Decide a swipe from the release point and stop stray snap-backs

- Track the pointerup position before choosing Try it, Pass or snap-back,
  so the outcome follows where the card was let go (SQ-107-01).
- Keep the snap-back animation and cancel it when a new drag or a
  decision starts (SQ-107-02).
- Treat losing pointer capture before the release as a cancel, springing
  the card back and resetting its stamps (SQ-107-03).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/discover/DeckCard.tsx

@@ -10,7 +10,10 @@ export const DECK_DEPTH = [0, 1, 2] as const
 const DIFFICULTY_LABEL: Record<Difficulty, string> = { easy: 'Easy', medium: 'Medium', hard: 'Hard' }
 
 // SwipeHandlers are the pointer handlers that drag the top card.
-export type SwipeHandlers = Pick<DOMAttributes<HTMLElement>, 'onPointerDown' | 'onPointerMove' | 'onPointerUp' | 'onPointerCancel'>
+export type SwipeHandlers = Pick<
+  DOMAttributes<HTMLElement>,
+  'onPointerDown' | 'onPointerMove' | 'onPointerUp' | 'onPointerCancel' | 'onLostPointerCapture'
+>
 
 export type DeckCardProps = {
   quest: SideQuest

web/src/discover/DiscoverPage.test.tsx

@@ -687,15 +687,18 @@ describe('DiscoverPage', () => {
     })
 
     // press, drag and release put a pointer down on the card at (200, 300),
-    // move it by dx, dy, and let go.
+    // move it by dx, dy, and let go where it is, or dx, dy from the press.
+    let pointer = { dx: 0, dy: 0 }
     function press(card: Element) {
+      pointer = { dx: 0, dy: 0 }
       fireEvent.pointerDown(card, { pointerId: 7, isPrimary: true, button: 0, clientX: 200, clientY: 300 })
     }
     function drag(card: Element, dx: number, dy: number) {
+      pointer = { dx, dy }
       fireEvent.pointerMove(card, { pointerId: 7, isPrimary: true, clientX: 200 + dx, clientY: 300 + dy })
     }
-    function release(card: Element) {
+    function release(card: Element, dx = pointer.dx, dy = pointer.dy) {
-      fireEvent.pointerUp(card, { pointerId: 7, isPrimary: true, button: 0 })
+      fireEvent.pointerUp(card, { pointerId: 7, isPrimary: true, button: 0, clientX: 200 + dx, clientY: 300 + dy })
     }
     const stamps = (card: HTMLElement) => [within(card).getByText('Try it!'), within(card).getByText('Pass')]
 
@@ -831,6 +834,123 @@ describe('DiscoverPage', () => {
       expect(sent(server.fetchMock)).toEqual([])
     })
 
+    it.each([
+      ['Try it', 60, 130, 'accept'],
+      ['Pass', -60, -130, 'decline'],
+    ] as const)('%s from where a release past 110 px lets go, though the last move was short of it', async (_, moved, at, action) => {
+      const server = stubServer([BOWLS, TIKKA], {
+        [`POST /api/v1/suggestions/s1/${action}`]: () => {
+          server.deck = [TIKKA]
+          return action === 'accept' ? accepted(BOWLS) : declined(BOWLS)
+        },
+      })
+      const animations = stubAnimate({ autoFinish: false })
+      await renderPage()
+      const card = await screen.findByRole('article', { name: 'Korean beef bowls' })
+
+      press(card)
+      drag(card, moved, 0)
+      release(card, at, 20)
+      const from = `translate(${at}px,6px) rotate(${at / 18}deg)`
+      await waitFor(() => expect(on(animations, card)).toHaveLength(1))
+      expect(on(animations, card).map((a) => a.keyframes[0]!.transform)).toEqual([action === 'accept' ? from : `${from} rotateY(0deg)`])
+      await finishRunning(animations)
+      expect(sent(server.fetchMock)).toEqual([`POST /api/v1/suggestions/s1/${action}`])
+    })
+
+    it.each([
+      ['right', 150, 40],
+      ['left', -150, -40],
+    ])('springs the card back from where a release short of 110 px %s lets go, though the last move was past it', async (_, moved, at) => {
+      const server = stubServer([BOWLS, TIKKA])
+      const animations = stubAnimate({ autoFinish: false })
+      await renderPage()
+      const card = await screen.findByRole('article', { name: 'Korean beef bowls' })
+
+      press(card)
+      drag(card, moved, 0)
+      release(card, at, 0)
+      expect(animations.map((a) => [a.target, a.keyframes, a.options])).toEqual([
+        [card, [{ transform: `translate(${at}px,0px) rotate(${at / 18}deg)` }, { transform: 'translate(0px,0px) rotate(0deg)' }], { duration: 420, easing: SPRING }],
+      ])
+      expect(card.style.transform).toBe('')
+      await act(async () => {
+        await Promise.resolve()
+      })
+      expect(sent(server.fetchMock)).toEqual([])
+    })
+
+    it('stops a snap-back when the card is grabbed again, so it follows the new drag', async () => {
+      stubServer([BOWLS, TIKKA])
+      const animations = stubAnimate({ autoFinish: false })
+      await renderPage()
+      const card = await screen.findByRole('article', { name: 'Korean beef bowls' })
+
+      press(card)
+      drag(card, 80, 0)
+      release(card)
+      const [spring] = animations
+      expect(spring!.playState).toBe('running')
+
+      press(card)
+      expect(spring!.playState).toBe('idle')
+      drag(card, 36, 0)
+      expect(card.style.transform).toBe('translate(36px,0px) rotate(2deg)')
+      expect(animations).toHaveLength(1)
+    })
+
+    it('stops a snap-back when a decision starts', async () => {
+      stubServer([BOWLS, TIKKA], { 'POST /api/v1/suggestions/s1/decline': () => declined(BOWLS) })
+      const animations = stubAnimate({ autoFinish: false })
+      await renderPage()
+      const card = await screen.findByRole('article', { name: 'Korean beef bowls' })
+
+      press(card)
+      drag(card, -80, 0)
+      release(card)
+      const [spring] = animations
+      fireEvent.click(screen.getByRole('button', { name: 'Pass' }))
+      expect(spring!.playState).toBe('idle')
+      expect(on(animations, card)).toHaveLength(2)
+    })
+
+    it('springs the card back when it loses the pointer capture before the release, deciding nothing', async () => {
+      const server = stubServer([BOWLS, TIKKA], { 'POST /api/v1/suggestions/s1/accept': () => accepted(BOWLS) })
+      const animations = stubAnimate({ autoFinish: false })
+      await renderPage()
+      const card = await screen.findByRole('article', { name: 'Korean beef bowls' })
+      const [tryStamp, passStamp] = stamps(card)
+
+      press(card)
+      drag(card, 150, 0)
+      fireEvent.lostPointerCapture(card, { pointerId: 7, isPrimary: true })
+      expect(animations.map((a) => [a.target, a.options])).toEqual([[card, { duration: 420, easing: SPRING }]])
+      expect(card.style.transform).toBe('')
+      expect(tryStamp!.style.opacity).toBe('')
+      expect(passStamp!.style.opacity).toBe('')
+
+      // The drag is over: later moves and the release do nothing.
+      drag(card, 180, 0)
+      release(card)
+      expect(card.style.transform).toBe('')
+      expect(animations).toHaveLength(1)
+      await act(async () => {
+        await Promise.resolve()
+      })
+      expect(sent(server.fetchMock)).toEqual([])
+
+      // The capture going after a release leaves its decision alone.
+      press(card)
+      drag(card, 140, 0)
+      release(card)
+      await waitFor(() => expect(on(animations, card)).toHaveLength(2))
+      fireEvent.lostPointerCapture(card, { pointerId: 7, isPrimary: true })
+      expect(animations).toHaveLength(3)
+      expect(card.style.transform).toBe('translate(140px,0px) rotate(7.777777777777778deg)')
+      await finishRunning(animations)
+      expect(sent(server.fetchMock)).toEqual(['POST /api/v1/suggestions/s1/accept'])
+    })
+
     it('springs the card back when the pointer is canceled, however far it went', async () => {
       const server = stubServer([BOWLS])
       const animations = stubAnimate({ autoFinish: false })

web/src/discover/DiscoverPage.tsx

@@ -1,6 +1,6 @@
 import { useQueryClient } from '@tanstack/react-query'
 import { Heart, X } from 'lucide-react'
-import { useCallback, useEffect, useId, useLayoutEffect, useMemo, useRef, useState, type Ref } from 'react'
+import { useCallback, useEffect, useId, useLayoutEffect, useMemo, useRef, useState, type PointerEvent, type Ref } from 'react'
 import { useJob } from '../api/index.ts'
 import { Card } from '../ui/Card.tsx'
 import { EmptyState } from '../ui/EmptyState.tsx'
@@ -127,6 +127,13 @@ export function DiscoverPage() {
   const exit = useRef<Exit | null>(null)
   const leaving = useRef<string | null>(null)
   const drag = useRef<Drag | null>(null)
+  // The top card's snap-back while it may still run; a new drag or a
+  // decision stops it so it does not fight the card's new motion.
+  const springing = useRef<Animation | null>(null)
+  const stopSpring = useCallback(() => {
+    springing.current?.cancel()
+    springing.current = null
+  }, [])
 
   const { mutate: mutateDecision } = decision
   const deciding = useRef(false)
@@ -168,6 +175,7 @@ export function DiscoverPage() {
   const decide = useCallback(
     (choice: Choice, from?: string) => {
       if (top === undefined || !lock()) return
+      stopSpring()
       const card = deckRef.current!.querySelector('article')!
       if (from === undefined && drag.current !== null) {
         drag.current = null
@@ -206,41 +214,54 @@ export function DiscoverPage() {
         },
       )
     },
-    [top, lock, send],
+    [top, lock, send, stopSpring],
   )
 
   // swipe drags the top card: it follows the pointer, captured from the
   // press, until the release decides past the threshold or springs it back
-  // short of it. Input while busy is ignored, and a drag held into a busy
+  // short of it. The release decides from where the pointer let go, which
-  // spell (a Retry) is put back on release.
+  // may differ from its last move. A cancel, or losing the capture before
+  // the release, springs it back from its last move. Input while busy is
+  // ignored, and a drag held into a busy spell (a Retry) is put back on
+  // release.
   const swipe = useMemo<SwipeHandlers>(() => {
-    function release(card: HTMLElement, pointerId: number, decides: boolean) {
+    function track(card: HTMLElement, current: Drag, event: PointerEvent<HTMLElement>) {
+      current.dx = event.clientX - current.x
+      current.transform = follow(card, current.dx, event.clientY - current.y)
+    }
+    function release(event: PointerEvent<HTMLElement>, decides: boolean) {
+      const card = event.currentTarget
       const current = drag.current
-      if (current === null || current.pointerId !== pointerId) return
+      if (current === null || current.pointerId !== event.pointerId) return
       drag.current = null
+      const moved = current.transform !== null || event.clientX !== current.x || event.clientY !== current.y
+      if (decides && moved && !deciding.current) track(card, current, event)
       if (current.transform === null) return
       if (deciding.current) unfollow(card)
       else if (decides && current.dx > SWIPE_THRESHOLD) decide('try', current.transform)
       else if (decides && current.dx < -SWIPE_THRESHOLD) decide('pass', current.transform)
       else if (prefersReducedMotion()) unfollow(card)
-      else snapBack(card, current.transform)
+      else springing.current = snapBack(card, current.transform)
     }
     return {
       onPointerDown: (event) => {
         if (deciding.current || !event.isPrimary || event.button !== 0) return
+        stopSpring()
         event.currentTarget.setPointerCapture(event.pointerId)
         drag.current = { pointerId: event.pointerId, x: event.clientX, y: event.clientY, dx: 0, transform: null }
       },
       onPointerMove: (event) => {
         const current = drag.current
         if (current === null || current.pointerId !== event.pointerId || deciding.current) return
-        current.dx = event.clientX - current.x
+        track(event.currentTarget, current, event)
-        current.transform = follow(event.currentTarget, current.dx, event.clientY - current.y)
       },
-      onPointerUp: (event) => release(event.currentTarget, event.pointerId, true),
+      onPointerUp: (event) => release(event, true),
-      onPointerCancel: (event) => release(event.currentTarget, event.pointerId, false),
+      onPointerCancel: (event) => release(event, false),
+      // After a release the drag is already over, so this only ends a drag
+      // whose capture was lost before it.
+      onLostPointerCapture: (event) => release(event, false),
     }
-  }, [decide])
+  }, [decide, stopSpring])
 
   // Leaving the page stops an exit before its decision is sent.
   useEffect(() => () => exit.current?.cancel(), [])