Ingest: Add post-indexing content date resolution (#3112)

* Search: Add post-indexing content date resolution via update_by_query

HashedBulkUpdate uses bulk update actions (scripted upserts) which skip
Elasticsearch ingest pipelines, so content_last_updated was never set
during normal indexing. This adds a ResolveContentDatesAsync step that
runs _update_by_query with the enrichment pipeline after indexing
completes, and switches StopAsync to use read aliases instead of the
write target (which is removed after CompleteAsync).

Includes integration tests against a real Elasticsearch container
validating cold-start, date preservation, change detection, and the
bulk-update pipeline gap.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Search: Fix lint warnings in content date enrichment tests

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

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

Author: 2 people

src/Elastic.Markdown/Exporters/Elasticsearch/ElasticsearchMarkdownExporter.cs

@@ -224,7 +224,14 @@ public async ValueTask StartAsync(Cancel ctx = default)
 	public async ValueTask StopAsync(Cancel ctx = default)
 	{
 		_ = await _orchestrator.CompleteAsync(null, ctx);
-		await _contentDateEnrichment.SyncLookupIndexAsync(_lexicalTypeContext.IndexStrategy!.WriteTarget!, ctx);
+
+		// Resolve content_last_updated for documents where the ingest pipeline didn't fire.
+		// HashedBulkUpdate uses bulk update actions, which skip ingest pipelines.
+		// Use the read alias (-latest) rather than WriteTarget, which is removed after CompleteAsync.
+		await _contentDateEnrichment.ResolveContentDatesAsync(_lexicalReadAlias, ctx);
+		await _contentDateEnrichment.ResolveContentDatesAsync(_semanticReadAlias, ctx);
+
+		await _contentDateEnrichment.SyncLookupIndexAsync(_lexicalReadAlias, ctx);
 	}
 
 		// Resolve content_last_updated for documents where the ingest pipeline didn't fire.