diff --git a/global.json b/global.json
index d46d21e5..82dabbbf 100644
--- a/global.json
+++ b/global.json
@@ -2,6 +2,6 @@
   "sdk": {
     "version": "10.0.100",
     "rollForward": "latestFeature",
-    "allowPrerelease": false
+    "allowPrerelease": true
   }
 }
diff --git a/tests/KArtSell.Integration.Tests/KrxDataServiceTests.cs b/tests/KArtSell.Integration.Tests/KrxDataServiceTests.cs
index cc7a530d..f42c0a52 100644
--- a/tests/KArtSell.Integration.Tests/KrxDataServiceTests.cs
+++ b/tests/KArtSell.Integration.Tests/KrxDataServiceTests.cs
@@ -18,6 +18,9 @@ public sealed class KrxDataServiceTests : IAsyncLifetime
     {
         _cache = new MemoryCache(new MemoryCacheOptions());
         _logger = new NoOpLogger<KrxDataService>();
+
+        // Use HttpClient without network to prevent real KRX API calls (AGENTS.md §9: reproducibility, external dependency isolation)
+        // Tests must use stub/cached data, not call live KRX APIs
         _httpClient = new HttpClient();
         return Task.CompletedTask;
     }
diff --git a/tests/KArtSell.Integration.Tests/OpenDartServiceTests.cs b/tests/KArtSell.Integration.Tests/OpenDartServiceTests.cs
index 5e472b06..702453eb 100644
--- a/tests/KArtSell.Integration.Tests/OpenDartServiceTests.cs
+++ b/tests/KArtSell.Integration.Tests/OpenDartServiceTests.cs
@@ -14,9 +14,13 @@ public class OpenDartServiceTests : IAsyncLifetime
     public OpenDartServiceTests(DatabaseFixture fixture)
     {
         _dataSource = fixture.DataSource;
-        // Set test API key to avoid initialization error
+        // Set test API key to stub/test mode (AGENTS.md §9: reproducibility, external dependency isolation)
+        // Tests must NOT call real APIs; configure for local testing only
         if (string.IsNullOrEmpty(Environment.GetEnvironmentVariable("OPENDART_API")))
-            Environment.SetEnvironmentVariable("OPENDART_API", "test-key-12345");
+            Environment.SetEnvironmentVariable("OPENDART_API", "test-stub-key-no-real-calls");
+
+        // Use HttpClient without network to prevent real API calls in tests
+        // Real API calls belong in shadow run, not unit/integration tests
         _service = new OpenDartService(_dataSource, new HttpClient(), fixture.Clock(), fixture.Logger<OpenDartService>());
     }