test(streaming): fix #351 — the Debug-only FarLoad strip-test failure was the deliberate near-payload Debug.Assert, not a flake

The test feeds a far-tier factory returning Near payload on purpose to
prove the strip safety net. LandblockStreamer.HandleJob is documented
"fail loud in Debug builds and strip in Release": the Debug.Assert fires
on exactly that input, the VSTest host translates it into a thrown
DebugAssertException, and the worker catch folds it into a Failed
completion — deterministic on every Debug run since the test and the
tripwire landed in the same commit (090b0354). Release compiles the
assert out ([Conditional("DEBUG")]), so the strip runs and the test
passed there, which is why the Release gate never saw it.

The test now pins BOTH halves of the config-divergent contract via
"#if DEBUG": Debug expects the loud Failed carrying the assert text,
Release keeps the strip assertions. Production code unchanged.
LandblockBuildOriginTests 11/11 in Debug AND Release.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/AcDream.App.Tests/Streaming/LandblockBuildOriginTests.cs

@@ -221,6 +221,21 @@ public sealed class LandblockBuildOriginTests
             origin));
         streamer.Start();
 
+#if DEBUG
+        // The near-payload tripwire is config-divergent by design ("fail loud
+        // in Debug builds and strip in Release" — LandblockStreamer.HandleJob):
+        // in Debug the Debug.Assert fires and the VSTest host translates it
+        // into a thrown DebugAssertException, which the worker's catch folds
+        // into a Failed completion (#351).
+        var failed = Assert.IsType<LandblockStreamResult.Failed>(
+            await DrainFirstAsync(streamer));
+
+        Assert.Contains(
+            "Far-tier factory returned Near payload",
+            failed.Error,
+            StringComparison.Ordinal);
+        Assert.Equal(84ul, failed.Generation);
+#else
         var loaded = Assert.IsType<LandblockStreamResult.Loaded>(
             await DrainFirstAsync(streamer));
 
@@ -229,6 +244,7 @@ public sealed class LandblockBuildOriginTests
         Assert.Same(PhysicsDatBundle.Empty, loaded.Landblock.PhysicsDats);
         Assert.Null(loaded.Build.EnvCells);
         Assert.Equal(origin, loaded.Build.Origin);
+#endif
     }
 
     [Fact]