Extract shared list and numeric input helpers

client/src/input/listNavigation.ts

@@ -0,0 +1,27 @@
+export function cycleIndex(currentIndex: number, length: number, direction: 'next' | 'prev'): number {
+  if (length <= 0) return 0;
+  if (direction === 'next') {
+    return (currentIndex + 1) % length;
+  }
+  return (currentIndex - 1 + length) % length;
+}
+
+export function findNextIndexByInitial<T>(
+  entries: readonly T[],
+  currentIndex: number,
+  key: string,
+  labelFor: (entry: T) => string,
+): number {
+  if (entries.length === 0 || key.length !== 1 || !/[a-z]/i.test(key)) {
+    return -1;
+  }
+  const target = key.toLowerCase();
+  for (let step = 1; step <= entries.length; step += 1) {
+    const candidateIndex = (currentIndex + step) % entries.length;
+    const label = labelFor(entries[candidateIndex]).trim().toLowerCase();
+    if (label.startsWith(target)) {
+      return candidateIndex;
+    }
+  }
+  return -1;
+}

client/src/input/numeric.ts

@@ -0,0 +1,19 @@
+export function snapNumberToStep(value: number, step: number, anchor = 0): number {
+  if (!(step > 0) || !Number.isFinite(value) || !Number.isFinite(anchor)) {
+    return value;
+  }
+  const normalized = Math.round((value - anchor) / step) * step + anchor;
+  const decimals = step >= 1 ? 0 : Math.min(6, Math.ceil(Math.abs(Math.log10(step))) + 1);
+  return Number(normalized.toFixed(decimals));
+}
+
+export function formatSteppedNumber(value: number, step: number): string {
+  const decimals = step >= 1 ? 0 : Math.min(6, Math.ceil(Math.abs(Math.log10(step))) + 1);
+  if (decimals <= 0) {
+    return String(Math.round(value));
+  }
+  return value
+    .toFixed(decimals)
+    .replace(/(\.\d*?[1-9])0+$/u, '$1')
+    .replace(/\.0+$/u, '');
+}