diff --git a/.github/workflows/tests-os.yml b/.github/workflows/tests-os.yml
index 1cb17c95f6..91bf910d49 100644
--- a/.github/workflows/tests-os.yml
+++ b/.github/workflows/tests-os.yml
@@ -81,7 +81,10 @@ jobs:
       - name: Set up locked Python and test dependencies
         uses: ./.github/actions/setup-pm
         with:
-          packages: ripgrep
+          # Installer stage tests inherit setup-pm's HERMES_RUNTIME_DIR. Prepare
+          # the verified Git pin once, before per-file parallelism; otherwise
+          # each isolated PowerShell stage races to download/extract the archive.
+          packages: ${{ matrix.marker == 'windows' && 'git,ripgrep' || 'ripgrep' }}
           extras: '["all", "telegram", "anthropic", "mistral", "fal", "modal", "daytona", "hindsight", "parallel-web"]'
           test-environment: 'true'
           prune-python-cache: true
diff --git a/tests/scripts/install/test_install_ps1_staged_git.py b/tests/scripts/install/test_install_ps1_staged_git.py
index 30fad69734..d839fd078a 100644
--- a/tests/scripts/install/test_install_ps1_staged_git.py
+++ b/tests/scripts/install/test_install_ps1_staged_git.py
@@ -43,6 +43,11 @@ def test_stage_processes_restore_pinned_git_and_never_fall_back(tmp_path):
     stage("prerequisites")
     staged = list(store.glob("git-*/cmd/git.exe"))
     assert len(staged) == 1
+    # A wrong Git earlier on the parent's PATH must not win in either new stage.
+    poison = tmp_path / "poison"
+    poison.mkdir()
+    (poison / "git.cmd").write_text("@echo unpinned git invoked 1>&2 & exit /b 73\r\n", encoding="utf-8")
+    env["PATH"] = str(poison) + os.pathsep + env["PATH"]
     stage("repository")  # new process; prerequisites' PATH cannot propagate
     stage("complete")  # the marker's bare git call is also a new process
     checkout = home / "hermes-agent"