test: exercise golden row comparison boundary

.superpowers/sdd/task-7-report.md

@@ -220,6 +220,7 @@ Fail-first evidence included:
 Final verification:
 
 - focused second-round trust-boundary suite: `39 passed`;
+- Golden negative tests use real file SHA-256 and equal-row content drift to exercise worker-side row comparison;
 - focused data-rule/API/migration suite from the initial delivery:
   `183 passed`;
 - Runner plus real PostgreSQL/MySQL/Polars regression: `126 passed`;

tests/runner/test_polars_worker.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import hashlib
 import os
 from concurrent.futures import ThreadPoolExecutor
 
@@ -14,6 +15,14 @@ from tests.core.data_rules.test_polars_compiler import (
 )
 
 
+def _sha256(path) -> str:
+    digest = hashlib.sha256()
+    with path.open("rb") as handle:
+        for chunk in iter(lambda: handle.read(1024 * 1024), b""):
+            digest.update(chunk)
+    return digest.hexdigest()
+
+
 def _compile_worker_plan(
     *,
     input_schema,
@@ -201,7 +210,7 @@ def test_worker_rejects_golden_row_drift_inside_isolated_boundary(tmp_path):
                 "lookup_paths": {},
                 "output_path": str(tmp_path / "golden-output.parquet"),
                 "golden_path": str(golden_path),
-                "golden_digest": "a" * 64,
+                "golden_digest": _sha256(golden_path),
                 "masking_policies": {},
             },
             memory_limit_bytes=plan["resource_limits"][
@@ -239,10 +248,18 @@ def test_concurrent_large_golden_comparisons_fail_closed(tmp_path):
     plan["resource_limits"]["memory_limit_bytes"] = 128 * 1024 * 1024
     input_path = tmp_path / "large-input.parquet"
     golden_path = tmp_path / "large-golden.parquet"
-    pl.DataFrame({"value": ["actual"]}).write_parquet(input_path)
+    row_count = 200_000
     pl.DataFrame(
-        {"value": [f"expected-{index:08d}" for index in range(200_000)]}
+        {"value": [f"actual-{index:08d}" for index in range(row_count)]}
+    ).write_parquet(input_path)
+    pl.DataFrame(
+        {
+            "value": [
+                f"expected-{index:08d}" for index in range(row_count)
+            ]
+        }
     ).write_parquet(golden_path)
+    golden_digest = _sha256(golden_path)
 
     def compare(index):
         try:
@@ -255,7 +272,7 @@ def test_concurrent_large_golden_comparisons_fail_closed(tmp_path):
                         tmp_path / f"large-output-{index}.parquet"
                     ),
                     "golden_path": str(golden_path),
-                    "golden_digest": "b" * 64,
+                    "golden_digest": golden_digest,
                     "masking_policies": {},
                 },
                 memory_limit_bytes=plan["resource_limits"][