Replace StringRange w/ an actual StrRVal + more command implementations

src/vm/commands/enclose.ts

@@ -1,4 +1,4 @@
-import {Command, ParseContext, StrTerm} from "./command.js";
+import {Command, ParseContext, StrTerm, unwrapString, wrapString} from "./command.js";
 import {LexInput} from "../lexer.js";
 import {StrVM} from "../vm.js";
 import {Awaitable} from "../../util/types.js";
@@ -25,14 +25,13 @@ export class Enclose extends Command<EncloseData> {
     }
 
     execute(vm: StrVM, data: EncloseData): Awaitable<StrVM> {
-        return vm.inPlace(ctx => {
+        return vm.tapInPlace(ctx => {
             const [left, right] = this.determineSurroundingStrings(
                 data.left ? ctx.resolveString(data.left) : undefined,
                 data.right ? ctx.resolveString(data.right) : undefined,
             )
 
-            return ctx.replaceSubject(sub =>
-                sub.modify(s => `${left}${s}${right}`))
+            return ctx.replaceSubjectAsString(sub => `${left}${sub}${right}`)
         })
     }