feat: pre-flight filter of untrainable task types before gate

tests/unit/test_harness_checkpoint.py

@@ -157,6 +157,7 @@ class _FakeConfig:
     diag_size: int = 30
     val_size: int = 50
     batch_correct_ratio: float = 0.5
+    trainable_min_units: int = 8
     edit_budget_start: int = 6
     edit_budget_end: int = 3
     early_stop_patience: int = 3
@@ -289,6 +290,7 @@ class TestFingerprintStructuralVsDecision:
             "diag_size",
             "val_size",
             "batch_correct_ratio",
+            "trainable_min_units",
         }
         decision = {
             "edit_budget_start",