This PR enhances the type safety of the ITextSearch<TRecord> interface by changing the GetSearchResultsAsync method to return KernelSearchResults<TRecord> instead of KernelSearchResults<object>. This improvement eliminates the need for manual casting and provides better IntelliSense support for consumers.

Motivation and Context

The current implementation of ITextSearch<TRecord>.GetSearchResultsAsync returns KernelSearchResults<object>, which requires consumers to manually cast results to the expected type. This reduces type safety and degrades the developer experience by losing compile-time type checking and IntelliSense support.

This change aligns the return type with the generic type parameter TRecord, providing the expected strongly-typed results that users of a generic interface would anticipate.

Changes Made

Interface (ITextSearch.cs)

• Changed ITextSearch<TRecord>.GetSearchResultsAsync return type from KernelSearchResults<object> to KernelSearchResults<TRecord>
• Updated XML documentation to reflect strongly-typed return value
• Legacy ITextSearch interface (non-generic) remains unchanged, continuing to return KernelSearchResults<object> for backward compatibility

Implementation (VectorStoreTextSearch.cs)

• Added new GetResultsAsTRecordAsync helper method returning IAsyncEnumerable<TRecord>
• Updated generic interface implementation to use the new strongly-typed helper
• Retained GetResultsAsRecordAsync method for the legacy non-generic interface

Tests (VectorStoreTextSearchTests.cs)

• Updated 3 unit tests to use strongly-typed DataModel or DataModelWithRawEmbedding instead of object
• Improved test assertions to leverage direct property access without casting
• All 19 tests pass successfully

Breaking Changes

Interface Change (Experimental API):

• ITextSearch<TRecord>.GetSearchResultsAsync now returns KernelSearchResults<TRecord> instead of KernelSearchResults<object>
• This interface is marked with [Experimental("SKEXP0001")], indicating that breaking changes are expected during the preview period
• Legacy ITextSearch interface (non-generic) is unaffected and maintains full backward compatibility

Benefits

• Improved Type Safety: Eliminates runtime casting errors by providing compile-time type checking
• Enhanced Developer Experience: Full IntelliSense support for TRecord properties and methods
• Cleaner Code: Consumers no longer need to cast results from object to the expected type
• Consistent API Design: Generic interface now behaves as expected, returning strongly-typed results
• Zero Impact on Legacy Code: Non-generic ITextSearch interface remains unchanged

Testing

• All 19 existing unit tests pass
• Updated tests demonstrate improved type safety with direct property access
• Verified both generic and legacy interfaces work correctly
• Confirmed zero breaking changes to non-generic ITextSearch consumers

Related Work

This PR is part of the Issue #10456 multi-PR chain for modernizing ITextSearch with LINQ-based filtering:

• PR .Net: feat: Implement type-safe LINQ filtering for ITextSearch interface (microsoft#10456) #13175: Foundation (ITextSearch interface) - Merged
• PR .NET: Add ITextSearch<TRecord> with LINQ filtering and deprecate legacy ITextSearch (#10456) #13179: VectorStoreTextSearch + deprecation pattern - In Review
• This PR (2.1): API refinement for improved type safety
• PR .Net: feat: Modernize BingTextSearch connector with ITextSearch<TRecord> interface (microsoft#10456) #13188-13191: Connector migrations (Bing, Google, Tavily, Brave) - Pending
• PR .Net: feat: Modernize samples and documentation for ITextSearch<TRecord> interface (microsoft#10456) #13194: Samples and documentation - Pending

All PRs target the feature-text-search-linq branch for coordinated release.

Migration Guide for Consumers

Before (Previous API)

ITextSearch<DataModel> search = ...;
KernelSearchResults<object> results = await search.GetSearchResultsAsync("query", options);

foreach (var obj in results.Results)
{
    var record = (DataModel)obj;  // Manual cast required
    Console.WriteLine(record.Name);
}

After (Improved API)

ITextSearch<DataModel> search = ...;
KernelSearchResults<DataModel> results = await search.GetSearchResultsAsync("query", options);

foreach (var record in results.Results)  // Strongly typed!
{
    Console.WriteLine(record.Name);  // Direct property access with IntelliSense
}

Checklist

• Changes build successfully
• All unit tests pass (19/19)
• XML documentation updated
• Breaking change documented (experimental API only)
• Legacy interface backward compatibility maintained
• Code follows project coding standards