# Proposal: EQ Device Disconnect / Cold-Start Revert

## Intent

When an audio device disconnects — or the app opens with no external device connected — the EQ must return to the phone/base configuration, not stay on a stale device preset. Today `_onDispositivoCambiado()` (`estado_ecualizador.dart:210-227`) treats every device event identically: there is no explicit disconnect path, no cold-start guarantee, and ZERO disconnect test coverage. On disconnect it re-resolves the hierarchy for the now-active device, which only *coincidentally* looks like a revert when no station/matrix override interferes. This closes a correctness gap, not a regression.

## Scope

### In Scope
- Explicit disconnect handling: re-resolve + APPLY the preset for the now-active device (typically `builtin_speaker`).
- Cold-start guarantee: app open with no device connected applies the phone/base resolution, never a stale persisted device preset.
- Verify the resolved preset reaches the native EQ via the existing `audio.aplicarPreset()` choke-point (not state-only mutation).
- Test coverage: disconnect event, cold start without device, connect→disconnect→reconnect cycle, station/matrix override interaction.
- Respect `_eqMultiDeviceEnabled`: when OFF, behavior is unchanged (2-level resolution).

### Out of Scope
- Audio-focus ducking EQ re-apply (separate change `eq-audiofocus-reapply`, Part B).
- Native Kotlin/Swift device detection (`MainActivity.kt`, `pluriwave/audio_devices`) — already emits add/remove correctly.
- New persistence fields or migration; matrix/station/device preset storage is unchanged.

## Capabilities

### New Capabilities
- None.

### Modified Capabilities
- `multi-device-eq`: revert-on-disconnect and cold-start resolution become explicit, guaranteed requirements. "Revert" = deterministic re-resolution of the existing 4-level hierarchy (matrix → station → device → global) for the now-active device — NOT a snapshot/restore. This is stateless, self-healing, and the only mechanism covering the cold-start case (no snapshot exists to restore).

## Approach

Make the disconnect path explicit inside the device-event handler (`_onDispositivoCambiado`, or a split connect/disconnect dispatch). On any device event — connect, disconnect, or cold-start seed — set `_dispositivoActualId` to the now-active device, run `_resolverPresetActivo()`, assign `_presetActual`, and push it through `audio.aplicarPreset()`. Cold start already flows through `_sembrarDispositivoActual()` → `obtenerDispositivoActual()` (fallback `builtin_speaker`); the change guarantees the resolved base preset is APPLIED on that path, not just seeded. The first-seen bootstrap (`presetsDispositivo` write) must NOT hijack revert resolution for the base device.

## Affected Areas

| Area | Impact | Description |
|------|--------|-------------|
| `lib/estado/estado_ecualizador.dart` | Modified | Explicit disconnect/cold-start resolve+apply in the device handler |
| `test/estado/estado_ecualizador_test.dart` | Modified | New disconnect, cold-start, reconnect-cycle, override-matrix cases |

## Risks

| Risk | Likelihood | Mitigation |
|------|------------|------------|
| Regress passing connect/4-level suite (Phase 5, tests 5.1–5.8, 2.x) | Med | Reuse `_resolverPresetActivo()`; run full `estado_ecualizador_test.dart` green before/after |
| First-seen bootstrap overwrites base on disconnect | Med | Guard bootstrap so revert to `builtin_speaker` resolves from hierarchy, not a forced copy |
| Double-apply / redundant native pushes on rapid events | Low | Idempotent apply choke-point; skip when resolved preset unchanged |

## Rollback Plan

Single-file logic change plus tests. Revert the commit(s) touching `estado_ecualizador.dart` and its test file; no persistence schema, native, or public-API change means rollback restores the prior coincidental-revert behavior with zero migration.

## Dependencies

- Shared exploration `sdd/eq-apply-lifecycle/explore` (Part A section). Locked decision: re-resolution, not snapshot/restore.

## Success Criteria

- [ ] Disconnect event re-resolves and applies the base-device preset via `aplicarPreset()`.
- [ ] Cold start with no device applies phone/base resolution, not a stale device preset.
- [ ] connect→disconnect→reconnect cycle lands on the correct preset at each step, including station/matrix overrides.
- [ ] With `_eqMultiDeviceEnabled=false`, behavior is byte-for-byte unchanged (2-level).
- [ ] Full `estado_ecualizador_test.dart` suite stays green (no connect-path regression).