24,6 +25,26 @@ ScopedFileSystem fileSystem
 {
 	private readonly ILogger _logger = logFactory.CreateLogger<RepositoryBuildMatchingService>();
 
+	private async Task<LinkRegistry> GetRegistryWithRetry(Aws3LinkIndexReader provider, Cancel ctx)
+	{
+		const int maxAttempts = 3;
+		for (var attempt = 1; attempt <= maxAttempts; attempt++)
+		{
+			try
+			{
+				return await provider.GetRegistry(ctx);
+			}
+			catch (Exception ex) when (attempt < maxAttempts)
+			{
+				var delay = TimeSpan.FromSeconds(Math.Pow(2, attempt));
+				_logger.LogWarning("S3 link registry fetch failed (attempt {Attempt}/{Max}), retrying in {Delay}s: {Message}",
+					attempt, maxAttempts, delay.TotalSeconds, ex.Message);
+				await Task.Delay(delay, ctx);
+			}
+		}
+		return await provider.GetRegistry(ctx);
+	}
+
 	//TODO return contentsourcematch
 	/// <summary>
 	/// Validates whether the <paramref name="branchOrTag"/> on <paramref name="repository"/> should be build and therefor published.
@@ -43,7 +64,7 @@ public async Task<bool> ShouldBuild(IDiagnosticsCollector collector, string? rep
 
 		// environment does not matter to check the configuration, defaulting to dev
 		var linkIndexProvider = Aws3LinkIndexReader.CreateAnonymous();
-		var linkRegistry = await linkIndexProvider.GetRegistry(ctx);
+		var linkRegistry = await GetRegistryWithRetry(linkIndexProvider, ctx);
 		var alreadyPublishing = linkRegistry.Repositories.ContainsKey(repo);
 		_logger.LogInformation("'{Repository}' publishing to link registry: {PublishState} ", repo, alreadyPublishing);
 		var assembleContext = new AssembleContext(configuration, configurationContext, "dev", collector, fileSystem, fileSystem, null, null);