feat(android): tap to play, hold to select

Phase 1 of #63, and the design the issue asks for as one piece is
.planning/plans/active/019-android-touch-model.md.

**A finger has no second button and no modifier keys**, so the primary
action has to be the primary gesture: tap plays the row, and the hold
that opened a context menu now enters selection mode with that row
selected.

Three decisions in it, and two diverge from the report.

**The predicate is the pointer, not the platform or the viewport.**
`pointerType === 'touch'`, per event, which is already how long-press.ts
decided and is the only such test in the frontend. This is #64's rule --
named after the capability -- and it carries #64's warning: keyed on a
width, an Android *tablet* at 600px gets click-selects/double-click-plays
on a touchscreen, which is the inversion this issue exists to fix, on
the platform it exists for. A touchscreen laptop cannot be described by
a width at all. Per event, a mouse keeps desktop semantics on the very
same row, and there is no second declaration of what a phone does.

**There is no double-tap, and the number is why.** The report asks for
single tap to play *and* double tap for the menu. Those cannot both be
honoured: the first tap of a double tap is indistinguishable from a
single tap until the interval expires, so "tap plays" becomes "tap
waits". Measured on the device, the play command to TrackChanged is
155/123/85/56/91 ms -- median ~100 -- and the app's own
DOUBLE_CLICK_GRACE_MS is 250. That is 3.5x the primary interaction,
250ms of it spent deliberately doing nothing, on every track anyone
plays, to reach a menu the hold already reaches. So the menu and the
selection action bar are the same surface, which is also the platform's
convention and removes a concept rather than adding one.

**Tap-to-play and selection mode ship together**, because splitting
them is a regression dressed as an increment: a touch user selects by
tapping today and acts through the long-press menu, so moving tap to
play on its own would leave a window with no way to select forty tracks
at all.

**What lets this reassign the hold without touching one of the fourteen
context menus**: the layer announces `yj-tap` / `yj-long-press`
(composed, cancelable) and acts on nothing. A component claims one with
preventDefault. An **unclaimed long press still becomes a
`contextmenu`**, so the card grids, Explore, the playlist rows and
every other menu behave exactly as they did, and only lists that opt in
get selection mode. An unclaimed *tap* does nothing at all and the
click follows normally, which is what leaves every button in the app
alone -- only a claimed tap has its click swallowed, or playing a track
would also select it.

**And the device found the one thing no browser tier can see.**
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 a context menu; they no longer do, so
standing down means the gesture silently does the *old* thing.
Measured, before the fix, holding a track row:

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

`yj-long-press` was never announced, the menu opened, and all 26 tests
passed -- dispatched pointer events do not make a browser synthesise
one. So the native event is a **trigger, not a competitor**: the
gesture is announced from it and only a claim suppresses it. Unclaimed
it propagates untouched, which is the same "browser wins" outcome
reached by asking instead of assuming.

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

Verified on the device by *performing* the gestures rather than
describing the page -- `adb shell input tap` and `input swipe x y x y
700` reach the WebView as real pointer events, which is new here and is
written down in the plan with the pixel mapping. Tap plays; a hold
raises the bar with one selected and no menu; a tap toggles to two,
back to one, and the mode ends with the last row; an album card still
opens its context menu.

29 new tests. The e2e spec is rewritten to assert **both** halves --
the row selects, and a card elsewhere still opens the real menu --
because a spec that only checked the row would pass on a build that had
silently broken the other thirteen.

Phases 2-4 (swipe to queue, the other three surfaces, and what #67
inherits) are in the plan and not in this commit.

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

@@ -0,0 +1,253 @@
+# 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.
+
+---
+
+## 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.
+
+---
+
+## 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.
+
+---
+
+## 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.
+
+---
+
+## 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.
+
+---
+
+## 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.
+
+---
+
+## 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.
+
+---
+
+## 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.
+
+---
+
+## 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.
+
+**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-link`s 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.
+
+---
+
+## 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.