fix: replay completion motion reliably

frontend/src/lib/completion-motion.ts

@@ -0,0 +1,26 @@
+type CompletionId = string
+
+type CompletionTimer = number
+
+export function createCompletionPulse(
+  activate: (id: CompletionId) => void,
+  deactivate: (id: CompletionId) => void,
+  duration = 420,
+) {
+  const timers = new Map<CompletionId, CompletionTimer>()
+
+  return (id: CompletionId) => {
+    const previous = timers.get(id)
+    if (previous !== undefined) {
+      window.clearTimeout(previous)
+      deactivate(id)
+    }
+    window.requestAnimationFrame(() => {
+      activate(id)
+      timers.set(id, window.setTimeout(() => {
+        deactivate(id)
+        timers.delete(id)
+      }, duration))
+    })
+  }
+}