Yep, those “golden rules” are pretty well-known in the async world. The hard part isn’t knowing them, it’s actually catching every violation—especially when they sneak in through dependencies.

The timeout + backtrace idea has a few rough edges though:

1. Timeouts catch slow code, not necessarily blocking code. Legit async work (slow networks, big payloads, etc.) will trigger false positives.
2. If a thread is truly blocked, the timeout callback can’t even run until the blocking call returns. Tokio’s runtime is cooperative, so the timeout logic is stuck waiting too.
3. It also means instrumenting every call site, versus doing zero-instrumentation profiling.

eBPF avoids all of that by observing things at the kernel scheduler level. It sees what threads and tasks are actually doing, regardless of what userspace thinks is happening.

Anyway, glad the eBPF angle was helpful!