Max characters of tool_output included in tool.result hook payloads.
Bounds payload size (data-amplification guard) while keeping enough of the
tool's output to be useful to audit/notification hooks. Applied in the single
shared builder _tool_stream.build_tool_result_payload, which both the
interactive and headless dispatch paths call, so the cap never drifts between
them. Only tool_output is capped; tool_args is passed through in full so hooks
that act on the arguments (e.g. a linter reading a write_file content) see
the exact value the tool received.
