From 666fb7cf39aeaf2e2a7890695099535ed8b5a67c Mon Sep 17 00:00:00 2001
From: Jonathan Swoboda <154711427+swoboda1337@users.noreply.github.com>
Date: Fri, 6 Mar 2026 07:18:28 -0500
Subject: [PATCH 1/7] [sx127x][sx126x][max6956] Fix null deref, unterminated
 string, and pin bounds check (#14529)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
---
 esphome/components/max6956/max6956.cpp | 2 ++
 esphome/components/sx126x/sx126x.cpp   | 3 ++-
 esphome/components/sx127x/sx127x.cpp   | 5 +++++
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/esphome/components/max6956/max6956.cpp b/esphome/components/max6956/max6956.cpp
index a350e66ee0..ce45541b63 100644
--- a/esphome/components/max6956/max6956.cpp
+++ b/esphome/components/max6956/max6956.cpp
@@ -111,6 +111,8 @@ void MAX6956::write_brightness_mode() {
 }
 
 void MAX6956::set_pin_brightness(uint8_t pin, float brightness) {
+  if (pin < MAX6956_MIN || pin > MAX6956_MAX)
+    return;
   uint8_t reg_addr = MAX6956_CURRENT_START + (pin - MAX6956_MIN) / 2;
   uint8_t config = 0;
   uint8_t shift = 4 * (pin % 2);
diff --git a/esphome/components/sx126x/sx126x.cpp b/esphome/components/sx126x/sx126x.cpp
index 64cd24b171..ec62fad10a 100644
--- a/esphome/components/sx126x/sx126x.cpp
+++ b/esphome/components/sx126x/sx126x.cpp
@@ -155,7 +155,8 @@ void SX126x::configure() {
   }
 
   // check silicon version to make sure hw is ok
-  this->read_register_(REG_VERSION_STRING, (uint8_t *) this->version_, 16);
+  this->read_register_(REG_VERSION_STRING, (uint8_t *) this->version_, sizeof(this->version_));
+  this->version_[sizeof(this->version_) - 1] = '\0';
   if (strncmp(this->version_, "SX126", 5) != 0 && strncmp(this->version_, "LLCC68", 6) != 0) {
     this->mark_failed();
     return;
diff --git a/esphome/components/sx127x/sx127x.cpp b/esphome/components/sx127x/sx127x.cpp
index f6aa11b634..66957a7342 100644
--- a/esphome/components/sx127x/sx127x.cpp
+++ b/esphome/components/sx127x/sx127x.cpp
@@ -260,6 +260,11 @@ SX127xError SX127x::transmit_packet(const std::vector<uint8_t> &packet) {
     return SX127xError::INVALID_PARAMS;
   }
 
+  if (this->dio0_pin_ == nullptr) {
+    ESP_LOGE(TAG, "DIO0 pin not configured, cannot wait for transmit completion");
+    return SX127xError::INVALID_PARAMS;
+  }
+
   SX127xError ret = SX127xError::NONE;
   if (this->modulation_ == MOD_LORA) {
     this->set_mode_standby();

From 6c07c15c504c7f0a66ab1a9e2c2f91943526ffa2 Mon Sep 17 00:00:00 2001
From: Jonathan Swoboda <154711427+swoboda1337@users.noreply.github.com>
Date: Fri, 6 Mar 2026 07:18:56 -0500
Subject: [PATCH 2/7] [mipi_dsi][e131] Fix semaphore cast, missing return, and
 light count overread (#14530)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
---
 esphome/components/e131/e131_addressable_light_effect.cpp | 4 +++-
 esphome/components/mipi_dsi/mipi_dsi.cpp                  | 3 ++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/esphome/components/e131/e131_addressable_light_effect.cpp b/esphome/components/e131/e131_addressable_light_effect.cpp
index 7d62f739a2..f6010a7cc9 100644
--- a/esphome/components/e131/e131_addressable_light_effect.cpp
+++ b/esphome/components/e131/e131_addressable_light_effect.cpp
@@ -54,8 +54,10 @@ bool E131AddressableLightEffect::process_(int universe, const E131Packet &packet
 
   int32_t output_offset = (universe - first_universe_) * get_lights_per_universe();
   // limit amount of lights per universe and received
+  // packet.count is the number of DMX bytes including start code; divide by channels to get the number of lights
+  int lights_in_packet = (packet.count > 0) ? (packet.count - 1) / channels_ : 0;
   int output_end =
-      std::min(it->size(), std::min(output_offset + get_lights_per_universe(), output_offset + packet.count - 1));
+      std::min(it->size(), std::min(output_offset + get_lights_per_universe(), output_offset + lights_in_packet));
   auto *input_data = packet.values + 1;
 
   auto effect_name = get_name();
diff --git a/esphome/components/mipi_dsi/mipi_dsi.cpp b/esphome/components/mipi_dsi/mipi_dsi.cpp
index 4d45cfb799..815b9d75a1 100644
--- a/esphome/components/mipi_dsi/mipi_dsi.cpp
+++ b/esphome/components/mipi_dsi/mipi_dsi.cpp
@@ -10,7 +10,7 @@ namespace mipi_dsi {
 static constexpr size_t MIPI_DSI_MAX_CMD_LOG_BYTES = 64;
 
 static bool notify_refresh_ready(esp_lcd_panel_handle_t panel, esp_lcd_dpi_panel_event_data_t *edata, void *user_ctx) {
-  auto *sem = static_cast<SemaphoreHandle_t *>(user_ctx);
+  auto sem = static_cast<SemaphoreHandle_t>(user_ctx);
   BaseType_t need_yield = pdFALSE;
   xSemaphoreGiveFromISR(sem, &need_yield);
   return (need_yield == pdTRUE);
@@ -190,6 +190,7 @@ void MIPI_DSI::draw_pixels_at(int x_start, int y_start, int w, int h, const uint
   if (bitness != this->color_depth_) {
     display::Display::draw_pixels_at(x_start, y_start, w, h, ptr, order, bitness, big_endian, x_offset, y_offset,
                                      x_pad);
+    return;
   }
   this->write_to_display_(x_start, y_start, w, h, ptr, x_offset, y_offset, x_pad);
 }

From c0b7f41397e41ff53ed2d551fcd0e3cf03f89147 Mon Sep 17 00:00:00 2001
From: Thomas Rupprecht <rupprecht.thomas@gmail.com>
Date: Fri, 6 Mar 2026 13:21:44 +0100
Subject: [PATCH 3/7] [esp32] Fix wrong variable usage in P4 pin validation
 error msg (#14539)

---
 esphome/components/esp32/gpio_esp32_p4.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/esphome/components/esp32/gpio_esp32_p4.py b/esphome/components/esp32/gpio_esp32_p4.py
index b98b567da2..2726c5932f 100644
--- a/esphome/components/esp32/gpio_esp32_p4.py
+++ b/esphome/components/esp32/gpio_esp32_p4.py
@@ -33,7 +33,7 @@ def esp32_p4_validate_supports(value):
     is_input = mode[CONF_INPUT]
 
     if num < 0 or num > 54:
-        raise cv.Invalid(f"Invalid pin number: {value} (must be 0-54)")
+        raise cv.Invalid(f"Invalid pin number: {num} (must be 0-54)")
     if is_input:
         # All ESP32 pins support input mode
         pass

From 5084c32f3c3da1bb857b79f6200825ec456000c8 Mon Sep 17 00:00:00 2001
From: Thomas Rupprecht <rupprecht.thomas@gmail.com>
Date: Fri, 6 Mar 2026 13:22:11 +0100
Subject: [PATCH 4/7] [esp32] Fix ESP32-S3 pin validation error message
 (#14540)

---
 esphome/components/esp32/gpio_esp32_s3.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/esphome/components/esp32/gpio_esp32_s3.py b/esphome/components/esp32/gpio_esp32_s3.py
index 7120504693..aea378f499 100644
--- a/esphome/components/esp32/gpio_esp32_s3.py
+++ b/esphome/components/esp32/gpio_esp32_s3.py
@@ -29,7 +29,7 @@ _LOGGER = logging.getLogger(__name__)
 
 def esp32_s3_validate_gpio_pin(value):
     if value < 0 or value > 48:
-        raise cv.Invalid(f"Invalid pin number: {value} (must be 0-46)")
+        raise cv.Invalid(f"Invalid pin number: {value} (must be 0-48)")
 
     if value in _ESP_32S3_SPI_PSRAM_PINS:
         raise cv.Invalid(
@@ -55,7 +55,7 @@ def esp32_s3_validate_supports(value):
     is_input = mode[CONF_INPUT]
 
     if num < 0 or num > 48:
-        raise cv.Invalid(f"Invalid pin number: {num} (must be 0-46)")
+        raise cv.Invalid(f"Invalid pin number: {num} (must be 0-48)")
     if is_input:
         # All ESP32 pins support input mode
         pass

From e59a2b3eded37c9de46d8148b2f8cb40b46d06ac Mon Sep 17 00:00:00 2001
From: tomaszduda23 <tomaszduda23@gmail.com>
Date: Fri, 6 Mar 2026 17:25:44 +0100
Subject: [PATCH 5/7] [nrf52] prepare for usb cdc (#14174)

Co-authored-by: Jonathan Swoboda <154711427+swoboda1337@users.noreply.github.com>
---
 esphome/components/esp32/__init__.py | 2 ++
 esphome/core/event_pool.h            | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/esphome/components/esp32/__init__.py b/esphome/components/esp32/__init__.py
index a14d3af69e..8ad84656ed 100644
--- a/esphome/components/esp32/__init__.py
+++ b/esphome/components/esp32/__init__.py
@@ -464,6 +464,8 @@ def only_on_variant(*, supported=None, unsupported=None, msg_prefix="This featur
         unsupported = [unsupported]
 
     def validator_(obj):
+        if not CORE.is_esp32:
+            raise cv.Invalid(f"{msg_prefix} is only available on ESP32")
         variant = get_esp32_variant()
         if supported is not None and variant not in supported:
             raise cv.Invalid(
diff --git a/esphome/core/event_pool.h b/esphome/core/event_pool.h
index 928a4e7dee..99541d4a17 100644
--- a/esphome/core/event_pool.h
+++ b/esphome/core/event_pool.h
@@ -1,6 +1,6 @@
 #pragma once
 
-#if defined(USE_ESP32)
+#if defined(USE_ESP32) || defined(USE_ZEPHYR)
 
 #include <atomic>
 #include <cstddef>

From 07e51886f3563061c09e6a8c9c36ab94300b0b1f Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Fri, 6 Mar 2026 06:57:52 -1000
Subject: [PATCH 6/7] [core] Move entity icon strings to PROGMEM on ESP8266
 (#14437)

---
 esphome/components/api/api_connection.h      |  3 +-
 esphome/components/mqtt/mqtt_component.cpp   | 10 ++---
 esphome/components/mqtt/mqtt_component.h     |  4 +-
 esphome/components/web_server/web_server.cpp |  3 +-
 esphome/config_validation.py                 | 17 ++++---
 esphome/core/config.py                       |  4 ++
 esphome/core/entity_base.cpp                 | 38 ++++++++++++++--
 esphome/core/entity_base.h                   | 33 +++++++++++---
 esphome/core/entity_helpers.py               | 47 +++++++++++++++++---
 tests/unit_tests/core/test_entity_helpers.py | 17 +++++++
 tests/unit_tests/test_config_validation.py   | 12 +++++
 11 files changed, 158 insertions(+), 30 deletions(-)

diff --git a/esphome/components/api/api_connection.h b/esphome/components/api/api_connection.h
index aae8db3c68..88f0ef82d6 100644
--- a/esphome/components/api/api_connection.h
+++ b/esphome/components/api/api_connection.h
@@ -354,7 +354,8 @@ class APIConnection final : public APIServerConnectionBase {
 
     // Set common EntityBase properties
 #ifdef USE_ENTITY_ICON
-    msg.icon = entity->get_icon_ref();
+    char icon_buf[MAX_ICON_LENGTH];
+    msg.icon = StringRef(entity->get_icon_to(icon_buf));
 #endif
     msg.disabled_by_default = entity->is_disabled_by_default();
     msg.entity_category = static_cast<enums::EntityCategory>(entity->get_entity_category());
diff --git a/esphome/components/mqtt/mqtt_component.cpp b/esphome/components/mqtt/mqtt_component.cpp
index f49069960b..98fa10def9 100644
--- a/esphome/components/mqtt/mqtt_component.cpp
+++ b/esphome/components/mqtt/mqtt_component.cpp
@@ -209,12 +209,11 @@ bool MQTTComponent::send_discovery_() {
 
         if (this->is_disabled_by_default_())
           root[MQTT_ENABLED_BY_DEFAULT] = false;
-        // NOLINTBEGIN(clang-analyzer-cplusplus.NewDeleteLeaks) false positive with ArduinoJson
-        const auto icon_ref = this->get_icon_ref_();
-        if (!icon_ref.empty()) {
-          root[MQTT_ICON] = icon_ref;
+        char icon_buf[MAX_ICON_LENGTH];
+        const char *icon = this->get_icon_to_(icon_buf);
+        if (icon[0] != '\0') {
+          root[MQTT_ICON] = icon;
         }
-        // NOLINTEND(clang-analyzer-cplusplus.NewDeleteLeaks)
 
         const auto entity_category = this->get_entity()->get_entity_category();
         if (entity_category != ENTITY_CATEGORY_NONE) {
@@ -413,7 +412,6 @@ const StringRef &MQTTComponent::friendly_name_() const { return this->get_entity
 StringRef MQTTComponent::get_default_object_id_to_(std::span<char, OBJECT_ID_MAX_LEN> buf) const {
   return this->get_entity()->get_object_id_to(buf);
 }
-StringRef MQTTComponent::get_icon_ref_() const { return this->get_entity()->get_icon_ref(); }
 bool MQTTComponent::is_disabled_by_default_() const { return this->get_entity()->is_disabled_by_default(); }
 bool MQTTComponent::compute_is_internal_() {
   if (this->custom_state_topic_.has_value()) {
diff --git a/esphome/components/mqtt/mqtt_component.h b/esphome/components/mqtt/mqtt_component.h
index 0ffe6341d3..2403ef64ea 100644
--- a/esphome/components/mqtt/mqtt_component.h
+++ b/esphome/components/mqtt/mqtt_component.h
@@ -298,8 +298,8 @@ class MQTTComponent : public Component {
   /// Get the friendly name of this MQTT component.
   const StringRef &friendly_name_() const;
 
-  /// Get the icon field of this component as StringRef
-  StringRef get_icon_ref_() const;
+  /// Get the icon field of this component into a stack buffer
+  const char *get_icon_to_(std::span<char, MAX_ICON_LENGTH> buf) const { return this->get_entity()->get_icon_to(buf); }
 
   /// Get whether the underlying Entity is disabled by default
   bool is_disabled_by_default_() const;
diff --git a/esphome/components/web_server/web_server.cpp b/esphome/components/web_server/web_server.cpp
index 6b94a103cc..bc90c88e57 100644
--- a/esphome/components/web_server/web_server.cpp
+++ b/esphome/components/web_server/web_server.cpp
@@ -568,7 +568,8 @@ static void set_json_id(JsonObject &root, EntityBase *obj, const char *prefix, J
     }
 #endif
 #ifdef USE_ENTITY_ICON
-    root[ESPHOME_F("icon")] = obj->get_icon_ref().c_str();
+    char icon_buf[MAX_ICON_LENGTH];
+    root[ESPHOME_F("icon")] = obj->get_icon_to(icon_buf);
 #endif
     root[ESPHOME_F("entity_category")] = obj->get_entity_category();
     bool is_disabled = obj->is_disabled_by_default();
diff --git a/esphome/config_validation.py b/esphome/config_validation.py
index 3b0e4da298..1eac53e9b2 100644
--- a/esphome/config_validation.py
+++ b/esphome/config_validation.py
@@ -400,14 +400,21 @@ def string_strict(value):
 
 def icon(value):
     """Validate that a given config value is a valid icon."""
+    from esphome.core.config import ICON_MAX_LENGTH
+
     value = string_strict(value)
     if not value:
         return value
-    if re.match("^[\\w\\-]+:[\\w\\-]+$", value):
-        return value
-    raise Invalid(
-        'Icons must match the format "[icon pack]:[icon]", e.g. "mdi:home-assistant"'
-    )
+    if not re.match("^[\\w\\-]+:[\\w\\-]+$", value):
+        raise Invalid(
+            'Icons must match the format "[icon pack]:[icon]", e.g. "mdi:home-assistant"'
+        )
+    if len(value) > ICON_MAX_LENGTH:
+        raise Invalid(
+            f"Icon string is too long ({len(value)} chars, max {ICON_MAX_LENGTH}). "
+            "Icons are stored in PROGMEM with a 64-byte buffer limit."
+        )
+    return value
 
 
 def sub_device_id(value: str | None) -> core.ID | None:
diff --git a/esphome/core/config.py b/esphome/core/config.py
index 4f526404fe..9093ab3fe9 100644
--- a/esphome/core/config.py
+++ b/esphome/core/config.py
@@ -188,6 +188,10 @@ else:
 # Keep in sync with ESPHOME_FRIENDLY_NAME_MAX_LEN in esphome/core/entity_base.h
 FRIENDLY_NAME_MAX_LEN = 120
 
+# Max icon string length (63 chars + null = 64-byte PROGMEM buffer)
+# Keep in sync with MAX_ICON_LENGTH in esphome/core/entity_base.h
+ICON_MAX_LENGTH = 63
+
 AREA_SCHEMA = cv.Schema(
     {
         cv.GenerateID(CONF_ID): cv.declare_id(Area),
diff --git a/esphome/core/entity_base.cpp b/esphome/core/entity_base.cpp
index eafc04f92a..1265277572 100644
--- a/esphome/core/entity_base.cpp
+++ b/esphome/core/entity_base.cpp
@@ -1,6 +1,7 @@
 #include "esphome/core/entity_base.h"
 #include "esphome/core/application.h"
 #include "esphome/core/helpers.h"
+#include "esphome/core/progmem.h"
 #include "esphome/core/string_ref.h"
 
 namespace esphome {
@@ -72,7 +73,27 @@ std::string EntityBase::get_unit_of_measurement() const {
   return std::string(this->get_unit_of_measurement_ref().c_str());
 }
 
-// Entity icon (from index)
+// Entity icon — buffer-based API for PROGMEM safety on ESP8266
+const char *EntityBase::get_icon_to([[maybe_unused]] std::span<char, MAX_ICON_LENGTH> buffer) const {
+#ifdef USE_ENTITY_ICON
+  const uint8_t idx = this->icon_idx_;
+#else
+  const uint8_t idx = 0;
+#endif
+#ifdef USE_ESP8266
+  if (idx == 0)
+    return "";
+  const char *icon = entity_icon_lookup(idx);
+  ESPHOME_strncpy_P(buffer.data(), icon, buffer.size() - 1);
+  buffer[buffer.size() - 1] = '\0';
+  return buffer.data();
+#else
+  return entity_icon_lookup(idx);
+#endif
+}
+
+#ifndef USE_ESP8266
+// Deprecated icon accessors — not available on ESP8266 (rodata is RAM)
 StringRef EntityBase::get_icon_ref() const {
 #ifdef USE_ENTITY_ICON
   return StringRef(entity_icon_lookup(this->icon_idx_));
@@ -80,7 +101,14 @@ StringRef EntityBase::get_icon_ref() const {
   return StringRef(entity_icon_lookup(0));
 #endif
 }
-std::string EntityBase::get_icon() const { return std::string(this->get_icon_ref().c_str()); }
+std::string EntityBase::get_icon() const {
+#ifdef USE_ENTITY_ICON
+  return std::string(entity_icon_lookup(this->icon_idx_));
+#else
+  return std::string(entity_icon_lookup(0));
+#endif
+}
+#endif  // !USE_ESP8266
 
 // Entity Object ID - computed on-demand from name
 std::string EntityBase::get_object_id() const {
@@ -154,8 +182,10 @@ ESPPreferenceObject EntityBase::make_entity_preference_(size_t size, uint32_t ve
 
 #ifdef USE_ENTITY_ICON
 void log_entity_icon(const char *tag, const char *prefix, const EntityBase &obj) {
-  if (!obj.get_icon_ref().empty()) {
-    ESP_LOGCONFIG(tag, "%s  Icon: '%s'", prefix, obj.get_icon_ref().c_str());
+  char icon_buf[MAX_ICON_LENGTH];
+  const char *icon = obj.get_icon_to(icon_buf);
+  if (icon[0] != '\0') {
+    ESP_LOGCONFIG(tag, "%s  Icon: '%s'", prefix, icon);
   }
 }
 #endif
diff --git a/esphome/core/entity_base.h b/esphome/core/entity_base.h
index 54d4ae311f..1ce1e658e0 100644
--- a/esphome/core/entity_base.h
+++ b/esphome/core/entity_base.h
@@ -36,6 +36,10 @@ static constexpr size_t OBJECT_ID_MAX_LEN = 128;
 // Maximum state length that Home Assistant will accept without raising ValueError
 static constexpr size_t MAX_STATE_LEN = 255;
 
+// Maximum icon string buffer size (63 chars + null terminator)
+// Icons are stored in PROGMEM; on ESP8266 they must be copied to a stack buffer.
+static constexpr size_t MAX_ICON_LENGTH = 64;
+
 enum EntityCategory : uint8_t {
   ENTITY_CATEGORY_NONE = 0,
   ENTITY_CATEGORY_CONFIG = 1,
@@ -124,12 +128,31 @@ class EntityBase {
                 "2026.3.0")
   std::string get_unit_of_measurement() const;
 
-  // Get/set this entity's icon
-  ESPDEPRECATED(
-      "Use get_icon_ref() instead for better performance (avoids string copy). Will be removed in ESPHome 2026.5.0",
-      "2025.11.0")
-  std::string get_icon() const;
+  // Get this entity's icon into a stack buffer.
+  // On ESP32: returns pointer to PROGMEM string directly (buffer unused).
+  // On ESP8266: copies from PROGMEM to buffer, returns buffer pointer.
+  const char *get_icon_to(std::span<char, MAX_ICON_LENGTH> buffer) const;
+
+#ifdef USE_ESP8266
+  // On ESP8266, rodata is RAM. Icons are in PROGMEM and cannot be accessed
+  // directly as const char*. Use get_icon_to() with a stack buffer instead.
+  template<typename T = int> StringRef get_icon_ref() const {
+    static_assert(sizeof(T) == 0,
+                  "get_icon_ref() unavailable on ESP8266 (rodata is RAM). Use get_icon_to() with a stack buffer.");
+    return StringRef("");
+  }
+  template<typename T = int> std::string get_icon() const {
+    static_assert(sizeof(T) == 0,
+                  "get_icon() unavailable on ESP8266 (rodata is RAM). Use get_icon_to() with a stack buffer.");
+    return "";
+  }
+#else
+  // Deprecated: use get_icon_to() instead. Icons are in PROGMEM.
+  ESPDEPRECATED("Use get_icon_to() instead. Will be removed in ESPHome 2026.9.0", "2026.3.0")
   StringRef get_icon_ref() const;
+  ESPDEPRECATED("Use get_icon_to() instead. Will be removed in ESPHome 2026.9.0", "2026.3.0")
+  std::string get_icon() const;
+#endif
 
 #ifdef USE_DEVICES
   // Get/set this entity's device id
diff --git a/esphome/core/entity_helpers.py b/esphome/core/entity_helpers.py
index 551e35df65..01fa27b833 100644
--- a/esphome/core/entity_helpers.py
+++ b/esphome/core/entity_helpers.py
@@ -17,6 +17,7 @@ from esphome.const import (
     CONF_UNIT_OF_MEASUREMENT,
 )
 from esphome.core import CORE, ID, CoroPriority, coroutine_with_priority
+from esphome.core.config import ICON_MAX_LENGTH
 from esphome.cpp_generator import MockObj, RawStatement, add, get_variable
 import esphome.final_validate as fv
 from esphome.helpers import cpp_string_escape, fnv1_hash_object_id, sanitize, snake_case
@@ -78,6 +79,8 @@ def _generate_category_code(
     table_var: str,
     lookup_fn: str,
     strings: dict[str, int],
+    *,
+    progmem_strings: bool = False,
 ) -> str:
     """Generate C++ code for one string category (PROGMEM pointer table + lookup).
 
@@ -85,14 +88,40 @@ def _generate_category_code(
     in flash (via PROGMEM) and read with progmem_read_ptr(). String literals
     themselves remain in RAM but benefit from linker string deduplication.
     Index 0 means "not set" and returns empty string.
+
+    When progmem_strings=True, each string is declared as a separate PROGMEM
+    char array. This ensures the string data itself is in flash on ESP8266
+    (where .rodata is RAM). On other platforms PROGMEM is a no-op.
     """
     if not strings:
         return ""
 
     sorted_strings = sorted(strings.items(), key=lambda x: x[1])
-    entries = ", ".join(cpp_string_escape(s) for s, _ in sorted_strings)
     count = len(sorted_strings)
 
+    if progmem_strings:
+        # Emit individual PROGMEM char arrays so string data lives in flash
+        lines: list[str] = []
+        var_names: list[str] = []
+        for i, (s, _) in enumerate(sorted_strings):
+            var_name = f"{table_var}_STR_{i}"
+            var_names.append(var_name)
+            lines.append(
+                f"static const char {var_name}[] PROGMEM = {cpp_string_escape(s)};"
+            )
+        entries = ", ".join(var_names)
+        # Empty string must also be PROGMEM — on ESP8266, callers use strncpy_P
+        empty_var = f"{table_var}_EMPTY"
+        lines.append(f'static const char {empty_var}[] PROGMEM = "";')
+        lines.append(f"static const char *const {table_var}[] PROGMEM = {{{entries}}};")
+        lines.append(f"const char *{lookup_fn}(uint8_t index) {{")
+        lines.append(f"  if (index == 0 || index > {count}) return {empty_var};")
+        lines.append(f"  return progmem_read_ptr(&{table_var}[index - 1]);")
+        lines.append("}")
+        return "\n".join(lines) + "\n"
+
+    entries = ", ".join(cpp_string_escape(s) for s, _ in sorted_strings)
+
     return (
         f"static const char *const {table_var}[] PROGMEM = {{{entries}}};\n"
         f"const char *{lookup_fn}(uint8_t index) {{\n"
@@ -103,9 +132,9 @@ def _generate_category_code(
 
 
 _CATEGORY_CONFIGS = (
-    ("ENTITY_DC_TABLE", "entity_device_class_lookup", "device_classes"),
-    ("ENTITY_UOM_TABLE", "entity_uom_lookup", "units"),
-    ("ENTITY_ICON_TABLE", "entity_icon_lookup", "icons"),
+    ("ENTITY_DC_TABLE", "entity_device_class_lookup", "device_classes", False),
+    ("ENTITY_UOM_TABLE", "entity_uom_lookup", "units", False),
+    ("ENTITY_ICON_TABLE", "entity_icon_lookup", "icons", True),
 )
 
 
@@ -117,8 +146,10 @@ async def _generate_tables_job() -> None:
     """
     pool = _get_pool()
     parts = ["namespace esphome {"]
-    for table_var, lookup_fn, attr in _CATEGORY_CONFIGS:
-        code = _generate_category_code(table_var, lookup_fn, getattr(pool, attr))
+    for table_var, lookup_fn, attr, progmem_strs in _CATEGORY_CONFIGS:
+        code = _generate_category_code(
+            table_var, lookup_fn, getattr(pool, attr), progmem_strings=progmem_strs
+        )
         if code:
             parts.append(code)
     parts.append("}  // namespace esphome")
@@ -160,6 +191,10 @@ def register_unit_of_measurement(value: str) -> int:
 
 def register_icon(value: str) -> int:
     """Register an icon string and return its 1-based index."""
+    if value and len(value) > ICON_MAX_LENGTH:
+        raise ValueError(
+            f"Icon string too long ({len(value)} chars, max {ICON_MAX_LENGTH}): '{value}'"
+        )
     return _register_string(value, _get_pool().icons, _MAX_ICONS, "icon")
 
 
diff --git a/tests/unit_tests/core/test_entity_helpers.py b/tests/unit_tests/core/test_entity_helpers.py
index a5cfad5ab6..79bc3095b9 100644
--- a/tests/unit_tests/core/test_entity_helpers.py
+++ b/tests/unit_tests/core/test_entity_helpers.py
@@ -23,6 +23,7 @@ from esphome.core.entity_helpers import (
     _setup_entity_impl,
     entity_duplicate_validator,
     get_base_entity_object_id,
+    register_icon,
     setup_entity,
 )
 from esphome.cpp_generator import MockObj
@@ -909,6 +910,22 @@ def test_register_string_overflow() -> None:
         _register_string("overflow", category, 3, "test")
 
 
+def test_register_icon_max_length() -> None:
+    """Test register_icon rejects icons exceeding 63 characters."""
+    # 63 chars should succeed
+    max_icon = "mdi:" + "a" * 59  # 63 total
+    idx = register_icon(max_icon)
+    assert idx > 0
+
+    # 64 chars should fail
+    too_long = "mdi:" + "a" * 60  # 64 total
+    with pytest.raises(ValueError, match="Icon string too long"):
+        register_icon(too_long)
+
+    # Empty string returns 0
+    assert register_icon("") == 0
+
+
 @pytest.mark.asyncio
 async def test_setup_entity_with_entity_category(
     setup_test_environment: list[str],
diff --git a/tests/unit_tests/test_config_validation.py b/tests/unit_tests/test_config_validation.py
index 9602010ad3..c1849daf4b 100644
--- a/tests/unit_tests/test_config_validation.py
+++ b/tests/unit_tests/test_config_validation.py
@@ -148,6 +148,18 @@ def test_icon__invalid():
         config_validation.icon("foo")
 
 
+def test_icon__max_length():
+    """Test that icons exceeding 63 characters are rejected."""
+    # Exactly 63 chars should pass
+    max_icon = "mdi:" + "a" * 59  # 63 chars total
+    assert config_validation.icon(max_icon) == max_icon
+
+    # 64 chars should fail
+    too_long = "mdi:" + "a" * 60  # 64 chars total
+    with pytest.raises(Invalid, match="Icon string is too long"):
+        config_validation.icon(too_long)
+
+
 @pytest.mark.parametrize("value", ("True", "YES", "on", "enAblE", True))
 def test_boolean__valid_true(value):
     assert config_validation.boolean(value) is True

From 74e4b69654c2dd77f81cd712fe1c7ece3db78bfa Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Fri, 6 Mar 2026 06:58:13 -1000
Subject: [PATCH 7/7] [core] Replace Application name/friendly_name std::string
 with StringRef (#14532)

Co-authored-by: Copilot <198982749+Copilot@users.noreply.github.com>
---
 .../components/api/api_frame_helper_noise.cpp |  2 +-
 esphome/components/esp32_ble/ble.cpp          |  2 +-
 esphome/components/mdns/mdns_component.cpp    |  2 +-
 esphome/components/mqtt/mqtt_component.cpp    |  6 +-
 esphome/components/openthread/openthread.cpp  |  2 +-
 .../components/web_server/web_server_v1.cpp   |  2 +-
 esphome/components/wifi/wifi_component.cpp    |  2 +-
 .../wifi/wifi_component_esp8266.cpp           |  2 +-
 esphome/core/application.h                    | 54 +++++++------
 esphome/core/config.py                        | 60 +++++++++++++--
 esphome/core/defines.h                        |  1 +
 esphome/core/entity_base.cpp                  |  6 +-
 tests/dummy_main.cpp                          |  4 +-
 tests/unit_tests/core/test_config.py          | 77 +++++++++++++++++++
 14 files changed, 181 insertions(+), 41 deletions(-)

diff --git a/esphome/components/api/api_frame_helper_noise.cpp b/esphome/components/api/api_frame_helper_noise.cpp
index 3ae35e9be8..ba4f2f0642 100644
--- a/esphome/components/api/api_frame_helper_noise.cpp
+++ b/esphome/components/api/api_frame_helper_noise.cpp
@@ -269,7 +269,7 @@ APIError APINoiseFrameHelper::state_action_() {
   }
   if (state_ == State::SERVER_HELLO) {
     // send server hello
-    const std::string &name = App.get_name();
+    const auto &name = App.get_name();
     char mac[MAC_ADDRESS_BUFFER_SIZE];
     get_mac_address_into_buffer(mac);
 
diff --git a/esphome/components/esp32_ble/ble.cpp b/esphome/components/esp32_ble/ble.cpp
index 9d26018800..bbe972b9f3 100644
--- a/esphome/components/esp32_ble/ble.cpp
+++ b/esphome/components/esp32_ble/ble.cpp
@@ -273,7 +273,7 @@ bool ESP32BLE::ble_setup_() {
       device_name = this->name_;
     }
   } else {
-    const std::string &app_name = App.get_name();
+    const auto &app_name = App.get_name();
     size_t name_len = app_name.length();
     if (name_len > 20) {
       if (App.is_name_add_mac_suffix_enabled()) {
diff --git a/esphome/components/mdns/mdns_component.cpp b/esphome/components/mdns/mdns_component.cpp
index 5e5e1279d9..342a6e6c64 100644
--- a/esphome/components/mdns/mdns_component.cpp
+++ b/esphome/components/mdns/mdns_component.cpp
@@ -59,7 +59,7 @@ void MDNSComponent::compile_records_(StaticVector<MDNSService, MDNS_SERVICE_COUN
     service.proto = MDNS_STR(SERVICE_TCP);
     service.port = api::global_api_server->get_port();
 
-    const std::string &friendly_name = App.get_friendly_name();
+    const auto &friendly_name = App.get_friendly_name();
     bool friendly_name_empty = friendly_name.empty();
 
     // Calculate exact capacity for txt_records
diff --git a/esphome/components/mqtt/mqtt_component.cpp b/esphome/components/mqtt/mqtt_component.cpp
index 98fa10def9..d31a78b090 100644
--- a/esphome/components/mqtt/mqtt_component.cpp
+++ b/esphome/components/mqtt/mqtt_component.cpp
@@ -267,7 +267,7 @@ bool MQTTComponent::send_discovery_() {
           root[MQTT_UNIQUE_ID] = unique_id_buf;
         }
 
-        const std::string &node_name = App.get_name();
+        const auto &node_name = App.get_name();
         if (discovery_info.object_id_generator == MQTT_DEVICE_NAME_OBJECT_ID_GENERATOR) {
           // node_name (max 31) + "_" (1) + object_id (max 128) + null
           char object_id_full[ESPHOME_DEVICE_NAME_MAX_LEN + 1 + OBJECT_ID_MAX_LEN + 1];
@@ -275,8 +275,8 @@ bool MQTTComponent::send_discovery_() {
           root[MQTT_OBJECT_ID] = object_id_full;
         }
 
-        const std::string &friendly_name_ref = App.get_friendly_name();
-        const std::string &node_friendly_name = friendly_name_ref.empty() ? node_name : friendly_name_ref;
+        const auto &friendly_name_ref = App.get_friendly_name();
+        const auto &node_friendly_name = friendly_name_ref.empty() ? node_name : friendly_name_ref;
         const char *node_area = App.get_area();
 
         JsonObject device_info = root[MQTT_DEVICE].to<JsonObject>();
diff --git a/esphome/components/openthread/openthread.cpp b/esphome/components/openthread/openthread.cpp
index 9452f5a41e..fb81481299 100644
--- a/esphome/components/openthread/openthread.cpp
+++ b/esphome/components/openthread/openthread.cpp
@@ -132,7 +132,7 @@ void OpenThreadSrpComponent::setup() {
   // set the host name
   uint16_t size;
   char *existing_host_name = otSrpClientBuffersGetHostNameString(instance, &size);
-  const std::string &host_name = App.get_name();
+  const auto &host_name = App.get_name();
   uint16_t host_name_len = host_name.size();
   if (host_name_len > size) {
     ESP_LOGW(TAG, "Hostname is too long, choose a shorter project name");
diff --git a/esphome/components/web_server/web_server_v1.cpp b/esphome/components/web_server/web_server_v1.cpp
index f7b90018dc..85a4e80541 100644
--- a/esphome/components/web_server/web_server_v1.cpp
+++ b/esphome/components/web_server/web_server_v1.cpp
@@ -75,7 +75,7 @@ void WebServer::set_js_url(const char *js_url) { this->js_url_ = js_url; }
 
 void WebServer::handle_index_request(AsyncWebServerRequest *request) {
   AsyncResponseStream *stream = request->beginResponseStream(ESPHOME_F("text/html"));
-  const std::string &title = App.get_name();
+  const auto &title = App.get_name();
   stream->print(ESPHOME_F("<!DOCTYPE html><html lang=\"en\"><head><meta charset=UTF-8><meta "
                           "name=viewport content=\"width=device-width, initial-scale=1,user-scalable=no\"><title>"));
   stream->print(title.c_str());
diff --git a/esphome/components/wifi/wifi_component.cpp b/esphome/components/wifi/wifi_component.cpp
index 8b60810d28..60764955cc 100644
--- a/esphome/components/wifi/wifi_component.cpp
+++ b/esphome/components/wifi/wifi_component.cpp
@@ -913,7 +913,7 @@ void WiFiComponent::setup_ap_config_() {
     static constexpr size_t AP_SSID_PREFIX_LEN = 25;
     static constexpr size_t AP_SSID_SUFFIX_LEN = 7;
 
-    const std::string &app_name = App.get_name();
+    const auto &app_name = App.get_name();
     const char *name_ptr = app_name.c_str();
     size_t name_len = app_name.length();
 
diff --git a/esphome/components/wifi/wifi_component_esp8266.cpp b/esphome/components/wifi/wifi_component_esp8266.cpp
index 355832b434..a9b26c5935 100644
--- a/esphome/components/wifi/wifi_component_esp8266.cpp
+++ b/esphome/components/wifi/wifi_component_esp8266.cpp
@@ -212,7 +212,7 @@ network::IPAddresses WiFiComponent::wifi_sta_ip_addresses() {
   return addresses;
 }
 bool WiFiComponent::wifi_apply_hostname_() {
-  const std::string &hostname = App.get_name();
+  const auto &hostname = App.get_name();
   bool ret = wifi_station_set_hostname(const_cast<char *>(hostname.c_str()));
   if (!ret) {
     ESP_LOGV(TAG, "Set hostname failed");
diff --git a/esphome/core/application.h b/esphome/core/application.h
index 40f8a00edd..87f9fdf59a 100644
--- a/esphome/core/application.h
+++ b/esphome/core/application.h
@@ -138,26 +138,36 @@ static constexpr uint32_t TEARDOWN_TIMEOUT_REBOOT_MS = 1000;  // 1 second for qu
 
 class Application {
  public:
-  void pre_setup(const std::string &name, const std::string &friendly_name, bool name_add_mac_suffix) {
+#ifdef ESPHOME_NAME_ADD_MAC_SUFFIX
+  /// Pre-setup with MAC suffix: overwrites placeholder in mutable static buffers with actual MAC.
+  void pre_setup(char *name, size_t name_len, char *friendly_name, size_t friendly_name_len) {
     arch_init();
-    this->name_add_mac_suffix_ = name_add_mac_suffix;
-    if (name_add_mac_suffix) {
-      // MAC address length: 12 hex chars + null terminator
-      constexpr size_t mac_address_len = 13;
-      // MAC address suffix length (last 6 characters of 12-char MAC address string)
-      constexpr size_t mac_address_suffix_len = 6;
-      char mac_addr[mac_address_len];
-      get_mac_address_into_buffer(mac_addr);
-      const char *mac_suffix_ptr = mac_addr + mac_address_suffix_len;
-      this->name_ = make_name_with_suffix(name, '-', mac_suffix_ptr, mac_address_suffix_len);
-      if (!friendly_name.empty()) {
-        this->friendly_name_ = make_name_with_suffix(friendly_name, ' ', mac_suffix_ptr, mac_address_suffix_len);
-      }
-    } else {
-      this->name_ = name;
-      this->friendly_name_ = friendly_name;
+    this->name_add_mac_suffix_ = true;
+    // MAC address length: 12 hex chars + null terminator
+    constexpr size_t mac_address_len = 13;
+    // MAC address suffix length (last 6 characters of 12-char MAC address string)
+    constexpr size_t mac_address_suffix_len = 6;
+    char mac_addr[mac_address_len];
+    get_mac_address_into_buffer(mac_addr);
+    // Overwrite the placeholder suffix in the mutable static buffers with actual MAC
+    // name is always non-empty (validated by validate_hostname in Python config)
+    memcpy(name + name_len - mac_address_suffix_len, mac_addr + mac_address_suffix_len, mac_address_suffix_len);
+    if (friendly_name_len > 0) {
+      memcpy(friendly_name + friendly_name_len - mac_address_suffix_len, mac_addr + mac_address_suffix_len,
+             mac_address_suffix_len);
     }
+    this->name_ = StringRef(name, name_len);
+    this->friendly_name_ = StringRef(friendly_name, friendly_name_len);
   }
+#else
+  /// Pre-setup without MAC suffix: StringRef points directly at const string literals in flash.
+  void pre_setup(const char *name, size_t name_len, const char *friendly_name, size_t friendly_name_len) {
+    arch_init();
+    this->name_add_mac_suffix_ = false;
+    this->name_ = StringRef(name, name_len);
+    this->friendly_name_ = StringRef(friendly_name, friendly_name_len);
+  }
+#endif
 
 #ifdef USE_DEVICES
   void register_device(Device *device) { this->devices_.push_back(device); }
@@ -274,10 +284,10 @@ class Application {
   void loop();
 
   /// Get the name of this Application set by pre_setup().
-  const std::string &get_name() const { return this->name_; }
+  const StringRef &get_name() const { return this->name_; }
 
   /// Get the friendly name of this Application set by pre_setup().
-  const std::string &get_friendly_name() const { return this->friendly_name_; }
+  const StringRef &get_friendly_name() const { return this->friendly_name_; }
 
   /// Get the area of this Application set by pre_setup().
   const char *get_area() const {
@@ -627,9 +637,9 @@ class Application {
 #endif
 #endif
 
-  // std::string members (typically 24-32 bytes each)
-  std::string name_;
-  std::string friendly_name_;
+  // StringRef members (8 bytes each: pointer + size)
+  StringRef name_;
+  StringRef friendly_name_;
 
   // 4-byte members
   uint32_t last_loop_{0};
diff --git a/esphome/core/config.py b/esphome/core/config.py
index 9093ab3fe9..8631726a02 100644
--- a/esphome/core/config.py
+++ b/esphome/core/config.py
@@ -50,6 +50,7 @@ from esphome.core import (
 )
 from esphome.helpers import (
     copy_file_if_changed,
+    cpp_string_escape,
     fnv1a_32bit_hash,
     get_str_env,
     walk_files,
@@ -58,6 +59,38 @@ from esphome.types import ConfigType
 
 _LOGGER = logging.getLogger(__name__)
 
+# C++ variable names and separators for app name buffers (used with MAC suffix)
+_APP_NAME_BUF_VAR = "esphome_app_name_buf"
+_APP_NAME_MAC_SEP = "-"
+_APP_FRIENDLY_NAME_BUF_VAR = "esphome_app_friendly_name_buf"
+_APP_FRIENDLY_NAME_MAC_SEP = " "
+# Placeholder suffix for MAC address (last 6 hex chars)
+_MAC_SUFFIX_PLACEHOLDER = "XXXXXX"
+
+
+def make_app_name_cpp(
+    value: str, var_name: str, sep: str, *, add_mac_suffix: bool
+) -> tuple[str, str | None, int]:
+    """Compute C++ expression and optional global declaration for an app name.
+
+    Returns (cpp_expr, global_decl_or_none, byte_length).
+    - cpp_expr: The C++ expression to pass to pre_setup (var name or string literal).
+    - global_decl: A static char[] declaration string, or None if not needed.
+    - byte_length: The UTF-8 byte length of the string value.
+    """
+    if add_mac_suffix:
+        buf_value = "" if not value else f"{value}{sep}{_MAC_SUFFIX_PLACEHOLDER}"
+        escaped = cpp_string_escape(buf_value)
+        return (
+            var_name,
+            f"static char {var_name}[] = {escaped};",
+            len(buf_value.encode("utf-8")),
+        )
+    if not value:
+        return '""', None, 0
+    return cpp_string_escape(value), None, len(value.encode("utf-8"))
+
+
 StartupTrigger = cg.esphome_ns.class_(
     "StartupTrigger", cg.Component, automation.Trigger.template()
 )
@@ -78,6 +111,8 @@ VALID_INCLUDE_EXTS = {".h", ".hpp", ".tcc", ".ino", ".cpp", ".c"}
 
 def validate_hostname(config):
     # Keep in sync with ESPHOME_DEVICE_NAME_MAX_LEN in esphome/core/entity_base.h
+    if not config[CONF_NAME]:
+        raise cv.Invalid("Hostname must not be empty", path=[CONF_NAME])
     max_length = 31
     if config[CONF_NAME_ADD_MAC_SUFFIX]:
         max_length -= 7  # "-AABBCC" is appended when add mac suffix option is used
@@ -555,13 +590,28 @@ async def to_code(config: ConfigType) -> None:
     # Construct App via placement new — see application.cpp for storage details
     cg.add_global(cg.RawStatement("#include <new>"))
     cg.add(cg.RawExpression("new (&App) Application()"))
-    cg.add(
-        cg.App.pre_setup(
-            config[CONF_NAME],
-            config[CONF_FRIENDLY_NAME],
-            config[CONF_NAME_ADD_MAC_SUFFIX],
+    name = config[CONF_NAME]
+    friendly_name = config[CONF_FRIENDLY_NAME]
+    name_add_mac_suffix = config[CONF_NAME_ADD_MAC_SUFFIX]
+
+    def _emit_app_name(
+        value: str, var_name: str, sep: str
+    ) -> tuple[cg.Expression, int]:
+        """Emit codegen for an app name and return (expression, byte_length)."""
+        cpp_expr, global_decl, byte_len = make_app_name_cpp(
+            value, var_name, sep, add_mac_suffix=name_add_mac_suffix
         )
+        if global_decl is not None:
+            cg.add_global(cg.RawStatement(global_decl))
+        return cg.RawExpression(cpp_expr), byte_len
+
+    name_expr, name_len = _emit_app_name(name, _APP_NAME_BUF_VAR, _APP_NAME_MAC_SEP)
+    friendly_expr, friendly_len = _emit_app_name(
+        friendly_name, _APP_FRIENDLY_NAME_BUF_VAR, _APP_FRIENDLY_NAME_MAC_SEP
     )
+    if name_add_mac_suffix:
+        cg.add_define("ESPHOME_NAME_ADD_MAC_SUFFIX")
+    cg.add(cg.App.pre_setup(name_expr, name_len, friendly_expr, friendly_len))
     # Define component count for static allocation
     cg.add_define("ESPHOME_COMPONENT_COUNT", len(CORE.component_ids))
 
diff --git a/esphome/core/defines.h b/esphome/core/defines.h
index be5fdc9006..c5f38ab9aa 100644
--- a/esphome/core/defines.h
+++ b/esphome/core/defines.h
@@ -13,6 +13,7 @@
 #define ESPHOME_PROJECT_VERSION "v2"
 #define ESPHOME_PROJECT_VERSION_30 "v2"
 #define ESPHOME_VARIANT "ESP32"
+#define ESPHOME_NAME_ADD_MAC_SUFFIX
 #define ESPHOME_DEBUG_SCHEDULER
 #define ESPHOME_DEBUG_API
 
diff --git a/esphome/core/entity_base.cpp b/esphome/core/entity_base.cpp
index 1265277572..37e7fcc998 100644
--- a/esphome/core/entity_base.cpp
+++ b/esphome/core/entity_base.cpp
@@ -23,13 +23,13 @@ void EntityBase::set_name(const char *name, uint32_t object_id_hash) {
       // Bug-for-bug compatibility with OLD behavior:
       // - With MAC suffix: OLD code used App.get_friendly_name() directly (no fallback)
       // - Without MAC suffix: OLD code used pre-computed object_id with fallback to device name
-      const std::string &friendly = App.get_friendly_name();
+      const auto &friendly = App.get_friendly_name();
       if (App.is_name_add_mac_suffix_enabled()) {
         // MAC suffix enabled - use friendly_name directly (even if empty) for compatibility
-        this->name_ = StringRef(friendly);
+        this->name_ = friendly;
       } else {
         // No MAC suffix - fallback to device name if friendly_name is empty
-        this->name_ = StringRef(!friendly.empty() ? friendly : App.get_name());
+        this->name_ = !friendly.empty() ? friendly : App.get_name();
       }
     }
     this->flags_.has_own_name = false;
diff --git a/tests/dummy_main.cpp b/tests/dummy_main.cpp
index 3ccf35e04d..6fa0c08aa3 100644
--- a/tests/dummy_main.cpp
+++ b/tests/dummy_main.cpp
@@ -12,7 +12,9 @@
 using namespace esphome;
 
 void setup() {
-  App.pre_setup("livingroom", "LivingRoom", false);
+  static char name[] = "livingroom";
+  static char friendly_name[] = "LivingRoom";
+  App.pre_setup(name, sizeof(name) - 1, friendly_name, sizeof(friendly_name) - 1);
   auto *log = new logger::Logger(115200);  // NOLINT
   log->pre_setup();
   log->set_uart_selection(logger::UART_SELECTION_UART0);
diff --git a/tests/unit_tests/core/test_config.py b/tests/unit_tests/core/test_config.py
index 88801a9ca0..474d31a90a 100644
--- a/tests/unit_tests/core/test_config.py
+++ b/tests/unit_tests/core/test_config.py
@@ -23,6 +23,7 @@ from esphome.const import (
 from esphome.core import CORE, config
 from esphome.core.config import (
     Area,
+    make_app_name_cpp,
     preload_core_config,
     valid_include,
     valid_project_name,
@@ -969,3 +970,79 @@ def test_config_hash_different_for_different_configs() -> None:
     hash2 = CORE.config_hash
 
     assert hash1 != hash2
+
+
+def test_make_app_name_cpp_no_mac_simple() -> None:
+    """Test simple name without MAC suffix returns string literal."""
+    cpp_expr, global_decl, byte_len = make_app_name_cpp(
+        "my-device", "buf", "-", add_mac_suffix=False
+    )
+    assert cpp_expr == '"my-device"'
+    assert global_decl is None
+    assert byte_len == 9
+
+
+def test_make_app_name_cpp_no_mac_empty() -> None:
+    """Test empty name without MAC suffix."""
+    cpp_expr, global_decl, byte_len = make_app_name_cpp(
+        "", "buf", "-", add_mac_suffix=False
+    )
+    assert cpp_expr == '""'
+    assert global_decl is None
+    assert byte_len == 0
+
+
+def test_make_app_name_cpp_mac_suffix() -> None:
+    """Test name with MAC suffix emits static buffer."""
+    cpp_expr, global_decl, byte_len = make_app_name_cpp(
+        "my-device", "esphome_app_name_buf", "-", add_mac_suffix=True
+    )
+    assert cpp_expr == "esphome_app_name_buf"
+    assert global_decl is not None
+    assert "static char esphome_app_name_buf[]" in global_decl
+    assert "my-device-XXXXXX" in global_decl
+    assert byte_len == len("my-device-XXXXXX")
+
+
+def test_make_app_name_cpp_mac_suffix_empty() -> None:
+    """Test empty name with MAC suffix emits empty static buffer."""
+    cpp_expr, global_decl, byte_len = make_app_name_cpp(
+        "", "esphome_app_name_buf", "-", add_mac_suffix=True
+    )
+    assert cpp_expr == "esphome_app_name_buf"
+    assert global_decl is not None
+    assert "static char esphome_app_name_buf[]" in global_decl
+    assert byte_len == 0
+
+
+def test_make_app_name_cpp_mac_suffix_space_sep() -> None:
+    """Test friendly name uses space separator for MAC suffix."""
+    cpp_expr, global_decl, byte_len = make_app_name_cpp(
+        "My Device", "esphome_app_friendly_name_buf", " ", add_mac_suffix=True
+    )
+    assert cpp_expr == "esphome_app_friendly_name_buf"
+    assert global_decl is not None
+    assert "My Device XXXXXX" in global_decl
+    assert byte_len == len("My Device XXXXXX")
+
+
+def test_make_app_name_cpp_non_ascii_utf8_length() -> None:
+    """Test non-ASCII characters use UTF-8 byte length."""
+    _, global_decl, byte_len = make_app_name_cpp(
+        "café", "buf", "-", add_mac_suffix=False
+    )
+    assert byte_len == len("café".encode())  # 5 bytes, not 4 chars
+    assert global_decl is None
+
+
+def test_make_app_name_cpp_non_ascii_mac_suffix_utf8_length() -> None:
+    """Test non-ASCII with MAC suffix uses UTF-8 byte length."""
+    _, _, byte_len = make_app_name_cpp("café", "buf", "-", add_mac_suffix=True)
+    assert byte_len == len("café-XXXXXX".encode())
+
+
+def test_make_app_name_cpp_special_chars_escaped() -> None:
+    """Test special characters are properly escaped in C++ string."""
+    cpp_expr, _, _ = make_app_name_cpp('my "device"', "buf", "-", add_mac_suffix=False)
+    # cpp_string_escape uses octal escapes for quotes
+    assert '"' not in cpp_expr[1:-1]  # no unescaped quotes inside the outer quotes