Pin. Remove. Pause.

Problem and state coverage. Recently Played reorders by recency. A song the user wants to keep within reach disappears as new plays push it down. The shelf needs a way to lock a favorite in place. The new Pin state machine covers seven moments—default, hover, press, pinned, disabled (cap reached), loading, error—each with two independent signals so the affordance never reads as ambiguous.

Feedback and the cap. Move first, confirm second. The tile animates to position one in 250 ms; the Pinned. Undo snackbar follows for five seconds; a persistent Pin chip stays on the tile after the snackbar dismisses. The cap is four pins, with a disabled fifth row rather than a soft limit and a warning toast. Engineering surfaced shelf-performance and ranking-signal degradation past four; four is also the cognitive ceiling for what a user can re-find by sight. Drag-to-reorder among pins, deliberately cut.

Persona impact. Ranger Dave on his commute is the primary beneficiary. Pin keeps his focus playlist within one tap regardless of what he plays after. Parent is neutral—Pin on a shared device is rarely worth doing. Explorer is neutral to negative; heavy browsing means the shelf turns over quickly and four pins barely scratch the volume.

Problem and state coverage. An accidental tap, a short preview, a one-off experiment lingers on the shelf and misrepresents what the user cares about. They need a way to clean it up before someone sees. The Remove state machine handles default, hover, press, the successful remove, the active toast, sync conflicts, and the restored state after Undo. Single-item rows and multi-item rows handled distinctly.

Feedback and scope. Slide first, undo second. The tile slides out in 220 ms; the Removed. Undo snackbar runs for five seconds; on undo, the item returns to its last position rather than the front. Scope is per-device, not per-account. Privacy lives at the device boundary. The cost is friction for multi-device users; the benefit is that the shelf can’t betray a user’s intent on Device A by changing on Device B.

Persona impact. Melodic Melanie, the primary beneficiary, can clear contextual plays before she shares her screen. Ranger Dave is positive on the shared-device case. Explorer is neutral—the shelf already turns over fast for them.

Problem and state coverage. A borrowed phone, a long drive with a guest, an overnight kid takeover. The user has no way to stop the shelf from logging without leaving the app or signing out. The Pause state machine surfaces the timer in every state—default, hover, press, paused, expiring, resumed, clock-skew error—because the timer is the design’s promise.

Feedback and the time-box. Three presets, no slider. The duration picker offers 30 minutes, 2 hours, or until tomorrow. The shelf shows the paused state with a countdown; a snackbar confirms when listening history resumes. The control is time-boxed only, not a permanent toggle. Permanent pause was ruled out because the ML signal would degrade. The cost: a user who really wants to opt out has to re-pause periodically, or use Settings · Privacy.

Persona impact. Parent is the primary beneficiary: Pause protects recommendations during somebody else’s listening session. Melodic Melanie is positive on the social case. Ranger Dave is positive on shared devices when his son’s music threatens to take over the shelf.