[core] Add preference key stability integration test (#18364)

tests/integration/fixtures/preference_key_stability.yaml

@@ -0,0 +1,35 @@
+esphome:
+  name: host-pref-key-stability
+
+host:
+api:
+logger:
+
+switch:
+  - platform: template
+    id: test_switch_restore
+    name: Test Switch
+    optimistic: true
+    restore_mode: RESTORE_DEFAULT_OFF
+
+number:
+  - platform: template
+    id: test_number_restore
+    name: Test Number
+    optimistic: true
+    restore_value: true
+    initial_value: 1.0
+    min_value: 0
+    max_value: 100
+    step: 0.5
+
+text:
+  - platform: template
+    id: test_text_restore
+    name: Test Text
+    mode: text
+    optimistic: true
+    restore_value: true
+    initial_value: fallback
+    min_length: 0
+    max_length: 20

tests/integration/host_prefs.py

@@ -25,15 +25,25 @@ def clear_host_prefs(device_name: str) -> None:
     host_prefs_path(device_name).unlink(missing_ok=True)
 
 
+def write_host_prefs(device_name: str, entries: dict[int, bytes]) -> Path:
+    """Write preference entries, replacing the file's contents.
+
+    Returns the path that was written.
+    """
+    payload = b""
+    for key, data in entries.items():
+        if len(data) > 255:
+            raise ValueError(f"Preference data too long: {len(data)} bytes (max 255)")
+        payload += struct.pack("<IB", key, len(data)) + data
+    path = host_prefs_path(device_name)
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.write_bytes(payload)
+    return path
+
+
 def write_host_pref(device_name: str, key: int, data: bytes) -> Path:
     """Write a single preference entry, replacing the file's contents.
 
     Returns the path that was written.
     """
-    if len(data) > 255:
-        raise ValueError(f"Preference data too long: {len(data)} bytes (max 255)")
-    path = host_prefs_path(device_name)
-    path.parent.mkdir(parents=True, exist_ok=True)
-    payload = struct.pack("<IB", key, len(data)) + data
-    path.write_bytes(payload)
-    return path
+    return write_host_prefs(device_name, {key: data})

tests/integration/test_preference_key_stability.py

@@ -0,0 +1,168 @@
+"""Integration test for entity preference key stability.
+
+Entity preferences are stored under keys derived from the sanitized object_id
+hash. This test seeds the host preferences file the way existing firmware
+wrote it and verifies the state is restored, proving the key scheme has not
+drifted; a save and reload round trip cannot catch drift because it writes
+and reads with the same code.
+
+The second run also seeds the raw-name-hash entries a 2026.8 beta device left
+behind (see https://github.com/esphome/esphome/pull/18361) and proves they are
+ignored: the object_id entries win and the beta leftovers are inert.
+"""
+
+from __future__ import annotations
+
+import socket
+import struct
+
+from aioesphomeapi import (
+    NumberInfo,
+    NumberState,
+    SwitchInfo,
+    SwitchState,
+    TextInfo,
+    TextState,
+)
+import pytest
+
+from esphome.helpers import fnv1_hash, fnv1_hash_name, fnv1_hash_object_id
+
+from .conftest import run_binary_and_wait_for_port, wait_and_connect_api_client
+from .host_prefs import clear_host_prefs, write_host_prefs
+from .state_utils import InitialStateHelper, require_entity
+from .types import CompileFunction, ConfigWriter
+
+DEVICE_NAME = "host-pref-key-stability"
+
+# All entities are on the main device (device_id 0) and their preferences use
+# no version salt, so the key is just the object_id hash.
+SWITCH_KEY = fnv1_hash_object_id("Test Switch")
+NUMBER_KEY = fnv1_hash_object_id("Test Number")
+
+# Raw-name-hash keys as written by 2026.8 beta firmware; never read by this build
+SWITCH_BETA_KEY = fnv1_hash_name("Test Switch")
+NUMBER_BETA_KEY = fnv1_hash_name("Test Number")
+
+# template_text salts its key with the length limits and pattern hash; this must
+# match TemplateText::setup() in template_text.cpp (min_length 0, max_length 20,
+# no pattern configured)
+TEXT_KEY_EXTRA = (0 << 2) + (20 << 4) + (fnv1_hash("") << 6)
+TEXT_KEY = (fnv1_hash_object_id("Test Text") + TEXT_KEY_EXTRA) & 0xFFFFFFFF
+TEXT_BETA_KEY = (fnv1_hash_name("Test Text") + TEXT_KEY_EXTRA) & 0xFFFFFFFF
+
+# TextSaver<20> stores a length-prefixed buffer of max_length + 1 bytes
+TEXT_MAX_LENGTH = 20
+
+
+def text_pref_payload(value: str) -> bytes:
+    """Build the length-prefixed buffer TextSaver stores for a value."""
+    data = value.encode("utf-8")
+    assert len(data) <= TEXT_MAX_LENGTH
+    return bytes([len(data)]) + data + b"\x00" * (TEXT_MAX_LENGTH - len(data))
+
+
+@pytest.mark.asyncio
+async def test_preference_key_stability(
+    yaml_config: str,
+    write_yaml_config: ConfigWriter,
+    compile_esphome: CompileFunction,
+    reserved_tcp_port: tuple[int, socket.socket],
+) -> None:
+    """Test that preferences stored by earlier firmware are restored."""
+    port, port_socket = reserved_tcp_port
+
+    assert SWITCH_KEY != SWITCH_BETA_KEY
+    assert NUMBER_KEY != NUMBER_BETA_KEY
+    assert TEXT_KEY != TEXT_BETA_KEY
+
+    # Write and compile once
+    config_path = await write_yaml_config(yaml_config)
+    binary_path = await compile_esphome(config_path)
+
+    # Release the reserved port so the binary can bind to it
+    port_socket.close()
+
+    async def boot_and_get_initial_states() -> tuple[
+        SwitchState, NumberState, TextState
+    ]:
+        """Boot the binary and return the restored entity states."""
+        async with (
+            run_binary_and_wait_for_port(binary_path, "127.0.0.1", port),
+            wait_and_connect_api_client(port=port) as client,
+        ):
+            device_info = await client.device_info()
+            assert device_info.name == DEVICE_NAME
+
+            entities, _ = await client.list_entities_services()
+            switch_entity = require_entity(
+                entities, "test_switch", SwitchInfo, "Test Switch"
+            )
+            number_entity = require_entity(
+                entities, "test_number", NumberInfo, "Test Number"
+            )
+            text_entity = require_entity(entities, "test_text", TextInfo, "Test Text")
+
+            initial_state_helper = InitialStateHelper(entities)
+            client.subscribe_states(
+                initial_state_helper.on_state_wrapper(lambda s: None)
+            )
+            await initial_state_helper.wait_for_initial_states()
+
+            switch_state = initial_state_helper.initial_states[switch_entity.key]
+            number_state = initial_state_helper.initial_states[number_entity.key]
+            text_state = initial_state_helper.initial_states[text_entity.key]
+            assert isinstance(switch_state, SwitchState)
+            assert isinstance(number_state, NumberState)
+            assert isinstance(text_state, TextState)
+            return switch_state, number_state, text_state
+
+    try:
+        # --- Run 1: entries under the object_id-hash keys, exactly as any
+        # earlier firmware wrote them. The restored states prove the key
+        # scheme has not drifted.
+        write_host_prefs(
+            DEVICE_NAME,
+            {
+                SWITCH_KEY: b"\x01",  # bool: switch was ON
+                NUMBER_KEY: struct.pack("<f", 42.5),
+                TEXT_KEY: text_pref_payload("hello"),
+            },
+        )
+        switch_state, number_state, text_state = await boot_and_get_initial_states()
+        assert switch_state.state is True, (
+            "Switch state stored under the object_id preference key was lost"
+        )
+        assert number_state.state == 42.5, (
+            "Number value stored under the object_id preference key was lost"
+        )
+        assert text_state.state == "hello", (
+            "Text value stored under the object_id preference key was lost"
+        )
+
+        # --- Run 2: raw-name-hash entries from a 2026.8 beta device present
+        # alongside the object_id entries. The object_id data must win; the
+        # beta entries are never read.
+        write_host_prefs(
+            DEVICE_NAME,
+            {
+                SWITCH_KEY: b"\x01",  # current: ON
+                SWITCH_BETA_KEY: b"\x00",  # beta leftover: OFF
+                NUMBER_KEY: struct.pack("<f", 13.5),  # current
+                NUMBER_BETA_KEY: struct.pack("<f", 99.5),  # beta leftover
+                TEXT_KEY: text_pref_payload("world"),  # current
+                TEXT_BETA_KEY: text_pref_payload("ignored"),  # beta leftover
+            },
+        )
+        switch_state, number_state, text_state = await boot_and_get_initial_states()
+        assert switch_state.state is True, (
+            "Beta raw-name-key data overrode the object_id switch state"
+        )
+        assert number_state.state == 13.5, (
+            "Beta raw-name-key data overrode the object_id number value"
+        )
+        assert text_state.state == "world", (
+            "Beta raw-name-key data overrode the object_id text value"
+        )
+    finally:
+        clear_host_prefs(DEVICE_NAME)