bench(harnessx-removal): deterministic baseline without the extra (task 1)

Equality script (design section 3) records suite outcomes, `ousast pairs --json`,
the python-vulnerable quick benchmark, one standard scan and `improve --dry-run`
from a frozen export with the harnessx extra absent and no model reachable.
Two independent records are byte-identical (determinism.json).

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

tests/test_harnessx_removal_equality.py

@@ -0,0 +1,65 @@
+"""The equality instrument (harnessx-removal design section 3) sees a difference when there is one.
+
+A comparison that always says "equal" would prove nothing, so these tests feed it records that differ in one
+place each and require it to name that place, and records that differ only in excluded fields and require it
+to pass.
+"""
+
+from __future__ import annotations
+
+import importlib.util
+import json
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[1]
+_SPEC = importlib.util.spec_from_file_location("hxr_equality", ROOT / "benchmarks" / "harnessx_removal_equality.py")
+assert _SPEC is not None and _SPEC.loader is not None
+equality = importlib.util.module_from_spec(_SPEC)
+_SPEC.loader.exec_module(equality)
+
+
+def _record(path: Path, *, findings: object, suite: dict[str, str], stdout: str = "findings=3\n") -> Path:
+    (path / "scan").mkdir(parents=True)
+    (path / "suite.json").write_text(equality.dump(suite))
+    (path / "scan" / "findings.json").write_text(equality.dump(findings))
+    (path / "scan" / "stdout.txt").write_text(stdout)
+    (path / "env.json").write_text(json.dumps({"tree_ish": str(path)}))
+    return path
+
+
+def _normalized(raw: dict[str, object], root: str) -> object:
+    return equality.normalize(raw, root, "/tmp/x")
+
+
+def test_excluded_fields_and_run_ids_do_not_count(tmp_path: Path) -> None:
+    a = _normalized({"rule": "sqli", "runtime_seconds": 1.2, "path": "/r1/runs/20260930T101010Z-0123abcd/f.py", "t_ms": 4}, "/r1")
+    b = _normalized({"rule": "sqli", "runtime_seconds": 9.9, "path": "/r2/runs/20261001T111111Z-ffffffff/f.py", "t_ms": 7}, "/r2")
+    suite = {"tests.test_x::test_a": "passed"}
+    diffs = equality.compare(_record(tmp_path / "a", findings=a, suite=suite), _record(tmp_path / "b", findings=b, suite=suite), {})
+    assert diffs == []
+
+
+def test_a_changed_finding_is_reported_with_its_key(tmp_path: Path) -> None:
+    suite = {"tests.test_x::test_a": "passed"}
+    a = _record(tmp_path / "a", findings=[{"rule": "sqli", "line": 3}], suite=suite)
+    b = _record(tmp_path / "b", findings=[{"rule": "sqli", "line": 4}], suite=suite)
+    assert equality.compare(a, b, {}) == ["scan/findings.json: $[0].line: 3 -> 4"]
+    assert equality.main(["compare", str(a), str(b)]) == 1
+
+
+def test_a_changed_outcome_or_unmapped_test_is_reported(tmp_path: Path) -> None:
+    a = _record(tmp_path / "a", findings=[], suite={"t::a": "passed", "t::gone": "passed", "t::old": "skipped"})
+    b = _record(tmp_path / "b", findings=[], suite={"t::a": "failure", "t::new": "skipped", "t::extra": "passed"}, stdout="findings=2\n")
+    diffs = equality.compare(a, b, {"deleted": ["t::gone"], "renamed": {"t::old": "t::new"}})
+    assert diffs == [
+        "suite.json: t::a passed -> failure",
+        "suite.json: t::extra new in candidate",
+        "scan/stdout.txt: first differing line 1: 'findings=3' -> 'findings=2'",
+    ]
+
+
+def test_a_file_present_on_one_side_only_is_reported(tmp_path: Path) -> None:
+    a = _record(tmp_path / "a", findings=[], suite={})
+    b = _record(tmp_path / "b", findings=[], suite={})
+    (b / "scan" / "fusion.json").write_text("[]\n")
+    assert equality.compare(a, b, {}) == ["scan/fusion.json: present only in candidate"]