yellowjacket/.planning/plans/active/019-android-touch-model.md

019 — The Android touch model

Issue: #63 (Area/Library-UI, Kind/Feature, Priority/High) Depends on: #60 (bottom-sheet menus) — closed, merged as PR #176 Relates: #67 (inline links into the menu), #71 ("More" nav), #54 (native feel), #5/#8 (selection, drag to queue — the desktop semantics being diverged from) Status: in flight.

#73 puts #60 first in Phase 4 because it is "the presentation every other item needs", and this is the next one. The Direction on #63 asks for the interaction model to be designed as one piece before any of it is built, because it reassigns an existing gesture rather than adding one — utils/long-press.ts currently owns the 500ms hold, and every context menu in the app is downstream of it.

This document is that design. Everything below is a measurement, or an argument for one of the choices #63 leaves open.

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The mapping

gesture	pointer is a finger	pointer is a mouse
single tap / click	play the row	select the row
double	—	play the row
long press (500ms)	enter selection mode	—
right-click	—	context menu
swipe right	add to queue	—
drag	reorder / drag to playlist	reorder / drag to playlist

Three of those are #63's report unchanged. Two are decisions it left open, and one is a deliberate divergence.

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Decision 1 — the predicate is the pointer, not the platform

#63 says "the row component needs a platform-aware interaction layer rather than shared handlers". It needs an interaction layer; it should not be platform-aware.

The question a row has to answer is not "am I on Android" or "is the viewport under 600px" but "what made this event". pointerType === 'touch', read off the event that is being handled, which is already how long-press.ts decides (if (e.pointerType !== 'touch') return) and is the only such test in the frontend today.

This is #64's rule — the predicate is named after the capability, not the platform — and it carries #64's warning with it. Keyed on a width:

• an Android tablet at 600px or more gets click-selects / double-click-plays on a touchscreen, which is the exact inversion this issue exists to fix, on the platform it exists for;
• a touchscreen laptop cannot be described at all, because both pointers are live in the same session on the same row;
• and a narrow desktop window gets phone semantics with a mouse.

Per event, all three are right for free, and there is no second declaration of what a phone does — the thing CLAUDE.md declines to add every time it comes up.

Measured, so this is not an assumption about the WebView. On the reference device (TLP301, Android 14, WebView Chrome 113, 424x439), driving a real tap with adb shell input tap:

[["down","touch",78,94],["touchstart","touchstart",0,0],["up","touch",78,94]]

PointerEvent exists, pointerType is "touch", maxTouchPoints is 5, and (pointer: coarse) / (hover: none) both match.

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Decision 2 — there is no double-tap, and the number is why

#63 asks for single tap → play and double tap → context menu. Those two cannot both be honoured. The first tap of a double tap is indistinguishable from a single tap until the interval expires, so "tap plays" necessarily becomes "tap waits to find out whether you meant something else, then plays". The app already owns that constant: utils/explore-link.ts holds a navigation for DOUBLE_CLICK_GRACE_MS = 250 for precisely this reason.

What it would be added to, measured on the device. Six runs, from the play command to the backend's TrackChanged:

155, 123, 85, 56, 91 ms          median ~100

So the app's primary interaction is ~100ms, and a double-tap discriminator makes it ~350 — 3.5x, of which 250ms is spent deliberately doing nothing — paid on every track anyone ever plays, in order to reach a menu.

It is also against the platform's convention, which counts for more than usual here because this is the phone build and nothing else: long-press is how you select on Android (Gmail, Files, Photos), double-tap is zoom or nothing, and a list's menu is either the long-press sheet or a per-row overflow.

So the menu and the selection action bar become the same surface, which is the convention and removes a concept rather than adding one. Long-press selects the row it was made on and raises the action bar; the bar's actions are the context menu's actions, contextualised to whatever is selected — one row or forty. #60's bottom sheet stays behind it as the overflow, so contextMenuStyles, MenuKeyboard and menu-surface are reused rather than reimplemented.

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Decision 3 — tap-to-play and selection mode ship together

The obvious phase order is "tap plays first, it is the smallest change". It is wrong, and the reason is a capability that exists today and is easy to miss.

A touch user can already multi-select: tap selects (the desktop semantics, which a finger currently gets), and the long-press menu then acts on the selection. Move tap to play without shipping selection mode in the same change and there is a window — a release, if it lands — in which selecting forty tracks to add to a playlist is impossible on a phone. That is a regression dressed as an increment.

So phase 1 is both, or neither.

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What the code looks like now

surface	how it binds	selection
track-list	delegated on the virtualizer: click, dblclick, contextmenu, dragstart	SelectionController
queue-panel	delegated, same shape	SelectionController
playlist-details	per row	SelectionController
smart-playlist-details	per row	SelectionController

All four already share SelectionController, and all four resolve a row from an event by data-index / data-file-path on the row. So the gesture layer has one shape to talk to, and "selection mode" is a flag on the controller they already have rather than a fifth concept.

utils/long-press.ts is one document-capture listener that synthesises a contextmenu — the seam that needed no component to opt in. This plan keeps that shape and changes what the gesture means, which is why it is a rewrite of that file rather than a second listener set: two document listeners both claiming the 500ms hold is the fault the file's own header warns about.

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Two measurements that decide the implementation

touch-action is auto on both the virtualizer and the rows. With auto the browser owns panning on both axes, so a horizontal drag can be claimed as a scroll and our gesture ends in pointercancel mid-swipe. A row that wants a horizontal swipe has to declare touch-action: pan-y: the browser keeps the vertical pan (which is the virtualizer's scroll, and must stay native or the list stutters) and hands us the horizontal axis. This is the single most likely way for swipe-to-queue to "work in Chromium and not on the phone".

The row is 424x52 on the device, so a swipe threshold in px is a fraction of a row height, not of a screen.

And the third one was found by building phase 1 and then running it — it is not something any browser tier can report. Chrome 113's Android WebView fires its own contextmenu on a long press. long-press.ts stood down when a trusted one arrived, which was right while both paths ended in the same place; once a hold can mean selection mode they end in different places, and standing down means the gesture silently does the old thing. Measured, before the fix:

{"log":["contextmenu isTrusted=true"],
 "state":{"bar":null,"menuActive":true,"selected":1}}

yj-long-press was never announced at all, the context menu opened, and all 26 tests in the component tier passed — dispatched pointer events do not make a browser synthesise a contextmenu.

So the browser's event is a trigger, not a competitor: the gesture is announced from it, and only a component that claims it suppresses the native menu. Unclaimed, it propagates untouched. That is the same "browser wins" outcome, reached by asking instead of assuming — and verified both ways on the device, a track row entering selection mode and an album card still opening its menu.

The tier could not find it and can hold it: a test cannot dispatch a trusted event, but this module has always told its own apart by identity rather than isTrusted, so an untrusted one from a test takes exactly the browser's path.

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A tier note: this one can be driven, not only measured

adb shell input tap|swipe reaches the WebView as real pointer events, which the log above is evidence of. So for the first time the Android tier can perform the thing under test rather than describe the page afterwards — a long press is input swipe X Y X Y 600, a swipe right is input swipe X Y X+N Y 120.

Device CSS pixels from device pixels, on this phone: css = (device - 59) / 2.564 vertically, css = device / 2.564 horizontally (measured from the tap above: 200,300 arrived as 78,94).

This does not make the device a spec tier — it does not run in CI and make ui-test still has to carry the assertions. It makes "does the gesture actually fire on Chrome 113" answerable in seconds.

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Phases

Phase 1 — the seam, tap-to-play, selection mode. utils/ touch-gestures.ts replacing long-press.ts: pointer-typed recognition of tap / long-press / horizontal swipe, dispatched as composed custom events so a delegated listener in any shadow root still works. SelectionController gains a mode. track-list acts on tap and enters the mode on long press. The action bar.

Phase 2 — swipe right to queue, with the touch-action: pan-y finding above and a reveal-and-snap affordance. Shipped; what the device said about it is the section below.

Phase 3 — the other three surfaces, which is mostly wiring, since they already share the controller.

Phase 4 — what this leaves behind. The inline explore-links in a row are a single-click target inside a row whose single tap now plays; that conflict is #67's, and this plan should not pre-empt its answer beyond making tap-to-play win on touch.

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What phase 2 measured, which was not what phase 2 predicted

The touch-action finding above is half of the answer, and shipping only that half would have been the exact failure it warns about. Driving a real finger with adb shell input swipe across a track row, three values, all three on the device:

touch-action: auto    pointerdown, 1 move,  pointercancel
touch-action: pan-y   pointerdown, 2 moves, pointercancel
touch-action: none    pointerdown, 2 moves, pointercancel

touchmove kept firing in all three. So Chrome 113's WebView cancels the pointer stream ~16px into any drag whatever touch-action says, and a swipe recognised from pointermove — which is what the rest of this module is built on — is a swipe that dies 16px in.

The other half is a non-passive touchmove calling preventDefault(): with it, the same swipe ran to 12 moves and a pointerup at full travel. And both halves are required, which was measured rather than assumed — with the preventDefault in place and touch-action back at auto, the gesture died after one move. The reading is that auto lets the browser commit to a horizontal pan on the first move past slop, before any threshold of ours can have been crossed, while pan-y leaves it undecided long enough for the second move to claim it.

none is the one value to avoid: the list stopped scrolling at all. With the shipped pair, a vertical drag still scrolls the virtualizer 81px on the same run that a horizontal one survives.

draggable="true" is not a competitor, which is the other thing the device was asked. No dragstart fires from a touch drag on this WebView at all, so the drag-to-playlist attribute on every row needs no pointer-type gate.

And it found a phase 1 defect that no tier can see

The native contextmenu arrives in either order, and phase 1 only handled one of them. nativeSeen covers the browser's menu arriving during the hold. The reverse — our 500ms timer firing first, a component claiming it, and Chrome delivering its own contextmenu 50–70ms later — was suppressed by nothing, so the context menu opened on top of the selection bar. Measured over four holds:

hold 1  yj-long-press, then contextmenu isTrusted=true   menu open
hold 2  yj-long-press                                    clean
hold 3  yj-long-press, then contextmenu isTrusted=true   menu open
hold 4  yj-long-press                                    clean

Two in four, on the one surface #63 exists to have changed, and invisible to both browser tiers because neither synthesises a contextmenu from a dispatched press. A press that has produced its outcome now suppresses a late one whichever branch it took; six holds on the fixed build, six clean.

The rules phase 2 settled

• A swipe is not a selection. It queues the row it was made on, unless that row is one of several explicitly selected — the same rule the context menu answers with, because a bar reading "40 selected" beside a gesture that quietly queues one of them is two answers to one question. It never changes the selection, which is where it differs from a right-click.
• Rightward only. Nothing is bound to a leftward swipe and claiming one would take a gesture away to do nothing with it.
• The commit threshold is a fraction of the row (0.3, floor 72px), because the row is 424x52 on this device and a bare pixel count is a fraction of a row height on one screen and a third of the width on the next.
• The affordance is not only a colour (WCAG 1.4.1, the rule the playing-row marker exists for): the pane carries the queue icon and words, the words change at the threshold ("Add to queue" → "Release to add" → "Added"), and the outcome is announced in a live region.
• The row does not move; its cells do. .track-row is contain: strict with overflow: hidden, so a pane held at the row's original position while the row translates is a pane at a negative offset inside a clipping box and is simply not painted. Sliding the cells needs no wrapper element in a row that is already a grid.
• The travel is written to the row's own style, not rendered. One render at the start, one at the threshold, one at the end; a virtualizer re-rendering every visible row per frame of one finger's travel is the thing perf.m1 is about.

Open questions

1. Does selection mode have an escape other than the bar's own close? Back is the platform's answer and the shell already owns the history stack (#6/#55). Pushing an entry for a mode rather than a place is the same argument #55 settled for the overlaid queue, and it should probably be settled the same way — but the queue is a screen and a selection mode is not, so it wants its own paragraph rather than an assumption.
2. Does a tap on a row's favourite icon still toggle it in normal mode? It is inside the row and the row now plays. It has to keep working — it is a 44px target since #56 — so the gesture layer needs the same "a control inside the row wins" rule the keyboard service has for a focused control that owns a key.