[micro_wake_word] Own the enabled-state preference key

voice_assistant derived the same fnv1_hash(id) key independently to restore
downloaded models, with nothing tying the two together. Expose the derivation as
WakeWordModel::enabled_preference_key so the component that owns the persistence
format owns the key too.

esphome/components/micro_wake_word/streaming_model.cpp

@@ -270,7 +270,7 @@ WakeWordModel::WakeWordModel(const std::string &id, const uint8_t *model_start,
   this->current_stride_step_ = 0;
   this->internal_only_ = internal_only;
 
-  this->pref_ = global_preferences->make_preference<bool>(fnv1_hash(id));
+  this->pref_ = global_preferences->make_preference<bool>(WakeWordModel::enabled_preference_key(id));
   bool enabled;
   if (this->pref_.load(&enabled)) {
     // Use the enabled state loaded from flash
@@ -305,7 +305,7 @@ WakeWordModel::WakeWordModel(const std::string &id, std::shared_ptr<ModelData> m
   this->current_stride_step_ = 0;
   this->internal_only_ = false;  // Runtime models are always exposed to Home Assistant
 
-  this->pref_ = global_preferences->make_preference<bool>(fnv1_hash(id));
+  this->pref_ = global_preferences->make_preference<bool>(WakeWordModel::enabled_preference_key(id));
   bool enabled;
   if (this->pref_.load(&enabled)) {
     // Use the enabled state loaded from flash

esphome/components/micro_wake_word/streaming_model.h

@@ -157,6 +157,13 @@ class WakeWordModel final : public StreamingModel {
 
   bool get_internal_only() { return this->internal_only_; }
 
+  /// @brief Derives the preference key holding a model's enabled state. This component owns the persistence
+  /// format, so anything reading or writing that state (voice_assistant restores downloaded models from it)
+  /// must derive the key through here rather than repeating the hash.
+  /// @param id (std::string) identifier for the model
+  /// @return The preference key for the model's enabled state
+  static uint32_t enabled_preference_key(const std::string &id) { return fnv1_hash(id); }
+
  protected:
   // Kept for runtime-downloaded models so the model buffer stays alive for the model's lifetime.
   // Null for compiled-in models (their data lives in flash).

esphome/components/voice_assistant/voice_assistant.cpp

@@ -1309,8 +1309,8 @@ void VoiceAssistant::restore_runtime_models_() {
     // Only re-download models the user had enabled before the reboot. Read the key directly: make_preference
     // allocates a backend that is never freed, and this runs for every advertised model on every request.
     bool enabled = false;
-    if (global_preferences->load_from_key(fnv1_hash(cached_ww.id), reinterpret_cast<uint8_t *>(&enabled),
-                                          sizeof(enabled)) &&
+    if (global_preferences->load_from_key(micro_wake_word::WakeWordModel::enabled_preference_key(cached_ww.id),
+                                          reinterpret_cast<uint8_t *>(&enabled), sizeof(enabled)) &&
         enabled) {
       ESP_LOGD(TAG, "Restoring runtime model %s", cached_ww.id.c_str());
       this->model_download_queue_.push_back(cached_ww);
@@ -1345,7 +1345,7 @@ void VoiceAssistant::erase_pending_wake_word_(const std::string &id) {
 void VoiceAssistant::mark_model_load_failed_(const std::string &id) {
   // Persist disabled so a broken model isn't retried on every boot, and drop the optimistic active entry so
   // HA sees the real (inactive) state.
-  auto pref = global_preferences->make_preference<bool>(fnv1_hash(id));
+  auto pref = global_preferences->make_preference<bool>(micro_wake_word::WakeWordModel::enabled_preference_key(id));
   bool enabled = false;
   pref.save(&enabled);
   this->erase_pending_wake_word_(id);