Writing archive

I started from a small tokio service and hit five classic async Rust problems: a huge future, a future that is not Send, one blocking call that stalls everything, a select! loop that loses data, and a shutdown that hangs. One small model of the compiler and the runtime explains all five.

A decision and failure matrix for combining low-latency webhooks with polling and reconciliation so an integration can recover from missed, duplicate, or reordered events.

A reference flow for keeping user identity, tenant, audience, and allowed actions attached to every AI tool call without trusting the model to enforce permissions.

The usual Fn(&T) -> Fut bound cannot describe a future borrowing from each call. See how AsyncFn enables lending callbacks on stable Rust.

A concrete schema and concurrency model for mapping external IDs to internal entities without duplicates, cross-tenant collisions, or unsafe retries.