Concurrency Control

Pain Signals — You Need This Pattern When:

• Model emits multiple tool calls per turn; serial execution multiplies latency
• Subagents run concurrently and may touch the same workspace
• Tool calls of mixed cost (fast read, slow API call) serialized waste time
• Two tool calls write to the same file and the second silently overwrites the first
• Cancellation needs to stop a fan-out cleanly without zombie operations

Concurrency is latency leverage. Done right: 5× speedup on independent work. Done wrong: race conditions, partial state, debugging nightmares.

Core Principle

Three orthogonal questions per turn: