#128 CRITICAL: Heartbeats not persisted - use separate connection

During disruption testing, heartbeat tests fail because heartbeats are NOT being committed to the database. Root cause: ctx.heartbeat() calls absurd_client.extend_claim() which uses the SAME connection as the main task transaction. If the task times out before the transaction commits, the heartbeat updates are never persisted. Evidence: absurd.r_*.last_heartbeat is NULL for all failed heartbeat tasks. Fix required: extend_claim() should use a SEPARATE connection that commits immediately.