refactor(web): extract optimistic timeline reconciliation

apps/web/src/hooks/useTimelineDrag.ts

@@ -17,6 +17,7 @@ import {
   finalizeMultiSelectDraft,
   updateMultiSelectDraft,
 } from "./timelineMultiSelect.js";
+import { reconcileOptimisticEntries } from "./timelineOptimisticAllocations.js";
 import { finalizeRangeSelection, updateRangeSelectionDraft } from "./timelineRangeSelection.js";
 import { getTouchPoint, resolveTouchDragDecision } from "./timelineTouch.js";
 
@@ -510,27 +511,9 @@ export function useTimelineDrag({
 
   const reconcileOptimisticAllocations = useCallback((entries: readonly OptimisticTimelineEntry[]) => {
     setOptimisticAllocations((prev) => {
-      if (prev.size === 0) return prev;
-
-      const next = new Map(prev);
-      for (const entry of entries) {
-        const override = next.get(entry.id);
-        if (!override) continue;
-
-        const startTime = new Date(entry.startDate).getTime();
-        const endTime = new Date(entry.endDate).getTime();
-        if (
-          startTime === override.startDate.getTime() &&
-          endTime === override.endDate.getTime()
-        ) {
-          next.delete(entry.id);
-          if (pendingOptimisticAllocationIdRef.current === entry.id) {
-            pendingOptimisticAllocationIdRef.current = null;
-          }
-        }
-      }
-
-      return next.size === prev.size ? prev : next;
+      const result = reconcileOptimisticEntries(prev, entries, pendingOptimisticAllocationIdRef.current);
+      pendingOptimisticAllocationIdRef.current = result.pendingOptimisticAllocationId;
+      return result.changed ? result.optimisticAllocations : prev;
     });
   }, []);