Add Entity lifecycle hook async_prepare_to_add_to_hass

[emontnemery]

Proposal

Add entity lifecycle hook Entity.async_prepare_to_add_to_hass

A draft implementation of the proposal can be found in home-assistant/core#182156

Rationale:

Some integrations need to do work before an entity is added. They currently accomplish that by overriding the method
Entity.add_to_platform_start which integrations are not meant to override.

Background

There are a handful of cases where integration override Entity.add_to_platform_xxx methods. Those methods are not meant for entities to override, and the fact that they do that means that when we change how the EntityPlatform helper interacts with entities we risk breaking integrations which rely on undocumented implementation details.

A full assessment of core and HACS custom integrations show the following cases of integrations overriding Entity.add_to_platform_xxx methods.

Core

Integration: device_tracker (ScannerEntity)
Method(s): add_to_platform_start
Why it overrides: Register MAC unconditionally so a disabled tracker can be auto-enabled
(disabled entities abort before finish)
Refactor verdict: Needs before-add hook (async_before_added_to_hass) - no clean domain/platform-level alternative
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Integration: energy (EnergyCostSensor, EnergyPowerSensor)
Method(s): add_to_platform_abort
Why it overrides: Resolve the add_finished future on abort so SensorManager doesn't deadlock
Refactor verdict: Refactorable → async_on_remove
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Integration: mqtt (MqttDiscoveryUpdateMixin)
Method(s): add_to_platform_finish + add_to_platform_abort
Why it overrides: finish: signal discovery-DONE after the initial state write; abort: release
pending discovery + clear hash
Refactor verdict: Refactorable, DONE ack moved caller-side; abort →
async_on_remove
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Integration: sensor (SensorEntity)
Method(s): add_to_platform_start
Why it overrides: Prime unit-of-measurement registry options before async_get_or_create reads
them
Refactor verdict: Needs before-add hook (async_before_added_to_hass) - genuinely
pre-registration
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Integration: tasmota (TasmotaDiscoveryUpdate)
Method(s): add_to_platform_abort
Why it overrides: Clear the producer-registered discovery hash on the abort path
(async_will_remove_from_hass isn't called there)
Refactor verdict: Refactorable → async_on_remove

Custom (forks of core integrations excluded)

Integration: evcc_intg (marq24)
Method(s): add_to_platform_finish
Why it overrides: Inject runtime vehicle-name select-option labels into the translation cache
Refactor verdict: Refactorable onto async_added_to_hass; real gap is a dynamic-translation API
(non-lifecycle)
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Integration: fordpass (marq24)
Method(s): add_to_platform_finish
Why it overrides: Inject unit-dependent (°C/°F) select-option labels into the translation
cache
Refactor verdict: Same as evcc - async_added_to_hass + dynamic-translation API
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Integration: illuminance
Method(s): add_to_platform_start
Why it overrides: Set per-config-entry poll interval + seed divisor before update_before_add's
first update
Refactor verdict: Refactorable, NO new hook - self-poll (async_track_time_interval) + drop
update_before_add; seed/listener in async_added_to_hass
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Integration: ShellyForHASS (StyraHem)
Method(s): add_to_platform_abort
Why it overrides: Unsubscribe a pyShelly observer on abort
Refactor verdict: Redundant → delete - already registers async_on_remove (base runs it on
abort since HA 2022.5)
────────────────────────────────────────
Integration: uniled (monty68)
Method(s): add_to_platform_start
Why it overrides: Nothing - pure super() pass-through
Refactor verdict: Dead code → delete

[emontnemery]

Approved by the core architecture meeting 2026-09-17