Fix stuck bottom bar on Home and use the Reanimated 4 spring curve

The header and bottom bar were being handed the same `withSpring()` animation
object. Animation objects carry their own state, so the second shared value
to receive it could stop partway, leaving the bar stuck half hidden after a
slow scroll on Home. Each shared value now gets its own animation.

Shell show/hide springs now share one config based on Reanimated 4's default
critically damped curve, with the perceptual duration shortened from 550ms to
400ms.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JWQciPDiipBhqiW922Nivs

src/lib/custom-animations/springs.ts

@@ -0,0 +1,11 @@
+import {type WithSpringConfig} from 'react-native-reanimated'
+
+/**
+ * Spring used for showing and hiding shell UI (header, bottom bar, and things
+ * attached to them). This is Reanimated 4's default critically damped curve,
+ * whose perceptual duration is 550ms, sped up a little.
+ */
+export const SHELL_SPRING_CONFIG = {
+  duration: 400,
+  dampingRatio: 1,
+} as const satisfies WithSpringConfig

src/lib/hooks/useContributionRegistry.ts

@@ -1,13 +1,14 @@
 import {useCallback, useState} from 'react'
 import {
   clamp,
-  Reanimated3DefaultSpringConfig,
   type SharedValue,
   useDerivedValue,
   withSpring,
 } from 'react-native-reanimated'
 import {scheduleOnRN} from 'react-native-worklets'
 
+import {SHELL_SPRING_CONFIG} from '#/lib/custom-animations/springs'
+
 type Contribution = {
   id: number
   value: SharedValue<number>
@@ -52,15 +53,11 @@ export function useContributionRegistry(base?: SharedValue<number>) {
       setContributions(prev => [...prev, {id, value}])
       return () => {
         value.set(
-          withSpring(
-            0,
-            {...Reanimated3DefaultSpringConfig, overshootClamping: true},
-            finished => {
-              if (finished) {
-                scheduleOnRN(remove, id)
-              }
-            },
-          ),
+          withSpring(0, SHELL_SPRING_CONFIG, finished => {
+            if (finished) {
+              scheduleOnRN(remove, id)
+            }
+          }),
         )
       }
     },

src/lib/hooks/useScreenPresence/index.tsx

@@ -1,6 +1,5 @@
 import {useContext, useEffect} from 'react'
 import {
-  Reanimated3DefaultSpringConfig,
   type SharedValue,
   useDerivedValue,
   useSharedValue,
@@ -16,6 +15,7 @@ import {
   type ParamListBase,
 } from '@react-navigation/native'
 
+import {SHELL_SPRING_CONFIG} from '#/lib/custom-animations/springs'
 import {ScreenPresenceContext} from './context'
 
 export {type ScreenPresence, useScreenPresence} from './context'
@@ -117,10 +117,10 @@ function useAncestorsFocused(navigation: NavigationProp<ParamListBase>) {
     if (ancestors.length === 0) return
     const update = () => {
       focused.set(
-        withSpring(areAncestorsFocused(navigation) ? 1 : 0, {
-          ...Reanimated3DefaultSpringConfig,
-          overshootClamping: true,
-        }),
+        withSpring(
+          areAncestorsFocused(navigation) ? 1 : 0,
+          SHELL_SPRING_CONFIG,
+        ),
       )
     }
     update()

src/lib/hooks/useScreenPresence/index.web.tsx

@@ -1,11 +1,8 @@
 import {useCallback} from 'react'
-import {
-  Reanimated3DefaultSpringConfig,
-  useSharedValue,
-  withSpring,
-} from 'react-native-reanimated'
+import {useSharedValue, withSpring} from 'react-native-reanimated'
 import {useFocusEffect} from '@react-navigation/native'
 
+import {SHELL_SPRING_CONFIG} from '#/lib/custom-animations/springs'
 import {ScreenPresenceContext} from './context'
 
 export {type ScreenPresence, useScreenPresence} from './context'
@@ -35,13 +32,8 @@ export function ScreenPresenceProvider({
 
   useFocusEffect(
     useCallback(() => {
-      const spring = (to: number) =>
-        withSpring(to, {
-          ...Reanimated3DefaultSpringConfig,
-          overshootClamping: true,
-        })
-      presence.set(spring(1))
-      return () => presence.set(spring(0))
+      presence.set(withSpring(1, SHELL_SPRING_CONFIG))
+      return () => presence.set(withSpring(0, SHELL_SPRING_CONFIG))
     }, [presence]),
   )
 

src/state/shell/minimal-mode.tsx

@@ -1,13 +1,13 @@
 import {createContext, useContext, useEffect, useMemo} from 'react'
 import {
   type DerivedValue,
-  Reanimated3DefaultSpringConfig,
   type SharedValue,
   useAnimatedReaction,
   useSharedValue,
   withSpring,
 } from 'react-native-reanimated'
 
+import {SHELL_SPRING_CONFIG} from '#/lib/custom-animations/springs'
 import {useContributionRegistry} from '#/lib/hooks/useContributionRegistry'
 import {useScreenPresence} from '#/lib/hooks/useScreenPresence'
 
@@ -84,12 +84,7 @@ export function useEnableMinimalShellMode({enabled} = {enabled: true}) {
   useEffect(() => {
     if (!enabled) return
     const unregister = register(contribution)
-    contribution.set(
-      withSpring(1, {
-        ...Reanimated3DefaultSpringConfig,
-        overshootClamping: true,
-      }),
-    )
+    contribution.set(withSpring(1, SHELL_SPRING_CONFIG))
     return unregister
   }, [enabled, register, contribution])
 }

src/view/com/util/MainScrollProvider.tsx

@@ -3,7 +3,6 @@ import {type NativeScrollEvent} from 'react-native'
 import {
   clamp,
   interpolate,
-  Reanimated3DefaultSpringConfig,
   type SharedValue,
   useAnimatedStyle,
   useSharedValue,
@@ -12,6 +11,7 @@ import {
 import {useSafeAreaInsets} from 'react-native-safe-area-context'
 import {EventEmitter} from 'eventemitter3'
 
+import {SHELL_SPRING_CONFIG} from '#/lib/custom-animations/springs'
 import {ScrollProvider} from '#/lib/ScrollContext'
 import {useMinimalShellScrollMode} from '#/state/shell/minimal-mode'
 import {useShellLayout} from '#/state/shell/shell-layout'
@@ -106,12 +106,9 @@ export function MainScrollProvider({children}: {children: React.ReactNode}) {
   const setMode = useCallback(
     (v: boolean) => {
       'worklet'
-      const target = withSpring(v ? 1 : 0, {
-        ...Reanimated3DefaultSpringConfig,
-        overshootClamping: true,
-      })
-      headerMode.set(target)
-      footerScrollMode.set(target)
+      // animation objects are stateful, so each shared value needs its own
+      headerMode.set(withSpring(v ? 1 : 0, SHELL_SPRING_CONFIG))
+      footerScrollMode.set(withSpring(v ? 1 : 0, SHELL_SPRING_CONFIG))
     },
     [headerMode, footerScrollMode],
   )

src/view/screens/Home.tsx

@@ -1,9 +1,6 @@
 import {useCallback, useEffect, useLayoutEffect, useMemo, useRef} from 'react'
 import {ActivityIndicator, AppState, StyleSheet} from 'react-native'
-import {
-  Reanimated3DefaultSpringConfig,
-  withSpring,
-} from 'react-native-reanimated'
+import {withSpring} from 'react-native-reanimated'
 import {useLingui} from '@lingui/react/macro'
 import {useFocusEffect} from '@react-navigation/native'
 
@@ -12,6 +9,7 @@ import {
   PROD_DEFAULT_FEED,
   TIMELINE_SAVED_FEED,
 } from '#/lib/constants'
+import {SHELL_SPRING_CONFIG} from '#/lib/custom-animations/springs'
 import {useNonReactiveCallback} from '#/lib/hooks/useNonReactiveCallback'
 import {useOTAUpdates} from '#/lib/hooks/useOTAUpdates'
 import {useSetTitle} from '#/lib/hooks/useSetTitle'
@@ -160,12 +158,9 @@ function HomeScreenReady({
   const footerScrollMode = useMinimalShellScrollMode()
   const showShell = useCallback(() => {
     'worklet'
-    const shown = withSpring(0, {
-      ...Reanimated3DefaultSpringConfig,
-      overshootClamping: true,
-    })
-    headerMode.set(shown)
-    footerScrollMode.set(shown)
+    // animation objects are stateful, so each shared value needs its own
+    headerMode.set(withSpring(0, SHELL_SPRING_CONFIG))
+    footerScrollMode.set(withSpring(0, SHELL_SPRING_CONFIG))
   }, [headerMode, footerScrollMode])
 
   useFocusEffect(