Fix DbContext concurrency error in parallel company verification

Use IDbContextFactory pattern to create isolated DbContext instances
for each cache operation, making parallel verification thread-safe.

Changes:
- Add IDbContextFactory<ApplicationDbContext> registration
- Update CompanyVerifierService to use factory for cache operations
- Update tests with InMemoryDatabaseRoot for shared test data

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/TrueCV.Tests/Services/CompanyVerifierServiceTests.cs

@@ -3,6 +3,8 @@ using System.Net.Http.Json;
 using System.Text.Json;
 using FluentAssertions;
 using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Diagnostics;
+using Microsoft.EntityFrameworkCore.Storage;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
 using Moq;
@@ -23,6 +25,8 @@ public class CompanyVerifierServiceTests : IDisposable
     private readonly ApplicationDbContext _dbContext;
     private readonly CompanyVerifierService _sut;
     private readonly HttpClient _httpClient;
+    private readonly DbContextOptions<ApplicationDbContext> _dbOptions;
+    private readonly InMemoryDatabaseRoot _dbRoot;
 
     private static readonly JsonSerializerOptions JsonOptions = new()
     {
@@ -46,13 +50,25 @@ public class CompanyVerifierServiceTests : IDisposable
 
         var client = new CompaniesHouseClient(_httpClient, settings, _mockClientLogger.Object);
 
-        var options = new DbContextOptionsBuilder<ApplicationDbContext>()
-            .UseInMemoryDatabase(databaseName: Guid.NewGuid().ToString())
+        // Use a shared InMemoryDatabaseRoot so all contexts share the same data store
+        _dbRoot = new InMemoryDatabaseRoot();
+        var dbName = Guid.NewGuid().ToString();
+
+        _dbOptions = new DbContextOptionsBuilder<ApplicationDbContext>()
+            .UseInMemoryDatabase(databaseName: dbName, databaseRoot: _dbRoot)
+            .ConfigureWarnings(w => w.Ignore(CoreEventId.ManyServiceProvidersCreatedWarning))
             .Options;
 
-        _dbContext = new ApplicationDbContext(options);
+        _dbContext = new ApplicationDbContext(_dbOptions);
 
-        _sut = new CompanyVerifierService(client, _dbContext, _mockServiceLogger.Object);
+        // Create a mock factory that returns a new context with the same in-memory database
+        var mockFactory = new Mock<IDbContextFactory<ApplicationDbContext>>();
+        mockFactory.Setup(f => f.CreateDbContext())
+            .Returns(() => new ApplicationDbContext(_dbOptions));
+        mockFactory.Setup(f => f.CreateDbContextAsync(It.IsAny<CancellationToken>()))
+            .ReturnsAsync(() => new ApplicationDbContext(_dbOptions));
+
+        _sut = new CompanyVerifierService(client, mockFactory.Object, _mockServiceLogger.Object);
     }
 
     public void Dispose()
@@ -313,8 +329,9 @@ public class CompanyVerifierServiceTests : IDisposable
         // Act
         await _sut.VerifyCompanyAsync(companyName, null, null);
 
-        // Assert
+        // Assert - use AsNoTracking to get fresh data from the store
         var cachedEntry = await _dbContext.CompanyCache
+            .AsNoTracking()
             .FirstOrDefaultAsync(c => c.CompanyNumber == "77777777");
 
         cachedEntry.Should().NotBeNull();
@@ -348,8 +365,9 @@ public class CompanyVerifierServiceTests : IDisposable
         // Act
         await _sut.VerifyCompanyAsync(companyName, null, null);
 
-        // Assert
+        // Assert - use AsNoTracking to get fresh data from the store
         var cachedEntry = await _dbContext.CompanyCache
+            .AsNoTracking()
             .FirstOrDefaultAsync(c => c.CompanyNumber == "55555555");
 
         cachedEntry.Should().NotBeNull();