Copy python files to avoid junction issues

MODULE.bazel

@@ -105,6 +105,11 @@ single_version_override(
 # Temporary until rules_pkg > 1.2.0 is in BCR
 archive_override(
     module_name = "rules_pkg",
+    patch_strip = 1,
+    patches = [
+        # Windows runfiles junctions cannot point at files; follow them on copy.
+        "//bazel/patches:rules_pkg-windows-junction-copy.patch",
+    ],
     sha256 = "9923c6c8855b153f837a953760159908507f571b4b77cb24ed862dda1de20f90",
     strip_prefix = "rules_pkg-401969d4367c42dcbb45d33a637eae87788d025e",
     urls = ["https://github.com/bazelbuild/rules_pkg/archive/401969d4367c42dcbb45d33a637eae87788d025e.tar.gz"],  # main as of April 22, 2026

bazel/AGENTS.md

@@ -881,6 +881,14 @@ local and remote execution to be configured.
 All Windows developers are expected to have **Developer Mode enabled**, which grants the necessary privileges for
 symlink creation without administrator elevation. The `.bazelrc` sets `--enable_runfiles` accordingly.
 
+**Runfiles file junctions.** `--enable_runfiles` builds the runfiles tree with directory junctions. Windows junctions
+cannot point at files, so a file runfile shows up as a directory (`d----l`) and `open()` fails with `Permission
+denied` / `The directory name is invalid`. `pkg_install` copies from that tree, not from the MANIFEST real path;
+`bazel/patches/rules_pkg-windows-junction-copy.patch` makes the copier follow the reparse point. For generated trees
+that must be reachable as a directory (not file-by-file), `copy_to_directory` so the runfiles entry is one directory
+junction to a real directory of real files (see `//rtloader/test:dir_with_python_home`). Prefer the runfiles library
+over constructing paths under `*.runfiles`.
+
 **No sandbox.** Windows uses `--strategy=standalone`. Builds are less hermetic by default — undeclared dependencies that
 happen to be present locally will succeed locally and fail in CI or RBE.
 

bazel/patches/rules_pkg-windows-junction-copy.patch

@@ -0,0 +1,15 @@
+diff --git a/pkg/private/install.py.tpl b/pkg/private/install.py.tpl
+index 5242b18a..00000000 100644
+--- a/pkg/private/install.py.tpl
++++ b/pkg/private/install.py.tpl
+@@ -82,6 +82,10 @@ class NativeInstaller(object):
+     def _do_file_copy(self, src, dest):
+         logging.debug("COPY %s <- %s", dest, src)
++        # Windows --enable_runfiles uses directory junctions for every runfile.
++        # Junctions cannot point at files, so open() fails with Permission denied.
++        # Follow the reparse point to the real bazel-out file.
++        src = os.path.realpath(src)
+         # Copy to a temporary directory and then move it to the destination.
+         # This ensures code-signed executables on certain platforms
+         # behave correctly.
+         # See: https://developer.apple.com/documentation/security/updating-mac-software

deps/cpython.BUILD.bazel

@@ -401,6 +401,7 @@ pkg_filegroup(
 pkg_files(
     name = "install_files_win",
     srcs = [":python_win"],
+    strip_prefix = "build",
 )
 
 # On Windows, python_win is built via MSBuild (not cc_shared_library), so there are no