fix(browser): strip PYTHONPATH/PYTHONHOME from browser-use CLI subprocess env (salvage #83471)

contributors/emails/benjamin-liang@outlook.com

@@ -0,0 +1 @@
+n1majne3

tests/tools/test_browser_use_cli.py

@@ -101,6 +101,28 @@ def test_browser_use_telemetry_defaults_off(self, monkeypatch):
         env = bu_cli._base_subprocess_env()
         assert env["ANONYMIZED_TELEMETRY"] == "false"
 
+    def test_subprocess_env_strips_parent_python_import_paths(self, monkeypatch):
+        """#83427/#84841/#86006/#86104: the browser-use CLI runs under its
+        own Python — inherited PYTHONPATH/PYTHONHOME pointing at Hermes's
+        venv make it import wrong-ABI C-extensions (pydantic_core) and
+        crash. Both must be stripped; unrelated vars survive."""
+        import sys
+        from types import ModuleType
+
+        browser_tool = ModuleType("tools.browser_tool")
+        browser_tool._build_browser_env = lambda: {
+            "PYTHONPATH": "/hermes:/hermes/venv/lib/site-packages",
+            "PYTHONHOME": "/hermes/venv",
+            "KEEP_ME": "yes",
+        }
+        monkeypatch.setitem(sys.modules, "tools.browser_tool", browser_tool)
+
+        env = bu_cli._base_subprocess_env()
+
+        assert "PYTHONPATH" not in env
+        assert "PYTHONHOME" not in env
+        assert env["KEEP_ME"] == "yes"
+
 
 class TestToolSurfaceSwap:
     def test_legacy_browser_tools_hidden_in_cli_mode(self, monkeypatch):

tools/browser_use_cli.py

@@ -60,6 +60,16 @@ def _base_subprocess_env() -> dict:
     from tools.browser_tool import _build_browser_env
 
     env = _build_browser_env()
+    # The browser-use CLI runs under its own Python (uv tool / uvx), which
+    # may differ from Hermes's venv Python. PYTHONPATH/PYTHONHOME inherited
+    # from the agent process point at Hermes's venv site-packages, and a
+    # child interpreter honors them ahead of its own site-packages — so the
+    # CLI imports compiled C-extensions (e.g. pydantic_core) built for the
+    # wrong interpreter and crashes on ABI mismatch (#83427, #84841, #86006,
+    # #86104). Strip both — the CLI manages its own environment and never
+    # needs Hermes's import path.
+    env.pop("PYTHONPATH", None)
+    env.pop("PYTHONHOME", None)
     env.setdefault("ANONYMIZED_TELEMETRY", "false")
     return env