feat: add LIS-based move detection for keyed children reconciliation

src/host/reconcile.ts

@@ -156,6 +156,46 @@ export function resetUpdateQueue(): void {
   flushScheduled = false;
 }
 
+export function longestIncreasingSubsequence(arr: number[]): number[] {
+  if (arr.length === 0) return [];
+
+  const tails: number[] = [];
+  const tailsIdx: number[] = [];
+  const prev: number[] = new Array(arr.length).fill(-1);
+
+  for (let i = 0; i < arr.length; i++) {
+    const val = arr[i]!;
+    let lo = 0;
+    let hi = tails.length;
+    while (lo < hi) {
+      const mid = (lo + hi) >>> 1;
+      if (tails[mid]! < val) {
+        lo = mid + 1;
+      } else {
+        hi = mid;
+      }
+    }
+    if (lo > 0) {
+      prev[i] = tailsIdx[lo - 1]!;
+    }
+    if (lo === tails.length) {
+      tails.push(val);
+      tailsIdx.push(i);
+    } else {
+      tails[lo] = val;
+      tailsIdx[lo] = i;
+    }
+  }
+
+  const result: number[] = new Array(tails.length);
+  let k = tailsIdx[tails.length - 1]!;
+  for (let j = tails.length - 1; j >= 0; j--) {
+    result[j] = k;
+    k = prev[k]!;
+  }
+  return result;
+}
+
 export interface MatchedChild<I> {
   oldFiber: Fiber<I>;
   newChild: UElement;
@@ -166,6 +206,7 @@ export interface ChildClassification<I> {
   matched: MatchedChild<I>[];
   added: { newChild: UElement; index: number }[];
   removed: Fiber<I>[];
+  moves: Map<number, Fiber<I>>;
 }
 
 export function reconcileChildren<I>(
@@ -267,5 +308,16 @@ export function reconcileChildren<I>(
     }
   }
 
-  return { matched, added, removed };
+  const oldIndices = matched.map((m) => oldFibers.indexOf(m.oldFiber));
+  const lisPositions = longestIncreasingSubsequence(oldIndices);
+  const lisSet = new Set(lisPositions);
+
+  const moves = new Map<number, Fiber<I>>();
+  for (let i = 0; i < matched.length; i++) {
+    if (!lisSet.has(i)) {
+      moves.set(i, matched[i]!.oldFiber);
+    }
+  }
+
+  return { matched, added, removed, moves };
 }