fix: add project root to PYTHONPATH in execute_code sandbox

The execute_code sandbox spawns a child process with cwd set to a
temporary directory, but never adds the hermes-agent project root to
PYTHONPATH. This makes project-root modules like minisweagent_path
unreachable from sandboxed scripts, causing ImportError when the
agent runs self-diagnostic or analysis code via execute_code.

Fix by prepending the hermes-agent root directory to PYTHONPATH in
the child process environment.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tools/code_execution_tool.py

@@ -440,6 +440,11 @@ def execute_code(
                 child_env[k] = v
         child_env["HERMES_RPC_SOCKET"] = sock_path
         child_env["PYTHONDONTWRITEBYTECODE"] = "1"
+        # Ensure the hermes-agent root is importable in the sandbox so
+        # modules like minisweagent_path are available to child scripts.
+        _hermes_root = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+        _existing_pp = child_env.get("PYTHONPATH", "")
+        child_env["PYTHONPATH"] = _hermes_root + (os.pathsep + _existing_pp if _existing_pp else "")
         # Inject user's configured timezone so datetime.now() in sandboxed
         # code reflects the correct wall-clock time.
         _tz_name = os.getenv("HERMES_TIMEZONE", "").strip()