/**
 * parsePiActivity turns ONE line of Pi's `--mode json` JSONL stream into a short
 * human label of what the agent is doing right now — used to fill the heartbeat
 * `activity` field so a long step shows "editing run-step.ts" instead of a bare
 * "working". Only `tool_execution_start` events carry that signal; every other
 * event (and any non-JSON line) yields undefined so the caller keeps the last
 * known activity or shows none.
 *
 * Shapes are taken verbatim from Pi's docs/json.md and its built-in tool
 * definitions (bash/edit/read/write/grep/find/ls), so this is grounded in the
 * real wire format, not a guess. Pure (no I/O) and total (never throws) — a
 * malformed line or missing arg degrades to a barer label.
 */
export declare function parsePiActivity(line: string): string | undefined;