Common gotchas

The "what bit me in code review" survival kit:

• Loop variable capture (Go 1.22+ helped, but you should still know).
• Nil interface vs nil concrete (a non-nil pointer inside an interface variable makes the interface non-nil).
• Slice aliasing — two slices sharing a backing array.
• Goroutine leaks — a goroutine waiting on a channel that nobody will ever send to.