fix(report): write the executive report atomically

strix/report/writer.py

@@ -114,12 +114,14 @@ def write_run_record(run_dir: Path, run_record: dict[str, Any]) -> None:
 
 
 def write_executive_report(run_dir: Path, final_scan_result: str) -> None:
-    path = run_dir / "penetration_test_report.md"
-    with path.open("w", encoding="utf-8") as f:
-        f.write("# Security Penetration Test Report\n\n")
-        f.write(f"**Generated:** {datetime.now(UTC).strftime('%Y-%m-%d %H:%M:%S UTC')}\n\n")
-        f.write(f"{final_scan_result}\n")
-    logger.info("Saved final penetration test report to: %s", path)
+    report_path = run_dir / "penetration_test_report.md"
+    payload = (
+        "# Security Penetration Test Report\n\n"
+        f"**Generated:** {datetime.now(UTC).strftime('%Y-%m-%d %H:%M:%S UTC')}\n\n"
+        f"{final_scan_result}\n"
+    )
+    _atomic_write_text(report_path, payload)
+    logger.info("Saved final penetration test report to: %s", report_path)
 
 
 def write_vulnerabilities(

tests/test_report_writer.py

@@ -4,6 +4,7 @@ from __future__ import annotations
 
 import csv
 import json
+import tempfile
 from typing import TYPE_CHECKING, Any
 
 import pytest
@@ -179,3 +180,20 @@ def test_write_executive_report_writes_markdown(tmp_path: Path) -> None:
     content = (tmp_path / "penetration_test_report.md").read_text(encoding="utf-8")
     assert "# Security Penetration Test Report" in content
     assert "Scan complete. No critical issues." in content
+
+
+def test_write_executive_report_failure_preserves_previous_report(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    target = tmp_path / "penetration_test_report.md"
+    target.write_text("previous report", encoding="utf-8")
+
+    def _disk_full(*_args: Any, **_kwargs: Any) -> None:
+        raise OSError("disk full")
+
+    monkeypatch.setattr(tempfile, "NamedTemporaryFile", _disk_full)
+
+    with pytest.raises(OSError, match="disk full"):
+        write_executive_report(tmp_path, "new content")
+
+    assert target.read_text(encoding="utf-8") == "previous report"