Config hot reload (SIGHUP + file watch)

Status

Accepted — extended in Phase 2.

Context

The exporter already supports reload via an HTTP /reload endpoint and an optional fsnotify file watcher (--config-watch). The family standard is a thread-safe rebuild-and-swap reload triggered by both SIGHUP and a file watch. The current watcher also misses atomic-rename-on-save (editors write a temp file then rename), which upstream PR #148 set out to fix.

Decision

Keep the rebuild-and-swap reload. Add a SIGHUP handler alongside the file watch. Handle fsnotify.Rename in addition to Write/Remove, and make watcher re-add resilient — but reimplement cleanly (no goroutine-leaking go WatchConfig() recursion, no in-loop time.Sleep blocking events) rather than copying PR #148 verbatim.

Consequences

Reload works from a signal or a file change, including editor atomic saves. Credentials that change are swapped and the affected target's collector is reset, as today.