Introduce TermOperator helper and refactor execute()s to use replaceSubjectMatchingTerm

src/vm/commands/suffix.ts

@@ -19,7 +19,8 @@ export class Suffix extends Command<{ with: StrTerm }> {
     }
 
     execute(vm: StrVM, data: { with: StrTerm }): Awaitable<StrVM> {
-        return vm.tapInPlace(ctx =>
-            ctx.replaceSubjectAsString(sub => `${sub}${ctx.resolveString(data.with)}`))
+        return vm.replaceContextMatchingTerm(ctx => ({
+            string: sub => `${sub}${ctx.resolveString(data.with)}`,
+        }))
     }
 }