fix(app): preserve todo dock across sessions (#33778)

packages/ui/src/components/motion-spring.tsx

@@ -1,6 +1,6 @@
 import { attachSpring, motionValue } from "motion"
 import type { SpringOptions } from "motion"
-import { createEffect, createSignal, onCleanup } from "solid-js"
+import { createComputed, createEffect, createSignal, onCleanup } from "solid-js"
 
 type Opt = Partial<Pick<SpringOptions, "visualDuration" | "bounce" | "stiffness" | "damping" | "mass" | "velocity">>
 const eq = (a: Opt | undefined, b: Opt | undefined) =>
@@ -11,17 +11,30 @@ const eq = (a: Opt | undefined, b: Opt | undefined) =>
   a?.mass === b?.mass &&
   a?.velocity === b?.velocity
 
-export function useSpring(target: () => number, options?: Opt | (() => Opt)) {
+export function useSpring(target: () => number, options?: Opt | (() => Opt), snapKey?: () => unknown) {
   const read = () => (typeof options === "function" ? options() : options)
   const [value, setValue] = createSignal(target())
   const source = motionValue(value())
   const spring = motionValue(value())
   let config = read()
+  let snapValue = snapKey?.()
   let stop = attachSpring(spring, source, config)
   let off = spring.on("change", (next: number) => setValue(next))
 
-  createEffect(() => {
-    source.set(target())
+  createComputed(() => {
+    const next = target()
+    const nextSnap = snapKey?.()
+    if (snapKey && nextSnap !== snapValue) {
+      // State boundaries should adopt their target without animating from the previous context.
+      snapValue = nextSnap
+      stop()
+      spring.jump(next)
+      source.jump(next)
+      stop = attachSpring(spring, source, config)
+      setValue(next)
+      return
+    }
+    source.set(next)
   })
 
   createEffect(() => {