pluriwave/openspec/changes/archive/2026-07-19-android-auto-eq-presets/proposal.md

Proposal: Android Auto EQ preset selection

Intent

Drivers cannot change the audio equalizer while on Android Auto — EQ selection is phone-UI only today. Expose the 6 fixed presets as a browsable folder in the existing Auto media tree so a preset can be applied from the car, without reaching for the phone and without interrupting the current station.

Scope

In Scope

• New top-level browsable Ecualizador folder in ConstructorArbolAuto.raiz(), listing the 6 fixed PresetEcualizador.presets by name.
• New media-id scheme eq_preset:<nombre>, intercepted in playFromMediaId BEFORE the emisora:/grupo: routing.
• Tapping a preset applies it through the existing headless-safe EQ seam and persists it as the principal preset (phone/car parity), with NO call to playMediaItem and NO mediaItem mutation.
• Strict-TDD tests: tree shape, eq_preset: id resolution, and the "preset tap does not disturb playback / now-playing" invariant.
• Optional (lower priority): mark the active preset in its row title (see Risks — no native selection UI exists in this model).

Out of Scope

• Custom band-level EQ editing or arbitrary EQ from the car (media-browser capability ceiling; stays phone-only).
• Per-station / per-device / matrix EQ writes from the car (global principal only).
• Custom transport-button EQ actions (button real-estate fits ~1-2 slots, not 6 named presets).
• Favorite-groups browse work (separate, already-shipped android-auto-favorite-groups).

Capabilities

New Capabilities

• None

Modified Capabilities

• android-auto-media: the browse tree gains an Ecualizador root folder plus an eq_preset: selection action that applies an EQ preset without starting or altering playback.

Approach

Mirror the proven emisora:/grupo: interception pattern already in navegacion_auto.dart + servicio_audio.dart. Preset rows are playable: true (the only tappable non-folder item type in the legacy MediaBrowserService model) and therefore route through playFromMediaId; a new eq_preset: branch resolves the preset by name and calls the EQ apply seam instead of the audio player. Reuse the phone's global-preset semantics (apply via PluriWaveAudioHandler.aplicarPreset + persist via ServicioEcualizador.guardarPrincipal, matching cambiarPresetPrincipal) so phone and car stay in sync. The write path MUST be headless-safe (handler + service, NOT the widget-tree EstadoEcualizador, which may never build on an Auto bind).

Affected Areas

Area	Impact	Description
lib/servicios/navegacion_auto.dart	Modified	Add Ecualizador root folder, eq_preset: id scheme, preset-row builder, resolver + selection routing helper
lib/servicios/servicio_audio.dart	Modified	Branch playFromMediaId on eq_preset: to the apply/persist seam before emisora:/grupo:
lib/modelos/preset_ecualizador.dart	Read-only	Source of the 6 fixed presets (name is the id key)
lib/servicios/servicio_ecualizador.dart	Read-only reuse	guardarPrincipal persistence seam (headless-safe)
openspec/specs/android-auto-media/spec.md	Delta only	Modified-capability delta in this change folder; base spec untouched

Risks

Risk	Likelihood	Mitigation
Preset tap looks like "now playing a new track" (playable item)	Med	Never call playMediaItem, never mutate mediaItem; dedicated eq_preset: branch + invariant test
Shared-file merge drift with just-shipped favorite-groups	Med	Read CURRENT post-f368bcc/066fedb state; add branch alongside existing grupo:/emisora: dispatch
No native "selected" UI for browsable rows	High	Active-preset marker only via title text (prefix); ship as optional, be explicit it is not a real checkmark
Persist path unavailable on headless Auto bind	Med	Route through service + handler (SharedPreferences), not EstadoEcualizador

Rollback Plan

Additive only — revert the feature commits. No schema/migration changes: removing the Ecualizador folder and the eq_preset: branch restores the exact prior tree (favorite-groups behavior unaffected).

Dependencies

• Sequenced after android-auto-favorite-groups (now on main) to avoid conflicts in the two shared files.

Success Criteria

• Ecualizador folder appears at the Auto root with all 6 presets by name.
• Tapping a preset applies it (native EQ gains change) and persists as principal.
• Current station playback / now-playing metadata is unchanged by a preset tap.
• Selecting a preset in the car is reflected in the phone EQ UI and vice versa.
• Unknown/stale eq_preset: id is a no-op (no throw).