[tire-fire]

Logging is meant to give every request an ID, which handlers then log through WriteInternalError and the other slog.Error calls. It never does: r.Context().Value("request_id") returns a nil any when the key is unset, and nil == "" is false, so the ID is never generated. Every request_id field in the logs is nil.

Changes:

• The request ID is stored under a typed context key, through api.WithRequestID and api.RequestID, next to the existing identity key. RequestID always returns a string, "" when unset, so the nil comparison that caused this bug can't happen again. This also resolves the staticcheck TODO in Logging and removes its nolint comment.
• IDs are 8 characters from crypto/rand.Text() instead of a 36-character UUID, so log lines stay short. That's enough to tell apart requests that are near each other in the logs.
• An ID that is already set is kept, as before.

Added TestLoggingSetsRequestID. It checks that the handler sees an 8-character ID, that each request gets a different one, and that an existing ID is kept. It fails on the current code.