Your agent calls a tool, the tool calls an external API, and that API takes 30 seconds, or never answers. The agent blocks, then dies with a cryptic error. One slow dependency took down the whole workflow. The fix is decades old: never let a synchronous caller block on a dependency you do not control. At the tool boundary, return a handle immediately and poll for the result. Watch a live demo turn a 300 second hang into about a 4 second response, and learn when a call must go asynchronous.

What you'll learn:
• Apply a simple rule to classify any tool call as safe to block or required to go asynchronous
• Build the async handle pattern: one tool returns a tracking id instantly, another polls for the result
• Design job lifecycle and cleanup so completed and stalled jobs do not leak memory
• Implement clear error and timeout states so failed dependencies surface instead of hanging
• Evaluate polling against callback delivery and choose per use case

Outline:
• One slow dependency, whole workflow down
• The pattern is older than agents
• Build the async boundary
• Make it production safe
• The decision checklist