The execute_code sandbox refuses background/notify modifiers on terminal(); heartbeat implies notify and rides the same delivery path, so it joins the blocked set (and the stub-drift test's mirror of it).
Behavior-neutral structural pass over tools/*: god-file extractions into sibling modules (file_operations_common/lint/search, file_tools_paths/ read_tracking/write, code_execution_env/rpc, tool_search_catalog/names/ validation, tts_command_provider, ...), duplicate helper unification, if/elif -> dispatch tables, dead-code removal, docstring compaction. Tool schemas (get_tool_definitions) verified byte-identical to base.
