Aaranya IT ke ek BFSI client ka live scenario imagine karo — ek customer-support agent ko ek angry Axis Bank customer ke liye teen cheezein chahiye: account balance, recent transactions, aur active dispute tickets. Aap sequential tool calls use kar rahe ho — pehle balance fetch karo, phir transactions, phir disputes. Total latency? 3 × 800 ms = 2.4 seconds. Customer already frustrated hai. Lekin agar aap Claude ko parallel tool calls issue karne do — ek hi turn mein teeno queries fan-out ho jayein — total latency sirf 800 ms. Yahi hai woh architectural decision jo aaj hum dissect karenge: kab fan-out karo, kab sequential rakho, aur latency math kaise justify karta hai yeh choice.