fix: write each export as its bytes and mode

write_text translated line ends on Windows, so FirmwareDatabase.cs's
CRLF would have come out CR CR LF; it replaced the published file in
place, so a run stopped mid-write left it truncated; and it dropped the
mode, while rocknix-systems is 100755 in ROCKNIX's tree. Files are
written atomically as UTF-8 bytes, and an exporter states the mode of
any file the platform does not publish as 0644.

scripts/export_native.py

@@ -562,10 +562,7 @@ def export_platform(
 
     platform_dir = output_dir / platform
     _remove_stale(platform_dir, set(produced))
-    for relative, content in produced.items():
-        path = platform_dir / relative
-        path.parent.mkdir(parents=True, exist_ok=True)
-        path.write_text(content, encoding="utf-8")
+    _write_produced(platform_dir, produced, exporter.file_modes())
 
     changes = landed_changes(exporter, systems)
     applied, filled = changes.applied, changes.filled
@@ -663,6 +660,21 @@ def export_platform(
     return True, messages
 
 
+def _write_produced(root: Path, produced: dict[str, str], modes: dict[str, int]) -> None:
+    """Write each file as its bytes, whole or not at all, with its mode.
+
+    write_text translated line ends on Windows, so FirmwareDatabase.cs's
+    CRLF would have come out CR CR LF, and a run stopped mid-write left a
+    truncated file in exports/. The scratch file mkstemp makes is 0600: the
+    mode is set from what the platform's own file has.
+    """
+    for relative, content in produced.items():
+        path = root / relative
+        path.parent.mkdir(parents=True, exist_ok=True)
+        write_bytes_atomic(str(path), content.encode("utf-8"))
+        path.chmod(modes.get(relative, 0o644))
+
+
 def write_report(path: Path, report: dict) -> None:
     """What one platform's export changed, for the page that publishes it.
 

scripts/exporter/base_exporter.py

@@ -126,6 +126,11 @@ class BaseExporter(ABC):
         """
         return True
 
+    @staticmethod
+    def file_modes() -> dict[str, int]:
+        """The mode of each file the platform publishes other than 0644."""
+        return {}
+
     @staticmethod
     def keys_by_system() -> bool:
         """Whether the platform finds a file through its system's own name.

scripts/exporter/rocknix_exporter.py

@@ -77,6 +77,11 @@ class Exporter(BatoceraExporter):
     def native_filename() -> str:
         return "rocknix-systems"
 
+    @staticmethod
+    def file_modes() -> dict[str, int]:
+        # 100755 in ROCKNIX's tree at the pinned tag (git/trees 20261001).
+        return {"rocknix-systems": 0o755}
+
     @staticmethod
     def native_sources() -> dict[str, str]:
         return {"rocknix-systems": SOURCE_URL, EMULATORS_MK: EMULATORS_URL}

tests/test_exporters.py

@@ -1153,7 +1153,35 @@ class AnExportLeavesNoStaleFile(unittest.TestCase):
     def test_the_export_clears_before_it_writes(self):
         source = (REPO_ROOT / "scripts" / "export_native.py").read_text()
         body = source[source.index("def export_platform("):]
-        self.assertLess(body.index("_remove_stale("), body.index(".write_text("))
+        self.assertLess(body.index("_remove_stale("), body.index("_write_produced("))
+
+
+class AnExportIsWrittenAsItsBytes(unittest.TestCase):
+    """write_text translated line ends on Windows (FirmwareDatabase.cs is
+    CRLF, it would have become CR CR LF), replaced the published file in
+    place, and dropped the mode: rocknix-systems is 100755 upstream."""
+
+    def test_bytes_mode_and_atomicity(self):
+        import stat  # noqa: PLC0415
+
+        import export_native  # noqa: PLC0415
+
+        with tempfile.TemporaryDirectory(dir=REPO_ROOT / "tmp") as tmp:
+            root = Path(tmp)
+            export_native._write_produced(root, {
+                "FirmwareDatabase.cs": "a\r\nb\r\n",
+                "rocknix-systems": "#!/usr/bin/python\n",
+            }, {"rocknix-systems": 0o755})
+            self.assertEqual((root / "FirmwareDatabase.cs").read_bytes(), b"a\r\nb\r\n")
+            mode = lambda name: stat.S_IMODE((root / name).stat().st_mode)  # noqa: E731
+            self.assertEqual(mode("rocknix-systems"), 0o755)
+            self.assertEqual(mode("FirmwareDatabase.cs"), 0o644)
+            self.assertEqual(sorted(p.name for p in root.iterdir()),
+                             ["FirmwareDatabase.cs", "rocknix-systems"])
+
+    def test_rocknix_says_its_script_is_executable(self):
+        self.assertEqual(discover_exporters()["rocknix"].file_modes(),
+                         {"rocknix-systems": 0o755})
 
 
 class AnExportWithoutTruthIsRefused(unittest.TestCase):