DEVX-156: fix: add tenacity retry to install_tools._download for transient network failures

tests/unit/test_install_tools.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import platform
+import urllib.error
 from pathlib import Path
 from unittest.mock import patch
 
@@ -68,6 +69,67 @@ class TestDownload:
         mock_urlopen.assert_called_once()
         assert dest.read_bytes() == b"data"
 
+    def test_download_retries_on_transient_error(self, tmp_path: Path) -> None:
+        """Download retries on URLError then succeeds."""
+        dest = tmp_path / "file.bin"
+        call_count = [0]
+
+        class _FakeResponse:
+            def __init__(self) -> None:
+                self._sent = False
+
+            def __enter__(self) -> _FakeResponse:
+                return self
+
+            def __exit__(self, *args: object) -> None:
+                pass
+
+            def read(self, n: int = -1) -> bytes:
+                if self._sent:
+                    return b""
+                self._sent = True
+                return b"data"
+
+        def _flaky_urlopen(url: str, timeout: int = 60):
+            call_count[0] += 1
+            if call_count[0] < 2:
+                raise urllib.error.URLError("Remote end closed connection")
+            return _FakeResponse()
+
+        with patch("urllib.request.urlopen", side_effect=_flaky_urlopen):
+            install_tools._download("https://example.com/file", dest, _sleep=lambda _: None)
+        assert call_count[0] == 2
+        assert dest.read_bytes() == b"data"
+
+    def test_download_fails_after_max_retries(self, tmp_path: Path) -> None:
+        """Download raises after MAX_DOWNLOAD_RETRIES attempts."""
+        dest = tmp_path / "file.bin"
+        call_count = [0]
+
+        def _always_fail(url: str, timeout: int = 60):
+            call_count[0] += 1
+            raise urllib.error.URLError("Remote end closed connection")
+
+        with patch("urllib.request.urlopen", side_effect=_always_fail):
+            with pytest.raises(urllib.error.URLError):
+                install_tools._download("https://example.com/file", dest, _sleep=lambda _: None)
+        assert call_count[0] == install_tools.MAX_DOWNLOAD_RETRIES
+        assert not dest.exists()
+
+    def test_download_no_retry_on_non_transient_error(self, tmp_path: Path) -> None:
+        """Download does not retry on non-network errors (e.g. ValueError)."""
+        dest = tmp_path / "file.bin"
+        call_count = [0]
+
+        def _fail_with_value_error(url: str, timeout: int = 60):
+            call_count[0] += 1
+            raise ValueError("not a network error")
+
+        with patch("urllib.request.urlopen", side_effect=_fail_with_value_error):
+            with pytest.raises(ValueError):
+                install_tools._download("https://example.com/file", dest, _sleep=lambda _: None)
+        assert call_count[0] == 1
+
 
 class TestDownloadBinary:
     def test_download(self, tmp_path: Path) -> None: