Spec: System Bar (MVP)

Implementable contract for v0.1 System Bar. Overview narrative: system-bars.md. Scope freeze: mvp.md.

Purpose

Persistent wayfinding chrome: slotted entries with large targets, stable positions, and restriction-aware activation.

Anatomy

┌──────────────────────────────────────────────────────────┐
│ [leading slots…]     [center slots…]     [trailing…]     │
└──────────────────────────────────────────────────────────┘

Region	Typical entries
Leading	Home / map
Center	Optional OEM mark or HVAC/media peek
Trailing	App grid / notifications (gated)

Slots are data-driven — OEMs configure without forking the widget (extension model).

States

State	Behavior
Default	All configured slots visible per policy
Restricted / Moving	Complex entries Substitute or Block per restriction-states
Day / Night	Token schemes
Focused	Rotary/DPAD focus ring from tokens
Disabled item	Visible, non-activatable (when Substitute/Disable)

Sizes & type (from tokens)

Token (stub)	Role
cabin.component.systemBar.height	Bar height
cabin.component.systemBar.iconSize	Icons
cabin.component.systemBar.itemMinSize	Touch minimum
cabin.component.systemBar.gap	Inter-item gap
cabin.type.role.label	Optional short labels
cabin.color.scheme.*.container / onContainer	Bar chrome fill + content
cabin.color.scheme.*.outline	Separators / unselected chrome
cabin.color.scheme.*.surface / onSurface	Surrounding surface roles

Stub file: tokens/cabin.tokens.json. Day/night schemes also carry locked warning / error / charging for adjacent Status chrome — see token-schema.

Compliance gates

Interaction	Gating
NavigateSimple	Allow in Moving/Restricted
MediaTransport / HvacPeek	Allow (limited); no deep setup
OpenComplexApp / OpenKeyboard / FilterOrSort	Block or Substitute while Moving/Restricted

Safety class: Convenience chrome — do not bury safety-critical controls exclusively here.

Missing CabinComplianceHost is fail-closed (GateDisposition.Block) for activating slot entries.

Planned Views API (MVP primary)

class CabinSystemBarView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
) : ViewGroup(context, attrs) {
    fun setSlots(slots: CabinSystemBarSlots) { /* … */ }
    fun setCompliance(host: CabinComplianceHost) { /* … */ }
}

Alpha implementation: dev.decoupled.cabin.views.CabinSystemBarView in cabin-views / CabinViews.

Compose API (Experimental parity)

@Composable
fun CabinSystemBar(
    slots: CabinSystemBarSlots,
    modifier: Modifier = Modifier,
)

Experimental implementation: dev.decoupled.cabin.compose.CabinSystemBar in cabin-compose / CabinCompose. Same Restriction Engine gates and token roles as Views; wrap with CabinTheme. Not for SystemUI Soong adoption.

Acceptance criteria (MVP)

• Slot configuration without core fork
• Matrix behavior matches restriction-states for System Bar
• Touch minima from tokens
• Day/night via Theme Kit
• Content descriptions on icon-only entries
• No dependency on cabin-compose

Related

• Status Bar spec
• Views
• Compose (Experimental parity)
• Build-tree