diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8f6207b..1c0aefa 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -112,9 +112,11 @@ jobs:
         cd rust && cargo clippy -- -D warnings
 
   # Critical test suite (parallel matrix)
+  # Push to main: runs on lab self-hosted runners (consistent perf, free minutes)
+  # PRs: runs on GitHub-hosted runners (untrusted code never touches lab infra)
   test-critical:
     name: Tests (Python ${{ matrix.python-version }})
-    runs-on: ubuntu-latest
+    runs-on: ${{ github.event_name == 'push' && 'cachekit' || 'ubuntu-latest' }}
     timeout-minutes: 15
     permissions:
       contents: read
diff --git a/tests/unit/test_consolidated_decorator.py b/tests/unit/test_consolidated_decorator.py
index 7bf0f48..8837e54 100644
--- a/tests/unit/test_consolidated_decorator.py
+++ b/tests/unit/test_consolidated_decorator.py
@@ -9,6 +9,8 @@
 Requirements: 5.1, 5.2, 5.3
 """
 
+from __future__ import annotations
+
 import asyncio
 import time
 from unittest.mock import patch
@@ -32,11 +34,11 @@ def test_all_feature_combinations_sync(
 
         # Use intent-based presets instead of individual feature flags
         if use_preset == "minimal":
-            decorator = cache.minimal(ttl=300, namespace="feature_test")
+            decorator = cache.minimal(ttl=300, namespace="feature_test_minimal")
         elif use_preset == "production":
-            decorator = cache.production(ttl=300, namespace="feature_test")
+            decorator = cache.production(ttl=300, namespace="feature_test_production")
         else:
-            decorator = cache(ttl=300, namespace="feature_test")
+            decorator = cache(ttl=300, namespace="feature_test_default")
 
         @decorator
         def test_function(x: int) -> str:
@@ -95,11 +97,11 @@ async def test_all_feature_combinations_async(
 
         # Use intent-based presets instead of individual feature flags
         if use_preset == "minimal":
-            decorator = cache.minimal(ttl=300, namespace="async_feature_test")
+            decorator = cache.minimal(ttl=300, namespace="async_feature_test_minimal")
         elif use_preset == "production":
-            decorator = cache.production(ttl=300, namespace="async_feature_test")
+            decorator = cache.production(ttl=300, namespace="async_feature_test_production")
         else:
-            decorator = cache(ttl=300, namespace="async_feature_test")
+            decorator = cache(ttl=300, namespace="async_feature_test_default")
 
         @decorator
         async def async_test_function(x: int) -> str:
diff --git a/tests/unit/test_key_generator_blake2b.py b/tests/unit/test_key_generator_blake2b.py
index 7bb8234..decf729 100644
--- a/tests/unit/test_key_generator_blake2b.py
+++ b/tests/unit/test_key_generator_blake2b.py
@@ -91,18 +91,36 @@ def test_func(data):
         # Should complete within reasonable time
         assert blake2b_time < 1.0
 
-    def test_blake2b_with_numpy_arrays_raises_type_error(self):
-        """Test that NumPy arrays raise TypeError (fail fast)."""
+    def test_blake2b_with_numpy_arrays_supported(self):
+        """Test that 1D NumPy arrays with supported dtypes generate valid keys."""
 
         def test_func(arr):
             return arr.sum()
 
-        arr = np.arange(1000)
+        arr = np.arange(1000)  # 1D, int64, well under 100KB
         gen = CacheKeyGenerator()
 
-        # Should raise TypeError for unsupported type
-        with pytest.raises(TypeError, match="Unsupported type for cache key generation"):
-            gen.generate_key(test_func, (arr,), {})
+        # Constrained numpy arrays are now supported (round-table review 2025-12-18)
+        key = gen.generate_key(test_func, (arr,), {})
+        assert isinstance(key, str)
+        assert len(key) > 0
+
+        # Deterministic
+        key2 = gen.generate_key(test_func, (arr,), {})
+        assert key == key2
+
+    def test_blake2b_with_unsupported_numpy_arrays_raises(self):
+        """Test that numpy arrays violating constraints raise TypeError."""
+
+        def test_func(arr):
+            return arr.sum()
+
+        gen = CacheKeyGenerator()
+
+        # 2D array — not supported
+        arr_2d = np.arange(100).reshape(10, 10)
+        with pytest.raises(TypeError, match="Only 1D arrays supported"):
+            gen.generate_key(test_func, (arr_2d,), {})
 
     def test_blake2b_with_custom_objects(self):
         """Test Blake2b with basic objects that can be pickled."""
@@ -223,14 +241,14 @@ def test_unsupported_types_raise_type_error(self):
         def test_func(data):
             return data
 
-        # Test datetime
+        # Test naive datetime (rejected for timezone ambiguity)
         import datetime
 
-        with pytest.raises(TypeError, match="Unsupported type"):
+        with pytest.raises(TypeError, match="Naive datetime not allowed"):
             gen.generate_key(test_func, (datetime.datetime.now(),), {})
 
-        # Test set
-        with pytest.raises(TypeError, match="Unsupported type"):
+        # Test set (rejected for non-deterministic sorting)
+        with pytest.raises(TypeError, match="set/frozenset not supported"):
             gen.generate_key(test_func, ({1, 2, 3},), {})
 
         # Test custom class