Announce batched refetches and cap preinstall workers

tests/unit_tests/test_platformio_prefetch.py

@@ -1729,3 +1729,52 @@ def test_platformio_private_api_contract() -> None:
     derived = PackageSpec("https://x/y/archive/master.zip")
     assert derived.name and not derived.has_custom_name()
     assert PackageSpec("Foo=https://x/y/archive/master.zip").has_custom_name()
+
+
+def test_preinstall_caps_workers(
+    tmp_path: Path, caplog: pytest.LogCaptureFixture
+) -> None:
+    """A high core count is capped; the workers share one disk."""
+
+    class _Mgr:
+        package_dir = str(tmp_path)
+        compatibility = None
+
+        def __init__(self, package_dir, **kwargs) -> None:
+            pass
+
+        def lock(self) -> None:
+            pass
+
+        def unlock(self) -> None:
+            pass
+
+        def memcache_reset(self) -> None:
+            pass
+
+        def get_tmp_dir(self) -> str:
+            return str(tmp_path)
+
+        def get_download_dir(self) -> str:
+            return str(tmp_path)
+
+        def get_package(self, spec):
+            return None
+
+        def get_pkg_dependencies(self, pkg):
+            return None
+
+        def _install(self, spec, skip_dependencies, compatibility=None) -> None:
+            pass
+
+    with (
+        caplog.at_level(logging.INFO),
+        patch.object(pf, "get_usable_cpu_count", return_value=64),
+    ):
+        pf._preinstall(
+            _Mgr(str(tmp_path)),
+            [(f"p{i}@1", _FakeSpec(name=f"p{i}")) for i in range(11)],
+        )
+    assert "Installing 11 PlatformIO package(s) with 10 extraction worker(s)" in (
+        caplog.text
+    )