How to hot-reload configuration

package watch turns the configuration cascade into a live stream for long-running processes. It uses fsnotify and re-runs the full resolve + validate pipeline when watched files change. The full function catalogue is in package watch.

Watch the app’s configuration

func (d *Daemon) Run(ctx context.Context, session *conga.Session) error {
  onChange := func(newCfg *CLI, err error) {
    if err != nil {
      fmt.Fprintf(session.Stderr(), "config invalid, keeping previous: %v\n", err)

      return
    }

    applyConfig(newCfg) // swap your settings atomically
  }

  return watch.Config(ctx, session, onChange)
}

watch.Config[T](ctx, session, onChange):

watches exactly the files reported by session.LoadedConfigFiles() / session.CandidateConfigFiles() for the active execution;
calls onChange with a freshly bound, fully validated *T after each change (the same result as session.Reload[T](ctx));
calls onChange with a non-nil error when a change produces an invalid configuration — your previous settings stay in effect;
returns watch.ErrNoCandidates when the candidate set is empty.

Watch arbitrary files

err := watch.File(ctx, "/etc/motd", func(err error) { ... })

err := watch.Paths(ctx, []string{"a.yaml", "b.yaml"}, func(err error) { ... })

Paths watches any file list; File is the single-file convenience form.

Combining with signal shutdown

app.Run() cancels its context on SIGINT/SIGTERM. Block on the watch call inside your command; when the context is cancelled the watchers stop and your Finally hook performs teardown — see example 16 (16-live-config-watcher) for a complete daemon and About the lifecycle for teardown semantics.