Implemented confi snapshots

internal/broker/broker.go

@@ -251,6 +251,31 @@ func (b *Broker) fanOut(ref SignalRef, sub *signalSub, rawCh <-chan datasource.V
 	}
 }
 
+// ReadNow performs a one-shot synchronous read of a signal's current value.
+// It starts a dedicated upstream subscription, returns the first value the data
+// source delivers, then tears the subscription down. The read is bounded by ctx
+// (callers should pass a timeout). This bypasses the shared fan-out cache because
+// not every signal of interest (e.g. arbitrary config-set targets) is otherwise
+// subscribed.
+func (b *Broker) ReadNow(ctx context.Context, ref SignalRef) (datasource.Value, error) {
+	ds, ok := b.Source(ref.DS)
+	if !ok {
+		return datasource.Value{}, fmt.Errorf("unknown data source %q", ref.DS)
+	}
+	ch := make(chan datasource.Value, 1)
+	cancel, err := ds.Subscribe(ctx, ref.Name, ch)
+	if err != nil {
+		return datasource.Value{}, fmt.Errorf("read %s/%s: %w", ref.DS, ref.Name, err)
+	}
+	defer cancel()
+	select {
+	case v := <-ch:
+		return v, nil
+	case <-ctx.Done():
+		return datasource.Value{}, ctx.Err()
+	}
+}
+
 // ActiveSubscriptions returns the number of currently active upstream signal
 // subscriptions. Useful for diagnostics and tests.
 func (b *Broker) ActiveSubscriptions() int {