diff --git a/Doxyfile b/Doxyfile
index d35c01b144..96faf3a1e0 100644
--- a/Doxyfile
+++ b/Doxyfile
@@ -48,7 +48,7 @@ PROJECT_NAME           = ESPHome
 # could be handy for archiving the generated documentation or if some version
 # control system is used.
 
-PROJECT_NUMBER         = 2025.9.0b2
+PROJECT_NUMBER         = 2025.9.0b3
 
 # Using the PROJECT_BRIEF tag one can provide an optional one line description
 # for a project that appears at the top of each page and should give viewer a
diff --git a/esphome/components/ade7880/ade7880.cpp b/esphome/components/ade7880/ade7880.cpp
index 55f834bf86..fd560e0676 100644
--- a/esphome/components/ade7880/ade7880.cpp
+++ b/esphome/components/ade7880/ade7880.cpp
@@ -113,7 +113,7 @@ void ADE7880::update() {
   if (this->channel_a_ != nullptr) {
     auto *chan = this->channel_a_;
     this->update_sensor_from_s24zp_register16_(chan->current, AIRMS, [](float val) { return val / 100000.0f; });
-    this->update_sensor_from_s24zp_register16_(chan->voltage, BVRMS, [](float val) { return val / 10000.0f; });
+    this->update_sensor_from_s24zp_register16_(chan->voltage, AVRMS, [](float val) { return val / 10000.0f; });
     this->update_sensor_from_s24zp_register16_(chan->active_power, AWATT, [](float val) { return val / 100.0f; });
     this->update_sensor_from_s24zp_register16_(chan->apparent_power, AVA, [](float val) { return val / 100.0f; });
     this->update_sensor_from_s16_register16_(chan->power_factor, APF,
diff --git a/esphome/components/ethernet/__init__.py b/esphome/components/ethernet/__init__.py
index a26238553c..151da7d0e5 100644
--- a/esphome/components/ethernet/__init__.py
+++ b/esphome/components/ethernet/__init__.py
@@ -77,6 +77,13 @@ ETHERNET_TYPES = {
     "DM9051": EthernetType.ETHERNET_TYPE_DM9051,
 }
 
+# PHY types that need compile-time defines for conditional compilation
+_PHY_TYPE_TO_DEFINE = {
+    "KSZ8081": "USE_ETHERNET_KSZ8081",
+    "KSZ8081RNA": "USE_ETHERNET_KSZ8081",
+    # Add other PHY types here only if they need conditional compilation
+}
+
 SPI_ETHERNET_TYPES = ["W5500", "DM9051"]
 SPI_ETHERNET_DEFAULT_POLLING_INTERVAL = TimePeriodMilliseconds(milliseconds=10)
 
@@ -345,6 +352,10 @@ async def to_code(config):
     if CONF_MANUAL_IP in config:
         cg.add(var.set_manual_ip(manual_ip(config[CONF_MANUAL_IP])))
 
+    # Add compile-time define for PHY types with specific code
+    if phy_define := _PHY_TYPE_TO_DEFINE.get(config[CONF_TYPE]):
+        cg.add_define(phy_define)
+
     cg.add_define("USE_ETHERNET")
 
     # Disable WiFi when using Ethernet to save memory
diff --git a/esphome/components/ethernet/ethernet_component.cpp b/esphome/components/ethernet/ethernet_component.cpp
index a48fd27383..ff14d19427 100644
--- a/esphome/components/ethernet/ethernet_component.cpp
+++ b/esphome/components/ethernet/ethernet_component.cpp
@@ -229,10 +229,12 @@ void EthernetComponent::setup() {
   ESPHL_ERROR_CHECK(err, "ETH driver install error");
 
 #ifndef USE_ETHERNET_SPI
+#ifdef USE_ETHERNET_KSZ8081
   if (this->type_ == ETHERNET_TYPE_KSZ8081RNA && this->clk_mode_ == EMAC_CLK_OUT) {
     // KSZ8081RNA default is incorrect. It expects a 25MHz clock instead of the 50MHz we provide.
     this->ksz8081_set_clock_reference_(mac);
   }
+#endif  // USE_ETHERNET_KSZ8081
 
   for (const auto &phy_register : this->phy_registers_) {
     this->write_phy_register_(mac, phy_register);
@@ -721,6 +723,7 @@ bool EthernetComponent::powerdown() {
 
 #ifndef USE_ETHERNET_SPI
 
+#ifdef USE_ETHERNET_KSZ8081
 constexpr uint8_t KSZ80XX_PC2R_REG_ADDR = 0x1F;
 
 void EthernetComponent::ksz8081_set_clock_reference_(esp_eth_mac_t *mac) {
@@ -749,6 +752,7 @@ void EthernetComponent::ksz8081_set_clock_reference_(esp_eth_mac_t *mac) {
     ESP_LOGVV(TAG, "KSZ8081 PHY Control 2: %s", format_hex_pretty((u_int8_t *) &phy_control_2, 2).c_str());
   }
 }
+#endif  // USE_ETHERNET_KSZ8081
 
 void EthernetComponent::write_phy_register_(esp_eth_mac_t *mac, PHYRegister register_data) {
   esp_err_t err;
diff --git a/esphome/components/ethernet/ethernet_component.h b/esphome/components/ethernet/ethernet_component.h
index 3d2713ee5c..bbb9d7fb60 100644
--- a/esphome/components/ethernet/ethernet_component.h
+++ b/esphome/components/ethernet/ethernet_component.h
@@ -104,8 +104,10 @@ class EthernetComponent : public Component {
   void start_connect_();
   void finish_connect_();
   void dump_connect_params_();
+#ifdef USE_ETHERNET_KSZ8081
   /// @brief Set `RMII Reference Clock Select` bit for KSZ8081.
   void ksz8081_set_clock_reference_(esp_eth_mac_t *mac);
+#endif
   /// @brief Set arbitratry PHY registers from config.
   void write_phy_register_(esp_eth_mac_t *mac, PHYRegister register_data);
 
diff --git a/esphome/components/mqtt/mqtt_client.cpp b/esphome/components/mqtt/mqtt_client.cpp
index 7675280f1a..7ab6efd1a1 100644
--- a/esphome/components/mqtt/mqtt_client.cpp
+++ b/esphome/components/mqtt/mqtt_client.cpp
@@ -491,7 +491,7 @@ bool MQTTClientComponent::publish(const std::string &topic, const std::string &p
 
 bool MQTTClientComponent::publish(const std::string &topic, const char *payload, size_t payload_length, uint8_t qos,
                                   bool retain) {
-  return publish({.topic = topic, .payload = payload, .qos = qos, .retain = retain});
+  return publish({.topic = topic, .payload = std::string(payload, payload_length), .qos = qos, .retain = retain});
 }
 
 bool MQTTClientComponent::publish(const MQTTMessage &message) {
diff --git a/esphome/components/select/select.cpp b/esphome/components/select/select.cpp
index 37887da27c..beb72aa320 100644
--- a/esphome/components/select/select.cpp
+++ b/esphome/components/select/select.cpp
@@ -28,12 +28,12 @@ bool Select::has_option(const std::string &option) const { return this->index_of
 bool Select::has_index(size_t index) const { return index < this->size(); }
 
 size_t Select::size() const {
-  auto options = traits.get_options();
+  const auto &options = traits.get_options();
   return options.size();
 }
 
 optional<size_t> Select::index_of(const std::string &option) const {
-  auto options = traits.get_options();
+  const auto &options = traits.get_options();
   auto it = std::find(options.begin(), options.end(), option);
   if (it == options.end()) {
     return {};
@@ -51,7 +51,7 @@ optional<size_t> Select::active_index() const {
 
 optional<std::string> Select::at(size_t index) const {
   if (this->has_index(index)) {
-    auto options = traits.get_options();
+    const auto &options = traits.get_options();
     return options.at(index);
   } else {
     return {};
diff --git a/esphome/components/select/select_call.cpp b/esphome/components/select/select_call.cpp
index 85f755645c..a8272f8622 100644
--- a/esphome/components/select/select_call.cpp
+++ b/esphome/components/select/select_call.cpp
@@ -45,7 +45,7 @@ void SelectCall::perform() {
   auto *parent = this->parent_;
   const auto *name = parent->get_name().c_str();
   const auto &traits = parent->traits;
-  auto options = traits.get_options();
+  const auto &options = traits.get_options();
 
   if (this->operation_ == SELECT_OP_NONE) {
     ESP_LOGW(TAG, "'%s' - SelectCall performed without selecting an operation", name);
diff --git a/esphome/const.py b/esphome/const.py
index 03dc33df89..e23c919bce 100644
--- a/esphome/const.py
+++ b/esphome/const.py
@@ -4,7 +4,7 @@ from enum import Enum
 
 from esphome.enum import StrEnum
 
-__version__ = "2025.9.0b2"
+__version__ = "2025.9.0b3"
 
 ALLOWED_NAME_CHARS = "abcdefghijklmnopqrstuvwxyz0123456789-_"
 VALID_SUBSTITUTIONS_CHARACTERS = (
diff --git a/esphome/core/defines.h b/esphome/core/defines.h
index 9a7e090b83..6e8d5ed74c 100644
--- a/esphome/core/defines.h
+++ b/esphome/core/defines.h
@@ -175,6 +175,7 @@
 #ifdef USE_ARDUINO
 #define USE_ARDUINO_VERSION_CODE VERSION_CODE(3, 2, 1)
 #define USE_ETHERNET
+#define USE_ETHERNET_KSZ8081
 #endif
 
 #ifdef USE_ESP_IDF
diff --git a/esphome/dashboard/web_server.py b/esphome/dashboard/web_server.py
index 294a180794..e6c5fd3d84 100644
--- a/esphome/dashboard/web_server.py
+++ b/esphome/dashboard/web_server.py
@@ -1038,12 +1038,9 @@ class ArchiveRequestHandler(BaseHandler):
         shutil.move(config_file, os.path.join(archive_path, configuration))
 
         storage_json = StorageJSON.load(storage_path)
-        if storage_json is not None:
+        if storage_json is not None and storage_json.build_path:
             # Delete build folder (if exists)
-            name = storage_json.name
-            build_folder = os.path.join(settings.config_dir, name)
-            if build_folder is not None:
-                shutil.rmtree(build_folder, os.path.join(archive_path, name))
+            shutil.rmtree(storage_json.build_path, ignore_errors=True)
 
 
 class UnArchiveRequestHandler(BaseHandler):
diff --git a/tests/dashboard/test_web_server.py b/tests/dashboard/test_web_server.py
index e206090ac0..1938617f20 100644
--- a/tests/dashboard/test_web_server.py
+++ b/tests/dashboard/test_web_server.py
@@ -589,7 +589,7 @@ async def test_archive_request_handler_post(
     mock_ext_storage_path: MagicMock,
     tmp_path: Path,
 ) -> None:
-    """Test ArchiveRequestHandler.post method."""
+    """Test ArchiveRequestHandler.post method without storage_json."""
 
     # Set up temp directories
     config_dir = Path(get_fixture_path("conf"))
@@ -616,6 +616,97 @@ async def test_archive_request_handler_post(
     ).read_text() == "esphome:\n  name: test_archive\n"
 
 
+@pytest.mark.asyncio
+async def test_archive_handler_with_build_folder(
+    dashboard: DashboardTestHelper,
+    mock_archive_storage_path: MagicMock,
+    mock_ext_storage_path: MagicMock,
+    mock_dashboard_settings: MagicMock,
+    mock_storage_json: MagicMock,
+    tmp_path: Path,
+) -> None:
+    """Test ArchiveRequestHandler.post with storage_json and build folder."""
+    config_dir = tmp_path / "config"
+    config_dir.mkdir()
+    archive_dir = tmp_path / "archive"
+    archive_dir.mkdir()
+    build_dir = tmp_path / "build"
+    build_dir.mkdir()
+
+    configuration = "test_device.yaml"
+    test_config = config_dir / configuration
+    test_config.write_text("esphome:\n  name: test_device\n")
+
+    build_folder = build_dir / "test_device"
+    build_folder.mkdir()
+    (build_folder / "firmware.bin").write_text("binary content")
+    (build_folder / ".pioenvs").mkdir()
+
+    mock_dashboard_settings.config_dir = str(config_dir)
+    mock_dashboard_settings.rel_path.return_value = str(test_config)
+    mock_archive_storage_path.return_value = str(archive_dir)
+
+    mock_storage = MagicMock()
+    mock_storage.name = "test_device"
+    mock_storage.build_path = str(build_folder)
+    mock_storage_json.load.return_value = mock_storage
+
+    response = await dashboard.fetch(
+        "/archive",
+        method="POST",
+        body=f"configuration={configuration}",
+        headers={"Content-Type": "application/x-www-form-urlencoded"},
+    )
+    assert response.code == 200
+
+    assert not test_config.exists()
+    assert (archive_dir / configuration).exists()
+
+    assert not build_folder.exists()
+    assert not (archive_dir / "test_device").exists()
+
+
+@pytest.mark.asyncio
+async def test_archive_handler_no_build_folder(
+    dashboard: DashboardTestHelper,
+    mock_archive_storage_path: MagicMock,
+    mock_ext_storage_path: MagicMock,
+    mock_dashboard_settings: MagicMock,
+    mock_storage_json: MagicMock,
+    tmp_path: Path,
+) -> None:
+    """Test ArchiveRequestHandler.post with storage_json but no build folder."""
+    config_dir = tmp_path / "config"
+    config_dir.mkdir()
+    archive_dir = tmp_path / "archive"
+    archive_dir.mkdir()
+
+    configuration = "test_device.yaml"
+    test_config = config_dir / configuration
+    test_config.write_text("esphome:\n  name: test_device\n")
+
+    mock_dashboard_settings.config_dir = str(config_dir)
+    mock_dashboard_settings.rel_path.return_value = str(test_config)
+    mock_archive_storage_path.return_value = str(archive_dir)
+
+    mock_storage = MagicMock()
+    mock_storage.name = "test_device"
+    mock_storage.build_path = None
+    mock_storage_json.load.return_value = mock_storage
+
+    response = await dashboard.fetch(
+        "/archive",
+        method="POST",
+        body=f"configuration={configuration}",
+        headers={"Content-Type": "application/x-www-form-urlencoded"},
+    )
+    assert response.code == 200
+
+    assert not test_config.exists()
+    assert (archive_dir / configuration).exists()
+    assert not (archive_dir / "test_device").exists()
+
+
 @pytest.mark.skipif(os.name == "nt", reason="Unix sockets are not supported on Windows")
 @pytest.mark.usefixtures("mock_trash_storage_path", "mock_archive_storage_path")
 def test_start_web_server_with_unix_socket(tmp_path: Path) -> None:
diff --git a/tests/unit_tests/conftest.py b/tests/unit_tests/conftest.py
index aac5a642f6..06d06d0506 100644
--- a/tests/unit_tests/conftest.py
+++ b/tests/unit_tests/conftest.py
@@ -9,8 +9,10 @@ not be part of a unit test suite.
 
 """
 
+from collections.abc import Generator
 from pathlib import Path
 import sys
+from unittest.mock import Mock, patch
 
 import pytest
 
@@ -36,3 +38,52 @@ def fixture_path() -> Path:
     Location of all fixture files.
     """
     return here / "fixtures"
+
+
+@pytest.fixture
+def setup_core(tmp_path: Path) -> Path:
+    """Set up CORE with test paths."""
+    CORE.config_path = str(tmp_path / "test.yaml")
+    return tmp_path
+
+
+@pytest.fixture
+def mock_write_file_if_changed() -> Generator[Mock, None, None]:
+    """Mock write_file_if_changed for storage_json."""
+    with patch("esphome.storage_json.write_file_if_changed") as mock:
+        yield mock
+
+
+@pytest.fixture
+def mock_copy_file_if_changed() -> Generator[Mock, None, None]:
+    """Mock copy_file_if_changed for core.config."""
+    with patch("esphome.core.config.copy_file_if_changed") as mock:
+        yield mock
+
+
+@pytest.fixture
+def mock_run_platformio_cli() -> Generator[Mock, None, None]:
+    """Mock run_platformio_cli for platformio_api."""
+    with patch("esphome.platformio_api.run_platformio_cli") as mock:
+        yield mock
+
+
+@pytest.fixture
+def mock_run_platformio_cli_run() -> Generator[Mock, None, None]:
+    """Mock run_platformio_cli_run for platformio_api."""
+    with patch("esphome.platformio_api.run_platformio_cli_run") as mock:
+        yield mock
+
+
+@pytest.fixture
+def mock_decode_pc() -> Generator[Mock, None, None]:
+    """Mock _decode_pc for platformio_api."""
+    with patch("esphome.platformio_api._decode_pc") as mock:
+        yield mock
+
+
+@pytest.fixture
+def mock_run_external_command() -> Generator[Mock, None, None]:
+    """Mock run_external_command for platformio_api."""
+    with patch("esphome.platformio_api.run_external_command") as mock:
+        yield mock
diff --git a/tests/unit_tests/core/test_config.py b/tests/unit_tests/core/test_config.py
index f5ba5221ed..46fe0148d8 100644
--- a/tests/unit_tests/core/test_config.py
+++ b/tests/unit_tests/core/test_config.py
@@ -1,15 +1,34 @@
 """Unit tests for core config functionality including areas and devices."""
 
 from collections.abc import Callable
+import os
 from pathlib import Path
+import types
 from typing import Any
+from unittest.mock import MagicMock, Mock, patch
 
 import pytest
 
 from esphome import config_validation as cv, core
-from esphome.const import CONF_AREA, CONF_AREAS, CONF_DEVICES
-from esphome.core import config
-from esphome.core.config import Area, validate_area_config
+from esphome.const import (
+    CONF_AREA,
+    CONF_AREAS,
+    CONF_BUILD_PATH,
+    CONF_DEVICES,
+    CONF_ESPHOME,
+    CONF_NAME,
+    CONF_NAME_ADD_MAC_SUFFIX,
+    KEY_CORE,
+)
+from esphome.core import CORE, config
+from esphome.core.config import (
+    Area,
+    preload_core_config,
+    valid_include,
+    valid_project_name,
+    validate_area_config,
+    validate_hostname,
+)
 
 from .common import load_config_from_fixture
 
@@ -245,3 +264,316 @@ def test_add_platform_defines_priority() -> None:
         f"_add_platform_defines priority ({config._add_platform_defines.priority}) must be lower than "
         f"globals priority ({globals_to_code.priority}) to fix issue #10431 (sensor count bug with lambdas)"
     )
+
+
+def test_valid_include_with_angle_brackets() -> None:
+    """Test valid_include accepts angle bracket includes."""
+    assert valid_include("<ArduinoJson.h>") == "<ArduinoJson.h>"
+
+
+def test_valid_include_with_valid_file(tmp_path: Path) -> None:
+    """Test valid_include accepts valid include files."""
+    CORE.config_path = str(tmp_path / "test.yaml")
+    include_file = tmp_path / "include.h"
+    include_file.touch()
+
+    assert valid_include(str(include_file)) == str(include_file)
+
+
+def test_valid_include_with_valid_directory(tmp_path: Path) -> None:
+    """Test valid_include accepts valid directories."""
+    CORE.config_path = str(tmp_path / "test.yaml")
+    include_dir = tmp_path / "includes"
+    include_dir.mkdir()
+
+    assert valid_include(str(include_dir)) == str(include_dir)
+
+
+def test_valid_include_invalid_extension(tmp_path: Path) -> None:
+    """Test valid_include rejects files with invalid extensions."""
+    CORE.config_path = str(tmp_path / "test.yaml")
+    invalid_file = tmp_path / "file.txt"
+    invalid_file.touch()
+
+    with pytest.raises(cv.Invalid, match="Include has invalid file extension"):
+        valid_include(str(invalid_file))
+
+
+def test_valid_project_name_valid() -> None:
+    """Test valid_project_name accepts valid project names."""
+    assert valid_project_name("esphome.my_project") == "esphome.my_project"
+
+
+def test_valid_project_name_no_namespace() -> None:
+    """Test valid_project_name rejects names without namespace."""
+    with pytest.raises(cv.Invalid, match="project name needs to have a namespace"):
+        valid_project_name("my_project")
+
+
+def test_valid_project_name_multiple_dots() -> None:
+    """Test valid_project_name rejects names with multiple dots."""
+    with pytest.raises(cv.Invalid, match="project name needs to have a namespace"):
+        valid_project_name("esphome.my.project")
+
+
+def test_validate_hostname_valid() -> None:
+    """Test validate_hostname accepts valid hostnames."""
+    config = {CONF_NAME: "my-device", CONF_NAME_ADD_MAC_SUFFIX: False}
+    assert validate_hostname(config) == config
+
+
+def test_validate_hostname_too_long() -> None:
+    """Test validate_hostname rejects hostnames that are too long."""
+    config = {
+        CONF_NAME: "a" * 32,  # 32 chars, max is 31
+        CONF_NAME_ADD_MAC_SUFFIX: False,
+    }
+    with pytest.raises(cv.Invalid, match="Hostnames can only be 31 characters long"):
+        validate_hostname(config)
+
+
+def test_validate_hostname_too_long_with_mac_suffix() -> None:
+    """Test validate_hostname accounts for MAC suffix length."""
+    config = {
+        CONF_NAME: "a" * 25,  # 25 chars, max is 24 with MAC suffix
+        CONF_NAME_ADD_MAC_SUFFIX: True,
+    }
+    with pytest.raises(cv.Invalid, match="Hostnames can only be 24 characters long"):
+        validate_hostname(config)
+
+
+def test_validate_hostname_with_underscore(caplog) -> None:
+    """Test validate_hostname warns about underscores."""
+    config = {CONF_NAME: "my_device", CONF_NAME_ADD_MAC_SUFFIX: False}
+    assert validate_hostname(config) == config
+    assert (
+        "Using the '_' (underscore) character in the hostname is discouraged"
+        in caplog.text
+    )
+
+
+def test_preload_core_config_basic(setup_core: Path) -> None:
+    """Test preload_core_config sets basic CORE attributes."""
+    config = {
+        CONF_ESPHOME: {
+            CONF_NAME: "test_device",
+        },
+        "esp32": {},
+    }
+    result = {}
+
+    platform = preload_core_config(config, result)
+
+    assert CORE.name == "test_device"
+    assert platform == "esp32"
+    assert KEY_CORE in CORE.data
+    assert CONF_BUILD_PATH in config[CONF_ESPHOME]
+    # Verify default build path is "build/<device_name>"
+    build_path = config[CONF_ESPHOME][CONF_BUILD_PATH]
+    assert build_path.endswith(os.path.join("build", "test_device"))
+
+
+def test_preload_core_config_with_build_path(setup_core: Path) -> None:
+    """Test preload_core_config uses provided build path."""
+    config = {
+        CONF_ESPHOME: {
+            CONF_NAME: "test_device",
+            CONF_BUILD_PATH: "/custom/build/path",
+        },
+        "esp8266": {},
+    }
+    result = {}
+
+    platform = preload_core_config(config, result)
+
+    assert config[CONF_ESPHOME][CONF_BUILD_PATH] == "/custom/build/path"
+    assert platform == "esp8266"
+
+
+def test_preload_core_config_env_build_path(setup_core: Path) -> None:
+    """Test preload_core_config uses ESPHOME_BUILD_PATH env var."""
+    config = {
+        CONF_ESPHOME: {
+            CONF_NAME: "test_device",
+        },
+        "rp2040": {},
+    }
+    result = {}
+
+    with patch.dict(os.environ, {"ESPHOME_BUILD_PATH": "/env/build"}):
+        platform = preload_core_config(config, result)
+
+    assert CONF_BUILD_PATH in config[CONF_ESPHOME]
+    assert "test_device" in config[CONF_ESPHOME][CONF_BUILD_PATH]
+    # Verify it uses the env var path with device name appended
+    build_path = config[CONF_ESPHOME][CONF_BUILD_PATH]
+    expected_path = os.path.join("/env/build", "test_device")
+    assert build_path == expected_path or build_path == expected_path.replace(
+        "/", os.sep
+    )
+    assert platform == "rp2040"
+
+
+def test_preload_core_config_no_platform(setup_core: Path) -> None:
+    """Test preload_core_config raises when no platform is specified."""
+    config = {
+        CONF_ESPHOME: {
+            CONF_NAME: "test_device",
+        },
+    }
+    result = {}
+
+    # Mock _is_target_platform to avoid expensive component loading
+    with patch("esphome.core.config._is_target_platform") as mock_is_platform:
+        # Return True for known platforms
+        mock_is_platform.side_effect = lambda name: name in [
+            "esp32",
+            "esp8266",
+            "rp2040",
+        ]
+
+        with pytest.raises(cv.Invalid, match="Platform missing"):
+            preload_core_config(config, result)
+
+
+def test_preload_core_config_multiple_platforms(setup_core: Path) -> None:
+    """Test preload_core_config raises when multiple platforms are specified."""
+    config = {
+        CONF_ESPHOME: {
+            CONF_NAME: "test_device",
+        },
+        "esp32": {},
+        "esp8266": {},
+    }
+    result = {}
+
+    # Mock _is_target_platform to avoid expensive component loading
+    with patch("esphome.core.config._is_target_platform") as mock_is_platform:
+        # Return True for known platforms
+        mock_is_platform.side_effect = lambda name: name in [
+            "esp32",
+            "esp8266",
+            "rp2040",
+        ]
+
+        with pytest.raises(cv.Invalid, match="Found multiple target platform blocks"):
+            preload_core_config(config, result)
+
+
+def test_include_file_header(tmp_path: Path, mock_copy_file_if_changed: Mock) -> None:
+    """Test include_file adds include statement for header files."""
+    src_file = tmp_path / "source.h"
+    src_file.write_text("// Header content")
+
+    CORE.build_path = str(tmp_path / "build")
+
+    with patch("esphome.core.config.cg") as mock_cg:
+        # Mock RawStatement to capture the text
+        mock_raw_statement = MagicMock()
+        mock_raw_statement.text = ""
+
+        def raw_statement_side_effect(text):
+            mock_raw_statement.text = text
+            return mock_raw_statement
+
+        mock_cg.RawStatement.side_effect = raw_statement_side_effect
+
+        config.include_file(str(src_file), "test.h")
+
+        mock_copy_file_if_changed.assert_called_once()
+        mock_cg.add_global.assert_called_once()
+        # Check that include statement was added
+        assert '#include "test.h"' in mock_raw_statement.text
+
+
+def test_include_file_cpp(tmp_path: Path, mock_copy_file_if_changed: Mock) -> None:
+    """Test include_file does not add include for cpp files."""
+    src_file = tmp_path / "source.cpp"
+    src_file.write_text("// CPP content")
+
+    CORE.build_path = str(tmp_path / "build")
+
+    with patch("esphome.core.config.cg") as mock_cg:
+        config.include_file(str(src_file), "test.cpp")
+
+        mock_copy_file_if_changed.assert_called_once()
+        # Should not add include statement for .cpp files
+        mock_cg.add_global.assert_not_called()
+
+
+def test_get_usable_cpu_count() -> None:
+    """Test get_usable_cpu_count returns CPU count."""
+    count = config.get_usable_cpu_count()
+    assert isinstance(count, int)
+    assert count > 0
+
+
+def test_get_usable_cpu_count_with_process_cpu_count() -> None:
+    """Test get_usable_cpu_count uses process_cpu_count when available."""
+    # Test with process_cpu_count (Python 3.13+)
+    # Create a mock os module with process_cpu_count
+
+    mock_os = types.SimpleNamespace(process_cpu_count=lambda: 8, cpu_count=lambda: 4)
+
+    with patch("esphome.core.config.os", mock_os):
+        # When process_cpu_count exists, it should be used
+        count = config.get_usable_cpu_count()
+        assert count == 8
+
+    # Test fallback to cpu_count when process_cpu_count not available
+    mock_os_no_process = types.SimpleNamespace(cpu_count=lambda: 4)
+
+    with patch("esphome.core.config.os", mock_os_no_process):
+        count = config.get_usable_cpu_count()
+        assert count == 4
+
+
+def test_list_target_platforms(tmp_path: Path) -> None:
+    """Test _list_target_platforms returns available platforms."""
+    # Create mock components directory structure
+    components_dir = tmp_path / "components"
+    components_dir.mkdir()
+
+    # Create platform and non-platform directories with __init__.py
+    platforms = ["esp32", "esp8266", "rp2040", "libretiny", "host"]
+    non_platforms = ["sensor"]
+
+    for component in platforms + non_platforms:
+        component_dir = components_dir / component
+        component_dir.mkdir()
+        (component_dir / "__init__.py").touch()
+
+    # Create a file (not a directory)
+    (components_dir / "README.md").touch()
+
+    # Create a directory without __init__.py
+    (components_dir / "no_init").mkdir()
+
+    # Mock Path(__file__).parents[1] to return our tmp_path
+    with patch("esphome.core.config.Path") as mock_path:
+        mock_file_path = MagicMock()
+        mock_file_path.parents = [MagicMock(), tmp_path]
+        mock_path.return_value = mock_file_path
+
+        platforms = config._list_target_platforms()
+
+    assert isinstance(platforms, list)
+    # Should include platform components
+    assert "esp32" in platforms
+    assert "esp8266" in platforms
+    assert "rp2040" in platforms
+    assert "libretiny" in platforms
+    assert "host" in platforms
+    # Should not include non-platform components
+    assert "sensor" not in platforms
+    assert "README.md" not in platforms
+    assert "no_init" not in platforms
+
+
+def test_is_target_platform() -> None:
+    """Test _is_target_platform identifies valid platforms."""
+    assert config._is_target_platform("esp32") is True
+    assert config._is_target_platform("esp8266") is True
+    assert config._is_target_platform("rp2040") is True
+    assert config._is_target_platform("invalid_platform") is False
+    assert config._is_target_platform("api") is False  # Component but not platform
diff --git a/tests/unit_tests/test_config_validation_paths.py b/tests/unit_tests/test_config_validation_paths.py
new file mode 100644
index 0000000000..f8f038390e
--- /dev/null
+++ b/tests/unit_tests/test_config_validation_paths.py
@@ -0,0 +1,187 @@
+"""Tests for config_validation.py path-related functions."""
+
+from pathlib import Path
+
+import pytest
+import voluptuous as vol
+
+from esphome import config_validation as cv
+
+
+def test_directory_valid_path(setup_core: Path) -> None:
+    """Test directory validator with valid directory."""
+    test_dir = setup_core / "test_directory"
+    test_dir.mkdir()
+
+    result = cv.directory("test_directory")
+
+    assert result == "test_directory"
+
+
+def test_directory_absolute_path(setup_core: Path) -> None:
+    """Test directory validator with absolute path."""
+    test_dir = setup_core / "test_directory"
+    test_dir.mkdir()
+
+    result = cv.directory(str(test_dir))
+
+    assert result == str(test_dir)
+
+
+def test_directory_nonexistent_path(setup_core: Path) -> None:
+    """Test directory validator raises error for non-existent directory."""
+    with pytest.raises(
+        vol.Invalid, match="Could not find directory.*nonexistent_directory"
+    ):
+        cv.directory("nonexistent_directory")
+
+
+def test_directory_file_instead_of_directory(setup_core: Path) -> None:
+    """Test directory validator raises error when path is a file."""
+    test_file = setup_core / "test_file.txt"
+    test_file.write_text("content")
+
+    with pytest.raises(vol.Invalid, match="is not a directory"):
+        cv.directory("test_file.txt")
+
+
+def test_directory_with_parent_directory(setup_core: Path) -> None:
+    """Test directory validator with nested directory structure."""
+    nested_dir = setup_core / "parent" / "child" / "grandchild"
+    nested_dir.mkdir(parents=True)
+
+    result = cv.directory("parent/child/grandchild")
+
+    assert result == "parent/child/grandchild"
+
+
+def test_file_valid_path(setup_core: Path) -> None:
+    """Test file_ validator with valid file."""
+    test_file = setup_core / "test_file.yaml"
+    test_file.write_text("test content")
+
+    result = cv.file_("test_file.yaml")
+
+    assert result == "test_file.yaml"
+
+
+def test_file_absolute_path(setup_core: Path) -> None:
+    """Test file_ validator with absolute path."""
+    test_file = setup_core / "test_file.yaml"
+    test_file.write_text("test content")
+
+    result = cv.file_(str(test_file))
+
+    assert result == str(test_file)
+
+
+def test_file_nonexistent_path(setup_core: Path) -> None:
+    """Test file_ validator raises error for non-existent file."""
+    with pytest.raises(vol.Invalid, match="Could not find file.*nonexistent_file.yaml"):
+        cv.file_("nonexistent_file.yaml")
+
+
+def test_file_directory_instead_of_file(setup_core: Path) -> None:
+    """Test file_ validator raises error when path is a directory."""
+    test_dir = setup_core / "test_directory"
+    test_dir.mkdir()
+
+    with pytest.raises(vol.Invalid, match="is not a file"):
+        cv.file_("test_directory")
+
+
+def test_file_with_parent_directory(setup_core: Path) -> None:
+    """Test file_ validator with file in nested directory."""
+    nested_dir = setup_core / "configs" / "sensors"
+    nested_dir.mkdir(parents=True)
+    test_file = nested_dir / "temperature.yaml"
+    test_file.write_text("sensor config")
+
+    result = cv.file_("configs/sensors/temperature.yaml")
+
+    assert result == "configs/sensors/temperature.yaml"
+
+
+def test_directory_handles_trailing_slash(setup_core: Path) -> None:
+    """Test directory validator handles trailing slashes correctly."""
+    test_dir = setup_core / "test_dir"
+    test_dir.mkdir()
+
+    result = cv.directory("test_dir/")
+    assert result == "test_dir/"
+
+    result = cv.directory("test_dir")
+    assert result == "test_dir"
+
+
+def test_file_handles_various_extensions(setup_core: Path) -> None:
+    """Test file_ validator works with different file extensions."""
+    yaml_file = setup_core / "config.yaml"
+    yaml_file.write_text("yaml content")
+    assert cv.file_("config.yaml") == "config.yaml"
+
+    yml_file = setup_core / "config.yml"
+    yml_file.write_text("yml content")
+    assert cv.file_("config.yml") == "config.yml"
+
+    txt_file = setup_core / "readme.txt"
+    txt_file.write_text("text content")
+    assert cv.file_("readme.txt") == "readme.txt"
+
+    no_ext_file = setup_core / "LICENSE"
+    no_ext_file.write_text("license content")
+    assert cv.file_("LICENSE") == "LICENSE"
+
+
+def test_directory_with_symlink(setup_core: Path) -> None:
+    """Test directory validator follows symlinks."""
+    actual_dir = setup_core / "actual_directory"
+    actual_dir.mkdir()
+
+    symlink_dir = setup_core / "symlink_directory"
+    symlink_dir.symlink_to(actual_dir)
+
+    result = cv.directory("symlink_directory")
+    assert result == "symlink_directory"
+
+
+def test_file_with_symlink(setup_core: Path) -> None:
+    """Test file_ validator follows symlinks."""
+    actual_file = setup_core / "actual_file.txt"
+    actual_file.write_text("content")
+
+    symlink_file = setup_core / "symlink_file.txt"
+    symlink_file.symlink_to(actual_file)
+
+    result = cv.file_("symlink_file.txt")
+    assert result == "symlink_file.txt"
+
+
+def test_directory_error_shows_full_path(setup_core: Path) -> None:
+    """Test directory validator error message includes full path."""
+    with pytest.raises(vol.Invalid, match=".*missing_dir.*full path:.*"):
+        cv.directory("missing_dir")
+
+
+def test_file_error_shows_full_path(setup_core: Path) -> None:
+    """Test file_ validator error message includes full path."""
+    with pytest.raises(vol.Invalid, match=".*missing_file.yaml.*full path:.*"):
+        cv.file_("missing_file.yaml")
+
+
+def test_directory_with_spaces_in_name(setup_core: Path) -> None:
+    """Test directory validator handles spaces in directory names."""
+    dir_with_spaces = setup_core / "my test directory"
+    dir_with_spaces.mkdir()
+
+    result = cv.directory("my test directory")
+    assert result == "my test directory"
+
+
+def test_file_with_spaces_in_name(setup_core: Path) -> None:
+    """Test file_ validator handles spaces in file names."""
+    file_with_spaces = setup_core / "my test file.yaml"
+    file_with_spaces.write_text("content")
+
+    result = cv.file_("my test file.yaml")
+    assert result == "my test file.yaml"
diff --git a/tests/unit_tests/test_external_files.py b/tests/unit_tests/test_external_files.py
new file mode 100644
index 0000000000..3fa7de2f64
--- /dev/null
+++ b/tests/unit_tests/test_external_files.py
@@ -0,0 +1,196 @@
+"""Tests for external_files.py functions."""
+
+from pathlib import Path
+import time
+from unittest.mock import MagicMock, patch
+
+import pytest
+import requests
+
+from esphome import external_files
+from esphome.config_validation import Invalid
+from esphome.core import CORE, TimePeriod
+
+
+def test_compute_local_file_dir(setup_core: Path) -> None:
+    """Test compute_local_file_dir creates and returns correct path."""
+    domain = "font"
+
+    result = external_files.compute_local_file_dir(domain)
+
+    assert isinstance(result, Path)
+    assert result == Path(CORE.data_dir) / domain
+    assert result.exists()
+    assert result.is_dir()
+
+
+def test_compute_local_file_dir_nested(setup_core: Path) -> None:
+    """Test compute_local_file_dir works with nested domains."""
+    domain = "images/icons"
+
+    result = external_files.compute_local_file_dir(domain)
+
+    assert result == Path(CORE.data_dir) / "images" / "icons"
+    assert result.exists()
+    assert result.is_dir()
+
+
+def test_is_file_recent_with_recent_file(setup_core: Path) -> None:
+    """Test is_file_recent returns True for recently created file."""
+    test_file = setup_core / "recent.txt"
+    test_file.write_text("content")
+
+    refresh = TimePeriod(seconds=3600)
+
+    result = external_files.is_file_recent(str(test_file), refresh)
+
+    assert result is True
+
+
+def test_is_file_recent_with_old_file(setup_core: Path) -> None:
+    """Test is_file_recent returns False for old file."""
+    test_file = setup_core / "old.txt"
+    test_file.write_text("content")
+
+    old_time = time.time() - 7200
+
+    with patch("os.path.getctime", return_value=old_time):
+        refresh = TimePeriod(seconds=3600)
+
+        result = external_files.is_file_recent(str(test_file), refresh)
+
+        assert result is False
+
+
+def test_is_file_recent_nonexistent_file(setup_core: Path) -> None:
+    """Test is_file_recent returns False for non-existent file."""
+    test_file = setup_core / "nonexistent.txt"
+    refresh = TimePeriod(seconds=3600)
+
+    result = external_files.is_file_recent(str(test_file), refresh)
+
+    assert result is False
+
+
+def test_is_file_recent_with_zero_refresh(setup_core: Path) -> None:
+    """Test is_file_recent with zero refresh period returns False."""
+    test_file = setup_core / "test.txt"
+    test_file.write_text("content")
+
+    # Mock getctime to return a time 10 seconds ago
+    with patch("os.path.getctime", return_value=time.time() - 10):
+        refresh = TimePeriod(seconds=0)
+        result = external_files.is_file_recent(str(test_file), refresh)
+        assert result is False
+
+
+@patch("esphome.external_files.requests.head")
+def test_has_remote_file_changed_not_modified(
+    mock_head: MagicMock, setup_core: Path
+) -> None:
+    """Test has_remote_file_changed returns False when file not modified."""
+    test_file = setup_core / "cached.txt"
+    test_file.write_text("cached content")
+
+    mock_response = MagicMock()
+    mock_response.status_code = 304
+    mock_head.return_value = mock_response
+
+    url = "https://example.com/file.txt"
+    result = external_files.has_remote_file_changed(url, str(test_file))
+
+    assert result is False
+    mock_head.assert_called_once()
+
+    call_args = mock_head.call_args
+    headers = call_args[1]["headers"]
+    assert external_files.IF_MODIFIED_SINCE in headers
+    assert external_files.CACHE_CONTROL in headers
+
+
+@patch("esphome.external_files.requests.head")
+def test_has_remote_file_changed_modified(
+    mock_head: MagicMock, setup_core: Path
+) -> None:
+    """Test has_remote_file_changed returns True when file modified."""
+    test_file = setup_core / "cached.txt"
+    test_file.write_text("cached content")
+
+    mock_response = MagicMock()
+    mock_response.status_code = 200
+    mock_head.return_value = mock_response
+
+    url = "https://example.com/file.txt"
+    result = external_files.has_remote_file_changed(url, str(test_file))
+
+    assert result is True
+
+
+def test_has_remote_file_changed_no_local_file(setup_core: Path) -> None:
+    """Test has_remote_file_changed returns True when local file doesn't exist."""
+    test_file = setup_core / "nonexistent.txt"
+
+    url = "https://example.com/file.txt"
+    result = external_files.has_remote_file_changed(url, str(test_file))
+
+    assert result is True
+
+
+@patch("esphome.external_files.requests.head")
+def test_has_remote_file_changed_network_error(
+    mock_head: MagicMock, setup_core: Path
+) -> None:
+    """Test has_remote_file_changed handles network errors gracefully."""
+    test_file = setup_core / "cached.txt"
+    test_file.write_text("cached content")
+
+    mock_head.side_effect = requests.exceptions.RequestException("Network error")
+
+    url = "https://example.com/file.txt"
+
+    with pytest.raises(Invalid, match="Could not check if.*Network error"):
+        external_files.has_remote_file_changed(url, str(test_file))
+
+
+@patch("esphome.external_files.requests.head")
+def test_has_remote_file_changed_timeout(
+    mock_head: MagicMock, setup_core: Path
+) -> None:
+    """Test has_remote_file_changed respects timeout."""
+    test_file = setup_core / "cached.txt"
+    test_file.write_text("cached content")
+
+    mock_response = MagicMock()
+    mock_response.status_code = 304
+    mock_head.return_value = mock_response
+
+    url = "https://example.com/file.txt"
+    external_files.has_remote_file_changed(url, str(test_file))
+
+    call_args = mock_head.call_args
+    assert call_args[1]["timeout"] == external_files.NETWORK_TIMEOUT
+
+
+def test_compute_local_file_dir_creates_parent_dirs(setup_core: Path) -> None:
+    """Test compute_local_file_dir creates parent directories."""
+    domain = "level1/level2/level3/level4"
+
+    result = external_files.compute_local_file_dir(domain)
+
+    assert result.exists()
+    assert result.is_dir()
+    assert result.parent.name == "level3"
+    assert result.parent.parent.name == "level2"
+    assert result.parent.parent.parent.name == "level1"
+
+
+def test_is_file_recent_handles_float_seconds(setup_core: Path) -> None:
+    """Test is_file_recent works with float seconds in TimePeriod."""
+    test_file = setup_core / "test.txt"
+    test_file.write_text("content")
+
+    refresh = TimePeriod(seconds=3600.5)
+
+    result = external_files.is_file_recent(str(test_file), refresh)
+
+    assert result is True
diff --git a/tests/unit_tests/test_platformio_api.py b/tests/unit_tests/test_platformio_api.py
new file mode 100644
index 0000000000..7c7883d391
--- /dev/null
+++ b/tests/unit_tests/test_platformio_api.py
@@ -0,0 +1,636 @@
+"""Tests for platformio_api.py path functions."""
+
+import json
+import os
+from pathlib import Path
+import shutil
+from types import SimpleNamespace
+from unittest.mock import MagicMock, Mock, patch
+
+import pytest
+
+from esphome import platformio_api
+from esphome.core import CORE, EsphomeError
+
+
+def test_idedata_firmware_elf_path(setup_core: Path) -> None:
+    """Test IDEData.firmware_elf_path returns correct path."""
+    CORE.build_path = str(setup_core / "build" / "test")
+    CORE.name = "test"
+    raw_data = {"prog_path": "/path/to/firmware.elf"}
+    idedata = platformio_api.IDEData(raw_data)
+
+    assert idedata.firmware_elf_path == "/path/to/firmware.elf"
+
+
+def test_idedata_firmware_bin_path(setup_core: Path) -> None:
+    """Test IDEData.firmware_bin_path returns Path with .bin extension."""
+    CORE.build_path = str(setup_core / "build" / "test")
+    CORE.name = "test"
+    prog_path = str(Path("/path/to/firmware.elf"))
+    raw_data = {"prog_path": prog_path}
+    idedata = platformio_api.IDEData(raw_data)
+
+    result = idedata.firmware_bin_path
+    assert isinstance(result, str)
+    expected = str(Path("/path/to/firmware.bin"))
+    assert result == expected
+    assert result.endswith(".bin")
+
+
+def test_idedata_firmware_bin_path_preserves_directory(setup_core: Path) -> None:
+    """Test firmware_bin_path preserves the directory structure."""
+    CORE.build_path = str(setup_core / "build" / "test")
+    CORE.name = "test"
+    prog_path = str(Path("/complex/path/to/build/firmware.elf"))
+    raw_data = {"prog_path": prog_path}
+    idedata = platformio_api.IDEData(raw_data)
+
+    result = idedata.firmware_bin_path
+    expected = str(Path("/complex/path/to/build/firmware.bin"))
+    assert result == expected
+
+
+def test_idedata_extra_flash_images(setup_core: Path) -> None:
+    """Test IDEData.extra_flash_images returns list of FlashImage objects."""
+    CORE.build_path = str(setup_core / "build" / "test")
+    CORE.name = "test"
+    raw_data = {
+        "prog_path": "/path/to/firmware.elf",
+        "extra": {
+            "flash_images": [
+                {"path": "/path/to/bootloader.bin", "offset": "0x1000"},
+                {"path": "/path/to/partition.bin", "offset": "0x8000"},
+            ]
+        },
+    }
+    idedata = platformio_api.IDEData(raw_data)
+
+    images = idedata.extra_flash_images
+    assert len(images) == 2
+    assert all(isinstance(img, platformio_api.FlashImage) for img in images)
+    assert images[0].path == "/path/to/bootloader.bin"
+    assert images[0].offset == "0x1000"
+    assert images[1].path == "/path/to/partition.bin"
+    assert images[1].offset == "0x8000"
+
+
+def test_idedata_extra_flash_images_empty(setup_core: Path) -> None:
+    """Test extra_flash_images returns empty list when no extra images."""
+    CORE.build_path = str(setup_core / "build" / "test")
+    CORE.name = "test"
+    raw_data = {"prog_path": "/path/to/firmware.elf", "extra": {"flash_images": []}}
+    idedata = platformio_api.IDEData(raw_data)
+
+    images = idedata.extra_flash_images
+    assert images == []
+
+
+def test_idedata_cc_path(setup_core: Path) -> None:
+    """Test IDEData.cc_path returns compiler path."""
+    CORE.build_path = str(setup_core / "build" / "test")
+    CORE.name = "test"
+    raw_data = {
+        "prog_path": "/path/to/firmware.elf",
+        "cc_path": "/Users/test/.platformio/packages/toolchain-xtensa32/bin/xtensa-esp32-elf-gcc",
+    }
+    idedata = platformio_api.IDEData(raw_data)
+
+    assert (
+        idedata.cc_path
+        == "/Users/test/.platformio/packages/toolchain-xtensa32/bin/xtensa-esp32-elf-gcc"
+    )
+
+
+def test_flash_image_dataclass() -> None:
+    """Test FlashImage dataclass stores path and offset correctly."""
+    image = platformio_api.FlashImage(path="/path/to/image.bin", offset="0x10000")
+
+    assert image.path == "/path/to/image.bin"
+    assert image.offset == "0x10000"
+
+
+def test_load_idedata_returns_dict(
+    setup_core: Path, mock_run_platformio_cli_run
+) -> None:
+    """Test _load_idedata returns parsed idedata dict when successful."""
+    CORE.build_path = str(setup_core / "build" / "test")
+    CORE.name = "test"
+
+    # Create required files
+    platformio_ini = setup_core / "build" / "test" / "platformio.ini"
+    platformio_ini.parent.mkdir(parents=True, exist_ok=True)
+    platformio_ini.touch()
+
+    idedata_path = setup_core / ".esphome" / "idedata" / "test.json"
+    idedata_path.parent.mkdir(parents=True, exist_ok=True)
+    idedata_path.write_text('{"prog_path": "/test/firmware.elf"}')
+
+    mock_run_platformio_cli_run.return_value = '{"prog_path": "/test/firmware.elf"}'
+
+    config = {"name": "test"}
+    result = platformio_api._load_idedata(config)
+
+    assert result is not None
+    assert isinstance(result, dict)
+    assert result["prog_path"] == "/test/firmware.elf"
+
+
+def test_load_idedata_uses_cache_when_valid(
+    setup_core: Path, mock_run_platformio_cli_run: Mock
+) -> None:
+    """Test _load_idedata uses cached data when unchanged."""
+    CORE.build_path = str(setup_core / "build" / "test")
+    CORE.name = "test"
+
+    # Create platformio.ini
+    platformio_ini = setup_core / "build" / "test" / "platformio.ini"
+    platformio_ini.parent.mkdir(parents=True, exist_ok=True)
+    platformio_ini.write_text("content")
+
+    # Create idedata cache file that's newer
+    idedata_path = setup_core / ".esphome" / "idedata" / "test.json"
+    idedata_path.parent.mkdir(parents=True, exist_ok=True)
+    idedata_path.write_text('{"prog_path": "/cached/firmware.elf"}')
+
+    # Make idedata newer than platformio.ini
+    platformio_ini_mtime = platformio_ini.stat().st_mtime
+    os.utime(idedata_path, (platformio_ini_mtime + 1, platformio_ini_mtime + 1))
+
+    config = {"name": "test"}
+    result = platformio_api._load_idedata(config)
+
+    # Should not call _run_idedata since cache is valid
+    mock_run_platformio_cli_run.assert_not_called()
+
+    assert result["prog_path"] == "/cached/firmware.elf"
+
+
+def test_load_idedata_regenerates_when_platformio_ini_newer(
+    setup_core: Path, mock_run_platformio_cli_run: Mock
+) -> None:
+    """Test _load_idedata regenerates when platformio.ini is newer."""
+    CORE.build_path = str(setup_core / "build" / "test")
+    CORE.name = "test"
+
+    # Create idedata cache file first
+    idedata_path = setup_core / ".esphome" / "idedata" / "test.json"
+    idedata_path.parent.mkdir(parents=True, exist_ok=True)
+    idedata_path.write_text('{"prog_path": "/old/firmware.elf"}')
+
+    # Create platformio.ini that's newer
+    idedata_mtime = idedata_path.stat().st_mtime
+    platformio_ini = setup_core / "build" / "test" / "platformio.ini"
+    platformio_ini.parent.mkdir(parents=True, exist_ok=True)
+    platformio_ini.write_text("content")
+    # Make platformio.ini newer than idedata
+    os.utime(platformio_ini, (idedata_mtime + 1, idedata_mtime + 1))
+
+    # Mock platformio to return new data
+    new_data = {"prog_path": "/new/firmware.elf"}
+    mock_run_platformio_cli_run.return_value = json.dumps(new_data)
+
+    config = {"name": "test"}
+    result = platformio_api._load_idedata(config)
+
+    # Should call _run_idedata since platformio.ini is newer
+    mock_run_platformio_cli_run.assert_called_once()
+
+    assert result["prog_path"] == "/new/firmware.elf"
+
+
+def test_load_idedata_regenerates_on_corrupted_cache(
+    setup_core: Path, mock_run_platformio_cli_run: Mock
+) -> None:
+    """Test _load_idedata regenerates when cache file is corrupted."""
+    CORE.build_path = str(setup_core / "build" / "test")
+    CORE.name = "test"
+
+    # Create platformio.ini
+    platformio_ini = setup_core / "build" / "test" / "platformio.ini"
+    platformio_ini.parent.mkdir(parents=True, exist_ok=True)
+    platformio_ini.write_text("content")
+
+    # Create corrupted idedata cache file
+    idedata_path = setup_core / ".esphome" / "idedata" / "test.json"
+    idedata_path.parent.mkdir(parents=True, exist_ok=True)
+    idedata_path.write_text('{"prog_path": invalid json')
+
+    # Make idedata newer so it would be used if valid
+    platformio_ini_mtime = platformio_ini.stat().st_mtime
+    os.utime(idedata_path, (platformio_ini_mtime + 1, platformio_ini_mtime + 1))
+
+    # Mock platformio to return new data
+    new_data = {"prog_path": "/new/firmware.elf"}
+    mock_run_platformio_cli_run.return_value = json.dumps(new_data)
+
+    config = {"name": "test"}
+    result = platformio_api._load_idedata(config)
+
+    # Should call _run_idedata since cache is corrupted
+    mock_run_platformio_cli_run.assert_called_once()
+
+    assert result["prog_path"] == "/new/firmware.elf"
+
+
+def test_run_idedata_parses_json_from_output(
+    setup_core: Path, mock_run_platformio_cli_run: Mock
+) -> None:
+    """Test _run_idedata extracts JSON from platformio output."""
+    config = {"name": "test"}
+
+    expected_data = {
+        "prog_path": "/path/to/firmware.elf",
+        "cc_path": "/path/to/gcc",
+        "extra": {"flash_images": []},
+    }
+
+    # Simulate platformio output with JSON embedded
+    mock_run_platformio_cli_run.return_value = (
+        f"Some preamble\n{json.dumps(expected_data)}\nSome postamble"
+    )
+
+    result = platformio_api._run_idedata(config)
+
+    assert result == expected_data
+
+
+def test_run_idedata_raises_on_no_json(
+    setup_core: Path, mock_run_platformio_cli_run: Mock
+) -> None:
+    """Test _run_idedata raises EsphomeError when no JSON found."""
+    config = {"name": "test"}
+
+    mock_run_platformio_cli_run.return_value = "No JSON in this output"
+
+    with pytest.raises(EsphomeError):
+        platformio_api._run_idedata(config)
+
+
+def test_run_idedata_raises_on_invalid_json(
+    setup_core: Path, mock_run_platformio_cli_run: Mock
+) -> None:
+    """Test _run_idedata raises on malformed JSON."""
+    config = {"name": "test"}
+    mock_run_platformio_cli_run.return_value = '{"invalid": json"}'
+
+    # The ValueError from json.loads is re-raised
+    with pytest.raises(ValueError):
+        platformio_api._run_idedata(config)
+
+
+def test_run_platformio_cli_sets_environment_variables(
+    setup_core: Path, mock_run_external_command: Mock
+) -> None:
+    """Test run_platformio_cli sets correct environment variables."""
+    CORE.build_path = str(setup_core / "build" / "test")
+
+    with patch.dict(os.environ, {}, clear=False):
+        mock_run_external_command.return_value = 0
+        platformio_api.run_platformio_cli("test", "arg")
+
+        # Check environment variables were set
+        assert os.environ["PLATFORMIO_FORCE_COLOR"] == "true"
+        assert (
+            setup_core / "build" / "test"
+            in Path(os.environ["PLATFORMIO_BUILD_DIR"]).parents
+            or Path(os.environ["PLATFORMIO_BUILD_DIR"]) == setup_core / "build" / "test"
+        )
+        assert "PLATFORMIO_LIBDEPS_DIR" in os.environ
+        assert "PYTHONWARNINGS" in os.environ
+
+        # Check command was called correctly
+        mock_run_external_command.assert_called_once()
+        args = mock_run_external_command.call_args[0]
+        assert "platformio" in args
+        assert "test" in args
+        assert "arg" in args
+
+
+def test_run_platformio_cli_run_builds_command(
+    setup_core: Path, mock_run_platformio_cli: Mock
+) -> None:
+    """Test run_platformio_cli_run builds correct command."""
+    CORE.build_path = str(setup_core / "build" / "test")
+    mock_run_platformio_cli.return_value = 0
+
+    config = {"name": "test"}
+    platformio_api.run_platformio_cli_run(config, True, "extra", "args")
+
+    mock_run_platformio_cli.assert_called_once_with(
+        "run", "-d", CORE.build_path, "-v", "extra", "args"
+    )
+
+
+def test_run_compile(setup_core: Path, mock_run_platformio_cli_run: Mock) -> None:
+    """Test run_compile with process limit."""
+    from esphome.const import CONF_COMPILE_PROCESS_LIMIT, CONF_ESPHOME
+
+    CORE.build_path = str(setup_core / "build" / "test")
+    config = {CONF_ESPHOME: {CONF_COMPILE_PROCESS_LIMIT: 4}}
+    mock_run_platformio_cli_run.return_value = 0
+
+    platformio_api.run_compile(config, verbose=True)
+
+    mock_run_platformio_cli_run.assert_called_once_with(config, True, "-j4")
+
+
+def test_get_idedata_caches_result(
+    setup_core: Path, mock_run_platformio_cli_run: Mock
+) -> None:
+    """Test get_idedata caches result in CORE.data."""
+    from esphome.const import KEY_CORE
+
+    CORE.build_path = str(setup_core / "build" / "test")
+    CORE.name = "test"
+    CORE.data[KEY_CORE] = {}
+
+    # Create platformio.ini to avoid regeneration
+    platformio_ini = setup_core / "build" / "test" / "platformio.ini"
+    platformio_ini.parent.mkdir(parents=True, exist_ok=True)
+    platformio_ini.write_text("content")
+
+    # Mock platformio to return data
+    idedata = {"prog_path": "/test/firmware.elf"}
+    mock_run_platformio_cli_run.return_value = json.dumps(idedata)
+
+    config = {"name": "test"}
+
+    # First call should load and cache
+    result1 = platformio_api.get_idedata(config)
+    mock_run_platformio_cli_run.assert_called_once()
+
+    # Second call should use cache from CORE.data
+    result2 = platformio_api.get_idedata(config)
+    mock_run_platformio_cli_run.assert_called_once()  # Still only called once
+
+    assert result1 is result2
+    assert isinstance(result1, platformio_api.IDEData)
+    assert result1.firmware_elf_path == "/test/firmware.elf"
+
+
+def test_idedata_addr2line_path_windows(setup_core: Path) -> None:
+    """Test IDEData.addr2line_path on Windows."""
+    raw_data = {"prog_path": "/path/to/firmware.elf", "cc_path": "C:\\tools\\gcc.exe"}
+    idedata = platformio_api.IDEData(raw_data)
+
+    result = idedata.addr2line_path
+    assert result == "C:\\tools\\addr2line.exe"
+
+
+def test_idedata_addr2line_path_unix(setup_core: Path) -> None:
+    """Test IDEData.addr2line_path on Unix."""
+    raw_data = {"prog_path": "/path/to/firmware.elf", "cc_path": "/usr/bin/gcc"}
+    idedata = platformio_api.IDEData(raw_data)
+
+    result = idedata.addr2line_path
+    assert result == "/usr/bin/addr2line"
+
+
+def test_patch_structhash(setup_core: Path) -> None:
+    """Test patch_structhash monkey patches platformio functions."""
+    # Create simple namespace objects to act as modules
+    mock_cli = SimpleNamespace()
+    mock_helpers = SimpleNamespace()
+    mock_run = SimpleNamespace(cli=mock_cli, helpers=mock_helpers)
+
+    # Mock platformio modules
+    with patch.dict(
+        "sys.modules",
+        {
+            "platformio.run.cli": mock_cli,
+            "platformio.run.helpers": mock_helpers,
+            "platformio.run": mock_run,
+            "platformio.project.helpers": MagicMock(),
+            "platformio.fs": MagicMock(),
+            "platformio": MagicMock(),
+        },
+    ):
+        # Call patch_structhash
+        platformio_api.patch_structhash()
+
+        # Verify both modules had clean_build_dir patched
+        # Check that clean_build_dir was set on both modules
+        assert hasattr(mock_cli, "clean_build_dir")
+        assert hasattr(mock_helpers, "clean_build_dir")
+
+        # Verify they got the same function assigned
+        assert mock_cli.clean_build_dir is mock_helpers.clean_build_dir
+
+        # Verify it's a real function (not a Mock)
+        assert callable(mock_cli.clean_build_dir)
+        assert mock_cli.clean_build_dir.__name__ == "patched_clean_build_dir"
+
+
+def test_patched_clean_build_dir_removes_outdated(setup_core: Path) -> None:
+    """Test patched_clean_build_dir removes build dir when platformio.ini is newer."""
+    build_dir = setup_core / "build"
+    build_dir.mkdir()
+    platformio_ini = setup_core / "platformio.ini"
+    platformio_ini.write_text("config")
+
+    # Make platformio.ini newer than build_dir
+    build_mtime = build_dir.stat().st_mtime
+    os.utime(platformio_ini, (build_mtime + 1, build_mtime + 1))
+
+    # Track if directory was removed
+    removed_paths: list[str] = []
+
+    def track_rmtree(path: str) -> None:
+        removed_paths.append(path)
+        shutil.rmtree(path)
+
+    # Create mock modules that patch_structhash expects
+    mock_cli = SimpleNamespace()
+    mock_helpers = SimpleNamespace()
+    mock_project_helpers = MagicMock()
+    mock_project_helpers.get_project_dir.return_value = str(setup_core)
+    mock_fs = SimpleNamespace(rmtree=track_rmtree)
+
+    with patch.dict(
+        "sys.modules",
+        {
+            "platformio": SimpleNamespace(fs=mock_fs),
+            "platformio.fs": mock_fs,
+            "platformio.project.helpers": mock_project_helpers,
+            "platformio.run": SimpleNamespace(cli=mock_cli, helpers=mock_helpers),
+            "platformio.run.cli": mock_cli,
+            "platformio.run.helpers": mock_helpers,
+        },
+    ):
+        # Call patch_structhash to install the patched function
+        platformio_api.patch_structhash()
+
+        # Call the patched function
+        mock_helpers.clean_build_dir(str(build_dir), [])
+
+        # Verify directory was removed and recreated
+        assert len(removed_paths) == 1
+        assert removed_paths[0] == str(build_dir)
+        assert build_dir.exists()  # makedirs recreated it
+
+
+def test_patched_clean_build_dir_keeps_updated(setup_core: Path) -> None:
+    """Test patched_clean_build_dir keeps build dir when it's up to date."""
+    build_dir = setup_core / "build"
+    build_dir.mkdir()
+    test_file = build_dir / "test.txt"
+    test_file.write_text("test content")
+
+    platformio_ini = setup_core / "platformio.ini"
+    platformio_ini.write_text("config")
+
+    # Make build_dir newer than platformio.ini
+    ini_mtime = platformio_ini.stat().st_mtime
+    os.utime(build_dir, (ini_mtime + 1, ini_mtime + 1))
+
+    # Track if rmtree is called
+    removed_paths: list[str] = []
+
+    def track_rmtree(path: str) -> None:
+        removed_paths.append(path)
+
+    # Create mock modules
+    mock_cli = SimpleNamespace()
+    mock_helpers = SimpleNamespace()
+    mock_project_helpers = MagicMock()
+    mock_project_helpers.get_project_dir.return_value = str(setup_core)
+    mock_fs = SimpleNamespace(rmtree=track_rmtree)
+
+    with patch.dict(
+        "sys.modules",
+        {
+            "platformio": SimpleNamespace(fs=mock_fs),
+            "platformio.fs": mock_fs,
+            "platformio.project.helpers": mock_project_helpers,
+            "platformio.run": SimpleNamespace(cli=mock_cli, helpers=mock_helpers),
+            "platformio.run.cli": mock_cli,
+            "platformio.run.helpers": mock_helpers,
+        },
+    ):
+        # Call patch_structhash to install the patched function
+        platformio_api.patch_structhash()
+
+        # Call the patched function
+        mock_helpers.clean_build_dir(str(build_dir), [])
+
+        # Verify rmtree was NOT called
+        assert len(removed_paths) == 0
+
+        # Verify directory and file still exist
+        assert build_dir.exists()
+        assert test_file.exists()
+        assert test_file.read_text() == "test content"
+
+
+def test_patched_clean_build_dir_creates_missing(setup_core: Path) -> None:
+    """Test patched_clean_build_dir creates build dir when it doesn't exist."""
+    build_dir = setup_core / "build"
+    platformio_ini = setup_core / "platformio.ini"
+    platformio_ini.write_text("config")
+
+    # Ensure build_dir doesn't exist
+    assert not build_dir.exists()
+
+    # Track if rmtree is called
+    removed_paths: list[str] = []
+
+    def track_rmtree(path: str) -> None:
+        removed_paths.append(path)
+
+    # Create mock modules
+    mock_cli = SimpleNamespace()
+    mock_helpers = SimpleNamespace()
+    mock_project_helpers = MagicMock()
+    mock_project_helpers.get_project_dir.return_value = str(setup_core)
+    mock_fs = SimpleNamespace(rmtree=track_rmtree)
+
+    with patch.dict(
+        "sys.modules",
+        {
+            "platformio": SimpleNamespace(fs=mock_fs),
+            "platformio.fs": mock_fs,
+            "platformio.project.helpers": mock_project_helpers,
+            "platformio.run": SimpleNamespace(cli=mock_cli, helpers=mock_helpers),
+            "platformio.run.cli": mock_cli,
+            "platformio.run.helpers": mock_helpers,
+        },
+    ):
+        # Call patch_structhash to install the patched function
+        platformio_api.patch_structhash()
+
+        # Call the patched function
+        mock_helpers.clean_build_dir(str(build_dir), [])
+
+        # Verify rmtree was NOT called
+        assert len(removed_paths) == 0
+
+        # Verify directory was created
+        assert build_dir.exists()
+
+
+def test_process_stacktrace_esp8266_exception(setup_core: Path, caplog) -> None:
+    """Test process_stacktrace handles ESP8266 exceptions."""
+    config = {"name": "test"}
+
+    # Test exception type parsing
+    line = "Exception (28):"
+    backtrace_state = False
+
+    result = platformio_api.process_stacktrace(config, line, backtrace_state)
+
+    assert "Access to invalid address: LOAD (wild pointer?)" in caplog.text
+    assert result is False
+
+
+def test_process_stacktrace_esp8266_backtrace(
+    setup_core: Path, mock_decode_pc: Mock
+) -> None:
+    """Test process_stacktrace handles ESP8266 multi-line backtrace."""
+    config = {"name": "test"}
+
+    # Start of backtrace
+    line1 = ">>>stack>>>"
+    state = platformio_api.process_stacktrace(config, line1, False)
+    assert state is True
+
+    # Backtrace content with addresses
+    line2 = "40201234 40205678"
+    state = platformio_api.process_stacktrace(config, line2, state)
+    assert state is True
+    assert mock_decode_pc.call_count == 2
+
+    # End of backtrace
+    line3 = "<<<stack<<<"
+    state = platformio_api.process_stacktrace(config, line3, state)
+    assert state is False
+
+
+def test_process_stacktrace_esp32_backtrace(
+    setup_core: Path, mock_decode_pc: Mock
+) -> None:
+    """Test process_stacktrace handles ESP32 single-line backtrace."""
+    config = {"name": "test"}
+
+    line = "Backtrace: 0x40081234:0x3ffb1234 0x40085678:0x3ffb5678"
+    state = platformio_api.process_stacktrace(config, line, False)
+
+    # Should decode both addresses
+    assert mock_decode_pc.call_count == 2
+    mock_decode_pc.assert_any_call(config, "40081234")
+    mock_decode_pc.assert_any_call(config, "40085678")
+    assert state is False
+
+
+def test_process_stacktrace_bad_alloc(
+    setup_core: Path, mock_decode_pc: Mock, caplog
+) -> None:
+    """Test process_stacktrace handles bad alloc messages."""
+    config = {"name": "test"}
+
+    line = "last failed alloc call: 40201234(512)"
+    state = platformio_api.process_stacktrace(config, line, False)
+
+    assert "Memory allocation of 512 bytes failed at 40201234" in caplog.text
+    mock_decode_pc.assert_called_once_with(config, "40201234")
+    assert state is False
diff --git a/tests/unit_tests/test_storage_json.py b/tests/unit_tests/test_storage_json.py
new file mode 100644
index 0000000000..e1abe565b1
--- /dev/null
+++ b/tests/unit_tests/test_storage_json.py
@@ -0,0 +1,660 @@
+"""Tests for storage_json.py path functions."""
+
+from datetime import datetime
+import json
+from pathlib import Path
+import sys
+from unittest.mock import MagicMock, Mock, patch
+
+import pytest
+
+from esphome import storage_json
+from esphome.const import CONF_DISABLED, CONF_MDNS
+from esphome.core import CORE
+
+
+def test_storage_path(setup_core: Path) -> None:
+    """Test storage_path returns correct path for current config."""
+    CORE.config_path = str(setup_core / "my_device.yaml")
+
+    result = storage_json.storage_path()
+
+    data_dir = Path(CORE.data_dir)
+    expected = str(data_dir / "storage" / "my_device.yaml.json")
+    assert result == expected
+
+
+def test_ext_storage_path(setup_core: Path) -> None:
+    """Test ext_storage_path returns correct path for given filename."""
+    result = storage_json.ext_storage_path("other_device.yaml")
+
+    data_dir = Path(CORE.data_dir)
+    expected = str(data_dir / "storage" / "other_device.yaml.json")
+    assert result == expected
+
+
+def test_ext_storage_path_handles_various_extensions(setup_core: Path) -> None:
+    """Test ext_storage_path works with different file extensions."""
+    result_yml = storage_json.ext_storage_path("device.yml")
+    assert result_yml.endswith("device.yml.json")
+
+    result_no_ext = storage_json.ext_storage_path("device")
+    assert result_no_ext.endswith("device.json")
+
+    result_path = storage_json.ext_storage_path("my/device.yaml")
+    assert result_path.endswith("device.yaml.json")
+
+
+def test_esphome_storage_path(setup_core: Path) -> None:
+    """Test esphome_storage_path returns correct path."""
+    result = storage_json.esphome_storage_path()
+
+    data_dir = Path(CORE.data_dir)
+    expected = str(data_dir / "esphome.json")
+    assert result == expected
+
+
+def test_ignored_devices_storage_path(setup_core: Path) -> None:
+    """Test ignored_devices_storage_path returns correct path."""
+    result = storage_json.ignored_devices_storage_path()
+
+    data_dir = Path(CORE.data_dir)
+    expected = str(data_dir / "ignored-devices.json")
+    assert result == expected
+
+
+def test_trash_storage_path(setup_core: Path) -> None:
+    """Test trash_storage_path returns correct path."""
+    CORE.config_path = str(setup_core / "configs" / "device.yaml")
+
+    result = storage_json.trash_storage_path()
+
+    expected = str(setup_core / "configs" / "trash")
+    assert result == expected
+
+
+def test_archive_storage_path(setup_core: Path) -> None:
+    """Test archive_storage_path returns correct path."""
+    CORE.config_path = str(setup_core / "configs" / "device.yaml")
+
+    result = storage_json.archive_storage_path()
+
+    expected = str(setup_core / "configs" / "archive")
+    assert result == expected
+
+
+def test_storage_path_with_subdirectory(setup_core: Path) -> None:
+    """Test storage paths work correctly when config is in subdirectory."""
+    subdir = setup_core / "configs" / "basement"
+    subdir.mkdir(parents=True, exist_ok=True)
+    CORE.config_path = str(subdir / "sensor.yaml")
+
+    result = storage_json.storage_path()
+
+    data_dir = Path(CORE.data_dir)
+    expected = str(data_dir / "storage" / "sensor.yaml.json")
+    assert result == expected
+
+
+def test_storage_json_firmware_bin_path_property(setup_core: Path) -> None:
+    """Test StorageJSON firmware_bin_path property."""
+    storage = storage_json.StorageJSON(
+        storage_version=1,
+        name="test_device",
+        friendly_name="Test Device",
+        comment=None,
+        esphome_version="2024.1.0",
+        src_version=None,
+        address="192.168.1.100",
+        web_port=80,
+        target_platform="ESP32",
+        build_path="build/test_device",
+        firmware_bin_path="/path/to/firmware.bin",
+        loaded_integrations={"wifi", "api"},
+        loaded_platforms=set(),
+        no_mdns=False,
+    )
+
+    assert storage.firmware_bin_path == "/path/to/firmware.bin"
+
+
+def test_storage_json_save_creates_directory(
+    setup_core: Path, tmp_path: Path, mock_write_file_if_changed: Mock
+) -> None:
+    """Test StorageJSON.save creates storage directory if it doesn't exist."""
+    storage_dir = tmp_path / "new_data" / "storage"
+    storage_file = storage_dir / "test.json"
+
+    assert not storage_dir.exists()
+
+    storage = storage_json.StorageJSON(
+        storage_version=1,
+        name="test",
+        friendly_name="Test",
+        comment=None,
+        esphome_version="2024.1.0",
+        src_version=None,
+        address="test.local",
+        web_port=None,
+        target_platform="ESP8266",
+        build_path=None,
+        firmware_bin_path=None,
+        loaded_integrations=set(),
+        loaded_platforms=set(),
+        no_mdns=False,
+    )
+
+    storage.save(str(storage_file))
+    mock_write_file_if_changed.assert_called_once()
+    call_args = mock_write_file_if_changed.call_args[0]
+    assert call_args[0] == str(storage_file)
+
+
+def test_storage_json_from_wizard(setup_core: Path) -> None:
+    """Test StorageJSON.from_wizard creates correct storage object."""
+    storage = storage_json.StorageJSON.from_wizard(
+        name="my_device",
+        friendly_name="My Device",
+        address="my_device.local",
+        platform="ESP32",
+    )
+
+    assert storage.name == "my_device"
+    assert storage.friendly_name == "My Device"
+    assert storage.address == "my_device.local"
+    assert storage.target_platform == "ESP32"
+    assert storage.build_path is None
+    assert storage.firmware_bin_path is None
+
+
+@pytest.mark.skipif(sys.platform == "win32", reason="HA addons don't run on Windows")
+@patch("esphome.core.is_ha_addon")
+def test_storage_paths_with_ha_addon(mock_is_ha_addon: bool, tmp_path: Path) -> None:
+    """Test storage paths when running as Home Assistant addon."""
+    mock_is_ha_addon.return_value = True
+
+    CORE.config_path = str(tmp_path / "test.yaml")
+
+    result = storage_json.storage_path()
+    # When is_ha_addon is True, CORE.data_dir returns "/data"
+    # This is the standard mount point for HA addon containers
+    expected = str(Path("/data") / "storage" / "test.yaml.json")
+    assert result == expected
+
+    result = storage_json.esphome_storage_path()
+    expected = str(Path("/data") / "esphome.json")
+    assert result == expected
+
+
+def test_storage_json_as_dict() -> None:
+    """Test StorageJSON.as_dict returns correct dictionary."""
+    storage = storage_json.StorageJSON(
+        storage_version=1,
+        name="test_device",
+        friendly_name="Test Device",
+        comment="Test comment",
+        esphome_version="2024.1.0",
+        src_version=1,
+        address="192.168.1.100",
+        web_port=80,
+        target_platform="ESP32",
+        build_path="/path/to/build",
+        firmware_bin_path="/path/to/firmware.bin",
+        loaded_integrations={"wifi", "api", "ota"},
+        loaded_platforms={"sensor", "binary_sensor"},
+        no_mdns=True,
+        framework="arduino",
+        core_platform="esp32",
+    )
+
+    result = storage.as_dict()
+
+    assert result["storage_version"] == 1
+    assert result["name"] == "test_device"
+    assert result["friendly_name"] == "Test Device"
+    assert result["comment"] == "Test comment"
+    assert result["esphome_version"] == "2024.1.0"
+    assert result["src_version"] == 1
+    assert result["address"] == "192.168.1.100"
+    assert result["web_port"] == 80
+    assert result["esp_platform"] == "ESP32"
+    assert result["build_path"] == "/path/to/build"
+    assert result["firmware_bin_path"] == "/path/to/firmware.bin"
+    assert "api" in result["loaded_integrations"]
+    assert "wifi" in result["loaded_integrations"]
+    assert "ota" in result["loaded_integrations"]
+    assert result["loaded_integrations"] == sorted(
+        ["wifi", "api", "ota"]
+    )  # Should be sorted
+    assert "sensor" in result["loaded_platforms"]
+    assert result["loaded_platforms"] == sorted(
+        ["sensor", "binary_sensor"]
+    )  # Should be sorted
+    assert result["no_mdns"] is True
+    assert result["framework"] == "arduino"
+    assert result["core_platform"] == "esp32"
+
+
+def test_storage_json_to_json() -> None:
+    """Test StorageJSON.to_json returns valid JSON string."""
+    storage = storage_json.StorageJSON(
+        storage_version=1,
+        name="test",
+        friendly_name="Test",
+        comment=None,
+        esphome_version="2024.1.0",
+        src_version=None,
+        address="test.local",
+        web_port=None,
+        target_platform="ESP8266",
+        build_path=None,
+        firmware_bin_path=None,
+        loaded_integrations=set(),
+        loaded_platforms=set(),
+        no_mdns=False,
+    )
+
+    json_str = storage.to_json()
+
+    # Should be valid JSON
+    parsed = json.loads(json_str)
+    assert parsed["name"] == "test"
+    assert parsed["storage_version"] == 1
+
+    # Should end with newline
+    assert json_str.endswith("\n")
+
+
+def test_storage_json_save(tmp_path: Path) -> None:
+    """Test StorageJSON.save writes file correctly."""
+    storage = storage_json.StorageJSON(
+        storage_version=1,
+        name="test",
+        friendly_name="Test",
+        comment=None,
+        esphome_version="2024.1.0",
+        src_version=None,
+        address="test.local",
+        web_port=None,
+        target_platform="ESP32",
+        build_path=None,
+        firmware_bin_path=None,
+        loaded_integrations=set(),
+        loaded_platforms=set(),
+        no_mdns=False,
+    )
+
+    save_path = tmp_path / "test.json"
+
+    with patch("esphome.storage_json.write_file_if_changed") as mock_write:
+        storage.save(str(save_path))
+        mock_write.assert_called_once_with(str(save_path), storage.to_json())
+
+
+def test_storage_json_from_esphome_core(setup_core: Path) -> None:
+    """Test StorageJSON.from_esphome_core creates correct storage object."""
+    # Mock CORE object
+    mock_core = MagicMock()
+    mock_core.name = "my_device"
+    mock_core.friendly_name = "My Device"
+    mock_core.comment = "A test device"
+    mock_core.address = "192.168.1.50"
+    mock_core.web_port = 8080
+    mock_core.target_platform = "esp32"
+    mock_core.is_esp32 = True
+    mock_core.build_path = "/build/my_device"
+    mock_core.firmware_bin = "/build/my_device/firmware.bin"
+    mock_core.loaded_integrations = {"wifi", "api"}
+    mock_core.loaded_platforms = {"sensor"}
+    mock_core.config = {CONF_MDNS: {CONF_DISABLED: True}}
+    mock_core.target_framework = "esp-idf"
+
+    with patch("esphome.components.esp32.get_esp32_variant") as mock_variant:
+        mock_variant.return_value = "ESP32-C3"
+
+        result = storage_json.StorageJSON.from_esphome_core(mock_core, old=None)
+
+    assert result.name == "my_device"
+    assert result.friendly_name == "My Device"
+    assert result.comment == "A test device"
+    assert result.address == "192.168.1.50"
+    assert result.web_port == 8080
+    assert result.target_platform == "ESP32-C3"
+    assert result.build_path == "/build/my_device"
+    assert result.firmware_bin_path == "/build/my_device/firmware.bin"
+    assert result.loaded_integrations == {"wifi", "api"}
+    assert result.loaded_platforms == {"sensor"}
+    assert result.no_mdns is True
+    assert result.framework == "esp-idf"
+    assert result.core_platform == "esp32"
+
+
+def test_storage_json_from_esphome_core_mdns_enabled(setup_core: Path) -> None:
+    """Test from_esphome_core with mDNS enabled."""
+    mock_core = MagicMock()
+    mock_core.name = "test"
+    mock_core.friendly_name = "Test"
+    mock_core.comment = None
+    mock_core.address = "test.local"
+    mock_core.web_port = None
+    mock_core.target_platform = "esp8266"
+    mock_core.is_esp32 = False
+    mock_core.build_path = "/build"
+    mock_core.firmware_bin = "/build/firmware.bin"
+    mock_core.loaded_integrations = set()
+    mock_core.loaded_platforms = set()
+    mock_core.config = {}  # No MDNS config means enabled
+    mock_core.target_framework = "arduino"
+
+    result = storage_json.StorageJSON.from_esphome_core(mock_core, old=None)
+
+    assert result.no_mdns is False
+
+
+def test_storage_json_load_valid_file(tmp_path: Path) -> None:
+    """Test StorageJSON.load with valid JSON file."""
+    storage_data = {
+        "storage_version": 1,
+        "name": "loaded_device",
+        "friendly_name": "Loaded Device",
+        "comment": "Loaded from file",
+        "esphome_version": "2024.1.0",
+        "src_version": 2,
+        "address": "10.0.0.1",
+        "web_port": 8080,
+        "esp_platform": "ESP32",
+        "build_path": "/loaded/build",
+        "firmware_bin_path": "/loaded/firmware.bin",
+        "loaded_integrations": ["wifi", "api"],
+        "loaded_platforms": ["sensor"],
+        "no_mdns": True,
+        "framework": "arduino",
+        "core_platform": "esp32",
+    }
+
+    file_path = tmp_path / "storage.json"
+    file_path.write_text(json.dumps(storage_data))
+
+    result = storage_json.StorageJSON.load(str(file_path))
+
+    assert result is not None
+    assert result.name == "loaded_device"
+    assert result.friendly_name == "Loaded Device"
+    assert result.comment == "Loaded from file"
+    assert result.esphome_version == "2024.1.0"
+    assert result.src_version == 2
+    assert result.address == "10.0.0.1"
+    assert result.web_port == 8080
+    assert result.target_platform == "ESP32"
+    assert result.build_path == "/loaded/build"
+    assert result.firmware_bin_path == "/loaded/firmware.bin"
+    assert result.loaded_integrations == {"wifi", "api"}
+    assert result.loaded_platforms == {"sensor"}
+    assert result.no_mdns is True
+    assert result.framework == "arduino"
+    assert result.core_platform == "esp32"
+
+
+def test_storage_json_load_invalid_file(tmp_path: Path) -> None:
+    """Test StorageJSON.load with invalid JSON file."""
+    file_path = tmp_path / "invalid.json"
+    file_path.write_text("not valid json{")
+
+    result = storage_json.StorageJSON.load(str(file_path))
+
+    assert result is None
+
+
+def test_storage_json_load_nonexistent_file() -> None:
+    """Test StorageJSON.load with non-existent file."""
+    result = storage_json.StorageJSON.load("/nonexistent/file.json")
+
+    assert result is None
+
+
+def test_storage_json_equality() -> None:
+    """Test StorageJSON equality comparison."""
+    storage1 = storage_json.StorageJSON(
+        storage_version=1,
+        name="test",
+        friendly_name="Test",
+        comment=None,
+        esphome_version="2024.1.0",
+        src_version=1,
+        address="test.local",
+        web_port=80,
+        target_platform="ESP32",
+        build_path="/build",
+        firmware_bin_path="/firmware.bin",
+        loaded_integrations={"wifi"},
+        loaded_platforms=set(),
+        no_mdns=False,
+    )
+
+    storage2 = storage_json.StorageJSON(
+        storage_version=1,
+        name="test",
+        friendly_name="Test",
+        comment=None,
+        esphome_version="2024.1.0",
+        src_version=1,
+        address="test.local",
+        web_port=80,
+        target_platform="ESP32",
+        build_path="/build",
+        firmware_bin_path="/firmware.bin",
+        loaded_integrations={"wifi"},
+        loaded_platforms=set(),
+        no_mdns=False,
+    )
+
+    storage3 = storage_json.StorageJSON(
+        storage_version=1,
+        name="different",  # Different name
+        friendly_name="Test",
+        comment=None,
+        esphome_version="2024.1.0",
+        src_version=1,
+        address="test.local",
+        web_port=80,
+        target_platform="ESP32",
+        build_path="/build",
+        firmware_bin_path="/firmware.bin",
+        loaded_integrations={"wifi"},
+        loaded_platforms=set(),
+        no_mdns=False,
+    )
+
+    assert storage1 == storage2
+    assert storage1 != storage3
+    assert storage1 != "not a storage object"
+
+
+def test_esphome_storage_json_as_dict() -> None:
+    """Test EsphomeStorageJSON.as_dict returns correct dictionary."""
+    storage = storage_json.EsphomeStorageJSON(
+        storage_version=1,
+        cookie_secret="secret123",
+        last_update_check="2024-01-15T10:30:00",
+        remote_version="2024.1.1",
+    )
+
+    result = storage.as_dict()
+
+    assert result["storage_version"] == 1
+    assert result["cookie_secret"] == "secret123"
+    assert result["last_update_check"] == "2024-01-15T10:30:00"
+    assert result["remote_version"] == "2024.1.1"
+
+
+def test_esphome_storage_json_last_update_check_property() -> None:
+    """Test EsphomeStorageJSON.last_update_check property."""
+    storage = storage_json.EsphomeStorageJSON(
+        storage_version=1,
+        cookie_secret="secret",
+        last_update_check="2024-01-15T10:30:00",
+        remote_version=None,
+    )
+
+    # Test getter
+    result = storage.last_update_check
+    assert isinstance(result, datetime)
+    assert result.year == 2024
+    assert result.month == 1
+    assert result.day == 15
+    assert result.hour == 10
+    assert result.minute == 30
+
+    # Test setter
+    new_date = datetime(2024, 2, 20, 15, 45, 30)
+    storage.last_update_check = new_date
+    assert storage.last_update_check_str == "2024-02-20T15:45:30"
+
+
+def test_esphome_storage_json_last_update_check_invalid() -> None:
+    """Test EsphomeStorageJSON.last_update_check with invalid date."""
+    storage = storage_json.EsphomeStorageJSON(
+        storage_version=1,
+        cookie_secret="secret",
+        last_update_check="invalid date",
+        remote_version=None,
+    )
+
+    result = storage.last_update_check
+    assert result is None
+
+
+def test_esphome_storage_json_to_json() -> None:
+    """Test EsphomeStorageJSON.to_json returns valid JSON string."""
+    storage = storage_json.EsphomeStorageJSON(
+        storage_version=1,
+        cookie_secret="mysecret",
+        last_update_check="2024-01-15T10:30:00",
+        remote_version="2024.1.1",
+    )
+
+    json_str = storage.to_json()
+
+    # Should be valid JSON
+    parsed = json.loads(json_str)
+    assert parsed["cookie_secret"] == "mysecret"
+    assert parsed["storage_version"] == 1
+
+    # Should end with newline
+    assert json_str.endswith("\n")
+
+
+def test_esphome_storage_json_save(tmp_path: Path) -> None:
+    """Test EsphomeStorageJSON.save writes file correctly."""
+    storage = storage_json.EsphomeStorageJSON(
+        storage_version=1,
+        cookie_secret="secret",
+        last_update_check=None,
+        remote_version=None,
+    )
+
+    save_path = tmp_path / "esphome.json"
+
+    with patch("esphome.storage_json.write_file_if_changed") as mock_write:
+        storage.save(str(save_path))
+        mock_write.assert_called_once_with(str(save_path), storage.to_json())
+
+
+def test_esphome_storage_json_load_valid_file(tmp_path: Path) -> None:
+    """Test EsphomeStorageJSON.load with valid JSON file."""
+    storage_data = {
+        "storage_version": 1,
+        "cookie_secret": "loaded_secret",
+        "last_update_check": "2024-01-20T14:30:00",
+        "remote_version": "2024.1.2",
+    }
+
+    file_path = tmp_path / "esphome.json"
+    file_path.write_text(json.dumps(storage_data))
+
+    result = storage_json.EsphomeStorageJSON.load(str(file_path))
+
+    assert result is not None
+    assert result.storage_version == 1
+    assert result.cookie_secret == "loaded_secret"
+    assert result.last_update_check_str == "2024-01-20T14:30:00"
+    assert result.remote_version == "2024.1.2"
+
+
+def test_esphome_storage_json_load_invalid_file(tmp_path: Path) -> None:
+    """Test EsphomeStorageJSON.load with invalid JSON file."""
+    file_path = tmp_path / "invalid.json"
+    file_path.write_text("not valid json{")
+
+    result = storage_json.EsphomeStorageJSON.load(str(file_path))
+
+    assert result is None
+
+
+def test_esphome_storage_json_load_nonexistent_file() -> None:
+    """Test EsphomeStorageJSON.load with non-existent file."""
+    result = storage_json.EsphomeStorageJSON.load("/nonexistent/file.json")
+
+    assert result is None
+
+
+def test_esphome_storage_json_get_default() -> None:
+    """Test EsphomeStorageJSON.get_default creates default storage."""
+    with patch("esphome.storage_json.os.urandom") as mock_urandom:
+        # Mock urandom to return predictable bytes
+        mock_urandom.return_value = b"test" * 16  # 64 bytes
+
+        result = storage_json.EsphomeStorageJSON.get_default()
+
+    assert result.storage_version == 1
+    assert len(result.cookie_secret) == 128  # 64 bytes hex = 128 chars
+    assert result.last_update_check is None
+    assert result.remote_version is None
+
+
+def test_esphome_storage_json_equality() -> None:
+    """Test EsphomeStorageJSON equality comparison."""
+    storage1 = storage_json.EsphomeStorageJSON(
+        storage_version=1,
+        cookie_secret="secret",
+        last_update_check="2024-01-15T10:30:00",
+        remote_version="2024.1.1",
+    )
+
+    storage2 = storage_json.EsphomeStorageJSON(
+        storage_version=1,
+        cookie_secret="secret",
+        last_update_check="2024-01-15T10:30:00",
+        remote_version="2024.1.1",
+    )
+
+    storage3 = storage_json.EsphomeStorageJSON(
+        storage_version=1,
+        cookie_secret="different",  # Different secret
+        last_update_check="2024-01-15T10:30:00",
+        remote_version="2024.1.1",
+    )
+
+    assert storage1 == storage2
+    assert storage1 != storage3
+    assert storage1 != "not a storage object"
+
+
+def test_storage_json_load_legacy_esphomeyaml_version(tmp_path: Path) -> None:
+    """Test loading storage with legacy esphomeyaml_version field."""
+    storage_data = {
+        "storage_version": 1,
+        "name": "legacy_device",
+        "friendly_name": "Legacy Device",
+        "esphomeyaml_version": "1.14.0",  # Legacy field name
+        "address": "legacy.local",
+        "esp_platform": "ESP8266",
+    }
+
+    file_path = tmp_path / "legacy.json"
+    file_path.write_text(json.dumps(storage_data))
+
+    result = storage_json.StorageJSON.load(str(file_path))
+
+    assert result is not None
+    assert result.esphome_version == "1.14.0"  # Should map to esphome_version