[api] Fix name max_data_length to match hostname limit, add suggested_area

- Fix HelloResponse.name and DeviceInfoResponse.name max_data_length
  from 120 to 31 to match ESPHOME_DEVICE_NAME_MAX_LEN (hostname limit)
- Add max_data_length=120 + force to suggested_area field
- Add static_asserts for ESPHOME_DEVICE_NAME_MAX_LEN and
  ESPHOME_FRIENDLY_NAME_MAX_LEN
- Fix comments to accurately describe guarantees

esphome/components/api/api.proto

@@ -132,9 +132,9 @@ message HelloResponse {
   // Currently set to ESPHOME_VERSION string literal.
   string server_info = 3 [(max_data_length) = 32, (force) = true];
 
-  // The name of the server (App.get_name())
-  // max_data_length matches config_validation.NAME_MAX_LENGTH
-  string name = 4 [(max_data_length) = 120, (force) = true];
+  // The name of the server (App.get_name() - device hostname)
+  // max_data_length matches ESPHOME_DEVICE_NAME_MAX_LEN (validated by validate_hostname)
+  string name = 4 [(max_data_length) = 31, (force) = true];
 }
 
 // DEPRECATED in ESPHome 2026.1.0 - Password authentication is no longer supported.
@@ -220,13 +220,15 @@ message SerialProxyInfo {
 }
 
 // DeviceInfoResponse max_data_length values:
-//   name/friendly_name = 120 (config_validation.NAME_MAX_LENGTH / core/config.FRIENDLY_NAME_MAX_LEN)
+//   name = 31 (ESPHOME_DEVICE_NAME_MAX_LEN, validated by validate_hostname)
+//   friendly_name = 120 (core/config.FRIENDLY_NAME_MAX_LEN)
 //   mac_address/bluetooth_mac_address = 17 (MAC_ADDRESS_PRETTY_BUFFER_SIZE - 1, constexpr)
 //   esphome_version = 32 (ESPHOME_VERSION string literal)
 //   compilation_time = 25 (Application::BUILD_TIME_STR_SIZE - 1, constexpr)
 //   manufacturer = 20 (longest hardcoded literal: "Nordic Semiconductor")
 //   model = 127 (core/config.BOARD_MAX_LENGTH, validated in platform schemas)
 //   project_name/project_version = 127 (core/config.PROJECT_MAX_LENGTH)
+//   suggested_area = 120 (core/config.FRIENDLY_NAME_MAX_LEN via AREA_SCHEMA)
 message DeviceInfoResponse {
   option (id) = 10;
   option (source) = SOURCE_SERVER;
@@ -235,8 +237,8 @@ message DeviceInfoResponse {
   // with older ESPHome versions that still send this field.
   bool uses_password = 1 [deprecated = true];
 
-  // The name of the node, given by "App.set_name()"
-  string name = 2 [(max_data_length) = 120, (force) = true];
+  // The name of the node, given by "App.set_name()" - device hostname
+  string name = 2 [(max_data_length) = 31, (force) = true];
 
   // The mac address of the device. For example "AC:BC:32:89:0E:A9"
   string mac_address = 3 [(max_data_length) = 17, (force) = true];
@@ -274,7 +276,7 @@ message DeviceInfoResponse {
   uint32 legacy_voice_assistant_version = 14 [deprecated=true, (field_ifdef) = "USE_VOICE_ASSISTANT"];
   uint32 voice_assistant_feature_flags = 17 [(field_ifdef) = "USE_VOICE_ASSISTANT"];
 
-  string suggested_area = 16 [(field_ifdef) = "USE_AREAS"];
+  string suggested_area = 16 [(max_data_length) = 120, (force) = true, (field_ifdef) = "USE_AREAS"];
 
   // The Bluetooth mac address of the device. For example "AC:BC:32:89:0E:AA"
   string bluetooth_mac_address = 18 [(max_data_length) = 17, (force) = true, (field_ifdef) = "USE_BLUETOOTH_PROXY"];

esphome/components/api/api_connection.cpp

@@ -77,6 +77,8 @@ static_assert(MAC_ADDRESS_PRETTY_BUFFER_SIZE - 1 == 17,
               "Update max_data_length for mac_address/bluetooth_mac_address in api.proto");
 static_assert(Application::BUILD_TIME_STR_SIZE - 1 == 25, "Update max_data_length for compilation_time in api.proto");
 static_assert(sizeof(ESPHOME_VERSION) - 1 <= 32, "Update max_data_length for esphome_version in api.proto");
+static_assert(ESPHOME_DEVICE_NAME_MAX_LEN <= 31, "Update max_data_length for name in api.proto");
+static_assert(ESPHOME_FRIENDLY_NAME_MAX_LEN <= 120, "Update max_data_length for friendly_name in api.proto");
 
 static const char *const TAG = "api.connection";
 #ifdef USE_CAMERA

esphome/components/api/api_pb2.cpp

@@ -119,7 +119,7 @@ uint8_t *DeviceInfoResponse::encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_
   ProtoEncode::encode_uint32(pos PROTO_ENCODE_DEBUG_ARG, 17, this->voice_assistant_feature_flags);
 #endif
 #ifdef USE_AREAS
-  ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 16, this->suggested_area);
+  ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 16, this->suggested_area, true);
 #endif
 #ifdef USE_BLUETOOTH_PROXY
   ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 18, this->bluetooth_mac_address, true);
@@ -181,7 +181,7 @@ uint32_t DeviceInfoResponse::calculate_size() const {
   size += ProtoSize::calc_uint32(2, this->voice_assistant_feature_flags);
 #endif
 #ifdef USE_AREAS
-  size += ProtoSize::calc_length(2, this->suggested_area.size());
+  size += 3 + this->suggested_area.size();
 #endif
 #ifdef USE_BLUETOOTH_PROXY
   size += 3 + this->bluetooth_mac_address.size();