khatru: add policies to validate event tags by kind and replace reactions.

khatru/policies/schema_validation.go

@@ -0,0 +1,18 @@
+package policies
+
+import (
+	"context"
+
+	"fiatjaf.com/nostr"
+	"fiatjaf.com/nostr/schema"
+)
+
+func ValidateAgainstSchema(ctx context.Context, evt nostr.Event) (bool, string) {
+	v := schema.NewDefaultValidator()
+	v.FailOnUnknown = true
+	err := v.ValidateEvent(evt)
+	if err != nil {
+		return true, err.Error()
+	}
+	return false, ""
+}