paseo/docs/mobile-panels.md

Mobile panels

Compact layouts have three mutually exclusive destinations:

• agent-list on the left
• agent in the center
• file-explorer on the right

They are one interaction, not two independent drawers. The implementation lives in packages/app/src/mobile-panels/.

Ownership

React/Zustand owns the durable intent:

interface MobilePanelSelection {
  target: "agent-list" | "agent" | "file-explorer";
  revision: number;
}

Every semantic target change increments revision. Repeating the current target is idempotent. Compact panel selection is not persisted; a cold start begins at agent.

The UI worklet owns transient motion:

• one normalized position (-1 left, 0 center, 1 right)
• the current motion target
• the active gesture's starting revision
• the last settled target

React also owns presentation lifecycle: whether an overlay is mounted/displayed and whether it may receive pointer events. Worklets never own display or pointerEvents.

Why one position

Both transforms and both backdrop opacities are derived from the same normalized position. Window width is only a projection input. Rotation changes the projection, not the panel state.

This makes these invalid states unrepresentable:

• a panel and its backdrop disagreeing
• left and right drawers both claiming to be open
• a width-sync effect resetting an active drag
• one animation context settling a transition owned by the other

Do not add another panel translate shared value, backdrop shared value, or width synchronization effect.

Ordering and interruption

A gesture captures the current revision when it becomes active. Per-frame updates are accepted only while that revision still owns the gesture.

When a React command arrives during a drag, its newer revision clears gesture ownership and starts motion toward the new target. The older gesture's remaining updates and finish callback are ignored. Canceled gestures return to the latest canonical target. Animation completion is accepted only when its target and revision still match the canonical command.

Manual gesture arbitration has two phases:

1. Before activation, determine whether horizontal intent may begin.
2. After activation, stop running begin checks and let the active revision own updates.

Re-running the begin gate after activation self-cancels the gesture because an active gesture is, by definition, no longer eligible to begin.

Integration rules

• Callers request semantic targets through panel-store; they never write shared values.
• Gesture behavior comes from the four explicit hooks in mobile-panels/gestures.ts.
• Keep SidebarModelProvider outside MobileGestureWrapper. The provider shares sidebar derivation across consumers, while Gesture Handler requires the wrapper's direct child to be a native View so its injected collapsable={false} reaches Android/Fabric.
• Mobile sidebars render through MobilePanelOverlay; do not duplicate overlay lifecycle or motion styles in sidebar components.
• Animated panel nodes use React Native static styles plus inline theme values. Do not attach Unistyles-generated styles to those nodes; Unistyles and Reanimated patching the same Fabric node has caused native crashes.
• The plain React wrapper owns display: none after settlement. This prevents a stale Fabric animated prop commit from resurrecting a closed overlay.

Tests

packages/app/src/mobile-panels/model.test.ts exercises command, drag, cancellation, interruption, rapid-command, stale-completion, and width-projection sequences through the transition model. Add a sequence there whenever ownership or ordering changes.