From c65e0a14347f98a7bab72a0cd791156d05e0080f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kasper=20Isager=20Dalsgar=C3=B0?= <kasperisager@hey.com>
Date: Fri, 19 Jun 2026 13:23:10 +0200
Subject: [PATCH 1/3] Add `js_create_snapshot()` and `js_take_snapshot()`

---
 include/js.h                            | 164 ++++-
 src/js.cc                               | 896 ++++++++++++++++++++++--
 test/CMakeLists.txt                     |   9 +
 test/boot-from-snapshot.c               | 441 ++++++++++++
 test/create-snapshot.c                  |  65 ++
 test/external-references.c              |  56 ++
 test/fixtures/snapshots/.gitignore      |   2 +
 test/run-from-snapshot-delegate.c       |  89 +++
 test/run-from-snapshot-dynamic-import.c | 165 +++++
 test/run-from-snapshot-function.c       |  88 +++
 test/run-from-snapshot-import-meta.c    |  78 +++
 test/run-from-snapshot-module.c         |  82 +++
 test/run-from-snapshot-wrap.c           |  75 ++
 test/run-from-snapshot.c                |  47 ++
 test/snapshot.h                         | 302 ++++++++
 15 files changed, 2508 insertions(+), 51 deletions(-)
 create mode 100644 test/boot-from-snapshot.c
 create mode 100644 test/create-snapshot.c
 create mode 100644 test/external-references.c
 create mode 100644 test/fixtures/snapshots/.gitignore
 create mode 100644 test/run-from-snapshot-delegate.c
 create mode 100644 test/run-from-snapshot-dynamic-import.c
 create mode 100644 test/run-from-snapshot-function.c
 create mode 100644 test/run-from-snapshot-import-meta.c
 create mode 100644 test/run-from-snapshot-module.c
 create mode 100644 test/run-from-snapshot-wrap.c
 create mode 100644 test/run-from-snapshot.c
 create mode 100644 test/snapshot.h

diff --git a/include/js.h b/include/js.h
index dd7b94b..501c56b 100644
--- a/include/js.h
+++ b/include/js.h
@@ -17,6 +17,7 @@ typedef struct js_platform_options_s js_platform_options_t;
 typedef struct js_platform_limits_s js_platform_limits_t;
 typedef struct js_env_s js_env_t;
 typedef struct js_env_options_s js_env_options_t;
+typedef struct js_snapshot_options_s js_snapshot_options_t;
 typedef struct js_handle_scope_s js_handle_scope_t;
 typedef struct js_escapable_handle_scope_s js_escapable_handle_scope_t;
 typedef struct js_context_s js_context_t;
@@ -40,6 +41,10 @@ typedef struct js_error_location_s js_error_location_t;
 typedef struct js_inspector_s js_inspector_t;
 typedef struct js_garbage_collection_tracking_s js_garbage_collection_tracking_t;
 typedef struct js_garbage_collection_tracking_options_s js_garbage_collection_tracking_options_t;
+typedef struct js_external_references_s js_external_references_t;
+typedef struct js_rebind_handlers_s js_rebind_handlers_t;
+typedef struct js_binding_payload_s js_binding_payload_t;
+typedef struct js_rebind_info_s js_rebind_info_t;
 
 enum {
   /**
@@ -179,6 +184,7 @@ typedef void (*js_deferred_teardown_cb)(js_deferred_teardown_t *, void *data);
 typedef void (*js_inspector_message_cb)(js_env_t *, js_inspector_t *, const char *message, size_t len, void *data);
 typedef bool (*js_inspector_paused_cb)(js_env_t *, js_inspector_t *, void *data);
 typedef void (*js_garbage_collection_cb)(js_garbage_collection_type_t, void *data);
+typedef bool (*js_rebind_cb)(js_env_t *, const js_rebind_info_t *info, void *data, js_binding_payload_t *result);
 
 /** @version 1 */
 struct js_platform_options_s {
@@ -265,7 +271,7 @@ struct js_platform_limits_s {
   size_t string_length;
 };
 
-/** @version 0 */
+/** @version 1 */
 struct js_env_options_s {
   int version;
 
@@ -276,6 +282,74 @@ struct js_env_options_s {
    * @since 0
    */
   size_t memory_limit;
+
+  /**
+   * A startup snapshot to boot the environment from instead of building its
+   * default context from scratch. When set, the bytes must remain valid for the
+   * lifetime of the environment.
+   *
+   * @since 1
+   */
+  const void *snapshot;
+
+  /**
+   * The length of `snapshot` in bytes.
+   *
+   * @since 1
+   */
+  size_t snapshot_len;
+
+  /**
+   * The external references reachable from the snapshot. Must be the same array,
+   * byte-for-byte, that was used to produce the snapshot, and must remain valid
+   * for the lifetime of the environment.
+   *
+   * @since 1
+   */
+  const js_external_references_t *external_references;
+
+  /**
+   * Handlers consulted while booting from a snapshot to re-supply the
+   * per-instance `data` of reconstructed native bindings. May be NULL, in which
+   * case reconstructed bindings get no `data`.
+   *
+   * @since 1
+   */
+  const js_rebind_handlers_t *rebind_handlers;
+};
+
+typedef enum {
+  /**
+   * Clear compiled function code from the blob. Smaller, but functions are
+   * recompiled lazily on first call.
+   */
+  js_snapshot_clear_function_code = 0,
+
+  /**
+   * Keep compiled function code in the blob. Larger and locked to the exact
+   * engine build, but faster first execution.
+   */
+  js_snapshot_keep_function_code = 1,
+} js_snapshot_function_code_handling_t;
+
+/** @version 0 */
+struct js_snapshot_options_s {
+  int version;
+
+  /**
+   * How to treat compiled function code when serializing.
+   *
+   * @since 0
+   */
+  js_snapshot_function_code_handling_t function_code_handling;
+
+  /**
+   * The external references reachable from the snapshot. Must be the same array
+   * later passed to `js_create_env()` when booting from the resulting blob.
+   *
+   * @since 0
+   */
+  const js_external_references_t *external_references;
 };
 
 /** @version 0 */
@@ -332,6 +406,48 @@ struct js_delegate_callbacks_s {
   js_delegate_own_keys_cb own_keys;
 };
 
+/** @version 0 */
+struct js_binding_payload_s {
+  /** @since 0 */
+  void *data;
+
+  /** @since 0 */
+  void *finalize_hint;
+};
+
+typedef enum {
+  js_binding_function = 0,
+  js_binding_finalizer = 1,
+  js_binding_delegate = 2,
+} js_binding_type_t;
+
+/** @version 0 */
+struct js_rebind_info_s {
+  int version;
+
+  /** @since 0 */
+  js_binding_type_t type;
+
+  union {
+    /** @since 0 */
+    struct {
+      js_function_cb cb;
+    } function;
+
+    /** @since 0 */
+    struct {
+      js_finalize_cb cb;
+      js_value_t *holder;
+    } finalizer;
+
+    /** @since 0 */
+    struct {
+      js_delegate_callbacks_t callbacks;
+      js_value_t *holder;
+    } delegate;
+  };
+};
+
 /** @version 0 */
 struct js_type_tag_s {
   /** @since 0 */
@@ -447,12 +563,50 @@ js_get_platform_limits(js_platform_t *platform, js_platform_limits_t *result);
 int
 js_get_platform_loop(js_platform_t *platform, uv_loop_t **result);
 
+int
+js_create_external_references(js_external_references_t **result);
+
+int
+js_add_external_reference(js_external_references_t *references, const void *address);
+
+int
+js_get_external_references(js_external_references_t *references, const intptr_t **data, size_t *len);
+
+int
+js_destroy_external_references(js_external_references_t *references);
+
+int
+js_create_rebind_handlers(js_rebind_handlers_t **result);
+
+int
+js_add_rebind_handler(js_rebind_handlers_t *handlers, js_rebind_cb cb, void *data);
+
+int
+js_destroy_rebind_handlers(js_rebind_handlers_t *handlers);
+
 int
 js_create_env(uv_loop_t *loop, js_platform_t *platform, const js_env_options_t *options, js_env_t **result);
 
 int
 js_destroy_env(js_env_t *env);
 
+/**
+ * Create an environment set up for serialization. The returned environment is
+ * warmed up with the regular run/compile APIs, then serialized and consumed by
+ * `js_take_snapshot()`.
+ */
+int
+js_create_snapshot(uv_loop_t *loop, js_platform_t *platform, const js_snapshot_options_t *options, js_env_t **result);
+
+/**
+ * Serialize a warmed-up snapshot environment into a blob and tear it down. The
+ * environment is consumed and must not be passed to `js_destroy_env()`. On
+ * success `*data` is a newly allocated buffer owned by the caller and freed with
+ * `free()`.
+ */
+int
+js_take_snapshot(js_env_t *env, void **data, size_t *len);
+
 /**
  * Add a callback for uncaught exceptions. By default, uncaught exceptions are
  * swallowed and do not affect JavaScript execution.
@@ -596,6 +750,14 @@ js_get_module_name(js_env_t *env, js_module_t *module, const char **result);
 int
 js_get_module_id(js_env_t *env, js_module_t *module, js_value_t **result);
 
+/**
+ * Look up a module reconstructed from a snapshot by its `id` and return its
+ * handle. Only fully evaluated modules survive a snapshot; their callbacks are
+ * never invoked again after restore, so none need to be re-supplied.
+ */
+int
+js_get_module_by_id(js_env_t *env, js_value_t *id, js_module_t **result);
+
 /**
  * Get the identifier shared by all compilation units that do not carry one of
  * their own, such as scripts run with `js_run_script()`. This is the `id`
diff --git a/src/js.cc b/src/js.cc
index dd64340..70ba4c6 100644
--- a/src/js.cc
+++ b/src/js.cc
@@ -35,6 +35,12 @@ using namespace v8_inspector;
 typedef struct js_callback_s js_callback_t;
 typedef struct js_typed_callback_s js_typed_callback_t;
 typedef struct js_finalizer_s js_finalizer_t;
+template <typename T>
+struct js_binding_callbacks_s;
+typedef struct js_binding_callbacks_s<js_callback_t> js_function_callbacks_t;
+typedef struct js_binding_callbacks_s<js_finalizer_t> js_finalizer_callbacks_t;
+typedef struct js_binding_state_s js_binding_state_t;
+typedef struct js_snapshot_state_s js_snapshot_state_t;
 typedef struct js_delegate_s js_delegate_t;
 typedef struct js_external_string_utf16le_s js_external_string_utf16le_t;
 typedef struct js_external_string_latin1_s js_external_string_latin1_t;
@@ -103,10 +109,15 @@ js_from_local(Local<Value> local) {
 
 namespace {
 
-static const ExternalPointerTypeTag js_callback_info_type_tag = 1;
-static const ExternalPointerTypeTag js_delegate_type_tag = 2;
-static const ExternalPointerTypeTag js_finalizer_type_tag = 3;
-static const ExternalPointerTypeTag js_external_type_tag = 4;
+static const ExternalPointerTypeTag js_external_type_tag = 1;
+
+static const EmbedderDataTypeTag js_delegate_type_tag = 1;
+
+static StartupData
+js_serialize_internal_field(Local<Object> holder, int index, void *data);
+
+static void
+js_deserialize_internal_field(Local<Object> holder, int index, StartupData payload, void *data);
 
 } // namespace
 
@@ -1305,6 +1316,59 @@ struct js_platform_s : public Platform {
   }
 };
 
+template <typename T>
+struct js_binding_callbacks_s {
+  std::vector<T *> entries;
+  std::vector<uint32_t> free;
+
+  inline uint32_t
+  add(T *entry) {
+    if (!free.empty()) {
+      auto index = free.back();
+
+      free.pop_back();
+
+      entries[index] = entry;
+
+      return index;
+    }
+
+    entries.push_back(entry);
+
+    return uint32_t(entries.size() - 1);
+  }
+
+  inline void
+  remove(uint32_t index, T *entry) {
+    if (index >= entries.size() || entries[index] != entry) return;
+
+    entries[index] = nullptr;
+
+    free.push_back(index);
+  }
+};
+
+struct js_binding_state_s {
+  js_function_callbacks_t functions;
+
+  js_finalizer_callbacks_t finalizers;
+
+  void
+  destroy_function_callbacks();
+};
+
+struct js_snapshot_state_s {
+  SnapshotCreator *creator;
+  SnapshotCreator::FunctionCodeHandling function_code_handling;
+
+  std::vector<intptr_t> external_references;
+
+  js_snapshot_state_s(std::vector<intptr_t> references)
+      : creator(nullptr),
+        function_code_handling(SnapshotCreator::FunctionCodeHandling::kClear),
+        external_references(std::move(references)) {}
+};
+
 struct js_env_s {
   uv_loop_t *loop;
   uv_prepare_t prepare;
@@ -1354,7 +1418,11 @@ struct js_env_s {
     void *dynamic_import_data;
   } callbacks;
 
-  js_env_s(uv_loop_t *loop, js_platform_t *platform, Isolate *isolate)
+  js_binding_state_t bindings;
+
+  js_snapshot_state_t snapshot;
+
+  js_env_s(uv_loop_t *loop, js_platform_t *platform, Isolate *isolate, std::vector<intptr_t> references, const js_rebind_handlers_t *rebind_handlers)
       : loop(loop),
         prepare(),
         check(),
@@ -1375,7 +1443,9 @@ struct js_env_s {
         unhandled_promises(),
         teardown_queue(),
         inspector(),
-        callbacks() {
+        callbacks(),
+        bindings(),
+        snapshot(std::move(references)) {
     int err;
 
     std::unique_lock guard(platform->lock);
@@ -1420,7 +1490,20 @@ struct js_env_s {
 
     auto scope = HandleScope(isolate);
 
-    context.Reset(isolate, Context::New(isolate));
+    // Pass the delegate deserialize hook so a delegate's per-instance pointer is
+    // reconstructed from its internal field when booting from a snapshot. It is
+    // never invoked for a freshly created context.
+    context.Reset(
+      isolate,
+      Context::New(
+        isolate,
+        nullptr,
+        MaybeLocal<ObjectTemplate>(),
+        MaybeLocal<Value>(),
+        DeserializeInternalFieldsCallback(js_deserialize_internal_field, const_cast<js_rebind_handlers_t *>(rebind_handlers))
+      )
+    );
+
     context.Get(isolate)->Enter();
 
     wrapper.Reset(isolate, Private::New(isolate));
@@ -1431,7 +1514,16 @@ struct js_env_s {
   ~js_env_s() {
     if (inspector) inspector.reset();
 
-    {
+    bindings.destroy_function_callbacks();
+
+    // The finalizer table does not own its entries, so just drop the lookup
+    // mappings; any finalizer destructor firing during disposal then sees an
+    // empty table and skips its slot removal.
+    bindings.finalizers.entries.clear();
+    bindings.finalizers.free.clear();
+
+    if (snapshot.creator) delete snapshot.creator;
+    else {
       auto scope = HandleScope(isolate);
 
       wrapper.Reset();
@@ -1442,9 +1534,10 @@ struct js_env_s {
 
       context.Get(isolate)->Exit();
       context.Reset();
+
+      isolate->Exit();
     }
 
-    isolate->Exit();
     isolate->Dispose();
 
     std::unique_lock guard(platform->lock);
@@ -2090,36 +2183,51 @@ struct js_deferred_s {
 };
 
 struct js_callback_s {
-  Global<External> external;
+  Global<Value> function;
+  uint32_t index;
   js_env_t *env;
   js_function_cb cb;
   void *data;
 
   js_callback_s(js_env_t *env, js_function_cb cb, void *data)
-      : external(env->isolate, External::New(env->isolate, this, js_callback_info_type_tag)),
+      : function(),
+        index(env->bindings.functions.add(this)),
         env(env),
         cb(cb),
-        data(data) {
-    external.SetWeak(this, on_finalize, WeakCallbackType::kParameter);
-  }
+        data(data) {}
+
+  js_callback_s(js_env_t *env, js_function_cb cb, void *data, uint32_t index)
+      : function(),
+        index(index),
+        env(env),
+        cb(cb),
+        data(data) {}
 
   js_callback_s(const js_callback_s &) = delete;
 
-  virtual ~js_callback_s() = default;
+  virtual ~js_callback_s() {
+    env->bindings.functions.remove(index, this);
+  }
 
   js_callback_s &
   operator=(const js_callback_s &) = delete;
 
   MaybeLocal<Function>
   to_function(Isolate *isolate, Local<Context> context) {
-    return Function::New(
+    auto function = Function::New(
       context,
       on_call,
-      external.Get(isolate),
+      Integer::NewFromUnsigned(isolate, index),
       0,
       ConstructorBehavior::kAllow,
       SideEffectType::kHasSideEffect
     );
+
+    Local<Function> local;
+
+    if (function.ToLocal(&local)) hold_weakly(isolate, local);
+
+    return function;
   }
 
   Local<FunctionTemplate>
@@ -2127,7 +2235,7 @@ struct js_callback_s {
     return FunctionTemplate::New(
       isolate,
       on_call,
-      external.Get(isolate),
+      Integer::NewFromUnsigned(isolate, index),
       signature,
       0,
       ConstructorBehavior::kAllow,
@@ -2135,12 +2243,18 @@ struct js_callback_s {
     );
   }
 
-protected:
+  void
+  hold_weakly(Isolate *isolate, Local<Value> function) {
+    this->function.Reset(isolate, function);
+
+    this->function.SetWeak(static_cast<js_callback_t *>(this), on_finalize, WeakCallbackType::kParameter);
+  }
+
   static void
   on_call(const FunctionCallbackInfo<Value> &info) {
-    auto callback = reinterpret_cast<js_callback_t *>(info.Data().As<External>()->Value(js_callback_info_type_tag));
+    auto env = js_env_t::from(info.GetIsolate());
 
-    auto env = callback->env;
+    auto callback = env->bindings.functions.entries[size_t(info.Data().As<Integer>()->Value())];
 
     auto result = callback->cb(env, reinterpret_cast<js_callback_info_t *>(const_cast<FunctionCallbackInfo<Value> *>(&info)));
 
@@ -2157,6 +2271,7 @@ struct js_callback_s {
     }
   }
 
+protected:
   static void
   on_finalize(const WeakCallbackInfo<js_callback_t> &info) {
     auto callback = info.GetParameter();
@@ -2165,6 +2280,19 @@ struct js_callback_s {
   }
 };
 
+void
+js_binding_state_s::destroy_function_callbacks() {
+  std::vector<js_callback_t *> callbacks;
+
+  std::swap(callbacks, functions.entries);
+
+  functions.free.clear();
+
+  for (auto callback : callbacks) {
+    delete callback;
+  }
+}
+
 struct js_typed_callback_s : js_callback_t {
   CTypeInfo result;
   std::vector<CTypeInfo> args;
@@ -2190,7 +2318,7 @@ struct js_typed_callback_s : js_callback_t {
     return FunctionTemplate::New(
       isolate,
       on_call,
-      external.Get(isolate),
+      Integer::NewFromUnsigned(isolate, index),
       signature,
       0,
       ConstructorBehavior::kThrow,
@@ -2201,22 +2329,30 @@ struct js_typed_callback_s : js_callback_t {
 };
 
 struct js_finalizer_s {
+  static constexpr uint32_t unregistered = UINT32_MAX;
+
   Global<Value> value;
+  uint32_t index;
   js_env_t *env;
   void *data;
   js_finalize_cb finalize_cb;
   void *finalize_hint;
+  bool is_delegate;
 
   js_finalizer_s(js_env_t *env, void *data, js_finalize_cb finalize_cb, void *finalize_hint)
       : value(),
+        index(unregistered),
         env(env),
         data(data),
         finalize_cb(finalize_cb),
-        finalize_hint(finalize_hint) {}
+        finalize_hint(finalize_hint),
+        is_delegate(false) {}
 
   js_finalizer_s(const js_finalizer_s &) = delete;
 
-  virtual ~js_finalizer_s() = default;
+  virtual ~js_finalizer_s() {
+    env->bindings.finalizers.remove(index, this);
+  }
 
   js_finalizer_s &
   operator=(const js_finalizer_s &) = delete;
@@ -2262,7 +2398,9 @@ struct js_delegate_s : js_finalizer_t {
 
   js_delegate_s(js_env_t *env, js_delegate_callbacks_t callbacks, void *data, js_finalize_cb finalize_cb, void *finalize_hint)
       : js_finalizer_t(env, data, finalize_cb, finalize_hint),
-        callbacks(std::move(callbacks)) {}
+        callbacks(std::move(callbacks)) {
+    is_delegate = true;
+  }
 
   js_delegate_s(const js_delegate_s &) = delete;
 
@@ -2271,38 +2409,42 @@ struct js_delegate_s : js_finalizer_t {
 
   Local<ObjectTemplate>
   to_object_template(Isolate *isolate) {
-    auto external = External::New(isolate, this, js_delegate_type_tag);
-
     auto tpl = ObjectTemplate::New(isolate);
 
+    tpl->SetInternalFieldCount(1);
+
     tpl->SetHandler(NamedPropertyHandlerConfiguration(
       on_get<Name>,
       on_set<Name>,
       nullptr,
       on_delete<Name>,
-      on_enumerate,
-      external
+      on_enumerate
     ));
 
     tpl->SetHandler(IndexedPropertyHandlerConfiguration(
       on_get_indexed,
       on_set_indexed,
       nullptr,
-      on_delete_indexed,
-      nullptr,
-      external
+      on_delete_indexed
     ));
 
     return tpl;
   }
 
 private:
+  template <typename T>
+  static js_delegate_t *
+  from(const PropertyCallbackInfo<T> &info) {
+    return reinterpret_cast<js_delegate_t *>(info.Holder()->GetAlignedPointerFromInternalField(0, js_delegate_type_tag));
+  }
+
+public:
   template <typename T>
   static Intercepted
   on_get(Local<T> property, const PropertyCallbackInfo<Value> &info) {
     auto env = js_env_t::from(info.GetIsolate());
 
-    auto delegate = static_cast<js_delegate_t *>(info.Data().As<External>()->Value(js_delegate_type_tag));
+    auto delegate = from(info);
 
     if (delegate->callbacks.has) {
       auto exists = delegate->callbacks.has(env, js_from_local(property), delegate->data);
@@ -2341,7 +2483,7 @@ struct js_delegate_s : js_finalizer_t {
   on_set(Local<T> property, Local<Value> value, const PropertyCallbackInfo<Boolean> &info) {
     auto env = js_env_t::from(info.GetIsolate());
 
-    auto delegate = static_cast<js_delegate_t *>(info.Data().As<External>()->Value(js_delegate_type_tag));
+    auto delegate = from(info);
 
     if (delegate->callbacks.set) {
       auto result = delegate->callbacks.set(env, js_from_local(property), js_from_local(value), delegate->data);
@@ -2372,7 +2514,7 @@ struct js_delegate_s : js_finalizer_t {
   on_delete(Local<T> property, const PropertyCallbackInfo<Boolean> &info) {
     auto env = js_env_t::from(info.GetIsolate());
 
-    auto delegate = static_cast<js_delegate_t *>(info.Data().As<External>()->Value(js_delegate_type_tag));
+    auto delegate = from(info);
 
     if (delegate->callbacks.delete_property) {
       auto result = delegate->callbacks.delete_property(env, js_from_local(property), delegate->data);
@@ -2402,7 +2544,7 @@ struct js_delegate_s : js_finalizer_t {
   on_enumerate(const PropertyCallbackInfo<Array> &info) {
     auto env = js_env_t::from(info.GetIsolate());
 
-    auto delegate = static_cast<js_delegate_t *>(info.Data().As<External>()->Value(js_delegate_type_tag));
+    auto delegate = from(info);
 
     if (delegate->callbacks.own_keys) {
       auto result = delegate->callbacks.own_keys(env, delegate->data);
@@ -3253,6 +3395,367 @@ js_option(const js_env_options_t *options, int min_version, T fallback = T(js_en
 
 } // namespace
 
+struct js_external_references_s {
+  std::vector<intptr_t> addresses;
+};
+
+extern "C" int
+js_create_external_references(js_external_references_t **result) {
+  *result = new js_external_references_t();
+
+  return 0;
+}
+
+extern "C" int
+js_add_external_reference(js_external_references_t *references, const void *address) {
+  auto &addresses = references->addresses;
+
+  // Drop any terminator a prior `js_get_external_references` appended so that
+  // adding remains valid regardless of call order. A real reference is never
+  // null, so a trailing zero can only be the terminator.
+  if (!addresses.empty() && addresses.back() == 0) addresses.pop_back();
+
+  addresses.push_back(reinterpret_cast<intptr_t>(address));
+
+  return 0;
+}
+
+extern "C" int
+js_get_external_references(js_external_references_t *references, const intptr_t **data, size_t *len) {
+  auto &addresses = references->addresses;
+
+  // V8 expects a null-terminated array. Maintain the terminator lazily so the
+  // returned pointer is stable and safe to hand to `Isolate::CreateParams`.
+  if (addresses.empty() || addresses.back() != 0) addresses.push_back(0);
+
+  if (data) *data = addresses.data();
+  if (len) *len = addresses.size() - 1; // Excluding the terminator.
+
+  return 0;
+}
+
+extern "C" int
+js_destroy_external_references(js_external_references_t *references) {
+  delete references;
+
+  return 0;
+}
+
+struct js_rebind_handlers_s {
+  struct entry {
+    js_rebind_cb cb;
+    void *data;
+  };
+
+  std::vector<entry> entries;
+};
+
+extern "C" int
+js_create_rebind_handlers(js_rebind_handlers_t **result) {
+  *result = new js_rebind_handlers_t();
+
+  return 0;
+}
+
+extern "C" int
+js_add_rebind_handler(js_rebind_handlers_t *handlers, js_rebind_cb cb, void *data) {
+  handlers->entries.push_back({cb, data});
+
+  return 0;
+}
+
+extern "C" int
+js_destroy_rebind_handlers(js_rebind_handlers_t *handlers) {
+  delete handlers;
+
+  return 0;
+}
+
+namespace {
+
+// Snapshot data slot layout, shared by `js_take_snapshot` (which `AddData`s in
+// this order) and `js_rebind_from_snapshot` (which reads it back). The metadata
+// array and the wrapper symbol occupy fixed slots; each serialized module record
+// follows in iteration order, so module `i` lands at `js_snapshot_data_modules
+// + i`.
+enum {
+  js_snapshot_data_metadata = 0,
+  js_snapshot_data_wrapper = 1,
+  js_snapshot_data_modules = 2,
+};
+
+// Metadata array layout: the manifests and id list `js_rebind_from_snapshot`
+// replays, indexed within the metadata array stored at
+// `js_snapshot_data_metadata`.
+enum {
+  js_snapshot_metadata_functions = 0,
+  js_snapshot_metadata_wraps = 1,
+  js_snapshot_metadata_module_ids = 2,
+};
+
+// Asks each handler, in order, to claim a reconstructed binding - described by
+// the populated `info` (its type tag, the resolved callbacks, and any holder) -
+// and supply its `data` / `finalize_hint`. Returns an empty payload when none
+// claim it.
+static js_binding_payload_t
+js_rebind(const js_rebind_handlers_t *handlers, js_env_t *env, const js_rebind_info_t &info) {
+  if (handlers != nullptr) {
+    for (const auto &entry : handlers->entries) {
+      js_binding_payload_t result = {nullptr, nullptr};
+
+      if (entry.cb(env, &info, entry.data, &result)) {
+        return result;
+      }
+    }
+  }
+
+  return {nullptr, nullptr};
+}
+
+// Finds a native address's position in the combined external-reference array, so
+// it can be named in a snapshot manifest. Every snapshotted callback must be a
+// registered reference.
+static uint32_t
+js_external_reference_index(js_env_t *env, const void *address) {
+  auto value = reinterpret_cast<intptr_t>(address);
+
+  size_t index = 0;
+  while (index < env->snapshot.external_references.size() && env->snapshot.external_references[index] != value) {
+    index++;
+  }
+
+  assert(index < env->snapshot.external_references.size());
+
+  return uint32_t(index);
+}
+
+// Resolves an index in the combined external-reference array back to its
+// address, the inverse of `js_external_reference_index`. A negative index
+// denotes an absent callback and resolves to null.
+static void *
+js_external_reference(js_env_t *env, int64_t index) {
+  return index < 0 ? nullptr : reinterpret_cast<void *>(env->snapshot.external_references[size_t(index)]);
+}
+
+// The serialized form of a delegate's internal field: its callbacks' positions
+// in the combined external-reference array (-1 for a null callback). `data` and
+// `finalize_hint` are not serializable and are re-supplied on load.
+struct js_delegate_fields_t {
+  int32_t version;
+  int32_t get;
+  int32_t has;
+  int32_t set;
+  int32_t delete_property;
+  int32_t own_keys;
+  int32_t finalize_cb;
+};
+
+static StartupData
+js_serialize_internal_field(Local<Object> holder, int index, void *data) {
+  auto env = js_env_t::from(Isolate::GetCurrent());
+
+  auto delegate = reinterpret_cast<js_delegate_t *>(holder->GetAlignedPointerFromInternalField(index, js_delegate_type_tag));
+
+  auto reference = [&](const void *address) {
+    return address ? int32_t(js_external_reference_index(env, address)) : -1;
+  };
+
+  auto fields = new js_delegate_fields_t{
+    delegate->callbacks.version,
+    reference(reinterpret_cast<const void *>(delegate->callbacks.get)),
+    reference(reinterpret_cast<const void *>(delegate->callbacks.has)),
+    reference(reinterpret_cast<const void *>(delegate->callbacks.set)),
+    reference(reinterpret_cast<const void *>(delegate->callbacks.delete_property)),
+    reference(reinterpret_cast<const void *>(delegate->callbacks.own_keys)),
+    reference(reinterpret_cast<const void *>(delegate->finalize_cb)),
+  };
+
+  return StartupData{reinterpret_cast<const char *>(fields), int(sizeof(js_delegate_fields_t))};
+}
+
+static void
+js_deserialize_internal_field(Local<Object> holder, int index, StartupData payload, void *data) {
+  if (payload.raw_size != int(sizeof(js_delegate_fields_t))) return;
+
+  auto handlers = reinterpret_cast<const js_rebind_handlers_t *>(data);
+
+  auto env = js_env_t::from(Isolate::GetCurrent());
+
+  auto fields = reinterpret_cast<const js_delegate_fields_t *>(payload.data);
+
+  auto resolve = [&](int32_t reference) -> void * {
+    return js_external_reference(env, reference);
+  };
+
+  js_delegate_callbacks_t callbacks = {};
+  callbacks.version = fields->version;
+  callbacks.get = reinterpret_cast<js_delegate_get_cb>(resolve(fields->get));
+  callbacks.has = reinterpret_cast<js_delegate_has_cb>(resolve(fields->has));
+  callbacks.set = reinterpret_cast<js_delegate_set_cb>(resolve(fields->set));
+  callbacks.delete_property = reinterpret_cast<js_delegate_delete_property_cb>(resolve(fields->delete_property));
+  callbacks.own_keys = reinterpret_cast<js_delegate_own_keys_cb>(resolve(fields->own_keys));
+
+  auto finalize_cb = reinterpret_cast<js_finalize_cb>(resolve(fields->finalize_cb));
+
+  js_rebind_info_t info = {};
+  info.version = 0;
+  info.type = js_binding_delegate;
+  info.delegate.callbacks = callbacks;
+  info.delegate.holder = js_from_local(holder);
+
+  auto rebound = js_rebind(handlers, env, info);
+
+  auto delegate = new js_delegate_t(env, callbacks, rebound.data, finalize_cb, rebound.finalize_hint);
+
+  holder->SetAlignedPointerInInternalField(index, delegate, js_delegate_type_tag);
+
+  delegate->attach_to(env->isolate, holder);
+}
+
+// Builds the null-terminated external-reference array V8 needs: libjs's stable
+// core addresses first, then the embedder's, in a fixed order shared by snapshot
+// production and consumption. Snapshot manifest entries index into the result.
+static void
+js_build_external_references(std::vector<intptr_t> &result, const js_external_references_t *references) {
+  result.clear();
+
+  result.push_back(reinterpret_cast<intptr_t>(&js_callback_t::on_call));
+  result.push_back(reinterpret_cast<intptr_t>(&js_env_t::on_uncaught_exception));
+  result.push_back(reinterpret_cast<intptr_t>(&js_env_t::on_promise_reject));
+  result.push_back(reinterpret_cast<intptr_t>(&js_module_t::on_dynamic_import));
+  result.push_back(reinterpret_cast<intptr_t>(&js_module_t::on_import_meta));
+  result.push_back(reinterpret_cast<intptr_t>(&js_delegate_t::on_get<Name>));
+  result.push_back(reinterpret_cast<intptr_t>(&js_delegate_t::on_set<Name>));
+  result.push_back(reinterpret_cast<intptr_t>(&js_delegate_t::on_delete<Name>));
+  result.push_back(reinterpret_cast<intptr_t>(&js_delegate_t::on_enumerate));
+  result.push_back(reinterpret_cast<intptr_t>(&js_delegate_t::on_get_indexed));
+  result.push_back(reinterpret_cast<intptr_t>(&js_delegate_t::on_set_indexed));
+  result.push_back(reinterpret_cast<intptr_t>(&js_delegate_t::on_delete_indexed));
+
+  if (references) {
+    for (auto address : references->addresses) {
+      if (address != 0) result.push_back(address); // Skip a lazily-added terminator.
+    }
+  }
+
+  result.push_back(0);
+}
+
+// Rebuilds native binding state after deserializing a snapshot, from the data
+// `js_take_snapshot` attaches: a `[function manifest, wrap manifest]` array at
+// index 0 and the wrapper `Private` symbol at index 1.
+//
+//   - function manifest: flat `[slot, cb-index]` pairs; rebuilds the function
+//     side table, with `data` from the rebind handlers.
+//   - wrapper symbol: adopted as `env->wrapper` so deserialized wrapped objects'
+//     private properties resolve.
+//   - wrap manifest: flat `[object, slot, cb-index]` triples; rebuilds the
+//     finalizer side table and re-arms each finalizer (`cb-index` < 0 means no
+//     finalize callback).
+static void
+js_rebind_from_snapshot(js_env_t *env, const js_rebind_handlers_t *handlers) {
+  auto isolate = env->isolate;
+
+  auto scope = HandleScope(isolate);
+
+  auto context = env->current_context();
+
+  Local<Value> value;
+  if (!context->GetDataFromSnapshotOnce<Value>(js_snapshot_data_metadata).ToLocal(&value)) return;
+  if (!value->IsArray()) return;
+
+  auto metadata = value.As<Array>();
+
+  auto functions = metadata->Get(context, js_snapshot_metadata_functions).ToLocalChecked().As<Array>();
+  auto wraps = metadata->Get(context, js_snapshot_metadata_wraps).ToLocalChecked().As<Array>();
+
+  // Adopt the serialized wrapper symbol so private properties on deserialized
+  // wrapped objects, keyed by it, resolve.
+  Local<Private> wrapper;
+  if (context->GetDataFromSnapshotOnce<Private>(js_snapshot_data_wrapper).ToLocal(&wrapper)) {
+    env->wrapper.Reset(isolate, wrapper);
+  }
+
+  for (uint32_t i = 0; i + 1 < functions->Length(); i += 2) {
+    auto slot = uint32_t(functions->Get(context, i).ToLocalChecked().As<Integer>()->Value());
+    auto cb_index = functions->Get(context, i + 1).ToLocalChecked().As<Integer>()->Value();
+
+    auto cb = reinterpret_cast<js_function_cb>(js_external_reference(env, cb_index));
+
+    js_rebind_info_t info = {};
+    info.version = 0;
+    info.type = js_binding_function;
+    info.function.cb = cb;
+
+    auto data = js_rebind(handlers, env, info).data;
+
+    if (env->bindings.functions.entries.size() <= slot) {
+      env->bindings.functions.entries.resize(slot + 1, nullptr);
+    }
+
+    env->bindings.functions.entries[slot] = new js_callback_t(env, cb, data, slot);
+  }
+
+  for (uint32_t i = 0; i + 2 < wraps->Length(); i += 3) {
+    auto object = wraps->Get(context, i).ToLocalChecked().As<Object>();
+    auto slot = uint32_t(wraps->Get(context, i + 1).ToLocalChecked().As<Integer>()->Value());
+    auto cb_index = wraps->Get(context, i + 2).ToLocalChecked().As<Integer>()->Value();
+
+    auto finalize_cb = reinterpret_cast<js_finalize_cb>(js_external_reference(env, cb_index));
+
+    js_rebind_info_t info = {};
+    info.version = 0;
+    info.type = js_binding_finalizer;
+    info.finalizer.cb = finalize_cb;
+    info.finalizer.holder = js_from_local(object);
+
+    auto payload = js_rebind(handlers, env, info);
+
+    auto finalizer = new js_finalizer_t(env, payload.data, finalize_cb, payload.finalize_hint);
+
+    finalizer->index = slot;
+
+    if (env->bindings.finalizers.entries.size() <= slot) {
+      env->bindings.finalizers.entries.resize(slot + 1, nullptr);
+    }
+
+    env->bindings.finalizers.entries[slot] = finalizer;
+
+    finalizer->attach_to(isolate, object);
+  }
+
+  // Module records: rebuild a `js_module_t` for each serialized module, paired by
+  // index with its id symbol. Only fully evaluated modules are serialized, so
+  // their callbacks are never invoked again and are left empty; the embedder
+  // reconnects its handles to the records by id via `js_get_module_by_id`.
+  auto modules = metadata->Get(context, js_snapshot_metadata_module_ids).ToLocalChecked().As<Array>();
+
+  for (uint32_t i = 0; i < modules->Length(); i++) {
+    auto id = modules->Get(context, i).ToLocalChecked().As<Symbol>();
+
+    Local<Module> module;
+    if (!context->GetDataFromSnapshotOnce<Module>(js_snapshot_data_modules + i).ToLocal(&module)) continue;
+
+    // Recover the name from the module's resource name (the same string passed at
+    // creation, for both source-text and synthetic modules).
+    std::string name;
+
+    auto resource = module->GetResourceName();
+    if (!resource.IsEmpty() && resource->IsString()) {
+      auto string = resource.As<String>();
+      auto length = string->Utf8LengthV2(isolate);
+      name.resize(length);
+      string->WriteUtf8V2(isolate, name.data(), length, String::WriteFlags::kReplaceInvalidUtf8);
+    }
+
+    auto record = new js_module_t(isolate, module, id, std::move(name));
+
+    env->modules.emplace(module->GetIdentityHash(), record);
+  }
+}
+
+} // namespace
+
 extern "C" int
 js_create_env(uv_loop_t *loop, js_platform_t *platform, const js_env_options_t *options, js_env_t **result) {
   Isolate::CreateParams params;
@@ -3276,6 +3779,33 @@ js_create_env(uv_loop_t *loop, js_platform_t *platform, const js_env_options_t *
     }
   }
 
+  auto user_references = js_option<&js_env_options_t::external_references, const js_external_references_t *>(options, 1);
+
+  auto snapshot = js_option<&js_env_options_t::snapshot, const void *>(options, 1);
+  auto snapshot_len = js_option<&js_env_options_t::snapshot_len, size_t>(options, 1);
+
+  // The combined core + embedder reference array. Built whenever a snapshot is
+  // consumed (the blob references libjs's core addresses) or the embedder
+  // supplies references. Moved onto the env below so it outlives the lazy
+  // deserialization that reads it.
+  std::vector<intptr_t> external_references;
+
+  if (snapshot || user_references) {
+    js_build_external_references(external_references, user_references);
+    params.external_references = external_references.data();
+  }
+
+  // Must outlive `Isolate::Initialize()` below; the snapshot bytes themselves
+  // must outlive the environment, as V8 deserializes from them lazily.
+  StartupData startup_data;
+
+  if (snapshot) {
+    startup_data.data = static_cast<const char *>(snapshot);
+    startup_data.raw_size = static_cast<int>(snapshot_len);
+
+    params.snapshot_blob = &startup_data;
+  }
+
   auto isolate = Isolate::Allocate();
 
   auto tasks = new js_task_runner_t(loop);
@@ -3300,7 +3830,15 @@ js_create_env(uv_loop_t *loop, js_platform_t *platform, const js_env_options_t *
 
   isolate->SetHostInitializeImportMetaObjectCallback(js_module_t::on_import_meta);
 
-  auto env = new js_env_t(loop, platform, isolate);
+  auto rebind_handlers = js_option<&js_env_options_t::rebind_handlers, const js_rebind_handlers_t *>(options, 1);
+
+  // The reference buffer is moved, not copied, so the pointer handed to V8 above
+  // stays valid for the lifetime of the env. The rebind handlers are needed
+  // during construction (the delegate deserialize hook fires inside
+  // `Context::New`) as well as for the function and wrap rebuild below.
+  auto env = new js_env_t(loop, platform, isolate, std::move(external_references), rebind_handlers);
+
+  if (snapshot) js_rebind_from_snapshot(env, rebind_handlers);
 
   *result = env;
 
@@ -3314,6 +3852,224 @@ js_destroy_env(js_env_t *env) {
   return 0;
 }
 
+namespace {
+
+static const js_snapshot_options_t js_snapshot_default_options = {
+  .version = 0,
+};
+
+template <auto js_snapshot_options_t::*P, typename T>
+static inline T
+js_option(const js_snapshot_options_t *options, int min_version, T fallback = T(js_snapshot_default_options.*P)) {
+  return T(options && options->version >= min_version ? options->*P : fallback);
+}
+
+} // namespace
+
+extern "C" int
+js_create_snapshot(uv_loop_t *loop, js_platform_t *platform, const js_snapshot_options_t *options, js_env_t **result) {
+  Isolate::CreateParams params;
+
+  params.array_buffer_allocator_shared = std::make_shared<js_allocator_t>();
+
+  auto user_references = js_option<&js_snapshot_options_t::external_references, const js_external_references_t *>(options, 0);
+
+  // The producer always needs the combined core + embedder references: `on_call`
+  // and the isolate callbacks installed below are serialized by index. Moved onto
+  // the env after construction so it outlives `CreateBlob`.
+  std::vector<intptr_t> external_references;
+  js_build_external_references(external_references, user_references);
+  params.external_references = external_references.data();
+
+  // Allocate the isolate ourselves and register its task runner *before* it is
+  // initialised, exactly as `js_create_env` does: the snapshot creator
+  // initialises and enters the isolate, which makes V8 call
+  // `GetForegroundTaskRunner` (an `operator[]` insert), and a later `emplace`
+  // would not overwrite that null entry. We therefore use the non-owning
+  // creator and dispose the isolate ourselves at teardown.
+  auto isolate = Isolate::Allocate();
+
+  auto tasks = new js_task_runner_t(loop);
+
+  std::unique_lock guard(platform->lock);
+
+  platform->foreground.emplace(isolate, std::move(tasks));
+
+  guard.unlock();
+
+  auto creator = new SnapshotCreator(isolate, params);
+
+  isolate->SetMicrotasksPolicy(MicrotasksPolicy::kExplicit);
+
+  isolate->AddMessageListener(js_env_t::on_uncaught_exception);
+
+  isolate->SetPromiseRejectCallback(js_env_t::on_promise_reject);
+
+  isolate->SetHostImportModuleDynamicallyCallback(js_module_t::on_dynamic_import);
+
+  isolate->SetHostInitializeImportMetaObjectCallback(js_module_t::on_import_meta);
+
+  auto env = new js_env_t(loop, platform, isolate, std::move(external_references), nullptr);
+
+  env->snapshot.creator = creator;
+
+  env->snapshot.function_code_handling =
+    js_option<&js_snapshot_options_t::function_code_handling, js_snapshot_function_code_handling_t>(options, 0) == js_snapshot_keep_function_code
+      ? SnapshotCreator::FunctionCodeHandling::kKeep
+      : SnapshotCreator::FunctionCodeHandling::kClear;
+
+  *result = env;
+
+  return 0;
+}
+
+extern "C" int
+js_take_snapshot(js_env_t *env, void **data, size_t *len) {
+  auto creator = env->snapshot.creator;
+
+  auto isolate = env->isolate;
+
+  {
+    auto scope = HandleScope(isolate);
+
+    auto context = env->context.Get(isolate);
+
+    // Snapshot metadata, built while the context is still entered and replayed by
+    // `js_rebind_from_snapshot` on load: a 3-element array
+    // `[function manifest, wrap manifest, module ids]`, plus the wrapper symbol
+    // and each module record attached as their own data slots.
+
+    // Function manifest: `[slot, cb-index]` pairs, `cb-index` indexing the
+    // combined external-reference array.
+    auto functions = Array::New(isolate);
+
+    uint32_t fn = 0;
+
+    for (uint32_t slot = 0; slot < env->bindings.functions.entries.size(); slot++) {
+      auto callback = env->bindings.functions.entries[slot];
+
+      if (callback == nullptr) continue;
+
+      auto cb_index = js_external_reference_index(env, reinterpret_cast<const void *>(callback->cb));
+
+      functions->Set(context, fn++, Integer::NewFromUnsigned(isolate, slot)).Check();
+      functions->Set(context, fn++, Integer::NewFromUnsigned(isolate, cb_index)).Check();
+    }
+
+    // Wrap manifest: `[object, slot, cb-index]` triples, the wrapped object
+    // stored inline so the consumer gets a handle to re-arm its finalizer
+    // (`cb-index` -1 when there is no finalize callback).
+    auto wraps = Array::New(isolate);
+
+    uint32_t wn = 0;
+
+    for (uint32_t slot = 0; slot < env->bindings.finalizers.entries.size(); slot++) {
+      auto finalizer = env->bindings.finalizers.entries[slot];
+
+      if (finalizer == nullptr || finalizer->value.IsEmpty() || finalizer->is_delegate) continue;
+
+      auto cb_index = finalizer->finalize_cb
+                        ? int32_t(js_external_reference_index(env, reinterpret_cast<const void *>(finalizer->finalize_cb)))
+                        : -1;
+
+      wraps->Set(context, wn++, finalizer->value.Get(isolate)).Check();
+      wraps->Set(context, wn++, Integer::NewFromUnsigned(isolate, slot)).Check();
+      wraps->Set(context, wn++, Integer::New(isolate, cb_index)).Check();
+    }
+
+    // Module ids: the id symbol of every module, in iteration order. Each
+    // module's compiled record is added below as snapshot data at index
+    // `js_snapshot_data_modules + i`, so the consumer pairs `ids[i]` with the
+    // module at the same offset.
+    auto modules = Array::New(isolate);
+
+    std::vector<Local<Module>> module_records;
+
+    uint32_t mn = 0;
+
+    for (const auto &entry : env->modules) {
+      auto module = entry.second;
+
+      auto record = module->module.Get(isolate);
+
+      // Only fully evaluated modules survive a snapshot: their callbacks are
+      // never invoked again, and other states (instantiating, mid-top-level-await,
+      // errored) carry no meaningful warmed-up result.
+      if (record->GetStatus() != Module::Status::kEvaluated) continue;
+
+      modules->Set(context, mn++, module->id.Get(isolate)).Check();
+      module_records.push_back(record);
+    }
+
+    auto metadata = Array::New(isolate);
+    metadata->Set(context, js_snapshot_metadata_functions, functions).Check();
+    metadata->Set(context, js_snapshot_metadata_wraps, wraps).Check();
+    metadata->Set(context, js_snapshot_metadata_module_ids, modules).Check();
+
+    // The wrapper symbol is a `Private`, not a `Value`, so it rides its own data
+    // slot rather than the metadata array.
+    auto wrapper = env->wrapper.Get(isolate);
+
+    context->Exit();
+
+    creator->SetDefaultContext(context, SerializeInternalFieldsCallback(js_serialize_internal_field));
+
+    // `AddData` assigns indices in call order; assert that order matches the
+    // shared slot layout the consumer reads back.
+    auto metadata_index = creator->AddData(context, metadata);
+    assert(metadata_index == size_t(js_snapshot_data_metadata));
+
+    auto wrapper_index = creator->AddData(context, wrapper);
+    assert(wrapper_index == size_t(js_snapshot_data_wrapper));
+
+    for (size_t i = 0; i < module_records.size(); i++) {
+      auto module_index = creator->AddData(context, module_records[i]);
+      assert(module_index == size_t(js_snapshot_data_modules) + i);
+    }
+  }
+
+  // Release every Global into the isolate before serializing: `CreateBlob()`
+  // takes ownership of the default context and rejects any lingering global
+  // handles into the serialized heap. The per-env privates are re-created from
+  // scratch when the blob is booted, and the side table's weak handles on each
+  // function instance are no longer needed (the table is rebuilt on load).
+  env->wrapper.Reset();
+  env->delegate.Reset();
+  env->tag.Reset();
+  env->exception.Reset();
+  env->default_module_id.Reset();
+  env->context.Reset();
+
+  for (auto callback : env->bindings.functions.entries) {
+    if (callback) callback->function.Reset();
+  }
+
+  for (auto finalizer : env->bindings.finalizers.entries) {
+    if (finalizer) finalizer->value.Reset();
+  }
+
+  for (auto &entry : env->modules) {
+    entry.second->module.Reset();
+    entry.second->id.Reset();
+  }
+
+  // Must run outside any handle scope.
+  auto blob = creator->CreateBlob(env->snapshot.function_code_handling);
+
+  *data = malloc(size_t(blob.raw_size));
+  memcpy(*data, blob.data, size_t(blob.raw_size));
+  *len = size_t(blob.raw_size);
+
+  // `CreateBlob()` hands back a buffer allocated with `new[]`.
+  delete[] blob.data;
+
+  // Consume the environment. The destructor deletes the creator, which disposes
+  // the isolate.
+  env->close_maybe();
+
+  return 0;
+}
+
 extern "C" int
 js_on_uncaught_exception(js_env_t *env, js_uncaught_exception_cb cb, void *data) {
   env->callbacks.uncaught_exception = cb;
@@ -3645,6 +4401,30 @@ js_get_module_id(js_env_t *env, js_module_t *module, js_value_t **result) {
   return 0;
 }
 
+extern "C" int
+js_get_module_by_id(js_env_t *env, js_value_t *id, js_module_t **result) {
+  if (env->is_exception_pending()) return js_error(env);
+
+  int err;
+
+  auto symbol = js_to_local<Symbol>(id);
+
+  for (const auto &entry : env->modules) {
+    auto module = entry.second;
+
+    if (module->id.Get(env->isolate) == symbol) {
+      *result = module;
+
+      return 0;
+    }
+  }
+
+  err = js_throw_error(env, NULL, "Could not find module");
+  assert(err == 0);
+
+  return js_error(env);
+}
+
 extern "C" int
 js_get_default_module_id(js_env_t *env, js_value_t **result) {
   // Allow continuing even with a pending exception
@@ -3982,11 +4762,13 @@ js_wrap(js_env_t *env, js_value_t *object, void *data, js_finalize_cb finalize_c
 
   auto finalizer = new js_finalizer_t(env, data, finalize_cb, finalize_hint);
 
-  auto external = External::New(env->isolate, finalizer, js_finalizer_type_tag);
+  finalizer->index = env->bindings.finalizers.add(finalizer);
+
+  auto token = Integer::NewFromUnsigned(env->isolate, finalizer->index);
 
   auto success = env->try_catch<bool>(
     [&] {
-      return local->SetPrivate(context, key, external);
+      return local->SetPrivate(context, key, token);
     }
   );
 
@@ -4013,15 +4795,17 @@ js_unwrap(js_env_t *env, js_value_t *object, void **result) {
 
   auto local = js_to_local<Object>(object);
 
-  auto external = env->try_catch<Value>(
+  auto token = env->try_catch<Value>(
     [&] {
       return local->GetPrivate(context, key);
     }
   );
 
-  if (external.IsEmpty()) return js_error(env);
+  if (token.IsEmpty()) return js_error(env);
+
+  auto index = size_t(token.ToLocalChecked().As<Integer>()->Value());
 
-  auto finalizer = reinterpret_cast<js_finalizer_t *>(external.ToLocalChecked().As<External>()->Value(js_finalizer_type_tag));
+  auto finalizer = env->bindings.finalizers.entries[index];
 
   *result = finalizer->data;
 
@@ -4038,17 +4822,19 @@ js_remove_wrap(js_env_t *env, js_value_t *object, void **result) {
 
   auto local = js_to_local<Object>(object);
 
-  auto external = env->try_catch<Value>(
+  auto token = env->try_catch<Value>(
     [&] {
       return local->GetPrivate(context, key);
     }
   );
 
-  if (external.IsEmpty()) return js_error(env);
+  if (token.IsEmpty()) return js_error(env);
 
   local->DeletePrivate(context, key).Check();
 
-  auto finalizer = reinterpret_cast<js_finalizer_t *>(external.ToLocalChecked().As<External>()->Value(js_finalizer_type_tag));
+  auto index = size_t(token.ToLocalChecked().As<Integer>()->Value());
+
+  auto finalizer = env->bindings.finalizers.entries[index];
 
   finalizer->detach();
 
@@ -4067,15 +4853,21 @@ js_create_delegate(js_env_t *env, const js_delegate_callbacks_t *callbacks, void
 
   auto delegate = new js_delegate_t(env, *callbacks, data, finalize_cb, finalize_hint);
 
+  delegate->index = env->bindings.finalizers.add(delegate);
+
   auto tpl = delegate->to_object_template(env->isolate);
 
   auto object = tpl->NewInstance(context);
 
   if (object.IsEmpty()) return js_error(env);
 
-  delegate->attach_to(env->isolate, object.ToLocalChecked());
+  auto local = object.ToLocalChecked();
 
-  *result = js_from_local(object.ToLocalChecked());
+  local->SetAlignedPointerInInternalField(0, delegate, js_delegate_type_tag);
+
+  delegate->attach_to(env->isolate, local);
+
+  *result = js_from_local(local);
 
   return 0;
 }
@@ -4698,6 +5490,8 @@ js_create_typed_function(js_env_t *env, const char *name, size_t len, js_functio
     local->SetName(string.ToLocalChecked());
   }
 
+  callback->hold_weakly(env->isolate, local);
+
   *result = js_from_local(local);
 
   return 0;
@@ -6636,7 +7430,7 @@ js_get_callback_info(js_env_t *env, const js_callback_info_t *info, size_t *argc
   if (receiver) *receiver = js_from_local(args->This());
 
   if (data) {
-    *data = reinterpret_cast<js_callback_t *>(args->Data().As<External>()->Value(js_callback_info_type_tag))->data;
+    *data = env->bindings.functions.entries[size_t(args->Data().As<Integer>()->Value())]->data;
   }
 
   return 0;
@@ -6648,10 +7442,12 @@ js_get_typed_callback_info(const js_typed_callback_info_t *info, js_env_t **env,
 
   auto args = reinterpret_cast<const FastApiCallbackOptions *>(info);
 
-  if (env) *env = js_env_t::from(args->isolate);
+  auto callback_env = js_env_t::from(args->isolate);
+
+  if (env) *env = callback_env;
 
   if (data) {
-    *data = reinterpret_cast<js_typed_callback_t *>(args->data.As<External>()->Value(js_callback_info_type_tag))->data;
+    *data = callback_env->bindings.functions.entries[size_t(args->data.As<Integer>()->Value())]->data;
   }
 
   return 0;
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 7244855..343db7d 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -82,6 +82,7 @@ list(APPEND tests
   create-reference-undefined
   create-sharedarraybuffer
   create-sharedarraybuffer-with-backing-store
+  create-snapshot
   create-string-latin1
   create-string-utf8
   create-string-utf8-with-null
@@ -127,6 +128,7 @@ list(APPEND tests
   dynamic-import-with-referrer-function
   dynamic-import-without-handler
   escapable-handle-scope
+  external-references
   fatal-exception
   garbage-collection-tracking
   get-array-elements
@@ -209,6 +211,13 @@ list(APPEND tests
   promise-rejection-unhandled-reentrant
   promise-rejection-unhandled-reentrant-deferred
   reference-unref
+  run-from-snapshot
+  run-from-snapshot-delegate
+  run-from-snapshot-dynamic-import
+  run-from-snapshot-function
+  run-from-snapshot-import-meta
+  run-from-snapshot-module
+  run-from-snapshot-wrap
   run-module
   run-module-async
   run-module-cyclic-import
diff --git a/test/boot-from-snapshot.c b/test/boot-from-snapshot.c
new file mode 100644
index 0000000..4a23a8c
--- /dev/null
+++ b/test/boot-from-snapshot.c
@@ -0,0 +1,441 @@
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <utf.h>
+#include <uv.h>
+
+#include "../include/js.h"
+
+// Verifies that a native function survives an isolate snapshot: the producer
+// binds a native `answer()` onto the global and serializes a blob; a separate
+// process boots from the blob and calls `globalThis.answer()`, expecting 42.
+//
+// Producer and consumer run in different processes (the test re-spawns itself)
+// because this build enables V8's shared read-only heap, which makes in-process
+// consumption of a freshly produced blob trip a debug-only checksum CHECK.
+
+static js_value_t *
+answer(js_env_t *env, js_callback_info_t *info) {
+  int e;
+
+  // Return the callback's `data`, so the test only passes if `data` is rebound
+  // after restore (it would read NULL, and return 0, without a rebind handler).
+  void *data;
+  e = js_get_callback_info(env, info, NULL, NULL, NULL, &data);
+  assert(e == 0);
+
+  js_value_t *result;
+  e = js_create_int32(env, (int32_t) (intptr_t) data, &result);
+  assert(e == 0);
+
+  return result;
+}
+
+static void
+on_wrap_finalize(js_env_t *env, void *data, void *finalize_hint) {}
+
+// A delegate getter that returns its data for any property.
+static js_value_t *
+delegate_get(js_env_t *env, js_value_t *property, void *data) {
+  int e;
+
+  js_value_t *result;
+  e = js_create_int32(env, (int32_t) (intptr_t) data, &result);
+  assert(e == 0);
+
+  return result;
+}
+
+static bool
+rebind(js_env_t *env, js_binding_type_t type, const void *cb, js_value_t *holder, void *context, js_binding_payload_t *result) {
+  if (type == js_binding_function && cb == (const void *) answer) {
+    result->data = (void *) (intptr_t) 42;
+
+    return true;
+  }
+
+  if (type == js_binding_finalizer && cb == (const void *) on_wrap_finalize) {
+    result->data = (void *) (intptr_t) 99;
+
+    return true;
+  }
+
+  if (type == js_binding_delegate && cb == (const void *) delegate_get) {
+    result->data = (void *) (intptr_t) 123;
+
+    return true;
+  }
+
+  return false;
+}
+
+static void
+on_meta(js_env_t *env, js_module_t *module, js_value_t *meta, void *data) {
+  int e;
+
+  js_value_t *value;
+  e = js_create_int32(env, 7, &value);
+  assert(e == 0);
+
+  e = js_set_named_property(env, meta, "answer", value);
+  assert(e == 0);
+}
+
+static js_external_references_t *
+references() {
+  int e;
+
+  js_external_references_t *references;
+  e = js_create_external_references(&references);
+  assert(e == 0);
+
+  e = js_add_external_reference(references, (const void *) answer);
+  assert(e == 0);
+
+  e = js_add_external_reference(references, (const void *) on_wrap_finalize);
+  assert(e == 0);
+
+  e = js_add_external_reference(references, (const void *) delegate_get);
+  assert(e == 0);
+
+  return references;
+}
+
+static int exit_status = -1;
+
+static void
+on_exit(uv_process_t *process, int64_t status, int signal) {
+  exit_status = (int) status;
+
+  uv_close((uv_handle_t *) process, NULL);
+}
+
+static void
+produce(uv_loop_t *loop, js_platform_t *platform) {
+  int e;
+
+  js_snapshot_options_t options = {
+    .version = 0,
+    .external_references = references(),
+  };
+
+  js_env_t *env;
+  e = js_create_snapshot(loop, platform, &options, &env);
+  assert(e == 0);
+
+  js_handle_scope_t *scope;
+  e = js_open_handle_scope(env, &scope);
+  assert(e == 0);
+
+  js_value_t *global;
+  e = js_get_global(env, &global);
+  assert(e == 0);
+
+  js_value_t *fn;
+  e = js_create_function(env, "answer", -1, answer, (void *) (intptr_t) 42, &fn);
+  assert(e == 0);
+
+  e = js_set_named_property(env, global, "answer", fn);
+  assert(e == 0);
+
+  // Wrap an object reachable from the global, with non-NULL data and a finalizer.
+  // After restore its finalizer side-table slot is rebuilt and the data rebound.
+  js_value_t *wrapped;
+  e = js_create_object(env, &wrapped);
+  assert(e == 0);
+
+  e = js_wrap(env, wrapped, (void *) (intptr_t) 99, on_wrap_finalize, NULL, NULL);
+  assert(e == 0);
+
+  e = js_set_named_property(env, global, "wrapped", wrapped);
+  assert(e == 0);
+
+  // Create a delegate reachable from the global. After restore its internal
+  // field is reconstructed and its data rebound, so property access routes
+  // through the rebound getter.
+  js_delegate_callbacks_t callbacks = {
+    .version = 0,
+    .get = delegate_get,
+  };
+
+  js_value_t *delegate;
+  e = js_create_delegate(env, &callbacks, (void *) (intptr_t) 123, NULL, NULL, &delegate);
+  assert(e == 0);
+
+  e = js_set_named_property(env, global, "delegate", delegate);
+  assert(e == 0);
+
+  // Exercise import.meta during warmup: a module reads import.meta.answer
+  // (populated by the meta callback) and stashes it on the global. This proves
+  // the producer installs the import.meta callback, and the value rides into the
+  // snapshot. The module is deleted before serializing so it leaves no global
+  // handles behind.
+  js_value_t *source;
+  e = js_create_string_utf8(env, (utf8_t *) "globalThis.meta = import.meta.answer", -1, &source);
+  assert(e == 0);
+
+  js_module_t *module;
+  e = js_create_module(env, "warmup.js", -1, 0, source, on_meta, NULL, &module);
+  assert(e == 0);
+
+  e = js_instantiate_module(env, module, NULL, NULL);
+  assert(e == 0);
+
+  js_value_t *promise;
+  e = js_run_module(env, module, &promise);
+  assert(e == 0);
+
+  js_promise_state_t state;
+  e = js_get_promise_state(env, promise, &state);
+  assert(e == 0);
+
+  assert(state == js_promise_fulfilled);
+
+  e = js_delete_module(env, module);
+  assert(e == 0);
+
+  // A module that survives the snapshot: created, instantiated, and evaluated,
+  // then left in place so its compiled record is serialized. Its id is stashed on
+  // the global so the consumer can look it up.
+  js_value_t *survivor_source;
+  e = js_create_string_utf8(env, (utf8_t *) "export const answer = 42", -1, &survivor_source);
+  assert(e == 0);
+
+  js_module_t *survivor;
+  e = js_create_module(env, "survivor.js", -1, 0, survivor_source, NULL, NULL, &survivor);
+  assert(e == 0);
+
+  e = js_instantiate_module(env, survivor, NULL, NULL);
+  assert(e == 0);
+
+  js_value_t *survivor_promise;
+  e = js_run_module(env, survivor, &survivor_promise);
+  assert(e == 0);
+
+  js_promise_state_t survivor_state;
+  e = js_get_promise_state(env, survivor_promise, &survivor_state);
+  assert(e == 0);
+
+  assert(survivor_state == js_promise_fulfilled);
+
+  js_value_t *survivor_id;
+  e = js_get_module_id(env, survivor, &survivor_id);
+  assert(e == 0);
+
+  e = js_set_named_property(env, global, "moduleId", survivor_id);
+  assert(e == 0);
+
+  e = js_close_handle_scope(env, scope);
+  assert(e == 0);
+
+  void *data;
+  size_t len;
+  e = js_take_snapshot(env, &data, &len);
+  assert(e == 0);
+
+  // Write the blob to a temp file the child process boots from.
+
+  char path[4096];
+  size_t path_len = sizeof(path);
+  e = uv_os_tmpdir(path, &path_len);
+  assert(e == 0);
+
+  strncat(path, "/libjs-boot-from-snapshot.blob", sizeof(path) - strlen(path) - 1);
+
+  FILE *file = fopen(path, "wb");
+  assert(file != NULL);
+
+  assert(fwrite(data, 1, len, file) == len);
+
+  fclose(file);
+
+  free(data);
+
+  // Re-spawn this executable in consume mode, pointed at the blob.
+
+  char exepath[4096];
+  size_t exepath_len = sizeof(exepath);
+  e = uv_exepath(exepath, &exepath_len);
+  assert(e == 0);
+
+  e = uv_os_setenv("JS_SNAPSHOT_BLOB", path);
+  assert(e == 0);
+
+  char *args[] = {exepath, NULL};
+
+  uv_process_options_t process_options = {0};
+  process_options.file = exepath;
+  process_options.args = args;
+  process_options.exit_cb = on_exit;
+
+  uv_process_t process;
+  e = uv_spawn(loop, &process, &process_options);
+  assert(e == 0);
+
+  e = uv_run(loop, UV_RUN_DEFAULT);
+  assert(e == 0);
+
+  remove(path);
+
+  assert(exit_status == 0);
+}
+
+static void
+consume(uv_loop_t *loop, js_platform_t *platform, const char *path) {
+  int e;
+
+  FILE *file = fopen(path, "rb");
+  assert(file != NULL);
+
+  fseek(file, 0, SEEK_END);
+  long len = ftell(file);
+  fseek(file, 0, SEEK_SET);
+
+  void *data = malloc(len);
+  assert(fread(data, 1, len, file) == (size_t) len);
+
+  fclose(file);
+
+  js_rebind_handlers_t *handlers;
+  e = js_create_rebind_handlers(&handlers);
+  assert(e == 0);
+
+  e = js_add_rebind_handler(handlers, rebind, NULL);
+  assert(e == 0);
+
+  js_env_options_t options = {
+    .version = 1,
+    .snapshot = data,
+    .snapshot_len = (size_t) len,
+    .external_references = references(),
+    .rebind_handlers = handlers,
+  };
+
+  js_env_t *env;
+  e = js_create_env(loop, platform, &options, &env);
+  assert(e == 0);
+
+  js_handle_scope_t *scope;
+  e = js_open_handle_scope(env, &scope);
+  assert(e == 0);
+
+  js_value_t *global;
+  e = js_get_global(env, &global);
+  assert(e == 0);
+
+  js_value_t *fn;
+  e = js_get_named_property(env, global, "answer", &fn);
+  assert(e == 0);
+
+  js_value_t *result;
+  e = js_call_function(env, global, fn, 0, NULL, &result);
+  assert(e == 0);
+
+  int32_t value;
+  e = js_get_value_int32(env, result, &value);
+  assert(e == 0);
+
+  assert(value == 42);
+
+  // The import.meta value computed during warmup survived the snapshot.
+  js_value_t *meta;
+  e = js_get_named_property(env, global, "meta", &meta);
+  assert(e == 0);
+
+  int32_t meta_value;
+  e = js_get_value_int32(env, meta, &meta_value);
+  assert(e == 0);
+
+  assert(meta_value == 7);
+
+  // The wrapped object survived: its finalizer side-table slot was rebuilt and
+  // the data rebound, so js_unwrap returns it.
+  js_value_t *wrapped;
+  e = js_get_named_property(env, global, "wrapped", &wrapped);
+  assert(e == 0);
+
+  void *wrapped_data;
+  e = js_unwrap(env, wrapped, &wrapped_data);
+  assert(e == 0);
+
+  assert((int32_t) (intptr_t) wrapped_data == 99);
+
+  // The delegate survived: its internal field was reconstructed and data rebound,
+  // so property access routes through the rebound getter.
+  js_value_t *delegate;
+  e = js_get_named_property(env, global, "delegate", &delegate);
+  assert(e == 0);
+
+  js_value_t *delegated;
+  e = js_get_named_property(env, delegate, "anything", &delegated);
+  assert(e == 0);
+
+  int32_t delegated_value;
+  e = js_get_value_int32(env, delegated, &delegated_value);
+  assert(e == 0);
+
+  assert(delegated_value == 123);
+
+  // The module graph survived: the evaluated module is rebuilt from the snapshot,
+  // looked up by the id stashed on the global, and its namespace still holds the
+  // evaluated export.
+  js_value_t *module_id;
+  e = js_get_named_property(env, global, "moduleId", &module_id);
+  assert(e == 0);
+
+  js_module_t *module;
+  e = js_get_module_by_id(env, module_id, &module);
+  assert(e == 0);
+
+  js_value_t *namespace;
+  e = js_get_module_namespace(env, module, &namespace);
+  assert(e == 0);
+
+  js_value_t *module_answer;
+  e = js_get_named_property(env, namespace, "answer", &module_answer);
+  assert(e == 0);
+
+  int32_t module_answer_value;
+  e = js_get_value_int32(env, module_answer, &module_answer_value);
+  assert(e == 0);
+
+  assert(module_answer_value == 42);
+
+  e = js_close_handle_scope(env, scope);
+  assert(e == 0);
+
+  e = js_destroy_env(env);
+  assert(e == 0);
+
+  e = js_destroy_rebind_handlers(handlers);
+  assert(e == 0);
+
+  free(data);
+}
+
+int
+main() {
+  int e;
+
+  uv_loop_t *loop = uv_default_loop();
+
+  js_platform_t *platform;
+  e = js_create_platform(loop, NULL, &platform);
+  assert(e == 0);
+
+  char path[4096];
+  size_t path_len = sizeof(path);
+
+  if (uv_os_getenv("JS_SNAPSHOT_BLOB", path, &path_len) == 0) {
+    consume(loop, platform, path);
+  } else {
+    produce(loop, platform);
+  }
+
+  e = js_destroy_platform(platform);
+  assert(e == 0);
+
+  e = uv_run(loop, UV_RUN_DEFAULT);
+  assert(e == 0);
+}
diff --git a/test/create-snapshot.c b/test/create-snapshot.c
new file mode 100644
index 0000000..f8f8fbc
--- /dev/null
+++ b/test/create-snapshot.c
@@ -0,0 +1,65 @@
+#include <assert.h>
+#include <stdlib.h>
+#include <utf.h>
+#include <uv.h>
+
+#include "../include/js.h"
+
+// Validates the snapshot producer: warm up an environment, serialize it, and
+// confirm a non-empty blob is handed back and the environment tears down
+// cleanly.
+//
+// The blob is deliberately not booted in this same process: this build enables
+// V8's shared read-only heap (a build-level setting), so loading a freshly
+// produced blob in a process that already has a shared read-only heap trips a
+// debug-only checksum CHECK. Snapshots are produced offline and consumed in a
+// separate process, so full round-trip coverage belongs to a release or
+// cross-process test.
+
+int
+main() {
+  int e;
+
+  uv_loop_t *loop = uv_default_loop();
+
+  js_platform_t *platform;
+  e = js_create_platform(loop, NULL, &platform);
+  assert(e == 0);
+
+  js_env_t *env;
+  e = js_create_snapshot(loop, platform, NULL, &env);
+  assert(e == 0);
+
+  js_handle_scope_t *scope;
+  e = js_open_handle_scope(env, &scope);
+  assert(e == 0);
+
+  js_value_t *script;
+  e = js_create_string_utf8(env, (utf8_t *) "globalThis.answer = 42", -1, &script);
+  assert(e == 0);
+
+  js_value_t *result;
+  e = js_run_script(env, NULL, 0, 0, script, &result);
+  assert(e == 0);
+
+  e = js_close_handle_scope(env, scope);
+  assert(e == 0);
+
+  void *data;
+  size_t len;
+  e = js_take_snapshot(env, &data, &len);
+  assert(e == 0);
+
+  // `env` is consumed by `js_take_snapshot()` and must not be destroyed.
+
+  assert(data != NULL);
+  assert(len > 0);
+
+  free(data);
+
+  e = js_destroy_platform(platform);
+  assert(e == 0);
+
+  e = uv_run(loop, UV_RUN_DEFAULT);
+  assert(e == 0);
+}
diff --git a/test/external-references.c b/test/external-references.c
new file mode 100644
index 0000000..ebb01f6
--- /dev/null
+++ b/test/external-references.c
@@ -0,0 +1,56 @@
+#include <assert.h>
+#include <stdint.h>
+#include <uv.h>
+
+#include "../include/js.h"
+
+static void
+fn_a() {}
+
+static void
+fn_b() {}
+
+int
+main() {
+  int e;
+
+  js_external_references_t *references;
+  e = js_create_external_references(&references);
+  assert(e == 0);
+
+  e = js_add_external_reference(references, (const void *) fn_a);
+  assert(e == 0);
+
+  e = js_add_external_reference(references, (const void *) fn_b);
+  assert(e == 0);
+
+  const intptr_t *data;
+  size_t len;
+  e = js_get_external_references(references, &data, &len);
+  assert(e == 0);
+
+  assert(len == 2);
+
+  assert(data[0] == (intptr_t) fn_a);
+  assert(data[1] == (intptr_t) fn_b);
+
+  // The array handed to V8 must be null-terminated.
+  assert(data[len] == 0);
+
+  // Adding after a read stays valid; the terminator is not left dangling in the
+  // middle of the array.
+  e = js_add_external_reference(references, (const void *) main);
+  assert(e == 0);
+
+  e = js_get_external_references(references, &data, &len);
+  assert(e == 0);
+
+  assert(len == 3);
+  assert(data[2] == (intptr_t) main);
+  assert(data[len] == 0);
+
+  e = js_destroy_external_references(references);
+  assert(e == 0);
+
+  return 0;
+}
diff --git a/test/fixtures/snapshots/.gitignore b/test/fixtures/snapshots/.gitignore
new file mode 100644
index 0000000..d6b7ef3
--- /dev/null
+++ b/test/fixtures/snapshots/.gitignore
@@ -0,0 +1,2 @@
+*
+!.gitignore
diff --git a/test/run-from-snapshot-delegate.c b/test/run-from-snapshot-delegate.c
new file mode 100644
index 0000000..d7481bd
--- /dev/null
+++ b/test/run-from-snapshot-delegate.c
@@ -0,0 +1,89 @@
+#include <assert.h>
+#include <stdint.h>
+
+#include "../include/js.h"
+#include "snapshot.h"
+
+// Verifies that a delegate survives an isolate snapshot: the producer creates a
+// delegate reachable from the global. After restore its internal field is
+// reconstructed and its data rebound, so property access routes through the
+// rebound getter, which returns its data.
+
+static js_value_t *
+delegate_get(js_env_t *env, js_value_t *property, void *data) {
+  int e;
+
+  js_value_t *result;
+  e = js_create_int32(env, (int32_t) (intptr_t) data, &result);
+  assert(e == 0);
+
+  return result;
+}
+
+static bool
+rebind(js_env_t *env, const js_rebind_info_t *info, void *context, js_binding_payload_t *result) {
+  if (info->type == js_binding_delegate && info->delegate.callbacks.get == delegate_get) {
+    result->data = (void *) (intptr_t) 123;
+
+    return true;
+  }
+
+  return false;
+}
+
+static void
+references(js_external_references_t *references) {
+  int e;
+
+  e = js_add_external_reference(references, (const void *) delegate_get);
+  assert(e == 0);
+}
+
+static void
+produce(js_env_t *env, js_value_t *global) {
+  int e;
+
+  js_delegate_callbacks_t callbacks = {
+    .version = 0,
+    .get = delegate_get,
+  };
+
+  js_value_t *delegate;
+  e = js_create_delegate(env, &callbacks, (void *) (intptr_t) 123, NULL, NULL, &delegate);
+  assert(e == 0);
+
+  e = js_set_named_property(env, global, "delegate", delegate);
+  assert(e == 0);
+}
+
+static void
+consume(js_env_t *env, js_value_t *global) {
+  int e;
+
+  js_value_t *delegate;
+  e = js_get_named_property(env, global, "delegate", &delegate);
+  assert(e == 0);
+
+  js_value_t *delegated;
+  e = js_get_named_property(env, delegate, "anything", &delegated);
+  assert(e == 0);
+
+  int32_t value;
+  e = js_get_value_int32(env, delegated, &value);
+  assert(e == 0);
+
+  assert(value == 123);
+}
+
+int
+main() {
+  snapshot_test_t test = {
+    .name = "run-from-snapshot-delegate",
+    .references = references,
+    .rebind = rebind,
+    .produce = produce,
+    .consume = consume,
+  };
+
+  snapshot_test_run(&test);
+}
diff --git a/test/run-from-snapshot-dynamic-import.c b/test/run-from-snapshot-dynamic-import.c
new file mode 100644
index 0000000..1d216a8
--- /dev/null
+++ b/test/run-from-snapshot-dynamic-import.c
@@ -0,0 +1,165 @@
+#include <assert.h>
+#include <stdbool.h>
+#include <utf.h>
+#include <uv.h>
+
+#include "../include/js.h"
+#include "snapshot.h"
+
+// Verifies that dynamic import() works after booting from a snapshot: the
+// producer warms up a plain global, and the consumer registers a dynamic import
+// handler and runs a script that imports a module. The import is resolved
+// asynchronously from a timer, so it only completes once the event loop runs,
+// proving the restored environment drives dynamic import end to end.
+//
+// The import handler is set at runtime with js_on_dynamic_import() rather than
+// serialized, so the consumer reinstates it after restore.
+
+static js_env_t *import_env;
+static js_deferred_t *import_deferred;
+static js_value_t *import_namespace;
+static uv_timer_t import_timer;
+static bool import_resolved;
+
+static void
+on_module_evaluate(js_env_t *env, js_module_t *module, void *data) {
+  int e;
+
+  js_value_t *name;
+  e = js_create_string_utf8(env, (utf8_t *) "answer", -1, &name);
+  assert(e == 0);
+
+  js_value_t *value;
+  e = js_create_uint32(env, 42, &value);
+  assert(e == 0);
+
+  e = js_set_module_export(env, module, name, value);
+  assert(e == 0);
+}
+
+// Fires from the event loop and resolves the pending dynamic import, so the
+// import only completes once the loop has run.
+static void
+on_timer(uv_timer_t *timer) {
+  int e;
+
+  e = js_resolve_deferred(import_env, import_deferred, import_namespace);
+  assert(e == 0);
+
+  import_resolved = true;
+
+  uv_close((uv_handle_t *) timer, NULL);
+}
+
+// Builds and evaluates the requested module synchronously, but defers handing
+// back its namespace until a timer fires on the event loop.
+static js_value_t *
+on_import(js_env_t *env, js_value_t *specifier, js_value_t *assertions, js_value_t *referrer, js_value_t *id, void *data) {
+  int e;
+
+  js_value_t *export_names[1];
+  e = js_create_string_utf8(env, (utf8_t *) "answer", -1, &export_names[0]);
+  assert(e == 0);
+
+  js_module_t *module;
+  e = js_create_synthetic_module(env, "synthetic", -1, export_names, 1, on_module_evaluate, NULL, &module);
+  assert(e == 0);
+
+  e = js_instantiate_module(env, module, NULL, NULL);
+  assert(e == 0);
+
+  js_value_t *evaluated;
+  e = js_run_module(env, module, &evaluated);
+  assert(e == 0);
+
+  e = js_get_module_namespace(env, module, &import_namespace);
+  assert(e == 0);
+
+  js_value_t *promise;
+  e = js_create_promise(env, &import_deferred, &promise);
+  assert(e == 0);
+
+  import_env = env;
+
+  uv_loop_t *loop;
+  e = js_get_env_loop(env, &loop);
+  assert(e == 0);
+
+  e = uv_timer_init(loop, &import_timer);
+  assert(e == 0);
+
+  e = uv_timer_start(&import_timer, on_timer, 0, 0);
+  assert(e == 0);
+
+  return promise;
+}
+
+static void
+produce(js_env_t *env, js_value_t *global) {
+  int e;
+
+  // Seed the slot the consumer overwrites once the import resolves, to prove the
+  // import ran after restore rather than during warmup.
+  js_value_t *value;
+  e = js_create_uint32(env, 0, &value);
+  assert(e == 0);
+
+  e = js_set_named_property(env, global, "answer", value);
+  assert(e == 0);
+}
+
+static void
+consume(js_env_t *env, js_value_t *global) {
+  int e;
+
+  e = js_on_dynamic_import(env, on_import, NULL);
+  assert(e == 0);
+
+  js_value_t *script;
+  e = js_create_string_utf8(env, (utf8_t *) "import('foo.js').then((ns) => { globalThis.answer = ns.answer })", -1, &script);
+  assert(e == 0);
+
+  js_value_t *result;
+  e = js_run_script(env, "test.js", -1, 0, script, &result);
+  assert(e == 0);
+
+  // The import is still pending; it resolves only once the timer fires.
+  js_value_t *answer;
+  e = js_get_named_property(env, global, "answer", &answer);
+  assert(e == 0);
+
+  uint32_t value;
+  e = js_get_value_uint32(env, answer, &value);
+  assert(e == 0);
+
+  assert(value == 0);
+
+  // Run the loop until the import resolves.
+  uv_loop_t *loop;
+  e = js_get_env_loop(env, &loop);
+  assert(e == 0);
+
+  while (!import_resolved) {
+    e = uv_run(loop, UV_RUN_ONCE);
+    assert(e >= 0);
+  }
+
+  e = js_get_named_property(env, global, "answer", &answer);
+  assert(e == 0);
+
+  e = js_get_value_uint32(env, answer, &value);
+  assert(e == 0);
+
+  assert(value == 42);
+}
+
+int
+main() {
+  snapshot_test_t test = {
+    .name = "run-from-snapshot-dynamic-import",
+    .produce = produce,
+    .consume = consume,
+  };
+
+  snapshot_test_run(&test);
+}
diff --git a/test/run-from-snapshot-function.c b/test/run-from-snapshot-function.c
new file mode 100644
index 0000000..f8cfc11
--- /dev/null
+++ b/test/run-from-snapshot-function.c
@@ -0,0 +1,88 @@
+#include <assert.h>
+#include <stdint.h>
+
+#include "../include/js.h"
+#include "snapshot.h"
+
+// Verifies that a native function survives an isolate snapshot: the producer
+// binds a native `answer()` onto the global, and the consumer calls it. The
+// function returns its `data`, which is NULL until rebound, so the test only
+// passes if the rebind handler reinstates it after restore.
+
+static js_value_t *
+answer(js_env_t *env, js_callback_info_t *info) {
+  int e;
+
+  void *data;
+  e = js_get_callback_info(env, info, NULL, NULL, NULL, &data);
+  assert(e == 0);
+
+  js_value_t *result;
+  e = js_create_int32(env, (int32_t) (intptr_t) data, &result);
+  assert(e == 0);
+
+  return result;
+}
+
+static bool
+rebind(js_env_t *env, const js_rebind_info_t *info, void *context, js_binding_payload_t *result) {
+  if (info->type == js_binding_function && info->function.cb == answer) {
+    result->data = (void *) (intptr_t) 42;
+
+    return true;
+  }
+
+  return false;
+}
+
+static void
+references(js_external_references_t *references) {
+  int e;
+
+  e = js_add_external_reference(references, (const void *) answer);
+  assert(e == 0);
+}
+
+static void
+produce(js_env_t *env, js_value_t *global) {
+  int e;
+
+  js_value_t *fn;
+  e = js_create_function(env, "answer", -1, answer, (void *) (intptr_t) 42, &fn);
+  assert(e == 0);
+
+  e = js_set_named_property(env, global, "answer", fn);
+  assert(e == 0);
+}
+
+static void
+consume(js_env_t *env, js_value_t *global) {
+  int e;
+
+  js_value_t *fn;
+  e = js_get_named_property(env, global, "answer", &fn);
+  assert(e == 0);
+
+  js_value_t *result;
+  e = js_call_function(env, global, fn, 0, NULL, &result);
+  assert(e == 0);
+
+  int32_t value;
+  e = js_get_value_int32(env, result, &value);
+  assert(e == 0);
+
+  assert(value == 42);
+}
+
+int
+main() {
+  snapshot_test_t test = {
+    .name = "run-from-snapshot-function",
+    .references = references,
+    .rebind = rebind,
+    .produce = produce,
+    .consume = consume,
+  };
+
+  snapshot_test_run(&test);
+}
diff --git a/test/run-from-snapshot-import-meta.c b/test/run-from-snapshot-import-meta.c
new file mode 100644
index 0000000..3606453
--- /dev/null
+++ b/test/run-from-snapshot-import-meta.c
@@ -0,0 +1,78 @@
+#include <assert.h>
+#include <utf.h>
+
+#include "../include/js.h"
+#include "snapshot.h"
+
+// Verifies that import.meta works during warmup and the value it produced rides
+// into the snapshot: the producer evaluates a module that reads
+// import.meta.answer (populated by the meta callback) and stashes it on the
+// global. The module is deleted before serializing so it leaves no global
+// handles behind. The consumer reads the stashed value.
+
+static void
+on_meta(js_env_t *env, js_module_t *module, js_value_t *meta, void *data) {
+  int e;
+
+  js_value_t *value;
+  e = js_create_int32(env, 7, &value);
+  assert(e == 0);
+
+  e = js_set_named_property(env, meta, "answer", value);
+  assert(e == 0);
+}
+
+static void
+produce(js_env_t *env, js_value_t *global) {
+  int e;
+
+  js_value_t *source;
+  e = js_create_string_utf8(env, (utf8_t *) "globalThis.meta = import.meta.answer", -1, &source);
+  assert(e == 0);
+
+  js_module_t *module;
+  e = js_create_module(env, "warmup.js", -1, 0, source, on_meta, NULL, &module);
+  assert(e == 0);
+
+  e = js_instantiate_module(env, module, NULL, NULL);
+  assert(e == 0);
+
+  js_value_t *promise;
+  e = js_run_module(env, module, &promise);
+  assert(e == 0);
+
+  js_promise_state_t state;
+  e = js_get_promise_state(env, promise, &state);
+  assert(e == 0);
+
+  assert(state == js_promise_fulfilled);
+
+  e = js_delete_module(env, module);
+  assert(e == 0);
+}
+
+static void
+consume(js_env_t *env, js_value_t *global) {
+  int e;
+
+  js_value_t *meta;
+  e = js_get_named_property(env, global, "meta", &meta);
+  assert(e == 0);
+
+  int32_t value;
+  e = js_get_value_int32(env, meta, &value);
+  assert(e == 0);
+
+  assert(value == 7);
+}
+
+int
+main() {
+  snapshot_test_t test = {
+    .name = "run-from-snapshot-import-meta",
+    .produce = produce,
+    .consume = consume,
+  };
+
+  snapshot_test_run(&test);
+}
diff --git a/test/run-from-snapshot-module.c b/test/run-from-snapshot-module.c
new file mode 100644
index 0000000..3036267
--- /dev/null
+++ b/test/run-from-snapshot-module.c
@@ -0,0 +1,82 @@
+#include <assert.h>
+#include <utf.h>
+
+#include "../include/js.h"
+#include "snapshot.h"
+
+// Verifies that the module graph survives an isolate snapshot: the producer
+// creates, instantiates, and evaluates a module, leaving it in place so its
+// compiled record is serialized, and stashes its id on the global. The consumer
+// rebuilds the module from the snapshot, looks it up by id, and reads its
+// evaluated export from the namespace.
+
+static void
+produce(js_env_t *env, js_value_t *global) {
+  int e;
+
+  js_value_t *source;
+  e = js_create_string_utf8(env, (utf8_t *) "export const answer = 42", -1, &source);
+  assert(e == 0);
+
+  js_module_t *module;
+  e = js_create_module(env, "survivor.js", -1, 0, source, NULL, NULL, &module);
+  assert(e == 0);
+
+  e = js_instantiate_module(env, module, NULL, NULL);
+  assert(e == 0);
+
+  js_value_t *promise;
+  e = js_run_module(env, module, &promise);
+  assert(e == 0);
+
+  js_promise_state_t state;
+  e = js_get_promise_state(env, promise, &state);
+  assert(e == 0);
+
+  assert(state == js_promise_fulfilled);
+
+  js_value_t *id;
+  e = js_get_module_id(env, module, &id);
+  assert(e == 0);
+
+  e = js_set_named_property(env, global, "moduleId", id);
+  assert(e == 0);
+}
+
+static void
+consume(js_env_t *env, js_value_t *global) {
+  int e;
+
+  js_value_t *id;
+  e = js_get_named_property(env, global, "moduleId", &id);
+  assert(e == 0);
+
+  js_module_t *module;
+  e = js_get_module_by_id(env, id, &module);
+  assert(e == 0);
+
+  js_value_t *namespace;
+  e = js_get_module_namespace(env, module, &namespace);
+  assert(e == 0);
+
+  js_value_t *answer;
+  e = js_get_named_property(env, namespace, "answer", &answer);
+  assert(e == 0);
+
+  int32_t value;
+  e = js_get_value_int32(env, answer, &value);
+  assert(e == 0);
+
+  assert(value == 42);
+}
+
+int
+main() {
+  snapshot_test_t test = {
+    .name = "run-from-snapshot-module",
+    .produce = produce,
+    .consume = consume,
+  };
+
+  snapshot_test_run(&test);
+}
diff --git a/test/run-from-snapshot-wrap.c b/test/run-from-snapshot-wrap.c
new file mode 100644
index 0000000..a6cc22b
--- /dev/null
+++ b/test/run-from-snapshot-wrap.c
@@ -0,0 +1,75 @@
+#include <assert.h>
+#include <stdint.h>
+
+#include "../include/js.h"
+#include "snapshot.h"
+
+// Verifies that a `js_wrap`'d object survives an isolate snapshot: the producer
+// wraps an object reachable from the global with non-NULL data and a finalizer.
+// After restore its finalizer side-table slot is rebuilt and the data rebound,
+// so `js_unwrap` returns it.
+
+static void
+on_wrap_finalize(js_env_t *env, void *data, void *finalize_hint) {}
+
+static bool
+rebind(js_env_t *env, const js_rebind_info_t *info, void *context, js_binding_payload_t *result) {
+  if (info->type == js_binding_finalizer && info->finalizer.cb == on_wrap_finalize) {
+    result->data = (void *) (intptr_t) 99;
+
+    return true;
+  }
+
+  return false;
+}
+
+static void
+references(js_external_references_t *references) {
+  int e;
+
+  e = js_add_external_reference(references, (const void *) on_wrap_finalize);
+  assert(e == 0);
+}
+
+static void
+produce(js_env_t *env, js_value_t *global) {
+  int e;
+
+  js_value_t *wrapped;
+  e = js_create_object(env, &wrapped);
+  assert(e == 0);
+
+  e = js_wrap(env, wrapped, (void *) (intptr_t) 99, on_wrap_finalize, NULL, NULL);
+  assert(e == 0);
+
+  e = js_set_named_property(env, global, "wrapped", wrapped);
+  assert(e == 0);
+}
+
+static void
+consume(js_env_t *env, js_value_t *global) {
+  int e;
+
+  js_value_t *wrapped;
+  e = js_get_named_property(env, global, "wrapped", &wrapped);
+  assert(e == 0);
+
+  void *data;
+  e = js_unwrap(env, wrapped, &data);
+  assert(e == 0);
+
+  assert((int32_t) (intptr_t) data == 99);
+}
+
+int
+main() {
+  snapshot_test_t test = {
+    .name = "run-from-snapshot-wrap",
+    .references = references,
+    .rebind = rebind,
+    .produce = produce,
+    .consume = consume,
+  };
+
+  snapshot_test_run(&test);
+}
diff --git a/test/run-from-snapshot.c b/test/run-from-snapshot.c
new file mode 100644
index 0000000..ff24d89
--- /dev/null
+++ b/test/run-from-snapshot.c
@@ -0,0 +1,47 @@
+#include <assert.h>
+#include <utf.h>
+
+#include "../include/js.h"
+#include "snapshot.h"
+
+// Verifies that plain JavaScript state survives an isolate snapshot: the
+// producer runs a script that assigns a global, and the consumer reads it back.
+
+static void
+produce(js_env_t *env, js_value_t *global) {
+  int e;
+
+  js_value_t *script;
+  e = js_create_string_utf8(env, (utf8_t *) "globalThis.answer = 42", -1, &script);
+  assert(e == 0);
+
+  js_value_t *result;
+  e = js_run_script(env, NULL, 0, 0, script, &result);
+  assert(e == 0);
+}
+
+static void
+consume(js_env_t *env, js_value_t *global) {
+  int e;
+
+  js_value_t *answer;
+  e = js_get_named_property(env, global, "answer", &answer);
+  assert(e == 0);
+
+  int32_t value;
+  e = js_get_value_int32(env, answer, &value);
+  assert(e == 0);
+
+  assert(value == 42);
+}
+
+int
+main() {
+  snapshot_test_t test = {
+    .name = "run-from-snapshot",
+    .produce = produce,
+    .consume = consume,
+  };
+
+  snapshot_test_run(&test);
+}
diff --git a/test/snapshot.h b/test/snapshot.h
new file mode 100644
index 0000000..bf3f2b2
--- /dev/null
+++ b/test/snapshot.h
@@ -0,0 +1,302 @@
+#ifndef JS_TEST_SNAPSHOT_H
+#define JS_TEST_SNAPSHOT_H
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <uv.h>
+
+#include "../include/js.h"
+
+// Shared harness for the snapshot round-trip tests.
+//
+// Each test warms up an environment in a producer process, serializes it to a
+// blob, and re-spawns the same executable in consume mode to boot from the
+// blob and assert the warmed-up state survived.
+//
+// Producer and consumer run in different processes because this build enables
+// V8's shared read-only heap, which makes in-process consumption of a freshly
+// produced blob trip a debug-only checksum CHECK.
+
+// Registers any external references the test needs (native callbacks reachable
+// from the snapshot). Called in both the producer and the consumer.
+typedef void (*snapshot_references_cb)(js_external_references_t *references);
+
+// Warms up the environment before it is serialized. `global` is the global
+// object, already inside an open handle scope.
+typedef void (*snapshot_produce_cb)(js_env_t *env, js_value_t *global);
+
+// Asserts the warmed-up state survived. `global` is the restored global object,
+// already inside an open handle scope.
+typedef void (*snapshot_consume_cb)(js_env_t *env, js_value_t *global);
+
+typedef struct {
+  // Distinguishes this test's blob file from other tests running in parallel.
+  const char *name;
+
+  // Optional; registers native callbacks reachable from the snapshot.
+  snapshot_references_cb references;
+
+  // Optional; rebinds per-instance `data` after restore.
+  js_rebind_cb rebind;
+
+  snapshot_produce_cb produce;
+  snapshot_consume_cb consume;
+} snapshot_test_t;
+
+static inline js_external_references_t *
+snapshot__references(const snapshot_test_t *test) {
+  if (test->references == NULL) return NULL;
+
+  int e;
+
+  js_external_references_t *references;
+  e = js_create_external_references(&references);
+  assert(e == 0);
+
+  test->references(references);
+
+  return references;
+}
+
+static inline void
+snapshot__blob_path(const snapshot_test_t *test, char *path, size_t path_len) {
+  snprintf(path, path_len, "test/fixtures/snapshots/%s", test->name);
+}
+
+static inline void *
+snapshot__read(uv_loop_t *loop, const char *path, size_t *len) {
+  int e;
+
+  uv_fs_t req;
+
+  int fd = uv_fs_open(loop, &req, path, UV_FS_O_RDONLY, 0, NULL);
+  assert(fd >= 0);
+
+  uv_fs_req_cleanup(&req);
+
+  e = uv_fs_fstat(loop, &req, fd, NULL);
+  assert(e == 0);
+
+  size_t size = (size_t) req.statbuf.st_size;
+
+  uv_fs_req_cleanup(&req);
+
+  void *data = malloc(size);
+  assert(data != NULL);
+
+  size_t offset = 0;
+
+  while (offset < size) {
+    uv_buf_t buf = uv_buf_init((char *) data + offset, size - offset);
+
+    e = uv_fs_read(loop, &req, fd, &buf, 1, offset, NULL);
+    assert(e > 0);
+
+    uv_fs_req_cleanup(&req);
+
+    offset += (size_t) e;
+  }
+
+  e = uv_fs_close(loop, &req, fd, NULL);
+  assert(e == 0);
+
+  uv_fs_req_cleanup(&req);
+
+  *len = size;
+
+  return data;
+}
+
+static inline void
+snapshot__write(uv_loop_t *loop, const char *path, void *data, size_t len) {
+  int e;
+
+  uv_fs_t req;
+
+  int fd = uv_fs_open(loop, &req, path, UV_FS_O_WRONLY | UV_FS_O_CREAT | UV_FS_O_TRUNC, 0644, NULL);
+  assert(fd >= 0);
+
+  uv_fs_req_cleanup(&req);
+
+  size_t offset = 0;
+
+  while (offset < len) {
+    uv_buf_t buf = uv_buf_init((char *) data + offset, len - offset);
+
+    e = uv_fs_write(loop, &req, fd, &buf, 1, offset, NULL);
+    assert(e > 0);
+
+    uv_fs_req_cleanup(&req);
+
+    offset += (size_t) e;
+  }
+
+  e = uv_fs_close(loop, &req, fd, NULL);
+  assert(e == 0);
+
+  uv_fs_req_cleanup(&req);
+}
+
+static int snapshot__exit_status = -1;
+
+static inline void
+snapshot__on_exit(uv_process_t *process, int64_t status, int signal) {
+  snapshot__exit_status = (int) status;
+
+  uv_close((uv_handle_t *) process, NULL);
+}
+
+static inline void
+snapshot__produce(const snapshot_test_t *test, uv_loop_t *loop, js_platform_t *platform) {
+  int e;
+
+  js_snapshot_options_t options = {
+    .version = 0,
+    .external_references = snapshot__references(test),
+  };
+
+  js_env_t *env;
+  e = js_create_snapshot(loop, platform, &options, &env);
+  assert(e == 0);
+
+  js_handle_scope_t *scope;
+  e = js_open_handle_scope(env, &scope);
+  assert(e == 0);
+
+  js_value_t *global;
+  e = js_get_global(env, &global);
+  assert(e == 0);
+
+  test->produce(env, global);
+
+  e = js_close_handle_scope(env, scope);
+  assert(e == 0);
+
+  void *data;
+  size_t len;
+  e = js_take_snapshot(env, &data, &len);
+  assert(e == 0);
+
+  // Write the blob to a file the child process boots from.
+
+  char path[4096];
+  snapshot__blob_path(test, path, sizeof(path));
+
+  snapshot__write(loop, path, data, len);
+
+  free(data);
+
+  // Re-spawn this executable in consume mode, pointed at the blob.
+
+  char exepath[4096];
+  size_t exepath_len = sizeof(exepath);
+  e = uv_exepath(exepath, &exepath_len);
+  assert(e == 0);
+
+  e = uv_os_setenv("SNAPSHOT_BLOB", path);
+  assert(e == 0);
+
+  char *args[] = {exepath, NULL};
+
+  uv_process_options_t process_options = {
+    .file = exepath,
+    .args = args,
+    .exit_cb = snapshot__on_exit,
+  };
+
+  uv_process_t process;
+  e = uv_spawn(loop, &process, &process_options);
+  assert(e == 0);
+
+  e = uv_run(loop, UV_RUN_DEFAULT);
+  assert(e == 0);
+
+  // The blob is left in place so it can be inspected after the test runs.
+
+  assert(snapshot__exit_status == 0);
+}
+
+static inline void
+snapshot__consume(const snapshot_test_t *test, uv_loop_t *loop, js_platform_t *platform, const char *path) {
+  int e;
+
+  size_t len;
+  void *data = snapshot__read(loop, path, &len);
+
+  js_rebind_handlers_t *handlers = NULL;
+
+  if (test->rebind != NULL) {
+    e = js_create_rebind_handlers(&handlers);
+    assert(e == 0);
+
+    e = js_add_rebind_handler(handlers, test->rebind, NULL);
+    assert(e == 0);
+  }
+
+  js_env_options_t options = {
+    .version = 1,
+    .snapshot = data,
+    .snapshot_len = len,
+    .external_references = snapshot__references(test),
+    .rebind_handlers = handlers,
+  };
+
+  js_env_t *env;
+  e = js_create_env(loop, platform, &options, &env);
+  assert(e == 0);
+
+  js_handle_scope_t *scope;
+  e = js_open_handle_scope(env, &scope);
+  assert(e == 0);
+
+  js_value_t *global;
+  e = js_get_global(env, &global);
+  assert(e == 0);
+
+  test->consume(env, global);
+
+  e = js_close_handle_scope(env, scope);
+  assert(e == 0);
+
+  e = js_destroy_env(env);
+  assert(e == 0);
+
+  if (handlers != NULL) {
+    e = js_destroy_rebind_handlers(handlers);
+    assert(e == 0);
+  }
+
+  free(data);
+}
+
+// Runs the producer, or the consumer if booted with `SNAPSHOT_BLOB` set
+// (as the producer re-spawns itself).
+static inline void
+snapshot_test_run(const snapshot_test_t *test) {
+  int e;
+
+  uv_loop_t *loop = uv_default_loop();
+
+  js_platform_t *platform;
+  e = js_create_platform(loop, NULL, &platform);
+  assert(e == 0);
+
+  char path[4096];
+  size_t path_len = sizeof(path);
+
+  if (uv_os_getenv("SNAPSHOT_BLOB", path, &path_len) == 0) {
+    snapshot__consume(test, loop, platform, path);
+  } else {
+    snapshot__produce(test, loop, platform);
+  }
+
+  e = js_destroy_platform(platform);
+  assert(e == 0);
+
+  e = uv_run(loop, UV_RUN_DEFAULT);
+  assert(e == 0);
+}
+
+#endif // JS_TEST_SNAPSHOT_H

From 29cfed550992f5b57076b60dbb4bd00f7f06f94d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kasper=20Isager=20Dalsgar=C3=B0?= <kasperisager@hey.com>
Date: Mon, 29 Jun 2026 13:40:20 +0200
Subject: [PATCH 2/3] Support prepared script snapshotting

---
 include/js.h                    |   8 +++
 src/js.cc                       | 101 ++++++++++++++++++++++++++++++--
 test/CMakeLists.txt             |   1 +
 test/run-from-snapshot-script.c |  77 ++++++++++++++++++++++++
 4 files changed, 183 insertions(+), 4 deletions(-)
 create mode 100644 test/run-from-snapshot-script.c

diff --git a/include/js.h b/include/js.h
index e9b653f..1f39238 100644
--- a/include/js.h
+++ b/include/js.h
@@ -765,6 +765,14 @@ js_get_script_name(js_env_t *env, js_script_t *script, const char **result);
 int
 js_get_script_id(js_env_t *env, js_script_t *script, js_value_t **result);
 
+/**
+ * Look up a prepared script reconstructed from a snapshot by its `id` and return
+ * its handle. A prepared script carries no callbacks or per-instance state, so
+ * nothing needs to be re-supplied after restore.
+ */
+int
+js_get_script_by_id(js_env_t *env, js_value_t *id, js_script_t **result);
+
 int
 js_create_module(js_env_t *env, const char *name, size_t len, int offset, js_value_t *source, js_module_meta_cb cb, void *data, js_module_t **result);
 
diff --git a/src/js.cc b/src/js.cc
index b0b506c..1fd3bda 100644
--- a/src/js.cc
+++ b/src/js.cc
@@ -1495,6 +1495,8 @@ struct js_env_s {
 
   std::multimap<int, js_module_t *> modules;
 
+  std::list<js_script_t *> scripts;
+
   Global<Symbol> default_module_id;
 
   std::list<Global<Promise>> unhandled_promises;
@@ -1535,6 +1537,7 @@ struct js_env_s {
         tag(),
         exception(),
         modules(),
+        scripts(),
         default_module_id(),
         unhandled_promises(),
         teardown_queue(),
@@ -1632,8 +1635,6 @@ struct js_env_s {
 
       context.Get(isolate)->Exit();
       context.Reset();
-
-      isolate->Exit();
     }
 
     isolate->Dispose();
@@ -3643,20 +3644,23 @@ namespace {
 // this order) and `js_rebind_from_snapshot` (which reads it back). The metadata
 // array and the wrapper symbol occupy fixed slots; each serialized module record
 // follows in iteration order, so module `i` lands at `js_snapshot_data_modules
-// + i`.
+// + i`. Each prepared script's `UnboundScript` follows the modules, so script
+// `j` lands at `js_snapshot_data_modules + module_count + j`; the consumer
+// recovers `module_count` from the length of the module id list.
 enum {
   js_snapshot_data_metadata = 0,
   js_snapshot_data_wrapper = 1,
   js_snapshot_data_modules = 2,
 };
 
-// Metadata array layout: the manifests and id list `js_rebind_from_snapshot`
+// Metadata array layout: the manifests and id lists `js_rebind_from_snapshot`
 // replays, indexed within the metadata array stored at
 // `js_snapshot_data_metadata`.
 enum {
   js_snapshot_metadata_functions = 0,
   js_snapshot_metadata_wraps = 1,
   js_snapshot_metadata_module_ids = 2,
+  js_snapshot_metadata_script_ids = 3,
 };
 
 // Asks each handler, in order, to claim a reconstructed binding - described by
@@ -3918,6 +3922,41 @@ js_rebind_from_snapshot(js_env_t *env, const js_rebind_handlers_t *handlers) {
 
     env->modules.emplace(module->GetIdentityHash(), record);
   }
+
+  // Prepared scripts: rebuild a `js_script_t` for each serialized `UnboundScript`,
+  // paired by index with its id symbol. A prepared script carries no callbacks
+  // and no per-instance `data`, so there is nothing to rebind; the embedder
+  // reconnects its handles to the records by id via `js_get_script_by_id`. The
+  // records follow the modules in the data slots, so they begin at
+  // `js_snapshot_data_modules + module_count`.
+  auto scripts = metadata->Get(context, js_snapshot_metadata_script_ids).ToLocalChecked().As<Array>();
+
+  auto script_base = js_snapshot_data_modules + modules->Length();
+
+  for (uint32_t j = 0; j < scripts->Length(); j++) {
+    auto id = scripts->Get(context, j).ToLocalChecked().As<Symbol>();
+
+    Local<Data> data;
+    if (!context->GetDataFromSnapshotOnce<Data>(script_base + j).ToLocal(&data)) continue;
+
+    auto script = *reinterpret_cast<Local<UnboundScript> *>(&data);
+
+    // Recover the name from the script's resource name (the same string passed
+    // as the file name at preparation), exactly as modules recover theirs.
+    std::string name;
+
+    auto resource = script->GetScriptName();
+    if (!resource.IsEmpty() && resource->IsString()) {
+      auto string = resource.As<String>();
+      auto length = string->Utf8LengthV2(isolate);
+      name.resize(length);
+      string->WriteUtf8V2(isolate, name.data(), length, String::WriteFlags::kReplaceInvalidUtf8);
+    }
+
+    auto record = new js_script_t(isolate, script, id, std::move(name));
+
+    env->scripts.push_back(record);
+  }
 }
 
 } // namespace
@@ -4167,10 +4206,26 @@ js_take_snapshot(js_env_t *env, void **data, size_t *len) {
       module_records.push_back(record);
     }
 
+    // Script ids: the id symbol of every prepared script, in iteration order.
+    // Each script's compiled `UnboundScript` is added below as snapshot data at
+    // index `js_snapshot_data_modules + module_count + j`, so the consumer pairs
+    // `ids[j]` with the script at the same offset.
+    auto scripts = Array::New(isolate);
+
+    std::vector<Local<UnboundScript>> script_records;
+
+    uint32_t sn = 0;
+
+    for (auto script : env->scripts) {
+      scripts->Set(context, sn++, script->id.Get(isolate)).Check();
+      script_records.push_back(script->script.Get(isolate));
+    }
+
     auto metadata = Array::New(isolate);
     metadata->Set(context, js_snapshot_metadata_functions, functions).Check();
     metadata->Set(context, js_snapshot_metadata_wraps, wraps).Check();
     metadata->Set(context, js_snapshot_metadata_module_ids, modules).Check();
+    metadata->Set(context, js_snapshot_metadata_script_ids, scripts).Check();
 
     // The wrapper symbol is a `Private`, not a `Value`, so it rides its own data
     // slot rather than the metadata array.
@@ -4192,6 +4247,11 @@ js_take_snapshot(js_env_t *env, void **data, size_t *len) {
       auto module_index = creator->AddData(context, module_records[i]);
       assert(module_index == size_t(js_snapshot_data_modules) + i);
     }
+
+    for (size_t j = 0; j < script_records.size(); j++) {
+      auto script_index = creator->AddData(context, script_records[j]);
+      assert(script_index == size_t(js_snapshot_data_modules) + module_records.size() + j);
+    }
   }
 
   // Release every Global into the isolate before serializing: `CreateBlob()`
@@ -4219,6 +4279,11 @@ js_take_snapshot(js_env_t *env, void **data, size_t *len) {
     entry.second->id.Reset();
   }
 
+  for (auto script : env->scripts) {
+    script->script.Reset();
+    script->id.Reset();
+  }
+
   // Must run outside any handle scope.
   auto blob = creator->CreateBlob(env->snapshot.function_code_handling);
 
@@ -4500,6 +4565,10 @@ js_prepare_script(js_env_t *env, const char *file, size_t len, int offset, js_va
 
   auto script = new js_script_t(env->isolate, compiled.ToLocalChecked(), id, std::move(script_name));
 
+  // Track the script so the snapshot producer can serialize its compiled record
+  // and reset its global handles before `CreateBlob()`.
+  env->scripts.push_back(script);
+
   *result = script;
 
   return 0;
@@ -4534,6 +4603,8 @@ js_delete_script(js_env_t *env, js_script_t *script) {
 
   js_env_scope_t env_scope(env);
 
+  env->scripts.remove(script);
+
   delete script;
 
   return 0;
@@ -4559,6 +4630,28 @@ js_get_script_id(js_env_t *env, js_script_t *script, js_value_t **result) {
   return 0;
 }
 
+extern "C" int
+js_get_script_by_id(js_env_t *env, js_value_t *id, js_script_t **result) {
+  if (env->is_exception_pending()) return js_error(env);
+
+  int err;
+
+  auto symbol = js_to_local<Symbol>(id);
+
+  for (auto script : env->scripts) {
+    if (script->id.Get(env->isolate) == symbol) {
+      *result = script;
+
+      return 0;
+    }
+  }
+
+  err = js_throw_error(env, NULL, "Could not find script");
+  assert(err == 0);
+
+  return js_error(env);
+}
+
 extern "C" int
 js_create_module(js_env_t *env, const char *name, size_t len, int offset, js_value_t *source, js_module_meta_cb cb, void *data, js_module_t **result) {
   if (env->is_exception_pending()) return js_error(env);
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 3d7ef90..847d9fc 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -235,6 +235,7 @@ list(APPEND tests
   run-from-snapshot-function
   run-from-snapshot-import-meta
   run-from-snapshot-module
+  run-from-snapshot-script
   run-from-snapshot-wrap
   run-module
   run-module-async
diff --git a/test/run-from-snapshot-script.c b/test/run-from-snapshot-script.c
new file mode 100644
index 0000000..48e8bb0
--- /dev/null
+++ b/test/run-from-snapshot-script.c
@@ -0,0 +1,77 @@
+#include <assert.h>
+#include <stdint.h>
+#include <string.h>
+#include <utf.h>
+
+#include "../include/js.h"
+#include "snapshot.h"
+
+// Verifies that a prepared script survives an isolate snapshot: the producer
+// prepares (but does not run) a script and stashes its id on the global. The
+// consumer rebuilds the script from the snapshot, looks it up by id, runs it,
+// and asserts both its result and its preserved name. A prepared script carries
+// no callbacks or per-instance data, so nothing needs to be rebound after
+// restore.
+
+static void
+produce(js_env_t *env, js_value_t *global) {
+  int e;
+
+  js_value_t *source;
+  e = js_create_string_utf8(env, (utf8_t *) "40 + 2", -1, &source);
+  assert(e == 0);
+
+  js_script_t *script;
+  e = js_prepare_script(env, "survivor.js", -1, 0, source, &script);
+  assert(e == 0);
+
+  js_value_t *id;
+  e = js_get_script_id(env, script, &id);
+  assert(e == 0);
+
+  e = js_set_named_property(env, global, "scriptId", id);
+  assert(e == 0);
+}
+
+static void
+consume(js_env_t *env, js_value_t *global) {
+  int e;
+
+  js_value_t *id;
+  e = js_get_named_property(env, global, "scriptId", &id);
+  assert(e == 0);
+
+  js_script_t *script;
+  e = js_get_script_by_id(env, id, &script);
+  assert(e == 0);
+
+  const char *name;
+  e = js_get_script_name(env, script, &name);
+  assert(e == 0);
+
+  assert(strcmp(name, "survivor.js") == 0);
+
+  js_value_t *result;
+  e = js_run_prepared_script(env, script, &result);
+  assert(e == 0);
+
+  int32_t value;
+  e = js_get_value_int32(env, result, &value);
+  assert(e == 0);
+
+  assert(value == 42);
+
+  e = js_delete_script(env, script);
+  assert(e == 0);
+}
+
+int
+main() {
+  snapshot_test_t test = {
+    .name = "run-from-snapshot-script",
+    .produce = produce,
+    .consume = consume,
+  };
+
+  snapshot_test_run(&test);
+}

From d8f782a11d8a48e2a35838788a1a7333a107a068 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kasper=20Isager=20Dalsgar=C3=B0?= <kasperisager@hey.com>
Date: Fri, 3 Jul 2026 08:29:25 +0200
Subject: [PATCH 3/3] Remove old test case

---
 test/boot-from-snapshot.c | 441 --------------------------------------
 1 file changed, 441 deletions(-)
 delete mode 100644 test/boot-from-snapshot.c

diff --git a/test/boot-from-snapshot.c b/test/boot-from-snapshot.c
deleted file mode 100644
index 4a23a8c..0000000
--- a/test/boot-from-snapshot.c
+++ /dev/null
@@ -1,441 +0,0 @@
-#include <assert.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <utf.h>
-#include <uv.h>
-
-#include "../include/js.h"
-
-// Verifies that a native function survives an isolate snapshot: the producer
-// binds a native `answer()` onto the global and serializes a blob; a separate
-// process boots from the blob and calls `globalThis.answer()`, expecting 42.
-//
-// Producer and consumer run in different processes (the test re-spawns itself)
-// because this build enables V8's shared read-only heap, which makes in-process
-// consumption of a freshly produced blob trip a debug-only checksum CHECK.
-
-static js_value_t *
-answer(js_env_t *env, js_callback_info_t *info) {
-  int e;
-
-  // Return the callback's `data`, so the test only passes if `data` is rebound
-  // after restore (it would read NULL, and return 0, without a rebind handler).
-  void *data;
-  e = js_get_callback_info(env, info, NULL, NULL, NULL, &data);
-  assert(e == 0);
-
-  js_value_t *result;
-  e = js_create_int32(env, (int32_t) (intptr_t) data, &result);
-  assert(e == 0);
-
-  return result;
-}
-
-static void
-on_wrap_finalize(js_env_t *env, void *data, void *finalize_hint) {}
-
-// A delegate getter that returns its data for any property.
-static js_value_t *
-delegate_get(js_env_t *env, js_value_t *property, void *data) {
-  int e;
-
-  js_value_t *result;
-  e = js_create_int32(env, (int32_t) (intptr_t) data, &result);
-  assert(e == 0);
-
-  return result;
-}
-
-static bool
-rebind(js_env_t *env, js_binding_type_t type, const void *cb, js_value_t *holder, void *context, js_binding_payload_t *result) {
-  if (type == js_binding_function && cb == (const void *) answer) {
-    result->data = (void *) (intptr_t) 42;
-
-    return true;
-  }
-
-  if (type == js_binding_finalizer && cb == (const void *) on_wrap_finalize) {
-    result->data = (void *) (intptr_t) 99;
-
-    return true;
-  }
-
-  if (type == js_binding_delegate && cb == (const void *) delegate_get) {
-    result->data = (void *) (intptr_t) 123;
-
-    return true;
-  }
-
-  return false;
-}
-
-static void
-on_meta(js_env_t *env, js_module_t *module, js_value_t *meta, void *data) {
-  int e;
-
-  js_value_t *value;
-  e = js_create_int32(env, 7, &value);
-  assert(e == 0);
-
-  e = js_set_named_property(env, meta, "answer", value);
-  assert(e == 0);
-}
-
-static js_external_references_t *
-references() {
-  int e;
-
-  js_external_references_t *references;
-  e = js_create_external_references(&references);
-  assert(e == 0);
-
-  e = js_add_external_reference(references, (const void *) answer);
-  assert(e == 0);
-
-  e = js_add_external_reference(references, (const void *) on_wrap_finalize);
-  assert(e == 0);
-
-  e = js_add_external_reference(references, (const void *) delegate_get);
-  assert(e == 0);
-
-  return references;
-}
-
-static int exit_status = -1;
-
-static void
-on_exit(uv_process_t *process, int64_t status, int signal) {
-  exit_status = (int) status;
-
-  uv_close((uv_handle_t *) process, NULL);
-}
-
-static void
-produce(uv_loop_t *loop, js_platform_t *platform) {
-  int e;
-
-  js_snapshot_options_t options = {
-    .version = 0,
-    .external_references = references(),
-  };
-
-  js_env_t *env;
-  e = js_create_snapshot(loop, platform, &options, &env);
-  assert(e == 0);
-
-  js_handle_scope_t *scope;
-  e = js_open_handle_scope(env, &scope);
-  assert(e == 0);
-
-  js_value_t *global;
-  e = js_get_global(env, &global);
-  assert(e == 0);
-
-  js_value_t *fn;
-  e = js_create_function(env, "answer", -1, answer, (void *) (intptr_t) 42, &fn);
-  assert(e == 0);
-
-  e = js_set_named_property(env, global, "answer", fn);
-  assert(e == 0);
-
-  // Wrap an object reachable from the global, with non-NULL data and a finalizer.
-  // After restore its finalizer side-table slot is rebuilt and the data rebound.
-  js_value_t *wrapped;
-  e = js_create_object(env, &wrapped);
-  assert(e == 0);
-
-  e = js_wrap(env, wrapped, (void *) (intptr_t) 99, on_wrap_finalize, NULL, NULL);
-  assert(e == 0);
-
-  e = js_set_named_property(env, global, "wrapped", wrapped);
-  assert(e == 0);
-
-  // Create a delegate reachable from the global. After restore its internal
-  // field is reconstructed and its data rebound, so property access routes
-  // through the rebound getter.
-  js_delegate_callbacks_t callbacks = {
-    .version = 0,
-    .get = delegate_get,
-  };
-
-  js_value_t *delegate;
-  e = js_create_delegate(env, &callbacks, (void *) (intptr_t) 123, NULL, NULL, &delegate);
-  assert(e == 0);
-
-  e = js_set_named_property(env, global, "delegate", delegate);
-  assert(e == 0);
-
-  // Exercise import.meta during warmup: a module reads import.meta.answer
-  // (populated by the meta callback) and stashes it on the global. This proves
-  // the producer installs the import.meta callback, and the value rides into the
-  // snapshot. The module is deleted before serializing so it leaves no global
-  // handles behind.
-  js_value_t *source;
-  e = js_create_string_utf8(env, (utf8_t *) "globalThis.meta = import.meta.answer", -1, &source);
-  assert(e == 0);
-
-  js_module_t *module;
-  e = js_create_module(env, "warmup.js", -1, 0, source, on_meta, NULL, &module);
-  assert(e == 0);
-
-  e = js_instantiate_module(env, module, NULL, NULL);
-  assert(e == 0);
-
-  js_value_t *promise;
-  e = js_run_module(env, module, &promise);
-  assert(e == 0);
-
-  js_promise_state_t state;
-  e = js_get_promise_state(env, promise, &state);
-  assert(e == 0);
-
-  assert(state == js_promise_fulfilled);
-
-  e = js_delete_module(env, module);
-  assert(e == 0);
-
-  // A module that survives the snapshot: created, instantiated, and evaluated,
-  // then left in place so its compiled record is serialized. Its id is stashed on
-  // the global so the consumer can look it up.
-  js_value_t *survivor_source;
-  e = js_create_string_utf8(env, (utf8_t *) "export const answer = 42", -1, &survivor_source);
-  assert(e == 0);
-
-  js_module_t *survivor;
-  e = js_create_module(env, "survivor.js", -1, 0, survivor_source, NULL, NULL, &survivor);
-  assert(e == 0);
-
-  e = js_instantiate_module(env, survivor, NULL, NULL);
-  assert(e == 0);
-
-  js_value_t *survivor_promise;
-  e = js_run_module(env, survivor, &survivor_promise);
-  assert(e == 0);
-
-  js_promise_state_t survivor_state;
-  e = js_get_promise_state(env, survivor_promise, &survivor_state);
-  assert(e == 0);
-
-  assert(survivor_state == js_promise_fulfilled);
-
-  js_value_t *survivor_id;
-  e = js_get_module_id(env, survivor, &survivor_id);
-  assert(e == 0);
-
-  e = js_set_named_property(env, global, "moduleId", survivor_id);
-  assert(e == 0);
-
-  e = js_close_handle_scope(env, scope);
-  assert(e == 0);
-
-  void *data;
-  size_t len;
-  e = js_take_snapshot(env, &data, &len);
-  assert(e == 0);
-
-  // Write the blob to a temp file the child process boots from.
-
-  char path[4096];
-  size_t path_len = sizeof(path);
-  e = uv_os_tmpdir(path, &path_len);
-  assert(e == 0);
-
-  strncat(path, "/libjs-boot-from-snapshot.blob", sizeof(path) - strlen(path) - 1);
-
-  FILE *file = fopen(path, "wb");
-  assert(file != NULL);
-
-  assert(fwrite(data, 1, len, file) == len);
-
-  fclose(file);
-
-  free(data);
-
-  // Re-spawn this executable in consume mode, pointed at the blob.
-
-  char exepath[4096];
-  size_t exepath_len = sizeof(exepath);
-  e = uv_exepath(exepath, &exepath_len);
-  assert(e == 0);
-
-  e = uv_os_setenv("JS_SNAPSHOT_BLOB", path);
-  assert(e == 0);
-
-  char *args[] = {exepath, NULL};
-
-  uv_process_options_t process_options = {0};
-  process_options.file = exepath;
-  process_options.args = args;
-  process_options.exit_cb = on_exit;
-
-  uv_process_t process;
-  e = uv_spawn(loop, &process, &process_options);
-  assert(e == 0);
-
-  e = uv_run(loop, UV_RUN_DEFAULT);
-  assert(e == 0);
-
-  remove(path);
-
-  assert(exit_status == 0);
-}
-
-static void
-consume(uv_loop_t *loop, js_platform_t *platform, const char *path) {
-  int e;
-
-  FILE *file = fopen(path, "rb");
-  assert(file != NULL);
-
-  fseek(file, 0, SEEK_END);
-  long len = ftell(file);
-  fseek(file, 0, SEEK_SET);
-
-  void *data = malloc(len);
-  assert(fread(data, 1, len, file) == (size_t) len);
-
-  fclose(file);
-
-  js_rebind_handlers_t *handlers;
-  e = js_create_rebind_handlers(&handlers);
-  assert(e == 0);
-
-  e = js_add_rebind_handler(handlers, rebind, NULL);
-  assert(e == 0);
-
-  js_env_options_t options = {
-    .version = 1,
-    .snapshot = data,
-    .snapshot_len = (size_t) len,
-    .external_references = references(),
-    .rebind_handlers = handlers,
-  };
-
-  js_env_t *env;
-  e = js_create_env(loop, platform, &options, &env);
-  assert(e == 0);
-
-  js_handle_scope_t *scope;
-  e = js_open_handle_scope(env, &scope);
-  assert(e == 0);
-
-  js_value_t *global;
-  e = js_get_global(env, &global);
-  assert(e == 0);
-
-  js_value_t *fn;
-  e = js_get_named_property(env, global, "answer", &fn);
-  assert(e == 0);
-
-  js_value_t *result;
-  e = js_call_function(env, global, fn, 0, NULL, &result);
-  assert(e == 0);
-
-  int32_t value;
-  e = js_get_value_int32(env, result, &value);
-  assert(e == 0);
-
-  assert(value == 42);
-
-  // The import.meta value computed during warmup survived the snapshot.
-  js_value_t *meta;
-  e = js_get_named_property(env, global, "meta", &meta);
-  assert(e == 0);
-
-  int32_t meta_value;
-  e = js_get_value_int32(env, meta, &meta_value);
-  assert(e == 0);
-
-  assert(meta_value == 7);
-
-  // The wrapped object survived: its finalizer side-table slot was rebuilt and
-  // the data rebound, so js_unwrap returns it.
-  js_value_t *wrapped;
-  e = js_get_named_property(env, global, "wrapped", &wrapped);
-  assert(e == 0);
-
-  void *wrapped_data;
-  e = js_unwrap(env, wrapped, &wrapped_data);
-  assert(e == 0);
-
-  assert((int32_t) (intptr_t) wrapped_data == 99);
-
-  // The delegate survived: its internal field was reconstructed and data rebound,
-  // so property access routes through the rebound getter.
-  js_value_t *delegate;
-  e = js_get_named_property(env, global, "delegate", &delegate);
-  assert(e == 0);
-
-  js_value_t *delegated;
-  e = js_get_named_property(env, delegate, "anything", &delegated);
-  assert(e == 0);
-
-  int32_t delegated_value;
-  e = js_get_value_int32(env, delegated, &delegated_value);
-  assert(e == 0);
-
-  assert(delegated_value == 123);
-
-  // The module graph survived: the evaluated module is rebuilt from the snapshot,
-  // looked up by the id stashed on the global, and its namespace still holds the
-  // evaluated export.
-  js_value_t *module_id;
-  e = js_get_named_property(env, global, "moduleId", &module_id);
-  assert(e == 0);
-
-  js_module_t *module;
-  e = js_get_module_by_id(env, module_id, &module);
-  assert(e == 0);
-
-  js_value_t *namespace;
-  e = js_get_module_namespace(env, module, &namespace);
-  assert(e == 0);
-
-  js_value_t *module_answer;
-  e = js_get_named_property(env, namespace, "answer", &module_answer);
-  assert(e == 0);
-
-  int32_t module_answer_value;
-  e = js_get_value_int32(env, module_answer, &module_answer_value);
-  assert(e == 0);
-
-  assert(module_answer_value == 42);
-
-  e = js_close_handle_scope(env, scope);
-  assert(e == 0);
-
-  e = js_destroy_env(env);
-  assert(e == 0);
-
-  e = js_destroy_rebind_handlers(handlers);
-  assert(e == 0);
-
-  free(data);
-}
-
-int
-main() {
-  int e;
-
-  uv_loop_t *loop = uv_default_loop();
-
-  js_platform_t *platform;
-  e = js_create_platform(loop, NULL, &platform);
-  assert(e == 0);
-
-  char path[4096];
-  size_t path_len = sizeof(path);
-
-  if (uv_os_getenv("JS_SNAPSHOT_BLOB", path, &path_len) == 0) {
-    consume(loop, platform, path);
-  } else {
-    produce(loop, platform);
-  }
-
-  e = js_destroy_platform(platform);
-  assert(e == 0);
-
-  e = uv_run(loop, UV_RUN_DEFAULT);
-  assert(e == 0);
-}