fix(tools): isolate external project environments

tools/code_execution_tool.py

@@ -1455,16 +1455,6 @@ def execute_code(
         # with a C/POSIX locale (containers, minimal base images).
         child_env["PYTHONIOENCODING"] = "utf-8"
         child_env["PYTHONUTF8"] = "1"
-        # Ensure the hermes-agent root is importable in the sandbox so
-        # repo-root modules are available to child scripts.  We also prepend
-        # the staging tmpdir so ``from hermes_tools import ...`` resolves even
-        # when the subprocess CWD is not tmpdir (project mode).
-        _hermes_root = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
-        _existing_pp = child_env.get("PYTHONPATH", "")
-        _pp_parts = [tmpdir, _hermes_root]
-        if _existing_pp:
-            _pp_parts.append(_existing_pp)
-        child_env["PYTHONPATH"] = os.pathsep.join(_pp_parts)
         # Inject user's configured timezone so datetime.now() in sandboxed
         # code reflects the correct wall-clock time.  Only TZ is set —
         # HERMES_TIMEZONE is an internal Hermes setting and must not leak
@@ -1487,6 +1477,22 @@ def execute_code(
         _child_cwd = _resolve_child_cwd(_mode, tmpdir, task_id=task_id or "")
         _script_path = os.path.join(tmpdir, "script.py")
 
+        # ``hermes_tools.py`` always lives in the staging directory, so that
+        # directory must be importable even when project mode changes CWD.
+        # Hermes's own package root is useful too, but only when the child
+        # uses the same Python environment. Project mode can select an
+        # external venv; exposing Hermes's site-packages to that interpreter
+        # can mix incompatible compiled extensions (for example, Python 3.12
+        # NumPy with a Python 3.9 project interpreter).
+        _hermes_root = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+        _existing_pp = child_env.get("PYTHONPATH", "")
+        _pp_parts = [tmpdir]
+        if _uses_hermes_python_environment(_child_python):
+            _pp_parts.append(_hermes_root)
+        if _existing_pp:
+            _pp_parts.append(_existing_pp)
+        child_env["PYTHONPATH"] = os.pathsep.join(_pp_parts)
+
         proc = subprocess.Popen(
             [_child_python, _script_path],
             cwd=_child_cwd,
@@ -1850,6 +1856,33 @@ def _is_usable_python(python_path: str) -> bool:
         return False
 
 
+@functools.lru_cache(maxsize=32)
+def _python_environment_prefix(python_path: str) -> str:
+    """Return the resolved ``sys.prefix`` reported by *python_path*, if any."""
+    try:
+        from agent.delegation_context import delegated_child_subprocess_env
+
+        result = subprocess.run(
+            [python_path, "-c", "import sys; print(sys.prefix)"],
+            timeout=5,
+            capture_output=True,
+            text=True,
+            creationflags=subprocess.CREATE_NO_WINDOW if _IS_WINDOWS else 0,
+            stdin=subprocess.DEVNULL,
+            env=delegated_child_subprocess_env(),
+        )
+        if result.returncode == 0 and result.stdout.strip():
+            return os.path.realpath(result.stdout.strip())
+    except (OSError, subprocess.TimeoutExpired, subprocess.SubprocessError):
+        pass
+    return ""
+
+
+def _uses_hermes_python_environment(python_path: str) -> bool:
+    """Whether *python_path* belongs to Hermes's active Python environment."""
+    return _python_environment_prefix(python_path) == os.path.realpath(sys.prefix)
+
+
 def _resolve_child_python(mode: str) -> str:
     """Pick the Python interpreter for the execute_code subprocess.