Wake the Agent on a File Cursor, Not on a Heartbeat

Anything that isn't a directly pushed message — cron output, log lines, inbox changes, external feeds — is only noticed at heartbeat granularity, and every heartbeat burns a full LLM turn even when nothing happened. Hold byte-offset cursors on the plaintext files those sources already write, wake the agent only on an actual append, and coalesce bursts into one turn. A polling loop's cost scales with wall-clock time; an event loop's cost scales with real events.