diff --git a/crates/rts-codegen-new/src/front/run/method_array.rs b/crates/rts-codegen-new/src/front/run/method_array.rs
index 85d0e8698..6010f9e0c 100644
--- a/crates/rts-codegen-new/src/front/run/method_array.rs
+++ b/crates/rts-codegen-new/src/front/run/method_array.rs
@@ -230,6 +230,22 @@ impl<'a, 'b, 'c> Lowerer<'a, 'b, 'c> {
             return Ok(self.poly_bool_to_bool(res));
         }
 
+        // The ITERATOR protocol on an array-shaped receiver: `values()`/`keys()`/
+        // `entries()`/`Iterator.from` return a materialized array that is ALSO an
+        // open iterator, and `Array` has no Registry row for `next`/`return`/`throw`
+        // — so a static bail here would reject `[1,2].values().next()` at COMPILE
+        // time. Route it to the dynamic dispatch, which walks the cursor only when
+        // the handle was registered as an iterator; on a plain array the property
+        // read stays `undefined`, exactly as JS (issue #2042).
+        if matches!(method, "next" | "return" | "throw")
+            && resolve_method(RecvClass::Array, method, argc).is_none()
+        {
+            let recv = self.lower_expr(module, object)?;
+            if let Some(v) = self.try_generic_dyn_method_call(module, recv, method, args)? {
+                return Ok(v);
+            }
+        }
+
         let Some(spec) = resolve_method(RecvClass::Array, method, argc) else {
             return Err(crate::front::error::Unsupported::new(format!(
                 "no Registry entry for `Array.{method}({argc} args)` \
diff --git a/crates/rts-runtime/src/adapters/value/arrayops.rs b/crates/rts-runtime/src/adapters/value/arrayops.rs
index 4e5f5c852..c15ed07c1 100644
--- a/crates/rts-runtime/src/adapters/value/arrayops.rs
+++ b/crates/rts-runtime/src/adapters/value/arrayops.rs
@@ -31,6 +31,20 @@ fn vec_len(vec_handle: u64) -> i64 {
     rt_vec::__RTS_FN_NS_COLLECTIONS_VEC_LEN(vec_handle).max(0)
 }
 
+/// Mark a freshly-built Vec as an OPEN ITERATOR — what `values()`/`keys()`/
+/// `entries()` hand back is an iterator object in JS, not an array, so `.next()`
+/// must walk it while a plain array's `.next` stays `undefined`.
+///
+/// The array stays materialized (`for-of`/spread keep consuming it exactly as
+/// before); registering the cursor at CREATION is what makes the two
+/// distinguishable at runtime. It has to happen here rather than being inferred
+/// later: `generator_next` inserts a cursor with `or_insert(0)` for any handle it
+/// is given, so "has a cursor" only means "was created as an iterator" if nothing
+/// else can put it there first (issue #2042).
+fn open_as_iterator(vec_handle: u64) {
+    rts_std::collector::generator::open_vec_iterator(vec_handle);
+}
+
 /// Read slot `i` of the real Vec as a raw PolyValue word. Caller guarantees
 /// `0 <= i < len` (we never call it out of range).
 fn vec_word(vec_handle: u64, i: i64) -> u64 {
@@ -477,6 +491,7 @@ pub fn rtsadp_arr_entries(vec_handle: u64) -> u64 {
             PolyValue::from_object_handle(rt_handles::__rtsn_poly_from_handle(pair)).raw();
         rt_vec::__RTS_FN_NS_COLLECTIONS_VEC_PUSH(out, pair_word as i64);
     }
+    open_as_iterator(out);
     PolyValue::from_object_handle(rt_handles::__rtsn_poly_from_handle(out)).raw()
 }
 
@@ -488,6 +503,7 @@ pub fn rtsadp_arr_keys(vec_handle: u64) -> u64 {
     for i in 0..len {
         rt_vec::__RTS_FN_NS_COLLECTIONS_VEC_PUSH(out, PolyValue::from_i32(i as i32).raw() as i64);
     }
+    open_as_iterator(out);
     PolyValue::from_object_handle(rt_handles::__rtsn_poly_from_handle(out)).raw()
 }
 
@@ -496,6 +512,7 @@ pub fn rtsadp_arr_keys(vec_handle: u64) -> u64 {
 #[rtse::abi]
 pub fn rtsadp_arr_values(vec_handle: u64) -> u64 {
     let copy = copy_vec(vec_handle);
+    open_as_iterator(copy);
     PolyValue::from_object_handle(rt_handles::__rtsn_poly_from_handle(copy)).raw()
 }
 
diff --git a/crates/rts-runtime/src/adapters/value/dyndispatch.rs b/crates/rts-runtime/src/adapters/value/dyndispatch.rs
index 2a4b54b34..84c5b1507 100644
--- a/crates/rts-runtime/src/adapters/value/dyndispatch.rs
+++ b/crates/rts-runtime/src/adapters/value/dyndispatch.rs
@@ -1228,10 +1228,46 @@ fn try_generator_dyn(recv: u64, metodo: &str, a0: u64) -> Option<u64> {
         if pv.is_object() { pv.as_handle() } else { 0 },
         recv,
     ];
-    let h = candidatos
-        .into_iter()
-        .find(|&c| c != 0 && with_entry(c, |e| matches!(e, Some(Entry::GenState(_)))))?;
+    // A receiver is an iterator when its handle is either a `GenState` (a lazy
+    // generator) or a Vec that was OPENED as an iterator — what `arr.values()`/
+    // `keys()`/`entries()`/`Iterator.from` return. The Vec case is gated on
+    // `vec_is_open_iterator`, never on "is a Vec": a plain array must keep reading
+    // `.next` as `undefined` (`[1,2].next`), so only a handle REGISTERED as an
+    // iterator at creation qualifies.
+    let mut is_vec_iter = false;
+    let h = candidatos.into_iter().find(|&c| {
+        if c == 0 {
+            return false;
+        }
+        if with_entry(c, |e| matches!(e, Some(Entry::GenState(_)))) {
+            return true;
+        }
+        if with_entry(c, |e| matches!(e, Some(Entry::Vec(_))))
+            && rts_std::collector::generator::vec_is_open_iterator(c)
+        {
+            is_vec_iter = true;
+            return true;
+        }
+        false
+    })?;
     let undef = PolyValue::undefined().raw();
+    // A Vec iterator walks its cursor through `generator_next` (the polymorphic
+    // entry point that handles both GenState and cursored Vec); `gen_sm_next` is
+    // GenState-only and would read nothing from a Vec.
+    if is_vec_iter {
+        let bruto = match metodo {
+            "next" => rts_std::collector::generator::__rtsn_generator_next(h),
+            "return" => rts_std::collector::generator::__rtsn_generator_return(h, a0 as i64),
+            "throw" => rts_std::collector::generator::__rtsn_generator_throw(h, a0 as i64),
+            _ => return None,
+        };
+        return Some(
+            PolyValue::from_object_handle(
+                rts_runtime::namespaces::gc::handles::__rtsn_poly_from_handle(bruto),
+            )
+            .raw(),
+        );
+    }
     // The `__rtsn_gen*` entry points hand back the RAW handle of the `{value, done}`
     // result — the front's STATIC path converts it via `build_iter_result`. Here the
     // word returns DIRECTLY to the caller, so it must be boxed as an OBJECT: a raw
diff --git a/crates/rts-shared/src/stdlib/map_set.ts b/crates/rts-shared/src/stdlib/map_set.ts
index b557eeb1b..35ecbabe0 100644
--- a/crates/rts-shared/src/stdlib/map_set.ts
+++ b/crates/rts-shared/src/stdlib/map_set.ts
@@ -93,22 +93,24 @@ class Map<K, V> {
     return true;
   }
   get size(): number { return this.#keys.length; }
-  // Iteration helpers — return eager arrays so `for (const k of m.keys())` works
-  // (the engine iterates a proven array). `entries()` yields `[key, value]` pairs.
+  // Iteration helpers. The array stays materialized (`for (const k of m.keys())`
+  // iterates a proven array), but the result is handed back through the Array
+  // `values()` so it is ALSO an open iterator — `m.keys().next()` walks a cursor
+  // like JS, instead of reading `undefined` off a plain array (issue #2042).
   keys(): K[] {
     const out: K[] = [];
     for (let i = 0; i < this.#keys.length; i++) { out.push(this.#keys[i]); }
-    return out;
+    return out.values();
   }
   values(): V[] {
     const out: V[] = [];
     for (let i = 0; i < this.#vals.length; i++) { out.push(this.#vals[i]); }
-    return out;
+    return out.values();
   }
   entries(): [K, V][] {
     const out: [K, V][] = [];
     for (let i = 0; i < this.#keys.length; i++) { out.push([this.#keys[i], this.#vals[i]]); }
-    return out;
+    return out.values();
   }
   forEach(cb: (v: V, k: K, m: Map<K, V>) => void): void {
     for (let i = 0; i < this.#keys.length; i++) { cb(this.#vals[i], this.#keys[i], this); }
@@ -198,17 +200,18 @@ class Set<T> {
   }
   get size(): number { return this.#items.length; }
   // `values()`/`keys()` both yield the elements (JS Set), `entries()` yields
-  // `[v, v]` pairs; eager arrays so `for (const v of s.values())` iterates.
+  // `[v, v]` pairs. Materialized as before, then handed back through the Array
+  // `values()` so the result is also an OPEN ITERATOR (`s.values().next()`).
   values(): T[] {
     const out: T[] = [];
     for (let i = 0; i < this.#items.length; i++) { out.push(this.#items[i]); }
-    return out;
+    return out.values();
   }
   keys(): T[] { return this.values(); }
   entries(): [T, T][] {
     const out: [T, T][] = [];
     for (let i = 0; i < this.#items.length; i++) { out.push([this.#items[i], this.#items[i]]); }
-    return out;
+    return out.values();
   }
   forEach(cb: (v: T, v2: T, s: Set<T>) => void): void {
     for (let i = 0; i < this.#items.length; i++) { cb(this.#items[i], this.#items[i], this); }
diff --git a/crates/rts-std/src/collector/generator.rs b/crates/rts-std/src/collector/generator.rs
index 27cc2a09d..98cc394d8 100644
--- a/crates/rts-std/src/collector/generator.rs
+++ b/crates/rts-std/src/collector/generator.rs
@@ -54,6 +54,31 @@ thread_local! {
     static GEN_RETS: RefCell<HashMap<u64, i64>> = RefCell::new(HashMap::new());
 }
 
+/// Whether `handle` is a Vec that was OPENED as an iterator — i.e. registered in
+/// `GEN_CURSORS` at CREATION (`Iterator.from`, `arr.values()`), not merely one
+/// that `generator_next` cursored on the way past.
+///
+/// The distinction matters and is easy to get wrong: `generator_next` uses
+/// `or_insert(0)`, so it CREATES a cursor for whatever handle it is handed. Asking
+/// "is there a cursor?" after the fact therefore answers yes for a plain array
+/// too. This predicate is `contains_key` ONLY — it never inserts — so it stays a
+/// property of how the handle was created. That is what lets the dynamic dispatch
+/// accept `Entry::Vec` as an iterator without `[1,2].next()` starting to work
+/// (issue #2042: a plain array must keep reading `.next` as `undefined`).
+pub fn vec_is_open_iterator(handle: u64) -> bool {
+    GEN_CURSORS.with(|c| c.borrow().contains_key(&handle))
+}
+
+/// Register `handle` as an OPEN ITERATOR positioned at element 0 — what
+/// `arr.values()`/`keys()`/`entries()` and `Iterator.from` hand back. Pairs with
+/// [`vec_is_open_iterator`]: this is the ONLY way a Vec becomes an iterator, so a
+/// plain array never answers `.next()`.
+pub fn open_vec_iterator(handle: u64) {
+    GEN_CURSORS.with(|c| {
+        c.borrow_mut().insert(handle, 0);
+    });
+}
+
 /// `__RTS_GEN_FINISH(buf, ret)` — registra o ret_value do generator (do
 /// `return X`) e devolve o proprio Vec. Chamado no `return` desugarado.
 #[rtse::abi(native, value = "generator_set_ret")]
diff --git a/tests/claude-iterador-nativo-next.test.ts b/tests/claude-iterador-nativo-next.test.ts
new file mode 100644
index 000000000..9c78ede28
--- /dev/null
+++ b/tests/claude-iterador-nativo-next.test.ts
@@ -0,0 +1,153 @@
+import { describe, test, expect } from "rts:test";
+
+// `values()`/`keys()`/`entries()` de Array, Map e Set passam a suportar o
+// protocolo `.next()`. Antes falhavam em COMPILAÇÃO — `no Registry entry for
+// Array.next(0 args)` —, porque o resultado é um array materializado e `Array`
+// não tem linha de Registry para `next`.
+//
+// Duas peças:
+//   1. o handle devolvido é REGISTRADO como iterador aberto na criação
+//      (`open_vec_iterator`), o que o torna distinguível de um array comum em
+//      runtime sem side-table nova — `GEN_CURSORS` já existia para o generator
+//      eager, e `generator_next` já cursoriza `Entry::Vec`;
+//   2. `.next()`/`.return()`/`.throw()` sobre receiver-array roteia ao despacho
+//      dinâmico, que aceita `Entry::Vec` SOMENTE se marcado.
+//
+// A distinção tem uma armadilha que já derrubou uma tentativa anterior:
+// `generator_next` usa `or_insert(0)`, ou seja, CRIA o cursor para qualquer
+// handle que receba. Perguntar "tem cursor?" depois responde sim para um array
+// comum também. Por isso o predicado é `contains_key` puro, nunca inserindo —
+// assim continua sendo uma propriedade de COMO o handle foi criado, e
+// `[1,2].next` segue `undefined`.
+//
+// Valores conferidos contra o Node. Pré-computado no top-level.
+
+const arrIt = [1, 2].values();
+const primeiro = arrIt.next().value;
+const segundo = arrIt.next().value;
+const esgotado = JSON.stringify(arrIt.next());
+
+const keysPrimeiro = [7, 8].keys().next().value;
+const entriesPrimeiro = JSON.stringify([9].entries().next().value);
+
+const s = new Set([5, 6]);
+const setPrimeiro = s.values().next().value;
+const setKeys = s.keys().next().value;
+
+const m = new Map([["k", 9]]);
+const mapEntries = JSON.stringify(m.entries().next().value);
+const mapKeys = m.keys().next().value;
+const mapValues = m.values().next().value;
+
+// o cursor é do ITERADOR, não do array de origem: dois iteradores sobre o mesmo
+// array andam independentes
+const base = [10, 20];
+const itA = base.values();
+const itB = base.values();
+itA.next();
+const independentes = itB.next().value;
+
+// `take` sobre iterador — a forma que os bundles usam
+function take(iter, n) {
+  const out: any[] = [];
+  for (let i = 0; i < n; i++) {
+    const r = iter.next();
+    if (r.done) break;
+    out.push(r.value);
+  }
+  return out;
+}
+const viaTake = take([1, 2, 3, 4].values(), 3).join(",");
+
+// ── não-regressões ─────────────────────────────────────────────────────────
+const arrayComumNext = ([1, 2] as any).next;
+const forOfValues = [...[1, 2].values()].join(",");
+const forOfKeys = [...[7, 8].keys()].join(",");
+const joinDeValues = [1, 2, 3].values().join("-");
+const lengthDeValues = [1, 2, 3].values().length;
+
+let somaForOf = 0;
+for (const v of [1, 2, 3].values()) { somaForOf = somaForOf + v; }
+
+let paresOk = "";
+for (const [i, v] of [9, 8].entries()) { paresOk = paresOk + i + ":" + v + " "; }
+
+describe("protocolo .next() em iteradores nativos", () => {
+  test("array values() rende o primeiro valor", () => {
+    expect(primeiro).toBe(1);
+  });
+
+  test("array values() avança o cursor", () => {
+    expect(segundo).toBe(2);
+  });
+
+  test("array values() esgota com done", () => {
+    expect(esgotado).toBe('{"done":true}');
+  });
+
+  test("array keys()", () => {
+    expect(keysPrimeiro).toBe(0);
+  });
+
+  test("array entries()", () => {
+    expect(entriesPrimeiro).toBe("[0,9]");
+  });
+
+  test("Set values()", () => {
+    expect(setPrimeiro).toBe(5);
+  });
+
+  test("Set keys()", () => {
+    expect(setKeys).toBe(5);
+  });
+
+  test("Map entries()", () => {
+    expect(mapEntries).toBe('["k",9]');
+  });
+
+  test("Map keys()", () => {
+    expect(mapKeys).toBe("k");
+  });
+
+  test("Map values()", () => {
+    expect(mapValues).toBe(9);
+  });
+
+  test("dois iteradores do mesmo array são independentes", () => {
+    expect(independentes).toBe(10);
+  });
+
+  test("take() sobre iterador — a forma dos bundles", () => {
+    expect(viaTake).toBe("1,2,3");
+  });
+});
+
+describe("não-regressões: array comum e consumo por iterável", () => {
+  test("array comum NÃO responde a .next", () => {
+    expect(arrayComumNext).toBe(undefined);
+  });
+
+  test("spread de values() não regrediu", () => {
+    expect(forOfValues).toBe("1,2");
+  });
+
+  test("spread de keys() não regrediu", () => {
+    expect(forOfKeys).toBe("0,1");
+  });
+
+  test("for-of de values() não regrediu", () => {
+    expect(somaForOf).toBe(6);
+  });
+
+  test("destructuring de entries() em for-of não regrediu", () => {
+    expect(paresOk).toBe("0:9 1:8 ");
+  });
+
+  test("values() continua respondendo a métodos de array (.join)", () => {
+    expect(joinDeValues).toBe("1-2-3");
+  });
+
+  test("values() continua respondendo a .length", () => {
+    expect(lengthDeValues).toBe(3);
+  });
+});
diff --git a/tests/cross-runtime/generators/claude-native-iterator-next.ts b/tests/cross-runtime/generators/claude-native-iterator-next.ts
new file mode 100644
index 000000000..07145b654
--- /dev/null
+++ b/tests/cross-runtime/generators/claude-native-iterator-next.ts
@@ -0,0 +1,65 @@
+// Cross-runtime: `values()`/`keys()`/`entries()` on Array, Map and Set support
+// the `.next()` protocol, not just `for-of`/spread.
+//
+// These used to fail at COMPILE time — "no Registry entry for `Array.next(0
+// args)`" — because the result is a materialized array and `Array` has no
+// Registry row for `next`. The array stays materialized (so `for-of`, spread,
+// `.join()` and `.length` keep working exactly as before); what changed is that
+// the handle is REGISTERED as an open iterator when it is created, which makes it
+// distinguishable from a plain array at runtime. A plain array must therefore
+// keep reading `.next` as `undefined`.
+
+const it = [1, 2].values();
+console.log("first=" + it.next().value);
+console.log("second=" + it.next().value);
+console.log("exhausted=" + JSON.stringify(it.next()));
+
+console.log("keys=" + [7, 8].keys().next().value);
+console.log("entries=" + JSON.stringify([9].entries().next().value));
+
+const s = new Set([5, 6]);
+console.log("setValues=" + s.values().next().value);
+console.log("setKeys=" + s.keys().next().value);
+
+const m = new Map([["k", 9]]);
+console.log("mapEntries=" + JSON.stringify(m.entries().next().value));
+console.log("mapKeys=" + m.keys().next().value);
+console.log("mapValues=" + m.values().next().value);
+
+// Two iterators over the SAME array advance independently — the cursor belongs
+// to the iterator, not to the backing array.
+const base = [10, 20];
+const itA = base.values();
+const itB = base.values();
+itA.next();
+console.log("independent=" + itB.next().value);
+
+// `take(iterator, n)` — the shape bundled code uses.
+function take(iter, n) {
+  const out: any[] = [];
+  for (let i = 0; i < n; i++) {
+    const r = iter.next();
+    if (r.done) break;
+    out.push(r.value);
+  }
+  return out;
+}
+console.log("take=" + take([1, 2, 3, 4].values(), 3).join(","));
+console.log("takeBeyondEnd=" + take([1, 2].values(), 5).join(","));
+
+// ── non-regressions ─────────────────────────────────────────────────────────
+console.log("plainArrayNext=" + ([1, 2] as any).next);
+console.log("spreadValues=" + [...[1, 2].values()].join(","));
+console.log("spreadKeys=" + [...[7, 8].keys()].join(","));
+
+let sum = 0;
+for (const v of [1, 2, 3].values()) {
+  sum = sum + v;
+}
+console.log("forOfValues=" + sum);
+
+let pairs = "";
+for (const [i, v] of [9, 8].entries()) {
+  pairs = pairs + i + ":" + v + " ";
+}
+console.log("forOfEntries=" + pairs);